Electrochemical temperature-controlled switch for nonenzymatic biosensor based on Fe3O4-PNIPAM microgels

The objective of the study is to construct a stimuli responsive membrane on the electrode and regulate the bioelectrocatalysis of hydrogen peroxide by temperature stimulation. Fe3O4-poly(N-isopropylacrylamide) microgels (Fe3O4-PNIPAM microgels) were prepared and developed as temperature-controlled nonenzymatic electrochemical switchable hydrogen peroxide biosensors in this study. The microgels were fabricated through a two-step way and characterizations such as scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), differential scanning calorimeter (DSC), dynamic light scattering (DLS) were used to prove the microgels. Then, Fe3O4-PNIPAM microgels were assembled to the electrode surface and the switchable electrochemical function relating to temperature stimuli was illustrated by electrochemical impedance spectroscopy (EIS). Cyclic voltammetry (CV) study showed a switchable electrocatalytic activity towards the oxidation process of H2O2 between 26.0 and 37.0 °C due to peroxidase-like behaviour of Fe3O4 nanoparticles (Fe3O4 NPs) and temperature-sensitive properties of PNIPAM. On the basis of concept, we constructed a switchable biosensor for the detection of H2O2. Under optimal conditions, we successfully detected H2O2 as low as 0.005 μM at 26.0 °C and 0.01 μM at 32.0 °C. By using Fe3O4 NPs instead of enzyme to construct the switchable biosensor in the experiment, the operation is simple and the strategy meets the demands of switchable biosensors when used in bioscience and biotechnology, which broadens the applications of electrochemical switching biosensors.