This work examines the fabrication regime and the properties of microgel and microgel/enzyme thin films adsorbed onto conductive substrates (graphite or gold). The films were formed via two sequential steps: the adsorption of a temperature- and pH-sensitive microgel synthesized by precipitation copolymerization of N-isopropylacrylamide (NIPAM) and 3-(N,N-dimethylamino)propylmethacrylamide (DMAPMA) (poly(NIPAM-co-DMAPMA) at the pH-condition corresponding to its noncharged state (first step of adsorption), followed by the enzyme, tyrosinase, adsorption at the pH-condition when the microgel and the enzyme are oppositely charged (second step of adsorption). The stimuli-sensitive properties of poly(NIPAM-co-DMAPMA) microgel were characterized by potentiometric titration and dynamic light scattering (DLS) in solution as well as by atomic force microscopy (AFM) and quartz crystal microbalance with dissipation monitoring (QCM-D) at solid interface. Enhanced deposition of poly(NIPAM-co-DMAPMA) microgel particles was shown at elevated temperatures exceeding the volume phase transition temperature (VPTT). The subsequent electrostatic interaction of the poly(NIPAM-co-DMAPMA) microgel matrix with tyrosinase was examined at different adsorption regimes. A considerable increase in the amount of the adsorbed enzyme was detected when the microgel film is first brought into a collapsed state but then was allowed to interact with the enzyme at T < VPTT. Spongelike approach to enzyme adsorption was applied for modification of screen-printed graphite electrodes by poly(NIPAM-co-DMAPMA)/tyrosinase films and the resultant biosensors for phenol were tested amperometrically. By temperature-induced stimulating both (i) poly(NIPAM-co-DMAPMA) microgel adsorption at T > VPTT and (ii) following spongelike tyrosinase loading at T < VPTT, we can achieve more than 3.5-fold increase in biosensor sensitivity for phenol assay. Thus, a very simple, novel, and fast strategy for physical entrapment of biomolecules by the polymeric matrix was proposed and tested. Being based on this unique stimuli-sensitive behavior of the microgel, this stimulated spongelike adsorption provides polymer films comprising concentrated biomaterial.

This study effectively demonstrates that thermoresponsive, cationic poly(N-isopropylacrylamide-co-methacrylamidopropyltrimethylammonium chloride) P(NIPAM-co-MAPTAC) microgels act as selective, closable carriers for trivalent hexacyanoferrate(III) (ferricyanide). At the same time, the microgel disregards even higher charged hexacyanoferrate(II) (ferrocyanide). This is seen by investigating the electrochemistry of hexacyanoferrates in the presence of porous microgel particles with help of cyclic voltammetry (CV), hydrodynamic voltammetry (rotating disk electrode, RDE), and electrochemical impedance spectroscopy (EIS). For analysis, temperature-corrected parameters for each technique are introduced. Assuming incorporation/complexation between hexacyanoferrates and microgels, different limiting scenarios for the electron pathway are proposed by discussing different life times of the hexacyanoferrates within the microgel: fast exchange (scenario 1: full electrochemical addressability of all counterions), permanent entrapment (scenario 2: still full addressability of all counterions by injection of electrons into the microgels), and full entrapment (scenario 3: only remaining free counterions are addressable). Also, negligible interaction between hexacyanoferrates and microgels can be postulated, as found experimentally for ferrocyanide [Fe(CN)6]4–. In contrast for ferricyanide [Fe(CN)6]3–, temperature even allows a switching between a dominant scenario 1 (fast exchange) in the cold and the scenario 3 (full entrapment) in the heat. In more detail, the attraction between ferricyanide and microgel is enhanced at elevated temperatures due to the collapse and increasing charge density induced by the thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) component, which in turn acts more as an insulator in the heat. Hence, only the free hexacyanoferrates are electrochemically accessible in the heat. In addition, EIS and CV indicate only a minor contribution of permanent entrapment (scenario 2) during charge transport.

This study demonstrates the effect of polymer topology and molar mass on the electrodeposition of preformed polyelectrolytes. The polyelectrolyte solubility is manipulated electrochemically using a counterion switching approach. Upon this, a triggered film formation occurs upon oxidation of hexacyanoferrate(II). The resulting Pt-electrode deposit consists of polycationic chains, namely poly{[2-(methacryloyloxy)ethyl]trimethylammonium chloride} (PMOTAC), which are physically crosslinked by polymer-complexing ferricyanides. Within this study the architecture of the polyelectrolyte is varied from monomeric units over linear and star-shaped polymers to network-like microgel colloids. Film deposition is observed only for linear and star-shaped polymers being pronounced for shorter linear chains at equimolar charge ratios. Quantification is achieved by help of the deposition efficiency DE obtained by analyzing the currents of a rotating ring disk electrode (RRDE) during hydrodynamic voltammetry. DE relates the amount of deposited ferricyanides to the total amount of electrochemically-produced ferricyanides. DE is used to estimate the deposited mass and film thickness showing good agreement with the film thickness determined experimentally by Scanning Force Microscopy. For future applications these results might help optimizing beneficial film formation or minimizing detrimental film formation during other procedures.

This work examines the adsorption regime and the properties of microgel/enzyme thin films deposited onto conductive graphite-based substrates. The films were formed via two-step sequential adsorption. A temperature- and pH-sensitive poly­(N-isopropylacrylamide)-co-(3-(N,N-dimethylamino)­propylmethacrylamide) microgel (poly­(NIPAM-co-DMAPMA microgel) was adsorbed first, followed by its interaction with the enzymes, choline oxidase (ChO), butyrylcholinesterase (BChE), or mixtures thereof. By temperature-induced stimulating both (i) poly­(NIPAM-co-DMAPMA) microgel adsorption at T > VPTT followed by short washing and drying and then (ii) enzyme loading at T < VPTT, we can effectively control the amount of the microgel adsorbed on a hydrophobic interface as well as the amount and the spatial localization of the enzyme interacted with the microgel film. Depending on the biomolecule size, enzyme molecules can (in the case for ChO) or cannot (in the case for BChE) penetrate into the microgel interior and be localized inside/outside the microgel particles. Different spatial localization, however, does not affect the specific enzymatic responses of ChO or BChE and does not prevent cascade enzymatic reaction involving both BChE and ChO as well. This was shown by the methods of electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), and amperometric analysis of enzymatic responses of immobilized enzymes. Thus, a novel simple and fast strategy for physical entrapment of biomolecules by the polymeric matrix was proposed, which can be used for engineering systems with spatially separated enzymes of different types.

Bacterial infection is a severe problem especially when associated with biomedical applications. This study effectively demonstrates that poly-N-isopropylmethacrylamide based microgel coatings prevent bacterial adhesion. The coating preparation via a spraying approach proved to be simple and both cost and time efficient creating a homogeneous dense microgel monolayer. In particular, the influence of cross-linking density, microgel size, and coating thickness was investigated on the initial bacterial adhesion. Adhesion of Staphylococcus aureus ATCC 12600 was imaged using a parallel plate flow chamber setup, which gave insights in the number of the total bacteria adhering per unit area onto the surface and the initial bacterial deposition rates. All microgel coatings successfully yielded more than 98% reduction in bacterial adhesion. Bacterial adhesion depends both on the cross-linking density/stiffness of the microgels and on the thickness of the microgel coating. Bacterial adhesion decreased when a lower cross-linking density was used at equal coating thickness and at equal cross-linking density with a thicker microgel coating. The highest reduction in the number of bacterial adhesion was achieved with the microgel that produced the thickest coating (h = 602 nm) and had the lowest cross-linking density. The results provided in this paper indicate that microgel coatings serve as an interesting and easy applicable approach and that it can be fine-tuned by manipulating the microgel layer thickness and stiffness.