Wide-field surface plasmon resonance microscope based on polyethylene oxide/polyacrylic acid brushes

Wide-field surface plasmon resonance microscope (WF-SPRM) based on polyethylene oxide/polyacrylic acid (PEO/PAA) polyelectrolyte brushes (PEBs) is presented for particle detection application. PEO acts as an H-bond acceptor, while PAA serves as an H-bond donor, forming hydrogen-bonding complexes within the brushes. Morphological, chemical, and crystal structural analyses confirm that the PEO/PAA brushes undergo a transition from a collapsed to a stretched state as the solvent pH is increased from 1 to 10. This pH-dependent change also renders the PEO/PAA brushes more hydrophilic. Additionally, the electrical conductivity and refractive index of the PEO/PAA brushes increase concomitantly with the increase of solvent pH. Furthermore, theoretical and experimental approaches study the sensitivity of WF-SPRM utilizing Au-(PEO/PAA) polyelectrolyte layers. The theoretical sensitivity of WF-SPRM is enhanced from 118.5 deg./RIU for the Au-layer to 178.1 deg./RIU for Au-(PEO/PAA PEBs). Moreover, the signal-to-noise ratio for the Au-(PEO/PAA PEBs) layer is 20 +/- 1, indicating improved sensing performance compared to the Au-layer (signal-to-noise ratio of 6 +/- 1). A mathematical model to describe the discrete particle detection by WF-SPRM is presented, where results demonstrate a good agreement between the calculated intensity profile and experimental data.