Electropolymerization of aniline in the presence of poly(acrylic acid) on Au electrodes yields a polyaniline/poly(acrylic acid) composite film, exhibiting reversible redox functions in aqueous solutions at pH = 7.0. In situ electrochemical-SPR measurements are used to identify the dynamics of swelling and shrinking of the polymer film upon the oxidation of the polyaniline (PAn) to its oxidized state (PAn(2+)) and the reduction of the oxidized polymer (PAn(2+)) back to its reduced state (PAn), respectively. Covalent attachment of N(6)-(2-aminoethyl)-flavin adenin dinucleotide (amino-FAD, 1) to the carboxylic groups of the composite polyaniline/poly(acrylic acid) film followed by the reconstitution of apoglucose oxidase on the functional polymer yields an electrically contacted glucose oxidase of unprecedented electrical communication efficiency with the electrode: electron-transfer turnover rate approximately 1000 s(-1) at 30 degrees C. In situ electrochemical-SPR analyses are used to characterize the bioelectrocatalytic functions of the biomaterial-polymer interface. The current responses of the bioelectrocatalytic system increase as the glucose concentrations are elevated. Similarly, the SPR spectra of the system are controlled by the concentration of glucose. The glucose concentration controls the steady-state concentration ratio of PAn/PAn(2+) in the film composition. Therefore, the SPR spectrum of the film measured upon its electrochemical oxidation is shifted from the spectrum typical for the oxidized PAn(2+) at low glucose concentration to the spectrum characteristic of the reduced PAn at high glucose concentration. Similarly, the polyaniline/poly(acrylic acid) film acts as an electrocatalyst for the oxidation of NADH. Accordingly, an integrated bioelectrocatalytic assembly was constructed on the electrode by the covalent attachment of N(6)-(2-aminoethyl)-beta-nicotinamide adenine dinucleotide (amino-NAD(+), 2) to the polymer film, and the two-dimensional cross-linking of an affinity complex formed between lactate dehydrogenase and the NAD(+)-cofactor units associated with the polymer using glutaric dialdehyde as a cross-linker. In situ electrochemical-SPR measurements are used to characterize the bioelectrocatalytic functions of the system. The amperometric responses of the system increase as the concentrations of lactate are elevated, and an electron-transfer turnover rate of 350 s(-1) between the biocatalyst and the electrode is estimated. As the PAn(2+) oxidizes the NADH units generated by the biocatalyzed oxidation of lactate, the PAn/PAn(2+) steady-state ratio in the film is controlled by the concentration of lactate. Accordingly, the SPR spectrum measured upon electrochemical oxidation of the film is similar to the spectrum of PAn(2+) at low lactate concentration, whereas the SPR spectrum resembles that of PAn at high concentrations of lactate.
Impedance measurements on ISFET devices are employed to develop new immunosensors. The analysis of the transconductance curves recorded at variable frequencies, upon the formation of antigen-antibody complexes on the ISFET devices, allows determination of the biomaterial film thicknesses. Complementary surface plasmon resonance measurements of analogous biosensor systems, using Au-coated glass slides as support, reveal similar film thicknesses of the biomaterials and comparable detection limits. A dinitrophenyl antigen layer is immobilized on the ISFET gate as a sensing interface for the anti-dinitrophenyl antibody (anti-DNP-Ab). The anti-DNP-Ab is analyzed with a sensitivity that corresponds to 0.1 microg mL(-1). The assembly of the biotinylated anti-anti-DNP-Ab and avidin layers on the base anti-DNP-Ab layer is characterized by impedance measurements. The development of an ISFET-based sensor for the cholera toxin is described. The anti-cholera toxin antibody is immobilized on the ISFET device. The association of the cholera toxin (CT) to the antibody is monitored by the impedance measurements. The detection limit for analyzing CT is 1.0 x 10(-11) M.
A polyacrylic acid film saturated with Cu2+ ions displays redox‐switchable electrorefractive, electrochromic, and conductivity functions upon reduction of Cu2+ to Cu0. Surface plasmon resonance spectroscopy, adsorption spectroscopy, and conductivity measurements are used to examine these functions, which are demonstrated to be fully reversible. New types of optical filters and modulators, optoelectronic devices, and smart windows could potentially be constructed from such hybrid polymers.
In this work, a previously undescribed phenomenon of orientation induced redox isomerism in a Langmuir monolayer is revealed in the case of cerium bis [tetra (15 crown 5) phthalocyaninate] (Ce[(15C5) 4 Pc] 2 ). It was established that intramolecular electron transfer (IET) from the electronic system of phthalocyanine to the 4f orbital of cerium atom occurs upon spreading of a (Ce[(15C5) 4 Pc] 2 ) chloroform solution onto the air−water interface (3D → 2D IET). This process is related to the transformation of Ce 4+ cation in the solution to Ce 3+ in the monolayer. It was also found that reversible Ce 3+ ↔ Ce 4+ IETs occur upon compression (π 1 → π 2 ) and expansion (π 2 → π 1 ) of monolayer (2D π1 ↔ 2D π2 IET, π surface pressure). The mechanism of genuine redox isomerism was confirmed by the results of in situ UV−vis spectral measurements performed on monolayers and Langmuir−Blodgett films, AFM, and XPS studies of Langmuir−Blodgett films transferred at different surface pressures. The understanding of this reversible IET mechanism is especially important due to possible applications of such redox isomeric systems in the development of nanoscale multibit information storage devices.
Surface plasmon resonance (SPR) spectroscopy is used to follow the swelling and shrinking processes of a polyaniline redox-active polymer; SPR provides a reading signal for the electrochemical stimuli that activate the polymer.
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