Design and analysis of surface plasmon resonance optical sensor for determining cobalt ion based on chitosan-graphene oxide decorated quantum dots-modified gold active layer

In this study, the incorporation of surface plasmon resonance (SPR) spectroscopy with novel chitosan-graphene oxide/cadmium sulphide quantum dots (CdS QDs) active layer for cobalt ion (Co²⁺) detection has been developed. The interaction of different Co²⁺ concentrations with the novel modified active layer was monitored using the SPR technique. From the SPR results, detection range, sensitivity, full width at half maximum (FWHM), detection accuracy (DA) and signal-to-noise ratio (SNR) have been analysed. The results showed the detection range of this optical sensor was 0.01 to 10 ppm, and it was saturated for higher concentration of Co²⁺. The sensitivity obtained was 0.1188 ppm⁻¹ for low concentration of Co²⁺ ranged from 0.01 to 1 ppm. The FWHM and DA were consistent for all concentration of Co²⁺, while the SNR of the SPR signal increased with the Co²⁺ concentration. The SPR angle shifts were also fitted using Langmuir, Freundlich and Sips (Langmuir-Freundlich) isotherm models, where Sips model fitted the best with the binding affinity of 0.939 ppm⁻¹. The results proved that the novel chitosan-graphene oxide/CdS QDs modified gold thin film can detect Co²⁺ via SPR spectroscopy.