Highly sensitive, stable g-CN decorated with AgNPs for SERS sensing of toluidine blue and catalytic reduction of crystal violet

SERS substrates with high sensitivity, SERS enhancement and stability are essential for fabrication of SERS sensors to detect dyes at low concentration. Such substrates generally have a versatile support bonded to metal nanoparticles of optimum size. Simple methodology that yields SERS substrates with reproducible results is mostly desired for sensor fabrication. In this study, silver ions were reduced with safe reducing agent NaBH₄ to Ag metal nanoparticles (AgNPs) in the presence of previously prepared g-CN to obtain g-CN decorated with silver nanoparticles (AgNPs@g-CN) of average diameter 22 nm. The results of XPS and UV–Vis spectroscopy unambiguously establish significant interaction between the nitrogen sites of g-CN and AgNPs. The AgNPs@g-CN yielded very high SERS enhancement for toluidine blue at very low concentration (2.5 × 10⁻⁰⁹ M), and the SERS results are reproducible. The surface enhancement factor (EF) is one of the important criteria to evaluate and compare SERS materials, and it was equal to 9.13 × 10⁶ toward toluidine blue. The catalytic activity of the substrate for the reduction of crystal violet (CV) to its leuco-form was tested with NABH₄. The reaction was monitored by UV Vis spectroscopy. There was a rapid fall in intensity of CV. The reduction of CV mainly occurred via electron transfer from AgNPs, and the product did not interfere with the absorbance of CV. Hence, AgNPs@g-CN could be a convenient choice for fabrication of commercial SERS sensors for detection of dyes at low concentrations. It is also useful as a catalyst for the reduction of organic dyes.