Fabrication of sandwich structures of Ag/analyte/MoO3sea urchins for SERS detection of methylene blue dye molecules

Abstract

A substrate for surface-enhanced Raman spectroscopy (SERS) in a sandwich configuration, noble metal/analyte/defect-rich metal oxide, is demonstrated for the detection of methylene blue(MB). The sandwich structure (Ag/MB/SUMoO₃) is fabricated by physical vapour deposition of Ag nanoparticles over the MB analytes that are adsorbed on sea urchin MoO₃(SUMoO₃). SUMoO₃are grown on a glass substrate by chemical bath deposition. The morphology of the fabricated sandwich structures shows serrated spikes of MoO₃from the core region decorated with strings of silver nanoparticles. The silver-decoration and the oxygen defects of SUMoO₃promote absorption in the visible region and facilitate charge transfer between MB and SUMoO₃, which are beneficial for achieving superior SERS properties in this configuration compared to the contribution from individual components alone. The sandwich structure is able to detect the MB molecule up to 100 nM with an enhancement factor of 8.1 × 10⁶. The relative standard deviation of SERS intensity for the 1618 cm^-1peak of MB across the substrate is 29.2%. The configuration offers stability to SERS substrate under ambient conditions. The combined effect of charge transfer, surface plasmon resonance, and MB resonance results in the improved SERS detection of MB molecules with the Ag/MB/SUMoO₃sandwich structure.

Keywords: Ag/MoO3; SERS; methylene blue; sandwich structures.