An application of a plasmonic chip with enhanced fluorescence to a simple biosensor with extended dynamic range

Plasmonic chips coated with thin silver and SiO2 layers were applied to a simple biosensor with wide dynamic range, which has some advantages in the points of sensitivity and surface selectivity in spite of a simple fluorescence detection system without complex optical stuffs. The enhanced fluorescence of fluorescent labeled-marker proteins, cy5-streptavidin (SA), excited by irradiation light from the rear panel of the chip was measured. To obtain the maximum fluorescence enhancement by excitation under an electric field enhanced by grating-coupled surface plasmon resonance from the rear irradiation, the optimal silver thickness was studied and found to be 30–35 nm. A directional fluorescence due to re-coupling between fluorescence and plasmon polaritons was also observed on the plasmonic chips and enhanced fluorescence 90 times compared with that on glass slides was superior to the others reported. The limit of detection (LOD) studied here was improved up to 50 pM after 10-min incubation and dynamic range was also extended by 2 order, compared with that on glass slides. The irradiation from the rear panel demonstrated advantage in the surface-selective detection of cy5-SA at 100 nM concentration. Our plasmonic chip has great potential in biosensing application due to its advantages of rapid detection, simple operation, high sensitivity (wide dynamic range), surface selectivity, and suppression of non-specific adsorption.