Dual-mode capacitive and localized surface plasmon resonance biosensor based on high-density Au nanoislands.

A capacitive-localized plasmon surface resonance (LSPR) dual-mode biosensor was developed using gold (Au) nanoislands modified on an Au interdigitated electrode (IDE). Au nanoislands were deposited through repeated thermal dewetting to increase their packing density and enhance sensor sensitivity. The response of the capacitive sensor to antibody-antigen interactions was optimized at 0.5 Hz in phosphate-buffered saline. Modification with Au nanoislands significantly reduced the effective electrode gap of the IDE, thereby enhancing the capacitive sensitivity, as evidenced by charge-transfer resistance and electric field analysis. Computer simulations confirmed that the effective electrode gap of a 5 μm gap Au IDE with an 88.1% packing density of Au nanoislands decreased to 525.9 nm. The influence of Au nanoislands on LSPR was assessed through parameters such as λmax, full width at half maximum, Q factor, and figure of merit. Additionally, the electric field enhancement factor, which indicates LSPR sensitivity, was calculated relative to the packing density of the Au nanoislands. The dual-mode sensor demonstrated efficacy in detecting Salmonella typhimurium, and the capacitive and LSPR sensor results showed a statistically significant correlation.