Scientia - Spring 2015

Scientia

A Journal by The Triple Helix at The University of Chicago

Produced in collaboration with

M i ds tat e s C onsort i uM for M at h a n d s Ci enCe

Spring 2015

The image depicted on the cover is the winner of the inaugural Scientia Photo Contest, submitted by Nate Earnest as part of a series of photographs visualizing research in the Schuster Lab. Depicted is a 3D Transmon quantum bit (qubit) coupled to a multimode cavity. The MultiMode Cavity, the metal box itself, is a cavity that has several characteristic frequencies. The coupled 3D Transmon is a specific type of superconducting qubit that uses a large capacitance to suppress sensitivity to noise from electron charge. A qubit, much like its classical counterpart, takes on the form of being 0 or 1 - just as a convenient way to represent information. However, unlike its classical counterpart, a qubit is capable of taking advantage of quantum laws such as entanglement and superposition of states, which allows for an improved processing speed for certain operations. This speedup in computation is important for some already foreseen reasons - such as encryption security, searching algorithms, and quantum simulations - but many applications are expected to emerge as the field develops. However, a key step in the development of quantum computing, and in the study of qubits in general, is quantum data storage. A potential goal is to use the depicted cavity to store several qubit states at once with each mode having a long lifetime.

As Scientia expands, we hope to continue introducing novel sections, such as the photo contest, to our journal. One of the primary goals of Scientia is to make research accessible and enticing. When we talk about abstract concepts such as the superposition of quantum states, we generally envision diagrams that are supposed to enable us to visualize those ideas. As such, the depictions can be just as ethereal as the concepts. Yet the image of a device used to study and preserve those quantum states can strike one as unexpectedly concrete, perhaps making the possibility of joining researchers in that field just as tangible. We hope that by depicting research with both words and images, Scientia can serve as a thoughtprovoking resource that will trigger the interests of our readers in a great variety of scientific frontiers. Of course, we also hope that you enjoy it.

Sincerely, Luizetta Navrazhnykh Co-Editor-in-Chief, Scientia

Scientia Inquiries:

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Particle Crasher: An Interview with Professor David Miller Gloria Wang

Abstracts: Physical Sciences Photodegradation of Imidazolinone Herbicides and Pesticides in Aqueous Solutions and on Plants Surfaces Investigating the Effects of Microstructure Patterns on the Optical Performance of Iron Oxide Pixel Devices

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Compounds Growth of Zinc Oxide Nanocones for Use in Neutron Detection Spin Hall Effect Based Magnetic Tunnel Junction Logic Devices Frictional Properties of Commercial Hard Disk Coatings: Understanding the Forces Inside High Speed, Microscopic Contacts Fatty Acid Derived Lactones: New Monomers for the Production of Bioplastics

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Historic Human Remains using ICP-MS Nanoscale Coordination Polymers for the Co-delivery of siRNAs and Cisplatin Synthesis of Poly(amide-b-ester)-Based Aerogels Synthetic Methods for Hybrid PVP-Cysteine Coated Silver Nanowires A Discrepancy between Two Criteria of Stability for Hybrid Stars Dipole Density: a Molecular Picture of Salt in Alcohols Constrained Bayesian Optimization on Set Functions

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Produced by The Triple Helix at the University of Chicago Layout and Design by Irene Zhang, Managing Editor Cover Photograph by Nate Earnest Cover Letter written by Khatcher O. Margossian, Co-Editor in Chief Scientia Board: Khatcher Margossian, Luizetta Navrazhnykh, Michael Cervia, Jake Russell, & Irene Zhang

Spring 2015

Biological Sciences Acute Effects of Alcohol and Ecstasy on Outcome Expectancies of Risky Sexual Events Edema Factor Amyloid Beta Postsynapic Signaling Through Anchored Calcineurin Development of a Reporter System to Study Cellular Plasticity in Gliomas Mission Monteverde: Mathematical Rainforest Modeling The Role of Xanthine Oxidoreductase in Tumor-Associated Macrophage Activation in Breast Cancer Investigating the Use of Targeted Therapies for Triple-Negative Breast Cancer

In Depth:

Colloidal Synthesis, Surface Chemistry and Functionalization of Nanocrystal Semiconductors Hannah C. Muir

Aperture:

Honorable Mentions from the Photo Contest

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Scientia

About Scientia Dear Reader, The Triple Helix, Inc. (TTH) at the University of Chicago is proud to present the Spring 2015 issue of Scientia. With its team of committed editors, this journal, now in its fourth year, features a wide spectrum of student research. This issue, produced in collaboration with the Midstates Consortium for Math and Science, marks the latest step in the journal’s expansion to a wider national audience. As you browse through the pages of Scientia, make note of the studies conducted by talented student-researchers at other universities.

This issue also marks the end of my time as an editor for Scientia. Over the last few years, our team has pushed this journal towards goals that were unrealizable when the journal was still in its nascent stages. Looking forward, I have no doubt that this growth will continue, and that the scope of the journal will widen even further.

We are thrilled to present this issue to you, both as an example of the insightful contributions that students make to research, and as a resource for our everexpanding community of scholars. We hope that with this growth, a new and diverse world of research will be available to students across the country, and we welcome you to use our journal to explore this world freely. Scientia is currently seeking writers and editors to contribute to future issues. We encourage all those with interest to get involved by contacting the members of our team.

Sincerely, Khatcher O. Margossian Co-Editor-in-Chief, Scientia Chief Financial Officer, The Triple Helix, Inc.

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Spring 2015

About The Triple Helix

at The University of Chicago

The Triple Helix, Inc. (TTH) is the world’s largest completely student-run organization dedicated to evaluating the true impact of historical and modern advances in science. Of TTH’s more than 25 chapters worldwide, the University of Chicago chapter is one of the largest and most active.

We, TTH at The University of Chicago, are extremely proud of our chapter’s accomplishments, which are perhaps best summed by our title as the William J. Michel Registered Student Organization of the Year in 2012.

We continue to work closely with an ever-increasing number of faculty members, and have notably acquired the generous support of the founding Pritzker Director of Chicago’s Institute for Molecular Engineering, Matthew Tirrell, and his department. We have expanded our local organization so that now, we can confidently say that there is a place here for each and every one of our fellow college students. We have consciously and dramatically increased the size of our production, marketing, and events teams, and have watched our group of talented writers and editors grow at unprecedented levels. In fact, we have further expanded the intellectual diversity of our chapter, with TTH members having declared for more than 30 of the University’s different major and minor programs. Finally, we are absolutely thrilled to present the newest issue of our journal of original undergraduate research, Scientia.

Over the years, TTH UChicago members have found themselves in research positions around campus, taking advantage of the hundreds of opportunities we are fortunate to have here. We found ourselves wishing, however, that there was an outlet where we could reach out to our peers on campus, to share our projects and project ideas – and to hear or read about their work as well. So we decided to create that outlet ourselves. This was the impetus for our journal, Scientia, which is the culmination of many of our members’ hard work. Since its inception, we have continued to strive for excellence in the diverse world of research by publishing the highest quality of undergraduate research. We hope you enjoy reading our latest issue!

Jawad Arshad and Stephen Yu President and Vice President of The Triple Helix, Inc.

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Inquiries Particle Crasher: An Interview with Professor David Miller Gloria Wang

What is it like working with some of the world’s largest instruments, in order to discover and to study the universe’s smallest particles? For Professor David Miller, a career as a high energy particle physicist allows him to experience this every day.

Becoming a high energy particle physicist was, as he describes, “a process of serendipity and circumstance.”[1] Coming from a family of Chicago Fire Department firefighters with additional jobs, he spent much of his time in the workshop of his father, who also worked as a construction worker. From there, he developed an interest in physics and engineering and, with a scholarship to The University of Chicago, would eventually go on to obtain a B.A. with honors in physics. As an undergraduate, he didn’t realize that he could work in a lab until he talked to a crew teammate who told him that he had “just knocked on people’s doors.”[1] Heeding his teammate’s advice, he joined an astrophysicist’s lab.

However, his interest in high energy particle physics

didn’t come about until his post-undergraduate gap year, during which he spent a year in Geneva, Switzerland, working on the Large Hadron Collider (LHC), the largest and most advanced particle accelerator in the world.[2]This interest would eventually lead to him obtaining a Ph.D. in physics from Stanford University. After completing a postdoctoral fellowship at the Enrico Fermi Institute, he is now a Neubauer Family Assistant Professor at his alma mater,[3] where he appreciates the opportunity “to think and help others think”[1] and work with enormously supportive colleagues, all while doing cutting-edge research.

In the field of high energy physics (HEP), scientists study the most fundamental building blocks, the subatomic particles that make up atoms and their interactions, which comprise the four fundamental forces. Much like the chemist’s periodic table, there is the Standard Model, which is the current understanding of these fundamental particles and forces.[1,3] But scientists

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Spring 2015 don’t want to just study the particles they already know; they want to discover new particles and interactions. All of these efforts require the use of impressive superconductors that can smash particles together with enormous energy, and a camera that can capture these collisions at very high speeds – about 40,000,000 snapshots per second. Enter the Large Hadron Collider, located in Geneva, Switzerland at the Conseil Européen pour la Recherche Nucléaire (CERN), otherwise known as the European Organization for Nuclear Research. This particle accelerator is a 27-kilometer ring of powerful electromagnets made to shoot particles in opposite directions nearly at the speed of light.[5] Professor Miller specifically focuses on quarks and gluons both “in their own right and as tools.”[1] Quarks are the elementary particles, with intriguing classifications like “charm” and “strange,” that comprise matter such as the A simulated event with the production of two supersymmetric particles called “gluinos” and protons and neutrons commonly described in the subsequent decay products as would be measured if such a process occurred in nature introductory-level science classes.[6] Gluons are of the contours. similar to photons; charged particles have an Professor Miller does not always work alone but also electromagnetic force between them where photons are exchanged, while quarks have a color force where gluons on a variety of teams. He is part of the ATLAS experiment, are exchanged.[7] Jets and their substructure are crucial which seeks new discoveries in particle physics, such as to illustrating what sort of interactions these particles are evidence for dark matter.[8] While there are small groups working on separate projects within the nearly 3000 involved in.

To illustrate these concepts, Professor Miller presents scientists involved, as I saw firsthand, some papers can some images he has collected from the Large Hadron have upwards of thousands of authors. This was the case Collider and asks me a question: What features did I see for the discovery of the Higgs-Boson, one of the most in those figures? I noted some clustered lines extending famous products of the ATLAS experiment. Professor out from the center, each containing warm and cool Miller indirectly played a role in the Higgs-Boson colors. These lines turn out to be what they examine in discovery by contributing various tools and techniques these images: the jet was the various clusters of particles, that he has utilized in his studies of quarks and gluons comprising the lines, and the energies and momenta and jets, since they are a factor in processes involving the of these particles would be measured, displayed on a production or decay of the Higgs-Boson. As a part of the cylindrical coordinate graph. In a third image, 2D plots High Energy Physics team at The University of Chicago, of various blobs show what is known as jet substructure, he is surrounded by not only talented researchers but and by observing the different topologies of these also many engineers. Often electronic and mechanical colored blobs, one can determine the types of particle engineers, they are physicists by training and work on the involved and what particles like gluons and quarks are electronics of the instruments in the experiments. He will doing in these collisions. Professor Miller’s lab has made also be hosting an international conference this coming great advances in the analysis of these images. One autumn for high energy physicists of all disciplines, of his students designed a hardware circuit to create including theorists and experimentalists, in order to find multilevel filtering of the images, determining which 500 “new ways of approaching a problem from a theoretical to 1000 images to keep among the 40 million snapshots perspective and the interplay between the experimental captured per second. Additionally, Professor Miller has and the instrumentation.”[1] His lab’s competitors are developed ways to analyze the topologies of the different invited as well, because, in his words, “Who’s to say that all substructures more accurately by increasing the precision interesting ideas will only happen in ATLAS or CMS…we

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Scientia need to work together to make sure we’re exploiting the data we’re recording to the highest degree possible.”[1] From all of this collaboration come new ideas and new insights and even new questions from which to go further.

While the physics involves small particles that require incredibly high amounts of energy to create, the basis of the experimental design to study the questions of the field has far-reaching implications outside of physics and academia. The World Wide Web is a classic example–it was invented by Sir Tim Berners-Lee, a software engineer at CERN at the time, in order to allow particle physicists working there to exchange information between labs that were scattered around the world.[9] Professor Miller cites the work of his colleague Professor Henry Frisch, whose studies on improving photodetectors could have wide-ranging effects on PET scans.[1,10] The design of the Large Hadron Collider itself utilizes impressive superconducting magnets and is the largest cryogenic system in the world, and improvements to the LHC have lasting implications for cryogenics, superconductivity, and materials science. Improvements to network switches in optical transmission fibers are important for the general telecommunications industry. As shown from these examples, Professor Miller notes, “There is a really wonderful interplay between [high energy physics] as a whole and the rest of the world, community, and other fields. [We’re] really pushing the envelope.”[1] Thanks to the efforts of Professor David Miller and his colleagues in the field, we can explore and utilize the full range of the knowledge and technology associated with the smallest particles of our universe. As Professor Miller suggests for anyone interested in physics, “Go knock on people’s doors.”

References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Wang, Gloria. Personal interview. 4 February 2015.

“The Large Hadron Collider.” CERN. Accessed 31 March 2015. http://home. web.cern.ch/topics/large-hadron-collider.

Miller, David. “David W. Miller curriculum vitae.” Accessed 1 April 2015 http:// hep.uchicago.edu/~DavidMiller/CV.html.

“The Standard Model.” CERN. Accessed 1 April 2015. http://home.web.cern.ch/ about/physics/standard-model.

“The Large Hadron Collider.” CERN. Accessed 1 April 2015. http://home.web. cern.ch/topics/large-hadron-collider.

“Quarks.” Georgia State University. Accessed 1 April 2015. http://hyperphysics. phy-astr.gsu.edu/hbase/particles/quark.html.

“Gluons.” Georgia State University. Accessed 1 April 2015. http://hyperphysics. phy-astr.gsu.edu/hbase/particles/expar.html.

“ATLAS Experiment”. CERN. Accessed 1 April 2015. http://atlas.ch/.

“Sir Tim Berners-Lee: Web Inventor and Founding Director of the World Wide Web Foundation.” World Wide Web Foundation. Accessed 4 April 2015. http:// webfoundation.org/about/sir-tim-berners-lee/.

“Henry Frisch.” UChicago News. University of Chicago. Accessed 4 April 2015. http://news.uchicago.edu/profile/henry-frisch.

A simulated event of a highly boosted top quark (the heaviest of all quarks) decaying to a W boson and a b-quark

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Abstracts Physical Sciences Photodegradation of Imidazolinone Herbicides and Pesticides in Aqueous Solutions and on Plants Surfaces Scott Anderson Gustavus Adolphus College, St. Peter, MN

Imazapic, imazamox, imazaquin, and imazethapyr are herbicides commonly used on corn and soybean plants in the Midwest. Photolysis has been shown in previous studies of imidazolinone herbicides to be a major pathway of degradation in the environment. The purpose of this study was to determine the rate at which each herbicide degraded under different conditions and to propose photoproducts of the degradation. Two different systems were used for the study: irradiation of the herbicides in aqueous solution as well as on the epicuticular waxes of corn and soybean leaves. Using ultraviolet light, these herbicides were irradiated at several pH values or at a constant pH with varying amounts of natural organic matter (NOM). The rates of degradation were analyzed using a high-performance liquid chromatograph (HPLC). To identify preliminary photoproducts, liquid chromatograph-mass spectrometer identifying (LC-MS) data was used. Future work will include obtaining more data on the corn and soybean waxes, identifying photoproduct pathways, and observing how the herbicides degrade when analyzed on intact corn and soybean plant leaves. This summer, the researchers involved with the project travelled to Clermont-Ferrand, France, to collaborate with Dr. Claire Richard at the University of Blaise-Pascal.

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Investigating the Effects of Microstructure Patterns on the Optical Performance of Iron Oxide Pixel Devices Jerry Chee University of Chicago, Chicago, IL

Structural coloration rises from the interference of light due to the periodic nanostructures found in a material.

In this project we investigated the application of structural colors in pixel display devices. Iron oxide nanoparticle suspensions were utilized as the source of color structuration. By placing a voltage across the pixel, the concentration of nanoparticles can be controlled, controlling the color. At sufficiently high voltages, the pixel devices can begin to demonstrate transparency.

It is desirable for a pixel device to be capable of demonstrating both a strong color response and high transparency. The aim of this project is to investigate the ability of microstructures placed within the pixel device to improve the color response and transparency of unmodified pixels. Line and pillar microstructures in the range of 10-100 um width were synthesized on the inner pixel surface using a photolithography technique.

With the addition of these microstructures, the transparency of the pixel devices greatly improved, while the modified pixel devices are still able to demonstrate a color response. The pillar microstructure pixel devices required a lower voltage to achieve a comparable state of transparency compared to the line microstructure pixel devices.

This technology can be used in a dynamically tintable window, or in outdoor electronic displays. Because structural coloration results from external light diffraction, structural color displays would perform optimally in sunlight.

Development of a Novel Method to Measure Margaret Dickinson Hope College, Holland, MI

Perfluorinated compounds (PFCs) are chemical compounds that contain carbon-fluorine bonds that are used to give water- and stain-resistance to consumer products. Because of the environmental persistence of PFCs, their ability to bioaccumulate, and their suspected human toxicity, new methods to identify these chemicals in consumer products are needed. Current techniques to measure PFCs involve liquid chromatography-tandem mass spectrometry, which is a costly and time consuming method. Particle Induced Gamma-ray Emission (PIGE) is an established ion beam analysis tool used to measure total fluorine concentrations in various objects, typically sediments and minerals. PIGE utilizes a beam of accelerated protons to excite 19F nuclei on the surface of a sample. As these nuclei de-excite, they emit characteristic gamma-rays that can be used to identify and even quantify the total fluorine content in a sample. In this study, an in-air PIGE methodology has been established as an effective tool to determine the presence or absence of PFCs used as coatings in consumer products such as paper, carpet and textiles. Limits of detection and application of this method to rapid, non-destructive screening for certain consumer products will be presented.

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Spring 2015

Growth of Zinc Oxide Nanocones for Use in Neutron Detection

James Gilhula University of Chicago, Chicago, IL

Terrorism in today’s world threatens national security, global safety, and political stability. Many nuclear weapons, to which terrorists may someday gain access, emit free neutrons as nuclear-reaction products from radioactive decay.

It will be helpful to have a relatively inexpensive device that can detect the presence of free neutrons, so that nuclear weapons can more easily be found before they are detonated. Currently, the main challenge in creating such a device is the inherently low efficiency of sensors used in neutron detection devices. The maximum theoretical efficiency of detection is about 40 percent, but the highest efficiency achieved to date is only about 10 percent. Our project was to develop a low-cost, n-type semiconducting zinc oxide nanocone architecture that can be used as a template in neutron detection devices. To grow the nanocones, we sputtered zinc oxide onto an ITO coated glass substrate. The nanocones were grown on the sputtered substrate via solid-vapor transport deposition of zinc oxide. Although the focus was on optimizing nanocone growth conditions, future work will use the nanocone material to more efficiently detect neutrons. To accomplish this, we will coat the nanocones with a p-type semiconducting polymer to create a p-n junction. Before depositing the polymer, poly-(3-hexylthiophene), we will functionalize it with a phosphonic ester, which improves the quality of the p-n junction, and then blend it with boron-10 nanoparticles, which readily react with stray neutrons to decay into lithium-7 and alpha particles. The emitted alpha particles will then induce a charge separation across the p-n junction, producing a measurable electrical signal. Because the unique morphology of the nanocones allows for a high surface area contact with the polymer, efficiency of charge conduction and neutron detection overall will be much greater. By this method, we expect to produce a more sensitive, cost-effective neutron detecting device.

Spin Hall Effect Based Magnetic Tunnel Junction Logic Devices Daniel Timothy Hickox-Young St. Olaf College, Northfield, MN

As the use of MTJ based devices becomes more widespread, one of the limitations of modern magnet-based computing is the necessity of an external magnetic field for clocking purposes. This necessity limits scalability and energy reduction. However, we can overcome both of these limitations by using logic devices with three innovations: magnetoresistive elements for read-out, spin transfer torque for writing of information, and the Spin Hall effect for clocking. Working primarily in the Minnesota Nano Center, we used photolithography, electron beam lithography, and ion milling to fabricate multiple MTJ pillars on top of a tantalum Hall bar. The MTJ pillars have perpendicular anisotropy and a TbFeCo/MgO/TbFeCo structure. We then used electron beam evaporation to deposit Ti/Au contacts. By measuring the magnetoresistance across the circuit while varying an external magnetic field, we observed each MTJ pillar switch from anti-parallel to parallel individually. Our results demonstrate the feasibility of using these different states to represent logic values of 0 and 1 in a majority logic function.

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Frictional Properties of Commercial Hard Disk Coatings: Understanding the Forces Inside High Speed, Microscopic Contacts Emily Johnson & Lucas Sletten St. Olaf College, Northfield, MN

As mechanical devices shrink to microscopic sizes, a pressing need rises for a more fundamental understanding of the friction and other surface phenomena that can limit device performance. We have developed an experimental setup capable of measuring the forces inside microscopic contacts subject to high speed shear. The technique combines a nanoindenter probe and quartz crystal microbalance (NI-QCM). The interfacial materials, pressures, and sliding speeds can be chosen to replicate the operating conditions of technologies currently under development, such as microelectromechanical systems (MEMS) and the reader-disk interface of computer hard drives. We are collaborating with researchers at Western Digital, Inc. to study the high speed frictional properties of hard disk coatings and lubricants. Because of the desire to increase data storage density, the read head must be engineered to fly closer and closer to the spinning substrate. Further advances may require the reader to come into physical contact with the disk and slide along the surface. It is far from clear whether friction and wear can be minimized enough to make such an arrangement feasible. Our collaborative effort aims to answer these questions and identify promising material/ lubricant combinations. Here we present results for a lubricant layer applied to a “hard carbon� disk coating.

Fatty Acid Derived Lactones: New Monomers for the Production of Bioplastics Reed Johnson & Claire Seitzinger Luther College, Decorah, IA

Biodegradable plastics derived from renewable, agricultural resources (e.g., corn and soybeans) have the potential to provide a foundation for sustainable commercial products that alleviate the environmental problems associated with their petroleum-based analogs. Recently, rapid advances have been made in the development of biodegradable polymers. For example, polylactides (PLA) are polyesters with the potential for commercialization in the fiber, film, and packaging industries. Despite its promise, PLA currently only displaces a limited range of petroleum-based plastics.

One reason is that commercially available PLA deforms at relatively low temperatures, thus making it unsuitable for applications such as microwave-safe containers. It has been theorized that increasing the bulkiness of lactide’s methyl groups should improve its physical properties. Here we report the synthesis of two different analogs of D,Llactide, prepared from palmitic and stearic acids by replacing one of the methyl substituents with either a fourteen- or sixteen-carbon chain. Upon polymerization, these new monomers are expected to yield comb polymers with more useful physical properties than current PLAs. Consequently, the potential commercial viability of these polyesters will hopefully promote further development of other related bio-plastics.

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Spring 2015

Metal Isotopes in Historic Human Remains using ICP-MS Kate Klesner Grinnell College, Grinnell, IA

Inorganic and analytical chemistry techniques and instrumentation have been integral in the identification and quantification of trace amounts of heavy metal isotopes in human remains. The presence of these heavy metals in skeletal remains can give insights into the lifestyle and social status of historic and prehistoric populations. This is especially true for the examination of trace amounts of lead (Pb), arsenic (As) and mercury (Hg) in human bone from the colonial period through the 19th century in America. In this research, human bone and teeth were analyzed using time of flight inductively coupled plasma mass spectrometry (TOF ICP-MS) to determine the concentrations of trace amounts of heavy metal isotopes in the remains. While the time and cost of preparing samples for this analysis is high, and analysis using the TOF ICP-MS is destructive, the instrument can detect relatively low concentrations of heavy metals with high accuracy and precision, making it ideal for this study. The samples analyzed come from archaeological excavations of historic sites in the Chesapeake area. Given the concentrations of heavy metals in the bone samples, we are able to better understand the extent of historic populations’ exposure to heavy metals through lead-glazed pottery and medicinal use.

Nanoscale Coordination Polymers for the Codelivery of siRNAs and Cisplatin Kristine Ma University of Chicago, Chicago, IL One of the major limitations for successful cancer treatment is the developed resistance to the chemotherapeutic agent, Cisplatin. The critical development of novel strategies to overcome intrinsic and acquired resistance to chemotherapy is important to effective treatment of ovarian cancer and other types of cancers. We have sought to re-sensitize resistant ovarian cancer cells to chemotherapy by co-delivering chemotherapeutics and pooled siRNAs targeting multi-drug resistance (MDR) genes using self-assembled nanoscale coordination polymers (NCPs). In this work, NCP-1 particles with trigger release properties were first constructed by linking cisplatin prodrug-based bisphosphonate bridging ligands with Zn2+ metal-connecting points and then coated with a cationic lipid layer, followed by the adsorption of pooled siRNAs targeting three MDR genes - including survivin, Bcl-2, and P-glycoprotein via electrostatic interactions. The resulting NCP-l/siRNA particles promoted cellular uptake of cisplatin and siRNA, and enabled efficient endosomal escape in cisplatin-resistant ovarian cancer cells. By down-regulating the expression of MDR genes, NCP-l/siRNAs enhanced the chemotherapeutic efficacy as indicated by cell viability assay, DNA ladder, and flow cytometry. Local administration of NCP-1/siRNAs effectively reduced tumor sizes of cisplatin-resistant SKOV-3 subcutaneous xenografts. This work shows that the NCP-1/siRNA platform is very promising by enhancing chemotherapeutic efficacy for the effective treatment of drug-resistant cancers.

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Synthesis of Poly(amide-b-ester)-Based Aerogels Katherine Oosterbaan University of Chicago, Chicago, IL

Aerogels are characterized as highly porous solids made by supercritical CO2 fluid extraction of a wet gel while maintaining pore size and integrity, resulting in dimensional stability. Because of their high porosity, high surface area, and low density, aerogels can make excellent, lightweight insulators for various aerospace, aeronautic, and commercial applications. We have performed the first synthesis of an aromatic poly(amide-b-ester) (PAE) aerogel in hopes to improve flexibility and processability. In this study, variables included the variation of polyamide (PA) and polyester (PE) chain lengths from n = 5-60, as well as different cross-linkers. Effects of different amines were also examined. It has been found that PAE aerogels having higher PE chain length display lower density, higher porosity, and lower shrinkage, while the opposite results were seen with PA chain length. It has also been observed that the incorporation of polyester into polyamide improved the gelation time and gel flexibility.

Synthetic Methods for Hybrid PVP-Cysteine Coated Silver Nanowires Emily Reeves St. Olaf College, Northfield, MN

Silver nanoparticles (Ag-NPs) have been proposed as potential drug delivery systems because of their effectiveness in combating HIV, MCF-7 (human breast cancer), and a number of bacterial species. Ag-NP cytotoxicity stems from particle dissolution to toxic silver ions in aqueous conditions, inducing apoptosis via cellular uptake or radical formation. While the development of nanosized drug delivery systems has gained extensive attention in the literature in recent years, tuning these materials for high target specificity and biocompatibility remains a major challenge. Our work seeks to address these challenges by synthesizing silver nanorods and nanowires with hybrid PVP-cysteine surface coatings.

The use of both materials provides both hard-soft and soft-soft interactions between silver cores and their coating, resulting in interactions of different strengths and consequential lability for controlling ion release. Incorporating an amino acid on the surface may also improve nanoparticle solubility and bioavailability in the target tissue. Surface design is explored through the lens of synthetic inorganic chemistry and utilizes characterization methods such as optical microscopy, NMR, UV-Vis, and IR spectroscopy.

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Spring 2015

A Discrepancy between Two Criteria of Stability for Hybrid Stars Pratik Sachdeva Washington University, St. Louis, MO

Neutron stars, along with other compact matter, are some of the most stable structures in the universe. Their stability can be disrupted, however, by radial oscillations, which may cause them to collapse into black holes. John Bardeen, in his Catalogue of Methods, detailed two methods by which we can determine the stability of compact stars for a given equation of state: direct calculation of the oscillation frequency with Chandrasekhar’s equation or a qualitative examination of a mass-radius plot. These two methods were believed to agree until Glendenning et al. proposed the existence of a white dwarf with a strange quark core. We observed that Glendenning’s white dwarf showed disagreement between Bardeen’s methods. With this motivation, we examined the stability of a similar family of hybrid stars, which contain a quark matter core surrounded by a nuclear matter envelope. The equations of state for such stars exhibit either a kink or discontinuity. By reproducing the calculations of these methods, we observed that Bardeen’s methods do not agree for these stars as well. We believe that this discrepancy stems from the fact that Chandrasekhar’s equation is incompatible with discontinuous equations of state.

Dipole Density: a Molecular Picture of Salt in Alcohols Caren Sullivan Lawrence University, Appleton, WI

The temperature and concentration dependence of ionic conductivity in electrolyte solutions plays a central role in the electrochemical industry; increasing concentration of salt results in an increase in conductivity. When another property, static dielectric constant, is increased, we also see conductivity increase. The static dielectric constant is directly proportional to the number of dipoles per unit volume of the solvent, connecting molecular level properties to bulk static dielectric constant measurements. Our system consists of 1- and 3- alcohols, due to their differing functional group placement and, ultimately differing hydrogen bonding networks. We have studied alcohols from hexanol to decanol, increasing the alkyl chain by one carbon, thereby decreasing the dipole density. A non-coordinating salt, tetrabutylammonium trifluoromethanesulfonate (TbaTf) was added to each solvent and dipole density data were taken from 5-85 °C over a concentration range of 0.035-0.35 moles of salt per kilogram solvent to demonstrate the effect the salt has on dipole density. My data show an increase in dipole density when concentration is increased and temperature is decreased. This data will help us to further understand the role of dipoles in ionically conducting hydrogen-bonded systems.

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Array-Based Detection Payton Weidenbacher University of Chicago, Chicago, IL

Cytosine methylation and further oxidative modifications resulting from TET family proteins may explain an active demethylation pathway or be associated with regulatory elements within the genome. Understanding the methylation, hydroxymethylation, formylation, and carboxylation patterns in the genome mapping of these modifications has becoming increasingly important. The opportunities to better understand DNA modification hinge on our ability to accurately, quickly, and inexpensively locate cytosine modifications. The difficulty of replicating methylation patterns without large amounts of DNA has stimulated an exploration into low input methods. The work in this project allows for a single base resolution mapping of cytosine modifications using a click chemistry based ligation at a small scope of modified positions. This method would allow for a minimal input, low cost mapping using a micro-array based identification method. By producing a low cost, array-based method, mapping of modification patterns in DNA can elucidate the functions of these modifications in select genomic regions like promoters and enhancers, thereby furthering our knowledge on the role of cytosine modification in DNA regulation.

Constrained Bayesian Optimization on Set Functions Fangzhou Xiao Washington University, St. Louis, MO

Given a function that is costly to evaluate such as production efficiency of a new drug, Bayesian optimization (BO) is a powerful framework that assumes a form of model based on the known data points and then actively select most informative points to evaluate in order to find the optimum of the function with as few points evaluated as possible.

Gardner et al. (2013) constructed a constrained Bayesian optimization (CBO) framework to work with addition of a costly-to-evaluate constraint function. Our work considers application of CBO to optimize set-functions (CBOS). Set functions appear naturally in many problems, and are important in machine learning in particular, such as cost of features and error rate as function of number of edges in a neural network. Reducing the cost of features, or reducing number of features, could improve learning algorithm performance in both prediction accuracy and efficiency, and allow better model interpretation, while reducing edges in neural network could improve accuracy and possibly reveal the mechanism underlying neural network. As a preliminary result, we modified the covariance function of the Gaussian Process model to work on set space and applied this CBOS framework to minimize number of edges in a convolutional neural network (CNN) on Cifarl0 dataset subject to constraint of no more error, and gained 0.4% out of 23.9% improvement in error rate, with 85 out of 3167 edges reduced.

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Spring 2015

Biological Sciences Acute Effects of Alcohol and Ecstasy on Outcome Expectancies of Risky Sexual Events Benjamin Trnka University of Chicago, Chicago, IL Populations who use substances such as alcohol and ecstasy have been linked with increased risky sexual behavior, potentially spreading sexually transmitted infections and posing a significant burden for public health. Several cognitive and biological predispositions may account for individual differences in pursuing risky sexual behavior within these drug-using populations. One such mediating link is individuals’ outcome expectancies, which have been quantified by the revised Cognitive Appraisal of Risky Events questionnaire (CARE-R). This measure asks participants to report expected positive outcomes (benefits) and negative outcomes (risk) of engaging in risky behaviors, including sexually risky behaviors (Katz, Fromme, and D’Amico, 2000). The acute effects of certain substances such as marijuana, nicotine, and alcohol may change these outcome expectancies and been investigated in previous studies. In our first study, we sought to validate the CARE-R in our laboratory conditions under the acute influences of alcohol. Our preliminary results suggest a decrease in conditions under the acute influences of alcohol. Our preliminary results suggest a decrease in perceived risk for sexually risky events without altering perceived benefits, consistent with previous studies. In our second study, we explore the acute effect of 3.4-methylenedioxy-N-methylamphetamine (MDMA; active ingredient in ecstasy) in a dose dependent manner. We predicted that due to MDMA’s attenuation of amygdala activity and augmentation of serotonin that subjects would report perceived risk and increased perceived benefit for risky sexual behavior under its effects. Our preliminary results affirm this hypothesis, and suggest increased perceived benefit and decreased perceived risk under a moderate (0.5mg/kg) dose of MDMA. We further explored if subjective mood ratings such as ‘liking’ and ‘disliking’ are related to outcome expectancies. Our preliminary results suggest a negative correlation between subjective liking and perceptions of risk under a moderate dose of MDMA. Our studies are suggestive of MDMA’s role in altering outcome expectancies for risky sexual events, and that subjective mood may mediate this cognitive process.

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Scientia

Agents Against Anthrax Edema Factor Mara Farcasanu University of Chicago, Chicago, IL Edema Factor (EF) is a class II adenylyl cyclase toxin secreted by anthrax-causing bacteria Bacillus antracis. Even low-dose exposure to EF overwhelms intracellular cAMP signaling pathways, weakening the host immune response and increasing its susceptibility to the disease. We applied synthetic antibody engineering technology to develop toxin-specific inhibitors of EF. Screening yielded seven antibody clones that bind to EF with nanomolar and even picomolar affinity. One of these antibodies, EB7, prevents cAMP-induced morphological change in Y1 mouse adrenocortical cells exposed to EF and PA at concentrations above 350 nM. EB7 can also prevent cAMP accumulation in Chinese Hamster Ovary cells incubated with EF and PA with an IC50 of 70 nM. In order to understand the cellular implications of antibody binding, we pursued several techniques for structural determination. Small Angle X-ray Scattering (SAXS) data for EF and EF-antibody complexes was collected at the Advanced Photon Source at Argonne National Labs and wide-scale crystallization screening was conducted for the EF-antibody complexes. Altogether, these approaches will provide insight into the molecular mechanisms of EF toxicity and the therapeutic value of synthetic antibodies in the treatment of anthrax infections.

Amyloid Beta Postsynapic Signaling Through Anchored Calcineurin Kendyl Greimann Gustavus Adolphus College, St. Peter, MN Alzheimer’s Disease (AD) is a serious neurodegenerative impairment that generally affects cognitive function and memory. This “mind robbing disease” is caused by the overproduction of amyloid beta (Ab) peptides, which are expressed from cleavage of the amyloid precursor protein (APP). Ab peptides can accumulate to form soluble oligomers at synapses where they alter excitatory synaptic plasticity underlying learning and memory by inhibiting long-term potentiation (LTP), inducing long-term depression (LTD), and causing loss of postsynaptic dendritic spines. These deleterious actions of Ab are mediated in part through activation of the calcium dependent phosphatase Calcineurin (caN). In particular, CaN dephosphorylation of postsynaptic AMPA-type glutamate receptors and the transcription factor NFAT may contribute to decreased LTP, increased LTD, and associated spine loss. Members from the Dell’Acqua lab and others show a key role for the postsynaptic scaffold protein AKAP 79/150 in targeting CaN to dendritic spines to control AMPAR phosphorylation and function during LTP and LTD. AKAp also promotes CaN activation of NFAT in response to Ca2+ influx through L-type voltage gated Ca2+ channels. NMDa receptor activation of CaN also signals a change in postsynaptic structure and the movement of AKAP from dendritic spines. Thus, we hypothesized that Ab also signals through postsynaptic anchored CaN to alter synaptic plasticity and trigger spine loss. To test this hypothesis, I used an AKAP150DPIX mouse deficient in CaN anchoring due to the deletion of its docking motif. Acute 24 hr. application of synthetic Ab (1-42) peptides led to spine loss in wild-type neurons, which was prevented by the AKAP150DPIX mutation. Acute 60 min. application of synthetic Ab (1-42) peptides, also led to AKAP movement from spines, similar to the effects of chemical induced LTD. In conclusion, we found that Ab postsynaptic signaling through anchored CaN has a negative effect on dendritic spine numbers, and that disruption of CaN anchoring to AKAP150 prevents Ab-induced spine loss.

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Spring 2015

Development of a Reporter System to Study Cellular Plasticity in Gliomas Donna Guo University of Chicago, Chicago, IL

Glioblastoma Multiforme (GBM) is the most common and lethal primary malignant brain tumor. Tumor recurrence following standard of care treatment is the most common cause of death in GMB patients. Cancer stem cells (CSCs) are strongly implicated in promoting tumor recurrence due to their multi-potency, self-renewal capacity, and most importantly, their tumor-initiatin ability. Recent studies have produced a novel dimension to the cancer stem cell theory; they observe plasticity between differentiated tumor cells and cancer stem cells. In gliomas, temozolomide treatment is found to induce the de-differentiation of glioma cells into a stem-like state both in vitro and in vivo.

Given the importance of glioma stem cells in promoting therapeutic resistance and recurrence, inter-conversion between the non-stem and stem state is a paradigm-shifting discovery in our understanding of GBM. The major challenge, however, is that there currently exist no tools to study cellular plasticity, a dynamic process involving bidirectional inter-conversions between the stem and non-stem states. IN this project, we address the challenge of studying cellular plasticity by developing a promoter-based real-time glioma stem cell-specific reporter system. Our reporter system uses the promoter sequence of one of four glioma stem cell specific genes, Sox2, OCT4, nanog, and CD133, to drive expression of red fluorescent protein (RFP). We verify that reporter activity accurately identifies the glioma stem cell population by comparing expression of stem cell markers in RFP(+) and RFP(-) populations. Using our reporter system, we observe that temozolomide treatment induces a distinct RFP(+)CD133(+)CD15(+) stemlike population. Additionally, we observe for the first time conversion of non-stem glioma cells to stem-like glioma cells on the single cell level and find that TMZ treatment increases the single-cell conversion rate of non-stem cells to a stem-like state. Finally, we detect expression of RFP(+) stem-like cells in vivo, indicating our reporter system can be used in future in vivo studies. Our reporter system is a novel tool that will serve invaluable in the study of cellular plasticity, its mechanism, and eventually identifying a method to inhibit such plasticity during therapy.

Mission Monteverde: Mathematical Rainforest Modeling Ben Johnson & Grace Wiesner Hope College, Holland, MI

The tropical rainforest is one of the earth’s most diverse and dynamic ecosystems. Tree or branch falls in the forest can open gaps in the canopy, allowing light to reach the forest floor. Pioneer plants are adapted to take advantage of these conditions, sometimes emerging many years after being deposited as seeds. Light conditions change as the gap closes, impacting rates of growth and reproduction. For the past 30 years, sizes and reproductive outputs of individuals of 6 pioneer plant species have been measured along 5 transects in the Monteverde Cloud Forest Preserve in Monteverde, Costa Rica. Each 500m transect was chosen to be representative of different conditions in some part of the cloud forest. To model the pioneer plant demographics, we classified canopy gaps by age and size and developed a matrix population model that accounts for the different gap environments. We also created a stochastic matrix model of gap formation and evolution to simulate the dynamics of rainforest canopy gaps. Combined, these models will allow us to simulate pioneer plant population dynamics in the changing forest environment, and to explore how reproduction and growth rate parameters, such as seed predation rates, impact pioneer population dynamics.

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The Role of Xanthine Oxidoreductase in Tumor-Associated Macrophage Activation in Breast Cancer

Petras Jans Colorado College, Colorado Springs, CO

Tumor associated macrophages (TAMs) play an important role in assisting in cancer growth and progression. While inflammation and cancer are closely linked, recent studies have shown that TAMs take on a tumor-helping role by secreting growth hormones and promoting angiogenesis, exhibiting an anti-inflammatory phenotype (M2). Another interesting phenomenon is the correlation between high levels of serum uric acid (UA), and increased cancer mortality and poor prognosis. UA is produced solely by the enzyme xanthine oxidoreductaase (XOR), which is thought to play a key role in regulating cell redox potential, and in macrophages, it is important in inflammation and innate immunity.

However, in breast cancer cells, UA levels are low and XOR activity is down regulated in the most aggressive cases.

Thus, we hypothesize that XOR activity in TAMs is responsible for the observed correlation between UA levels and cancer mortality through its activation of the inflammatory microenvironment in breast cancer tumors. To being testing our hypothesis, preliminary in vivo and in vitro experiments were carried out, utilizing a syngeneic mouse model. An analysis of survival and tumor histology was carried out on macrophage XOR knockout and wild type mice injected with an aggressive murine breast cancer cell line. Subsequently, breast cancer conditioned media treatments on bone marrow derived macrophages were carried out ot being characterizing the interactions between tumor-associated macrophages and breast cancer cells. Results suggest that XOR may play a role in promoting tumor growth and mortality, as well as recruitment of macrophages into the tumor. Preliminary data also suggests that increased XOR activity in TAMs may be induced by signals derived from the cancer cells themselves. Furthermore, we propose that the classification of M1 and M2 macrophages cannot adequately describe the complex nature of TAMs.

Investigating the Use of Targeted Therapies for Triple-Negative Breast Cancer Wendy Bindeman St. Olaf College, Northfield, MN Triple-negative breast cancer (TNBC) accounts for 15-20% of all diagnosed breast cancers. It is characterized by lack of expression of estrogen receptor and progesterone receptor, and an absence of HER2 amplification. TNBC is aggressive, highly metastatic, and resistant to current chemotherapies. Recent work has demonstrated that TNBC often harbors mutations in TP53, suggesting that therapies which exploit this vulnerability may be an effective treatment option. In particular, p53-deficient cells are hypothesized to be highly sensitive to inhibitors of checkpoint kinase 1 (Chk1) due to checkpoint abrogation.

We have evaluated the use of mammosphere cultures as an in vitro system for testing the sensitivity of triple-negative breast cancer (TNBC) tumor cells to chemotherapy and targeted therapy. We hypothesized that mammospheres would display higher levels of chemo-resistance than adherent cells, due to their ability to enrich for tumor initiating cells (TICs), which have been shown to display chemo-resistance. However, we reasoned that molecularly targeted therapies should maintain their effect in TICs, since the pathways that are targeted would remain vulnerable. To test these hypotheses, we evaluated the effect of cisplatin (DNA damaging agent, chemotherapy) and LY2606368 (inhibitor of CHk1, targeted therapy) on the viability of TNBC cells. Our data suggest that the TIC population of a tumor may retain its sensitivity to targeted therapy despite resistance to cytotoxic chemotherapy. Further studies are necessary to determine if targeted therapy can impair TIC self-renewal capacity, to evaluate combination therapies, and to verify these results in vivo.

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Spring 2015

In Depth Colloidal Synthesis, Surface Chemistry and Functionalization of Nanocrystal Semiconductors Hannah C. Muir

Nanocrystal (NC) semiconductors are at the forefront of nanotechnology research. With understanding of the quantum confinement that governs individual NCs and their quantum mechanical coupling as a result of interparticle communications, appropriate control of NC size, shape, and surface chemistry can be applied as a means to design novel electronic devices. In this paper we present the most successful solution-based NC synthesis, the hot injection method, and discuss ligand exchange for NC stability in polar (aqueous) solutions, focusing on the promising metal chalcogenide complexes (MCCs). We also outline current and future methods for bulk functionalization of NCs and introduce the most recent advance in immobilization of NCs in rock salt crystalline matrices.

Introduction Modern technology is rapidly expanding and with it the demand to make goods cheaper, smaller, and more efficient. These circumstances have opened the door to the field of nanotechnology, where nanometer scale materials can provide more sensitive control over properties once thought possible only in bulk materials. One interesting class of particles found in these components is nanocrystals (NCs), particles of less than 20 nm in diameter containing only a few thousand to a million atoms of one (metal) or more (metal/nonmetal) elemental components.[1] Of particular interest in optoelectronic applications are binary NCs, specifically

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II-VI, III-V, or IV-VI type structures. These NCs exhibit sizedependent properties, including photoluminescence (PL) (fluorescence) (Figure 1), magnetism, and semiconducting behavior. These properties can be tailored for functional applications, from biomedical (as fluorescent labels)[2] to electronics (as transistors and light emitting devices (LED)).[3] A robust synthesis of NCs known as the hot-injection method is reported throughout literature,[4,5,6] first in 1993

by Murray et al. This simple design enables controlled growth of monodisperse colloidal NC solutions providing essential control of their electronic structure. To date, there is no other synthesis that has similarly stood the

Scientia

Figure 1: Fluorescence emission for CdSe/ZnS core-shell nanocrystals under UV illumination shown from blue (~1.7 nm CdSe core) to red (~5 nm) (D. V. Talapin, 2010)

test of time. In order to provide sufficient stability for NC colloids, an organic surfactant is employed to coat NC surfaces. While useful for steric stability in nonpolar solutions and surface passivation essential for PL, these long-chain hydrocarbons are charge insulating and therefore constrain electronic communication between NCs. These properties are not desirable for solution-processed electronic devices. As a result, ligand exchange is utilized for smaller chain hydrophilic ligands.

In particular, compounds of metal chalcogenide complex (MCC) ligands have recently been brought to attention as a result of enhancement of NC communication via increased NC proximity and electron transport through ligands in solid-state. Furthermore, MCCs enable NC dispersal in polar solutions, a necessity for many functionalization processes.

Of particular interest for optoelectronic applications are binary NC semiconductors, which exhibit the same bulk electronic properties as traditional semiconductors, but allow more band-gap control, which permits us to tune for a desired applied wavelength.

Nanocrystal semiconductors In bulk semiconductors, the large number of atoms creates a high-density of electronic states, so dense that they are considered as bands of continuous delocalized energy states (Figure 2).[7] The upper-most filled band is termed the valence band (VB) and the lower-most unfilled band is the conduction band (CB). The energy difference between the VB and CB is known as the band gap, with energy Eg. The defining principle of all semiconducting materials is the following: when a photon of energy greater than Eg is absorbed by the material, it excites an electron from the VB to the CB. This absorption generates an electron-hole pair, formally known as an exciton, that migrates through the semiconducting material when

attached to anodic and cathodic terminals. Since Eg of nanocrystalline particles correlates to visible and nearinfrared (NIR) wavelengths, these materials are useful for electronic applications such as solar cells.[9] Alternatively, if the electron relaxes back to the VB from the CB without migration, photons of energy equivalent to Eg are emitted. This relaxation generates luminescence and makes semiconducting materials suitable for light-dependent applications like LEDs. In NC semiconductors, known as quantum dots (QDs), these bulk semiconductor properties are also observed, though with additional opportunities to control Eg by varying NC size. This property lies in the fundamentals of quantum mechanics, specifically quantum confinement.

Quantum confinement Quantum confinement is a size-dependent phenomenon describing the restrictions placed on the electronic wavefunctions in nanoscale materials. It predicts that, as the radius of a particle shrinks below the size of the Bohr radius of the bulk material, it becomes more confined in all three dimensions and the energies of the exciton wavefunctions increase, becoming discrete energy values.[1] For example, the exciton Bohr radius of bulk PbS is ~ 18 nm,[10] so any PbS crystal with a radius less than 18 nm will exhibit quantum confinement effects. As the particle size decreases, confinement strengthens, and the energy difference between the hole and electron states increases. This decrease shows size control of Eg, thus having implications for observable semiconducting properties.

Figure 2: (A) a schematic illustration of the density of states in metal and semiconductor clusters. (B) density of states in one band of a semiconductor as a function of dimension (A. P. Alivisatos, 1996)

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Spring 2015 For many device applications, size-tunable NC semiconductors must be assembled in close proximity so as to overlap electronic wavefunctions.[11] This overlap is quantum coupling, in which QDs exhibit band-like conductance via discrete energy levels while maintaining size dependent band-gap control.[12] This phenomenon is illustrated by Choi et al. who show carrier mobility greater than 1 (cm2/V s) in thin-film assemblies,[7] suggestive of the band-like electron transport.

In order to make use of QDs, the simple and robust hot-injection method is used to synthesize colloidal organic NC solutions with essential control of size, shape, and size-dispersity.

Figure 4: Ligand exchange of long chain organic ligands for: shorter hydrophobic or hydrophilic chains, with head group retention; smaller hydrophobic or hydrophillic ions (full exchange); smaller hydrophobic or hydrophillic bridging ions

Colloidal solution phase synthesis The hot-injection method Solution phase synthesis, otherwise known as a ‘sol’ process, is the most commonly used technique for NC synthesis.[13,14,15] First reported by Murray et al. in 1993,[5] the hot-injection method has since been replicated and revised, dominating today’s literature.[13,15,16] The original approach uses a surfactant solution containing cadmium and selenium precursors (Me2Cd and trioctylphosphine selenide (TOPSe) in Tri-n-octylphosphine (TOP)) that is rapidly injected at room temperature into a heated ‘hot’ solution of non-polar surfactant (TOP oxide (TOPO)) at 240-300 oC in an inert argon atmosphere.[5] This method induces pyrolysis of the precursors in the reaction mixture, causing an increase in precursor concentration beyond the nucleation threshold (supersaturation). The number of ‘free’ particles in solution initiates a short ‘nucleation burst’ (chemical precipitation) and subsequent NC growth.[17] The overall decrease in temperature of the reaction solution leads to quenching of the reaction, inhibiting further nuclelation. This inhibition is followed by gentle heating of the reaction solution, around 190290 oC,[5] during which growth of the existing particles dominates.[17] The reaction is then quenched by cooling to room temperature when the desired NC size is reached (Figure 3). a b

Figure 3: Transmission electron microscope image of PbS nanocrystals with reaction times of 10 s (a) and 2 minutes (b). Scale bar 5 nm. (D. V. Talapin, 2010)

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During synthesis, it is essential that size be controlled and monodispersity achieved. Size enables bandgap control, dictating the energy for absorption and luminescence. Organic surfactants are considered one of the main aids to size control, as they limit diffusion of precursor monomers towards the surface of nucleated particles, thus creating slower, more controlled growth pathways.[15] Moreover, varying surfactant concentration has been shown to dictate overall attainable NC size and to provide additional control of shape. This variation effect is observed for lead chalcogenides with oleic acid (OA) ligands, where final size increased from 10 to 80 nm and shape transitioned from spherical to cubic under increasing OA concentration.[13,15] Monodispersity (around 5-10% dispersity)[1] is desirable for LEDs that rely on one wavelength to give color purity.[18] One method of achieving monodispersity is to have independent nucleation and growth stages. Newer methods propose rapid injection of one room temperature precursor solution into the heated ‘hot’ precursor solution of another, so that essentially spontaneous nucleation occurs at high temperature. Not only does this newer method provide a short time frame for reaction before depletion of precursors, but it also prevents preemptive reaction of the mixed precursors at room temperature, as could happen for the method used by Murray et al.

Surface chemistry In addition to size and shape control, stabilizing ligands are added to the surface of NCs during synthesis to prevent particle aggregation. In most synthetic techniques, a non-polar organic surfactant is used, with a long aliphatic hydrocarbon tail for steric stabilization,

Scientia and surface passivation with a charged head group for strong binding to the NC surface.[1] However, long organic chain ligands are not always desired. Many functionalization methods are carried out in polar media that require hydrophilic ligands for NC stabilization.

Furthermore, charge insulation and large inter-particle separation prevent efficient charge transfer between electrons in solid state, which proves ineffective in electronic materials. Hydrophilic ligands, on the other hand, produce stable NC colloids in polar solutions.

These ligands are often shorter to increase NC proximity, enhancing electronic coupling, and have been shown to assist charge transport, while retaining size and shape control of NCs. As most hot-injection syntheses utilize hydrophobic surfactants, ligand exchange for hydrophilic ligands must be employed for polar colloidal solutions (Figure 4).

Polar colloidal solutions Ligand exchange can be performed in the solid state or in solution.[19] Methods of ligand exchange vary from partial ligand exchange, such as exchange of the organic ligand tail whilst retaining the original head group (commonly thiol, carboxylate, or amine),[20] to full ligand exchange of small ionic molecules, such as thiocyanate ion (SCN-) and chalcogenide ions (S2-, Se2-, and Te2-).[21,16] It is also possible to synthesize ligands with two coordinating heads that can ‘bridge’ two NCs with the potential to enhance communication via direct linking.

Metal chalcogenide complexes (MCCs) One of the most recent developments of bridging ligands is molecular metal chalcogenide ions, including Sn2S64- and In2Se42-.[22] MCCs are a group of strongly nucleophilic ligands that coordinate via the anionic Zintl ion to the ‘undercoordinated surface metal cations’ of

Figure 5: Sketch of a nanocrystal capped with the Sn2S64- Zintl ion of the metal chalcogenide complex (N2H5)4Sn2S6 .

Figure 6: Transmission electron microscopy on 2D superlattices of Au nanocrystals capped with (a) dodecanethiol and (b) Sn2S64- ligands (M. V. Kovalenko, 2009)

NCs (Figure 5).[1] These complexes are charge-balanced by counter cations such as N2H5+. In colloidal polar solution they exhibit desirable properties, such as Coulombic stabilization generated by their surplus negative charge[11] and they enhance photoluminescence quantum yield (PLQY) by eliminating dangling bonds.[1] Furthermore, MCCs decrease inter-particle separation which, in solid-state, increases quantum coupling between QDs. The most unique and promising feature of MCCs arises after gentle heating (200 oC), when MCCs are thermally decomposed to their metal chalcogenide constituents, becoming a conductor medium between NCs (Figure 6). The effect of this decomposition is observed in optical absorption spectra when in the crystalline state. Crystalline absorption shows a red shift relative to colloidal solution, implying relaxation of quantum confinement and thus enhanced delocalization of electronic states.[11] This delocalization enables more efficient charge transfer through NC solids and finer and more specific tailoring of electronic nanomaterials in the future.

However, MCCs are not without their limitations.

While like other ligands that enhance PL-QY in the solutionstate, MCCs lose this property when in the solid-state and in some cases show reduction of PL-QY.[22] This loss can be from as high as 50% PL-QY for organic capped NCs[23] to less than 1% using MCCs.[24] Another major constriction is their synthesis in highly toxic hydrazine (N2H4) solvent.

This synthesis requires an inert atmosphere, which limits its wider application and increases commercial cost.

While different solvents have been reported in place of hydrazine, such as dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), and water,[11] not all MCCs are soluble in these and so they cannot be used.

Once NC stability in a desired solvent is achieved, NCs can be processed into useful optical, electrical, and magnetic materials. However, current solid-state processing from colloidal solution often sacrifices unique QD properties and reduces PL by particle aggregation and generation of surface traps (dangling bonds). These issues often arise by ligand detachment from the NC surface during processing, which exposes previously protected trap-states and increases cationic disorder of

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Spring 2015 the NC surface,[25] with stoichiometric Cd/Se ratios such as 4:1 observed.[16] Current methods used to reduce the presence of trap-states involve ligands that remove traps from the band-gap whilst remaining strongly attached to the NC surface during solid-state processing,[20] such as MCCs. Slower growth regimes are also used to reduce overall trap-state generation, or growth of different NC layers over the core of another, as core/shell structures.[26] Nanocrystal solids The most simple immobilization method is NC selfassembly, in which a colloidal solution of NCs is drop-cast or spin-coated onto a conducting surface as a thin film, followed by gentle annealing to remove excess solvent.[11] Thin films are used in optoelectronic devices, such as solar cells, and in characterization techniques, such as X-ray diffraction (XRD) or transmission electron microscopy (TEM).

It is possible to apply post-deposition modification of thin films. One such technique involves fusion of neighboring NCs via vacant crystal facets. This process includes oriented attachment or post-synthesis colloidal atomic layer deposition (PS-cALD). In oriented attachment a dilute coordinating surfactant such as oleic acid induces weaker bound ligands to detach from the NC surface to expose uncoordinated crystal facets which favorably attach.[27] In PS-cALD, long organic ligands exchange for shorter inorganic ligands, decreasing intraparticle distances so much so that crystal facets fuse.

[28] In particular, oriented attachment shows promise for solution based crystal assembly, as the NC layers are processed in a liquid medium that can be directly transferred to a desired solid surface.

In contrast to depositional layering techniques, NCs can also be immobilized by incorporation into solid media. When looking to encapsulate semiconductor NCs into a solid it is vital that the solid is thermally and chemically stable, provides good surface passivation, and retains monodispersity of NCs, and is suitably transparent for light penetration. A variety of methods and host media have been explored, including semiconductor matrix embedded nanocrystal array (SMENA),[29] perovskites,[30,31] and ionic salts.[18] SMENA utilizes core/shell NCs, which fuse together via shells of adjacent NCs producing a structure of one NC type (core) embedded in a bulk-like support of another NC type (shell). Insertion of NCs into perovskite structures, such as methylammonium lead iodide (CH3NH3PbI3) is also proposed.[30] The ability to express band-gap control not only in QDs but also by utilizing different

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halide composites and displaying encouraging power conversion efficiencies (PCEs) up to 15%, give these NC solids a promising future such as in solar cells.[30,31] Mixed crystal rock salts One of the most recent developments in QD research since 2012 is incorporation of NCs into the crystal matrix of common metal halide rock salts, such as NaCl, KCl, or KBr.[18,32,33,34] Ionic rock salts are beneficial for light-dependent devices as they have light, chemical, and thermal stability, along with well-known simple syntheses and structures. More significantly to optoelectronic devices is their transparency and high refractive index (RI).[32] Both features enable efficient radiative flux to the NCs, as transparency prevents absorption of light energy by the ionic salt support and a high RI increases the amount of applied light energy reaching the NCs by recycling of light through the crystal.

Current methods utilize colloidally synthesized cadmium chalcogenide QDs,[18,32] capped with thioglycolic acid (TGA)[18] or mercaptopropionic acid (MPA)[33] in aqueous solution, and carbon based QDs that are then embedded into the salt matrix of NaCl, KCl, and KBr.[18,32,33,34] Results deem this method promising for PL applications, as the salt structure is shown not only to retain PL-QY of QDs but also enhance it by as much as 80% (in smaller QDs), compared to colloidal solution.[32] This enhancement is significant because in other assembly approaches, such as organic polymer matrices, the PLQY is sacrificed when QDs are incorporated into a solid due to chemical, thermal, and photo-oxidation. In rock salts, the tightly bound matrix around the embedded QDs lends resistance to these degradation pathways.[34] A suggested reason for enhancement of PL-QY of cadmium chalcogenide NCs in NaCl salt matrix is the formation of a thin CdClx layer on ‘free’ Cd surface cations. This formation passivates the NC surface by reducing the number of dangling bonds, which can act as exciton traps. It is also considered the reason for higher emission lifetime, due to reduced non-radiative recombination that is often a consequence of surface traps.[33] Additionally, the dielectric surrounding of the QD is proposed to increase when incorporated in NaCl, thus further enhancing PL-QY. Processing of NC/salt powder by blending into a poly(methyl methacrylate) matrix and layering onto a UV LED showed little loss in PL-QY of QDs, maintaining 95% of the original PL-QY, and no change in the emission wavelength (Figure 7).[33] This finding demonstrates significant potential for LED development and other

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b

Figure 7: (a) QD-salt composite in silicone under room-light, (b) QD-salt composite in silicone under UV-light [37], (c) CdTe QD based LEDs (applied voltage 3.1 V) of five different QD sizes, and (d) corresponding normalized emission spectra (S. Kalytchuk, 2013)

light-dependent devices. However, currently the loading value of QDs into the salt is less than 1%, so future directions will focus on increased NC loading.[18] One possible direction is to increase colloidal stability in aqueous salt solution to lengthen the time frame in which NCs are suspended, allowing them to be trapped inside the forming crystal structure. Control of NC size, carbon chain length of ligands, solution pH, and ionic strength are all considered factors of colloidal stability.

As yet, there has been little research outside of PL applications of QD rock salt mixed crystals to LEDs. However, future research could look into incorporation of other metal chalcogenide QDs with different capping ligands, in order to analyze spectroscopic data or intrinsic QD electronic properties, such as multiple exciton generation.[35] This direction is viable due to the minimal light or electronic interference from these metal halide salts.

Summary and outlook Over the past few decades, a robust solution-based colloidal synthesis of NCs has been achieved with current research, showing successful outcomes for solution stability in a wide range of polar and non-polar solutions, using organic and inorganic ligands. However, functionalization of NCs by incorporation into bulk media via solution-based processes is far from optimal. Tried methods include simple layering of NC thin films onto conducting media and post-depositional treatment, mixing with polymers, and embedding into mixed crystal structures. An interesting recent venture is mixed crystal assembly of NCs in common rock salts. Current achievements show positive NC loading and effective

luminescence when applied to LEDs. Future research will focus on stability of NC/salt solutions and improved crystallization conditions for greater NC loading by adjusting parameters including pH, temperature, and NC concentration. Different capping ligands will also be tested to improve NC coupling within the salt. MCC ligands, such as (N2H5)4Sn2S6, provide a promising research avenue for such improvements. In addition to current luminescence studies, the intrinsic properties of QDs can be probed in the zero interference rock salt media. If successful, this method could provide a fundamental template for future spectroscopic and electronic studies.

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K.-L. Ou, J.-C. Fan, J.-K. Chem, C.-C. Huang, L.-Y. Chen, J.-H. Ho, J.-Y. Chang, J. Mater. Chem. 2012, 22, XX. C. B. Murray, D. J. Norris, M. G. Bawendi, J. Am. Chem. Soc. 1993, 115, 8706-8715.

H. Ge, L. Hai, R. R. Prabhakar, L. Y. Ming, T. Sritharan, RSC Adv. 2014, 4, 16489-16496.

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Spring 2015

Aperture Honorable Mentions from the Photo Contest

Derek Wong

This photo is a result of pointing a laser at the Charged Coupled Device with no lens and using a short shutter speed. This is used to determine the width of the laser beam for better systematic characterization.

Nate Earnest

26

Scientia

Cecilia Jiang

Matthew Cheung

Nate Earnest

8E5 [derivative of CEM] human peripheral T cells with Acute Lymphoblastic Leukemia appear to have suddenly acquired a cell cycle defect that leads to abnormally large cell size (as designated by the two red arrows). These cells have remained culturable after several passages and continue to reach extraordinary sizes of at most 40-50x normal volume after surpassing the log phase.

Depicted is a BluFors Dilution Refrigerator - a machine used to cool devices down to near absolute zero temperatures. The lines going down the center are microwave lines that allows communication with other devices when the fridge is cooled down.

27

Acknowledgements The Triple Helix at the University of Chicago would like to thank the following individuals for their generous and continued support: Dr. Matthew Tirrell

Founding Pritzker Director of the Institute for Molecular Engineering

Eleanor Daugherty

Assistant Vice President for Student Life and Associate Dean of the College

Arthur Lundberg

Assistant Director of the Student Activities Center

Brandon Kurzweg

Student Activities Advisor

We also thank the following departments and groups: The Institute for Molecular Engineering The Biological Sciences Division The Physical Sciences Division The Social Sciences Division University of Chicago Annual Allocations Student Government Finance Committee (SGFC) Midstates Consortium for Math and Science

Finally, we would like to acknowledge all our Faculty Review Board members and the mentors of our abstract authors for their time and effort.

Research Submission Undergraduates who have completed substantial work on a topic are highly encouraged to submit their manuscripts. We welcome both full-length research articles and abstracts. Please email submissions to uchicago.print@thetriplehelix.org. Please include a short description of the motivation behind the work, relevance of the results, and where and when you completed your research.

If you would like to learn more about Scientia and The Triple Helix, visit http://thetriplehelix.uchicago.edu or contact us at uchicago@thetriplehelix.org.

Meet the Staff Scientia Editors in Chief Khatcher Margossian Luizetta Navrazhnykh Managing Editors Irene Zhang Jake Russell Michael Cervia Associate Editors Stephen Yu Amanuel Kibrom Erin Fuller Helena Zhang Donna Guo Salman Arif Writers Scientia Inquiries Gloria Wang Scientia Abstracts Scott Anderson Jerry Chee Margaret Dickinson James Gilhula Daniel Timothy Hickox-Young Emily Johnson & Lucas Sletten Reed Johnson & Claire Seitzinger

Kate Klesner Kristine Ma Katherine Oosterbaan Emily Reeves Pratik Sachdeva Caren Sullivan Payton Weidenbacher Fangzhou Xiao Benjamin Trnka Mara Farcasanu Kendyl Greimann Donna Guo Ben Johnson & Grace Wiesner Petras Jans Wendy Bindeman In Depth Hannah C. Muir Photographers Nate Earnest Derek Wong Cecilia Jiang Matthew Cheung Scientia Inquiry Faculty David Miller, PhD

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