Graft-then-Shrink Polymer Coatings for Localized Surface Plasmon Resonance Active Interfaces

Increasing the polymer content on biosensors is important to improve sensor function by altering surface properties and increasing the number of capture sites for analytes. Grafting-to methods are often employed but may be limited by insufficient polymer immobilization. Herein, we have utilized Graft-then-Shrink (GtS) to simultaneously increase polymer content on grafting-to surfaces and produce low-cost, local surface plasmon resonance (LSPR) Au biosensors. The biosensors were incorporated within microwell plates, where the translocation of materials across biological barriers can be tracked by visible light absorbance shifts as a platform for biological barrier crossing molecules. Biosensors were constructed by coating a flat Au layer on stretched polystyrene (PS) with thiol-terminated polymers that, upon heating, produced LSPR active wrinkled Au layers with ∼78% greater polymer content and lower water contact angles (WCA; ∼15°) compared to Shrink-then-Graft (StG) controls (∼55°) for PEG₂MA coatings. To demonstrate translocation detection, 48-well microplates were 3D printed for GtS biosensor incorporation in the presence of a phospholipid bilayer. Using visible light to track LSPR peak shifts, cell penetrating peptides (CPPs) were screened for bilayer translocation and rate kinetics. GtS offers a simple method to increase the polymer content within coatings and an LSPR fabrication platform to track biomolecule translocation.