As medicine and pharmacology investigate nanoscale processes, it has become increasingly important to identify and characterize different molecules.

Raman spectroscopy, a technique that exploits the dispersion of laser light to identify molecules, has a limited capacity to detect molecules in diluted samples due to low signal performance.

A team of researchers from the University of Hyderabad, in India, has improved molecular detection at low concentration levels by organizing nanoparticles in nanowires to improve Raman spectroscopy.

Enhanced surface Raman spectroscopy (SERS) uses electromagnetic fields to improve Raman scattering and increase sensitivity in standard dyes such as R6G by more than one billion times.

The team decorated silicon nanowires aligned vertically with varying densities of silver nanoparticles, using and improving the three-dimensional shape of the structure. Their results, published in the Journal of Applied Physics, show that their device was able to improve Raman signals for the protein cytosine and ammonium perchlorate by a factor of 100,000.

“The beauty is that we can improve the density of these nanowires using simple chemistry,” says one of the authors of the research, Soma Venugopal Rao. “If you have a large density of nanowires, you can put more silver nanoparticles in the substrate and increase the sensitivity of the substrate,” adds this expert.

Improves sensitivity

Applying the necessary nanostructures to SERS devices remains a challenge for the field. The construction of these structures in three dimensions with silicon nanowires has attracted attention for its greater surface area and superior performance, but silicon nanowires are still expensive to produce.

Instead, the team was able to find a more economical way to make silicone nanowires and used a technique called electroless engraving to create a wide range of nanowires. These experts “decorated” these cables with silver nanoparticles with variable and controlled densities, which increased the surface area of the nanowires.

“The optimization of these vertically aligned structures took a lot of time at the beginning,” says Nageswara Rao, another author of the article. “We increase the surface area and to do this we need to change the aspect ratio,” he adds.

After optimizing its system to detect Rhodamine dye at a nanomolar level, these new substrates that the team built improved 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 to detect explosives, in concentrations as diluted as 50 and 10 micromolar, respectively.

The results have given the team reason to believe that it might soon be possible to detect compounds at concentrations on the nanomolar or even picomolar scale, says Nageswara Rao. The work of the team has opened several ways for future research, from experimenting with different nanoparticles such as gold, increasing the clarity of the nanowires or testing these devices in various types of molecules.

Source: Europa Press

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