INVESTIGATION OF THE pH EFFECT OF METHYL RED ADSORBED ON SILVER NANO PLATE SQUARE TO SURFACE ENHANCED RAMAN SCATTERING

Abstract

In this study, we present the results of investigating the pH effect of methyl red (MR) on surface-enhanced Raman spectroscopy (SERS) using the substrate of the silver nanoparticles (Ag-NPs) and silver plates square (Ag-PS). Ag-PS were fabricated by photochemical method under green light-emitting diode (LED) irradiation (λ = 532 nm) onto a solution of silver nanoparticles. Morphology and size of the as-obtained Ag-PS were characterized by scanning electron microscopy (SEM) and transmition electron microscopy (TEM). Optical properties were characterized by ultraviolet- visible absorption. The crystal structure of the samples was investigated by X-ray diffraction (XRD). Surface-enhanced Raman scattering spectroscopy (SERS) was used to investigate the effect of pH = 2.01; 3.91; 5.1; 6.36 and 8.96. The results show that when pH < 5 the Raman spectral intensity is strongly enhanced at 1609 cm^-1 while at pH > 5 it is enhanced at 1396 cm^-1. Interestingly at pH = 2.01, the linear dependence between the logarithm of the SERS signal intensity (log I) and the logarithm of the MR concentration (log C) occurred in the range from 3*10^-8 M to 10^-4 M and detection of limit (LOD) reach 3*10^-8 M.