GREEN SYNTHESIS OF BIOGENIC NANOPARTICLES: A STUDY OF METAL ION DETECTION, SUNLIGHT INDUCED REVERSIBLE AGGREGATION AND SERS S. Kaviya and Edamana Prasad * Department of Chemistry, Indian Institute of Technology Madras, Chennai-600 036, India Abstract Nature provides abundant resources to prepare nanomaterials with novel structures and properties. The work describes an eco-friendly synthesis of silver and gold nanoparticles using an aqueous extract of the bone powder of a dry marine organism (seahorse), which acts both as a reducing as well as stabilizing agent. The novel photo-induced formation of the nanoparticles (NPs) was characterized by UV-vis absorption, dynamic light scattering, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) experiments. The role of pH on the feasibility of nanoparticle formation has been investigated. The results suggest that photoinduced electron transfer from the amino acids present in the bone extract is responsible for the reduction of the nanoparticle precursors. The as-synthesized nanoparticles have been utilized as ‘naked eye’ sensors for the detection of multiple ions (Cu2+, Cr3+,V4+ and UO22+) at micromolar concentration of the analytes. Furthermore, the NPs were found to enhance the surface Raman peaks from dye molecule (rhodamine 6G) at nano molar concentration of the analyte. More significantly, a novel and efficient sunlight induced reversible aggregation pathway for the as-synthesized nanoparticles has been demonstrated. a)
Introduction
-6
200 µl of 10 M -6 300 µl of 10 M -6 350 µl of 10 M -6 400 µl of 10 M
0.4 Absorbance
• Synthesis and stabilization of nanoparticles using bio-compatible capping agents from natural resources such as microorganisms (e.g. alga and fungi) and plant extract provide great advancement over existing chemical and physical methods since they are renewable, cost effective and ecofriendly. • NPs with suitable capping agents have been effectively utilized as sensors for toxic metal ions through monitoring the shifts in the surface plasmon resonance (SPR) absorption band. • Sensing of toxic metal ions will be attractive if the detection of the analyte can be monitored by naked eye, at relatively lower concentration of the analyte.
100 nm
0.0 400
600
Figure 3. (a) UV-vis absorption spectra of AgNP with the addition of different aliquots of V4+ [µM] at pH 7 and (b) TEM image of black color aggregates. 1.2
Absorbance
Seahorse extract
boiled for 15 min, filtered
800
Wave length (nm)
a)
Seahorse bone powder
b)
0.2
Preparation of the extract distilled water
4+
V at pH 7 4+ V at pH 7 4+ V at pH 7 4+ V at pH 7
Synthesis of metal nanoparticles (NPs)
15 min 12 min 9 min 6 min 3 min 0 sec
0.8
0.4
seahorse extract
Aqueous solution of AgNO3/HAuCl4
0.0 450
AgNP/AuNP
sunlight
600
750
Wave length (nm)
b)
Colorimetric detection of metal ions and surface enhanced Raman scattering studies (SERS)
c)
aqueous solution of analyte Sensing of analyte
AgNP/AuNP in water
0 sec
200 nm
Results
AuNP
Absorbance
1.6
15 min
20 nm
Figure 4. (a) UV-vis spectra of reversible aggregation of AuNPs in the presence of sunlight at different time intervals, (b & c) the corresponding TEM images of the photograph in the inset.
2.0
a)
9 min
AgNP
a)
b)
1.2
0.8
AgNP at pH 7 AgNP at pH 9 AuNP at pH 7 AuNP at pH 9
0.4
0.0
400
500
600
700
10 µm
20 µm
800
Wavelength (nm)
c)
AgNP + Rhodamine 6G AuNP + Rhodamine 6G Rhodamine 6G
c) Intensity (a.u)
b)
1200
Figure 1. (a) UV-vis absorption spectra of Ag and AuNPs stabilized by dry seahorse extract at two different pH (7 & 9) and the corresponding photographs (Inset). (b & c) TEM images of Ag and AuNPs , respectively. The insets in (b) and (c) are the corresponding SAED pattern (above) and EDAX profile (below).
-1
Wavenumber (cm )
1600
Figure 5. (a & b) Confocal laser Raman microscopic image of Ag and AuNPs in the presence of rhodamine 6G (109 M), (c) surface enhanced Raman signals of Ag and AuNPs in the presence of rhodamine 6G (109 M).
Conclusions -6
0.4
Absorbance
2+
100 µl of 10 M cu at pH 7 -6 2+ 150 µl of 10 M cu at pH 7 -6 2+ 200 µl of 10 M cu at pH 7 -6 2+ 250 µl of 10 M cu at pH 7 -6 2+ 300 µl of 10 M cu at pH 7 -6 2+ 400 µl of 10 M cu at pH 7
0.2
b)
Absorbance
a)
0.4
-6
+3
100 µl of 10 M cr at pH 7 -6 +3 200 µl of 10 M cr at pH 7 -6 +3 250 µl of 10 M cr at pH 7 -6 +3 300 µl of 10 M cr at pH 7 -6 +3 400 µl of 10 M cr at pH 7
0.2
• The
photo-assisted preparation involves simple, cost effective steps and no labeling techniques are required.
• Photoinduced regeneration mechanism of NPs from the NPs aggregates without addition of any external reagents has been achieved.
• Rapid 600
750
Wave length (nm)
c)
-6
600
Absorbance
Wave length (nm)
750
750
-6
2+
-6
2+
-6
2+
-6
2+
-6
2+
100 µl of 10 M UO2 at pH 7
4+
0.2
0.0
600
Wave length (nm)
d)
200 µl of 10 M V at pH 7 -6 4+ 250 µl of 10 M V at pH 7 -6 4+ 300 µl of 10 M V at pH 7 -6 4+ 350 µl of 10 M V at pH 7 -6 4+ 400 µl of 10 M V at pH 7
0.4
0.0
900
• The
nano systems were found to be useful to generate surface enhanced Raman signals for a dye molecule.
200 µl of 10 M UO2 at pH 7
0.4
250 µl of 10 M UO2 at pH 7
Absorbance
0.0
detection of multi-ions in aqueous system in the absence of any commercial instrument.
300 µl of 10 M UO2 at pH 7 350 µl of 10 M UO2 at pH 7 0.2
0.0
Acknowledgments S. Kaviya thanks for the INSPIRE fellowship from DST, Govt. of India. We thank the financial support from DST Nano Mission {Ref. No. SR/NM/MS-115/2010 (G)} and SAIF, IITM for instruments.
600
750
Wave length (nm)
Figure 2. UV-vis absorption spectra shows the detection of (a) cu2+, (b) Cr3+, (c) V4+ and UO22+ by AuNPs at pH 7.
References • Lu, L.; Kobayashi, A.; Tawa, K.; Ozaki, Y. Chem. Mater., 2006, 18, 4894-4901. • Chien, Y. H.; Huang, C. C.; Wang, S. W.; Yeh, C. S. Green Chem., 2011, 13, 1162-1166.