What is it about?
Si Nanowires decorated with silver nanoparticles are developed and used for detection of molecules at trace levels.
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Why is it important?
Molecular based detection of materials is important in different fields. Three-dimensional silver nanoparticles decorated vertically aligned Si nanowires (Si NWs) are effective surface-enhanced Raman spectroscopy (SERS) substrates for molecular detection at low concentration levels. The length of Si NWs prepared by silver assisted electroless etching is increased with an increase in etching time, which resulted in the reduced optical reflection in the visible region. These substrates were tested and optimized by measuring the Raman spectrum of standard dye Rhodamine 6G (R6G) of 10nM concentration. Further, effective SERS enhancements of 105 and 104 were observed for the cytosine protein (concentration of 50 lM) and ammonium perchlorate (oxidizer used in explosives composition with a concentration of 10 lM), respectively. It is established that these three-dimensional SERS substrates yielded considerably higher enhancement factors for the detection of R6G when compared to previous reports. The sensitivity can further be increased and optimized since the Raman enhancement was found to increase with an increase in the density of silver nanoparticles decorated on the walls of Si NWs.
Perspectives
Three-dimensional SERS substrates have been prepared by decorating the vertically aligned silicon nanowires with Ag nanoparticles. Significant enhancements in the Raman signals from diverse molecules at low concentration levels have been achieved. The length of Si nanowires monotonically increases with an increase in etching time. It was observed that the optical reflectance of Si NWs decreases with an increase in etching time. The minimum reflectance value achieved was 1% for 35 lm long Si NWs in the wavelength range of 400–800 nm due to multiple scattering. The SERS spectra of standard dyes such as R6G (as low concentration as 10 nM) were measured with an effective enhancement factor of 107. Furthermore, Raman enhancements of 105 and 104 were observed for cytosine protein and ammonium perchlorate, respectively, for higher distribution of Ag NPs decorated on the walls of Si NWs. The Raman peak at 760 cm1 clearly signifies the detection of ammonium perchlorate (AP) molecules. This study demonstrates the importance and versatility of these 3D SERS substrates for molecular detection at low level concentrations.
Professor Venugopal Rao Soma
University of Hyderabad
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This page is a summary of: Three-dimensional hybrid silicon nanostructures for surface enhanced Raman spectroscopy based molecular detection, Journal of Applied Physics, January 2018, American Institute of Physics,
DOI: 10.1063/1.5000994.
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