Stable and sensitive silver surface plasmon resonance imaging sensor using trilayered metallic structures

The silver surface plasmon resonance (SPR) sensor has long been explored due to its intrinsic sensitivity enhancement over the conventional single-layered gold SPR sensor. However, the silver SPR sensor has not been exploited for practical applications because of pronounced instability problems. We propose a novel gold-silver-gold trilayered SPR sensor chip, in which an extra buffer layer of gold is added between the silver and substrate adhesion layer (i.e., chromium) compared to the previously reported silver-gold bilayered SPR sensors. Subjected to prolonged agitation in phosphate-buffered saline (PBS) solution, the new chip exhibited high integrity according to both optical and atomic force microscopy (AFM) analysis. Having undergone repeated cycles of calibration, binding, and regeneration in various chemical solutions, 25 regions of interest (ROIs) over a 14 mm ×14 mm area were chosen and monitored by large detection area SPR microscopy; the new sensor chip exhibited stability comparable to the single gold layered SPR chip. In terms of sensing performances, over 50% increases in sensitivity and signal-to-noise ratio (S/N) than those of the single gold layered SPR chip were determined by SPR microscopy at 660 nm. Protein arrays of protein A and bovine serum albumin (BSA) on both the new chip and single-layered gold SPR chip were fabricated and underwent biomolecular interactions with human IgG, for the purpose of consistency, comparison on kinetics parameters, values from the microarray trilayered chip showed reasonable consistency with those from the single gold layered SPR chip. This study suggests that the new chip is a viable alternative to the conventional single gold layered SPR chip with improved sensing performances.