Developing surface plasmon resonance imaging for discrete particle detection based on a silver layer coated with polyacrylic acid/iodine polyelectrolyte brushes

The detection and analysis of low concentrations of chemical and biological particles presents an enduring challenge in scientific exploration. Among the various techniques employed for this purpose, surface plasmon resonance (SPR) stands as a powerful label-free method with a wide-range applications in advanced detection and sensing. Traditional SPR, while highly effective, encounters inherent limitations when it comes to scrutinizing individual particles. To overcome this limitation, wide-field surface plasmon resonance microscopy emerges as a promising approach, offering real-time detection capabilities for suspended particles in solution. In this study, an innovative wide-field surface plasmon resonance microscope is presented, strategically combining a silver layer coated with polyelectrolyte brushes-polyacrylic acid/iodine, to enhance the detection sensitivity and mitigate silver's susceptibility to oxidation. It is demonstrated that coating the silver layer with polyacrylic acid/iodine enhances the sensitivity of discrete particle imaging with a high spatial resolution of the recorded image. Since wide-field surface plasmon resonance microscopy can detect discrete particles, a mathematical model is proposed to describe the SPR sensing mechanism based on discrete particles for precisely characterizing and interpreting the experimental observations. This work demonstrates a capability for comprehensive analysis of low concentrations of chemical and biological particles at the single particle level.