Although nano-silver has been used for surface-enhanced Raman scattering detection, it can achieve a stronger detection effect by combining with a three-dimensional structure of nano-silicon wires. Recently, the research team of the University of Yderabad in India, through the nano-silver-decorated 3D nano-silicon wire as the carrier of the laser Raman, has improved the detection sensitivity of some biochemical molecules by 100,000 times! Has great application value. The results were published in the American Journal of Applied Physics.

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A team of researchers from the University of Hyderabad in India has improved molecular detection at low concentration levels by arranging nanoparticles on nanowires to enhance Raman spectroscopy. Surface-enhanced Raman spectroscopy (SERS) uses electromagnetic fields to improve Raman scattering and boost sensitivity in standard dyes Such as R6G by more than one billionfold.

The team decorated vertically aligned silicon nanowires with varying densities of silver nanoparticles, utilizing and enhancing the structure's 3-D shape. Their results, published in the Journal of Applied Physics , show that their device was able to enhance the Raman signals for cytosine protein and Ammonium perchlorate by a factor of 100,000.

"The beauty is that we can improve the density of these nanowires using simple chemistry," said Soma Venugopal Rao, one of the paper's authors. "If you have a large density of nanowires, you can put more silver nanoparticles into the substrate and can Increase the sensitivity of the substrate."

Applying the necessary nanostructures to SERS devices remains a challenge for the field. Building these structures in three dimensions with silicon nanowires has garnered attention for their higher surface area and superior performance, but silicon nanowires are still expensive to produce.

Instead, the team was able to find a cheaper way to make silicon nanowires and used a technique called electroless etching to make a wide range of nanowires. They "decorated" these wires with silver nanoparticles with variable and controlled densities, which increased the nanowires' Surface area.

"Optimizing these vertically aligned structures took a lot of time in the beginning," said Nageswara Rao, another of the paper's authors. "We increased the surface area and to do this we needed to change the aspect ratio."

After optimizing their system to detect Rhodamine dye on a nanomolar level, these new substrates the team built enhanced Raman sensitivity by a factor of 10,000 to 100,000. The substrates detected concentrations of cytosine, a nucleotide found in DNA, and ammonium perchlorate, a molecule with Potential for detecting explosives, in as dilute concentrations as 50 and 10 micromolar, respectively.

The results have given the team reason to believe that it might soon be possible to detect compounds in concentrations on the scale of nanomolar or even picomolar, Nageswara Rao said. The team's work has opened several avenues for future research, from experimenting with different nanoparticles such As gold, increasing the sharpness of the nanowires or testing these devices across several types of molecules.

The same research results used nano-silica carrier to enhance the detection ability of infrared spectrum as early as 2005 (Journal of Applied Physics 98 , 114310 (2005); https://doi.org/10.1063/1.2138376 ) (Applied Surface Science, Volume 252, Issue 5 , 15 December 2005 , Pages 1197-1201 ) its detection capability increased by 1000 times.

More information: VS Vendamani et al, Three-dimensional hybrid silicon nanostructures for surface enhanced Raman spectroscopy based molecular detection, Journal of Applied Physics (2018). DOI: 10.1063/1.5000994