Indium tin oxide/gold/graphene oxide composite membrane structure and gold nanoparticles synergistically enhanced fiber optic sensor for mercury ion detection

Mercury ion is a highly toxic heavy metal pollutant that poses significant risks to both environmental and human health, underscoring the need for the development of highly sensitive, rapid-response, and convenient detection methods. In this study, we present an optical fiber sensor based on indium tin oxide/gold/graphene oxide composite membrane structure and gold nanoparticles for sensitivity mercury ion detection. The sensor achieves enhanced sensitivity by coupling surface plasmon resonance excited in the indium tin oxide/gold/graphene oxide composite film with the localized surface plasmon resonance induced by gold nanoparticles. In order to achieve highly selective mercury ion detection, two special single-stranded DNAs thymine rich and asymmetrically matched that are modified on the sensing region and gold nanoparticles, respectively. In the presence of mercury ion, the single-stranded DNAs strands form a double-helix thymine-mercury ion-thymine complex, anchoring the gold nanoparticles to the fiber surface. This leads to a pronounced change in the refractive index near the sensing region, resulting in a red shift in the SPR spectrum. Furthermore, by reducing the single-stranded DNAs length, the distance between the gold nanoparticles and the fiber surface can be minimized, thereby enhancing the near-field coupling effect and increasing detection sensitivity. Experimental results demonstrate that reducing the single-stranded DNAs length from 15 nm to 3 nm enhances the sensitivity of mercury ion detection by to 173 % of the original and lowers the detection limit to 8.8 × 10 −10 M. This sensor combines high sensitivity, selectivity and low cost, with significant potential for applications in environmental monitoring.