Controlling solubility of polymeric anions in supramolecular assemblies with poly(aniline) for microsensors and actuators in human tissue

The supramolecular assembly of poly(aniline) and poly(vinylsulfonate) (PAni/PVS) represents a particularly suitable catalytic material for oxidation of Vitamin C in sensor applications. PAni/PVS assemblies were prepared on platinum at increasing deoxygenation levels (LD → MD → HD) and in two thickness sizes of 2 μm (thick) and 200 nm (thin). Thick HD disks with diameters of 500 μm and 2 μm were stable over 90 min in a stirred buffer solution at pH 7 containing 300 μM Vitamin C. Stirring stability was lost after storage in air, but not after storage under argon. In MD disks PVS was partly lost after 3 h exposure to unstirred neutral buffer solution. Loss could be significantly reduced by oxidative enforcement with ferulic acid (F), a precursor of plant lignin. Application of elliptical F-PAni/PVS microelectrodes with diameters of 20 μm × 30 μm in brain parenchyma of rats showed surprisingly weak influence of intraperitoneal Vitamin C injections on the brain tissue level of Vitamin C. After 3 h of tissue exposure poly(aniline) redox activity in acidic solution decreased slightly. Factors which caused enhanced PVS solubility are discussed in detail.