New Portable Device Identifies Pathogens
THE CORNELL DAILY SUN | Wednesday, February 8, 2012 13
SCIENCE
By MARIA MINSKER Sun Senior Writer
In an effort to simplify the process of diagnosing diseases caused by such pathogens as tuberculosis, chlamydia, gonorrhea and even HIV, Prof. Dan Luo, biological and environmental engineering, and Prof. Edwin Kan, electrical and computer engineering, have combined inventions from their respective fields to potentially revolutionize the way diseases are detected in the developing world with a new handheld device. In Luo’s laboratory, he and his team have developed a way to amplify the size of small samples of pathogen DNA, RNA and proteins, said Luo. His team has observed that DNA formations are analogous to Lego blocks in that a strand of DNA can connect to another strand of DNA if the two contain complementary genetic codes. The strands can be shaped into different forms. “If DNA strands that correspond are combined over only a portion of their length, then interesting shapes can be made, such as the letter Y,” Luo said. The base of the Y shape, the part that points straight down, is either a strand of DNA or an antibody, designed to connect with a pathogen, just like two Lego blocks connect when corresponding parts are brought together Luo said. The top section of the Y, the part that consists of the two outward pointed lines, is the site where molecules called monomers attach and chemically combine with each other in a process called polymerization. The monomers polymerize when exposed to ultraviolent light. The “Y” detects various pathogens by matching and
connecting with them. When a pathogen is added to a solution of the corresponding Y-shaped molecules, a part of the pathogen will attach to a matching stem on the Y. “So if a pathogen is present in solution, the result is the formation of many double-Ys linked together by a
KELLY YANG / SUN STAFF PHOTOGRAPHER
Pathogen Pair | Prof. Edwin Kan and Prof. Dan Luo examine their pathogen detecting device.
pathogen molecule, each assembly carrying two molecules capable of polymerizing,” Luo said. Then, when the mixture is exposed to UV light, polymerization occurs, meaning the Y-shaped molecules link up to each other and form long polymer chains. If polymerization does not occur, then no pathogen is present. “The polymerization won’t happen if there is no pathogen present to link two Ys together,” Luo explained. “A single
Y with only one polymer molecule attached can only link to one other single Y, and no chain will form.” Kan’s research has made an important implementation to this new method. He has designed a computer chip that responds to the amplified samples targeted by Luo’s method, and sends a signal that tells scientists whether or not a pathogen is present. Typically, when a strand of Y-shaped DNA attaches to a single molecule, a very weak signal is emitted, and it requires highly tuned and precise sensors to detect a pathogen. If polymerization occurs, however, the signal becomes stronger and easier to detect. Kan’s chip uses common, inexpensive semiconductor technology compatible with other common electronic devices, such as a mobile phone. Kan’s device is capable of measuring both the mass and charge of molecules, two measurements that can determine whether the Y chains contain pathogen particles. Kan and Luo’s work on their joint invention is supported by the Bill & Melinda Gates Foundation as part of the Grand Challenge program to develop “point-of-care diagnostics” for developing countries that do not have the laboratory and research space to test and diagnose diseases. According to Luo, the foundation has distributed $25 million to 12 teams, with each team working on a different element to include in a practical, durable and low-cost testing and diagnostic kit. Maria Minsker can be reached at mminsker@cornellsun.com.
Prof.Spencer Wells Traces the Path of the Human Race By SHAUNTLE BARLEY Sun Staff Writer
The classic explorer, valiantly sails out to discover new lands, penciling in the blank edges of the map, may no longer hold a place in today’s society. But, in this explorer’s absence emerges a modern adventurer who traverses the world, filling in not the missing parts of the globe, but rather the gaps in the map of human existence. Spencer Wells, Frank H.T. Rhodes Class of ’56 Professor and Explorer-inResidence at National Geographic and Director of the Genographic Project, has adventured to almost 80 countries, ridden ex-Soviet tanks in -70 degree temperatures in far-eastern Russia, traversed the worst part of the Sahara Desert in Chad and crossed mine fields in Bolivia, while on a quest to discover how the human race migrated the globe. The goal of the ongoing Genographic project is to understand human origins and the genetic relations that are common to all people, according to Wells. The project analyzes in particular the genes of remote populations along the Silk Road, from London to Mongolia, which is a region that has seen substantial human traffic throughout history. These populations often have relatively “old genes” according to Wells, which means that these groups have reproduced minimally with other populations since ancient times and thus their genes represent an older, purer version, similar to that of humanity’s oldest ancestors. “The core of the science in this project is based on the work we do around the world with indigenous and traditional peoples,” Wells said. “Because they retain that geographic link back to their ancestors that most of us have lost that recently because our ancestors have moved around so much.” By examining the number of genetic differences in populations and factoring in the normal rate of genetic mutation, he can determine how long a population has been in a certain region and through where it traveled to get there.
COURTESY OF NATIONAL GEOGRAPHIC
Academic Adventurer | Prof. Spencer Wells is a National Geographic reporter and director of the Human Genographic project.
Unlike other academic geneticists, Wells gets to meet the people who give their samples to the Genographic project while in the field. In doing so he gets to better understand the cultural patterns
behind each sample, he said. “It’s amazing being able to piece the story of human migration together by meeting the people who provided the clues,” Wells said. In conducting the Genographic project, Wells found that humans are 99.9 percent genetically similar to each other. The superficial differences between people are the result of small variation in only a few genes. From the initial pool of genes, superficial changes have been those evolutionarily advantageous for survival in specific regions. For example, pale skin is necessary for sufficient vitamin D production in areas where there is little direct light and similarly, dark skin is advantageous in areas of relentless solar radiation. Other changes, such as hair type, can be attributed to sexual selection among individual populations, Wells said.The genetic homogeneity of Homo sapiens can be contributed to a near extinction
event 70,000 years ago. At this time, there were only a few thousand humans alive in the world, all of them living in Africa. When compared with the rest of the large apes, who have between four and 10 times more within-species diversity than humans, people are significantly more similar than outward appearances would suggest. “I think this message of people being much more closely connected genetically than we might suspect by looking at surface features is an important social message that to me can't be overstated.” To learn more about Spencer Wells and The Genographic Project check out our interview with the National Geographic Explorer at cornellsun.com/video. Shauntle Barley can be reached at skim@cornellsun.com.
COURTESY OF NATIONAL GEOGRAPHIIC
Indigenous Genes | Prof. Spencer Wells has traveled to close to 80 countries collecting samples from native peoples.