Optimized bi-metallic film over nanosphere SERS substrate for sensitive detection of folic acid

We report an optimized bi-metallic film over nanosphere (BMFON) substrate platform for Surface Enhanced Raman Scattering- (SERS-) based detection of folic acid. Initially, the substrate was fabricated by spin-coating a mixture of polystyrene (PS) nanoparticle of diameter 400 nm and sodium dodecyl sulphate on glass slide. These hexagonally packed nanostructures were subsequently coated with 80 nm of silver, followed by 120 nm of gold layer. The optimized substrate was analyzed by studying the SERS performance with covalently anchored Raman-active analyte, 2-naphthalene thiol. It was found that by increasing the PS concentration, the coverage of SERS-active sites was increased and also standard deviation of the SERS intensity at various location of the substrate was found to be only around 10% to as low as 3%. We used these substrates for proof-of-concept detection of folic acid, which has been identified as a factor for risk of cancers when consumed in high dosage. We found that optimized BMFON substrates could provide a means for sensitive SERS detection of folic acid.