The effect of temperature on the impedimetric response of bioreceptor hosting hydrogels

Biocompatible hydrogels that serve as the hosting membrane for various bioreceptors contribute to the response of impedimetric biosensors. The temperature response of poly(2-hydroxymethacrylate) [p(HEMA)]-based hydrogel networks prepared with poly(ethylene glycol) methacrylate (PEGMA) for enhanced biocompatibility and with N-[tris(hydroxymethyl)methyl] acrylamide (HMMA) was studied. Hydrogels were cross-linked with tetraethyleneglycol diacrylate (TEGDA) and synthesized by UV initiation (2M% DMPA photoinitiator). The p(HEMA-co-PEGMA-co-HMMA) based hydrogels were fabricated as discrete gel pads (D=2.5 mm, H=2 mm and V=9.82 μL) on top of 250 μm diameter cysteamine modified and acryloyl (polyethylene glycol)(110) N-hydroxy succinamide ester (acryloyl-PEG-NHS) derivatized gold microelectrodes set within 8-well (8W1E) cell culture biochips. Gel pads were fabricated with cross-link densities corresponding to 1, 3, 5, 7, 9 and 12 M% TEGDA and were studied by frequency dependent 3-electrode electrochemical impedance spectroscopy (1 mHz to 100 kHz; 50 mV p-t-p) and by temporal 2-electrode impedimetry (64 kHz; 50 mV p-t-p) over the temperature range 30-45°C at 90% RH or in aqueous 0.1 M Tris/KCl at pH 7.2 buffer. The p(HEMA-co-PEGMA-co-HMMA) hydrogels showed an increase in the real component of impedance with increasing cross-link density and demonstrated activation energies for impedimetric transport that ranged from 15 kJ/mol (3 M%) to 20 kJ/mol (12 M%) confirming the dominance of proton migration in the impedance of the hydrogels.