Enhanced Molecular Vibrations of Phenylalanine, Beta-alanine, Leucine and Glycine Amino Acids Using Ag Nanoparticles for Their Detection

Ag nanoparticles were deposited using the chemical method of Tollens to have silvery active substrates which they were utilized in Surface Enhanced Raman Spectroscopy (SERS) to detect phenylalanine, beta-alanine, leucine and glycine amino-acids. Silvery active SERS substrates were characterized using UV-Vis spectroscopy, X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Plasmonic peak at around 439 nm in UV-Vis spectrum as well as FCC structure in XRD spectrum confirmed the formation of Ag structures. According to the FE-SEM image, although the most Ag particles have the sizes between 100 - 300 nm, particles with the smaller size of 50 nm and the larger size of 1000 nm have been synthesized. The presence of the large particles causes the light scatters from them. Then, different concentrations of the amino acids were engraved on the active SERS substrates to detect their molecular vibrations using Raman spectroscopy. The molecular vibrations of the amino acids are enhanced when they were engraved on the active SERS substrates due to surface plasmon resonance of the smaller Ag nanoparticles as well as light scattering from the larger Ag particles. In the other hand, the SERS intensity of the amino acids are stronger than their Raman intensity. The active SERS substrates could identify the concentration of 10-7 M of the amino-acids.