Microgels in Tandem with Enzymes: Tuning Adsorption of a pH- and Thermoresponsive Microgel for Improved Design of Enzymatic Biosensors

The benefits of stimuli-responsiveness of microgels for surface modification and further engineering of microgel-enzyme biosensor constructs are highlighted. Accordingly, the adsorption behavior of the pH- and temperature-sensitive poly(N-isopropylacrylamide-co-N-(3-dimethylaminopropyl)methacrylamide) microgel (P(NIPAM-co-DMAPMA) microgel) is examined by means of atomic force microscopy (AFM) and quartz-crystal microbalance with dissipation monitoring (QCM-D). An enhanced adsorption of the microgel onto relatively hydrophobic surfaces is observed at elevated pH and temperature as manifested by a high surface coverage and a large adsorbed mass. This is a consequence of pronounced hydrophobization of the microgel as revealed by means of dynamic light scattering (DLS) and turbidimetry (cloud points). The subsequent electrostatic loading of the surface-bound microgel with enzymes is examined by means of QCM-D and demonstrates a highly-capacious integration of biomolecules into the microgel films. Finally, the biosensor responses of the microgel-enzyme films fabricated onto screen-printed graphite electrodes are assessed to demonstrate a biorelated application. Thus, a comprehensive conceptual understanding is attained on the key points: (1) how the stimuli-responsive properties of the microgel correlate with its amount deposited onto the surface, (2) what determines the highly-capacious loading of the surface-bound microgel with the enzymes, and ultimately (3) how the tandem of the stimuli-sensitive microgels and enzymes can be used for easy engineering of biosensor systems.