Optically tunable hydrogel biosensor material

Colloidal crystal hydrogels with tunable optical properties are useful materials to construct thermoresponsive tunable photonic crystals(1) and optical switch that responds in nanoseconds(2). We report here instead, the fabrication of optically tunable colloidal crystal hydrogel material that can also behave as biosensors, responding to the presence of antigens or antibodies. Optically tunable hydrogel material was fabricated from submicron sized, thermoresponsive poly-N-isopropyl acrylamide (pNIPAM) particles and pNIPAM-co-acrylic acid (pNIPAM-AA) copolymer particles. The color of this translucent hydrogel material can be tuned from blue to green to red by changing the concentration of pNIPAM particles. PNIPAM-AA with covalently linked protein A (pNIPAM-AA-protein A) formed light blue colored hydrogel material that respond to the presence of anti-Protein A antibodies to form an opaque, crosslinked networked hydrogel particles aggregate which could be detected visually. A similar response was observed when pNIPAM-AA particles, with attached anti-protein A antibodies (pNIPAM-AA-Anti Protein A), were treated with protein A. The lowest limit of detection, based on visual observation of aggregate, of anti-protein A antibodies was 0.5 mu g or a concentration of 1 mu g/mu l, whereas for protein A the lowest limit of detection was 0.25 mu g or a concentration of 0.5 mu g/mu l. We expect this optically tunable hydrogel biosensor material to find applications as photonic crystals that respond to the presence of microbial antigens or human antibodies, to control laser transmission and the optically switching of devices.