Streptavidin-Coated Au Nanoparticles Coupled with Biotinylated Antibody-Based Bifunctional Linkers as Plasmon-Enhanced Immunobiosensors

The localized surface plasmon resonance (LSPR) effect of aggregating gold nanoparticles (AuNPs) has facilitated the development of colorimetric biosensors that can potentially be employed on site. We have developed an effective strategy to enhance the LSPR color-change signal by decoupling target detection and signal generation steps during immunobiosensing. The biosensor consists of streptavidin-coated AuNPs coupled with biotinylated antibacteria antibody as bifunctional linkers (BLs). While a BL can function both as an immunoreactor to bind to the target and as a cross-linker to aggregate AuNPs, its cross-linking function is largely limited when it binds with the target. We investigated the effect of number density (D_n) of AuNPs on the LSPR signal enhancement and the attendant improvement in detection sensitivity and rapidity of our biosensor by changing the particle size (5 to 50 nm diameter) when holding the absorbance of the AuNPs solution constant (Abs = 0.4 at 10× dilution). The performance enhancement of the biosensor was demonstrated by detecting a model target, streptavidin, and two bacteria, Escherichia coli and Legionella pneumophila. The results show that when Abs is held constant, the systems with lower D_n but larger particles perform better. Therefore, our visual biosensing system can be suitably composed to maximize the limit of detection and rapidity.