Ultrasensitive Detection of Methylene Blue Using an Electrochemically Synthesized SERS Sensor Based on Gold and Silver Nanoparticles: Roles of Composition and Purity on Sensing Performance and Reliability

Abstract

An electrochemical approach has been used for green synthesis of gold and silver nanoparticles (e-AuNPs and e-AgNPs) with high levels of purity and scalability. The electrochemically synthesized noble-metal nanoparticles were characterized by ultraviolet–visible (UV–Vis) spectroscopy and scanning electron microscopy (SEM), confirming the formation of spherical e-AuNPs and e-AgNPs with average size of 19 nm and 24 nm, respectively. These green nanoparticles were deposited on aluminum substrates using the drop-drying method for surface-enhanced Raman scattering (SERS)-based detection of Methylene Blue (MB) within the ranges from 10−5 M to 10−8 M and 10−7 M to 10−10 M, respectively. The SERS sensors also exhibited outstanding sensing performance for MB detection with limits of detection (LOD) of 9 × 10−11 M for e-AuNPs and 5 × 10−12 M for e-AgNPs. The enhancement factors (EFs) of the two noble-metal NPs were estimated to be 4.4 × 107 for e-AuNPs and 1.98 × 109 for e-AgNPs at an MB concentration of 10−8 M. We then clarified the roles of the purity and composition of these nanoparticles (NPs) on their SERS sensing performance by comparing our sensors with several reported sensing systems, as well as comparing our two kinds of NPs, in terms of sensitivity, stability, and reproducibility. We also propose a possible mechanism for the enhancement of the SERS signal observed for our two electrochemically synthesized Nps.