Catalytic Biosensors Operating under Quasi-Equilibrium Conditions for Mitigating the Changes in Substrate Diffusion.

Despite the success of continuous glucose measuring systems operating through the skin for about 14 days, long-term implantable biosensors are facing challenges caused by the foreign-body reaction. We present a conceptually new strategy using catalytic enzyme-based biosensors based on a measuring sequence leading to minimum disturbance of the substrate equilibrium concentration by controlling the sensor between "on" and "off" state combined with short potentiometric data acquisition. It is required that the enzyme activity can be completely switched off and no parasitic side reactions allow substrate turnover. This is achieved by using an O2 -independent FAD-dependent glucose dehydrogenase embedded within a crosslinked redox polymer. A short measuring interval allows the glucose concentration equilibrium to be restored quickly which enables the biosensor to operate under quasi-equilibrium conditions.

Glutamate detection at the cellular level by means of polymer/enzyme multilayer modified carbon nanoelectrodes.

Carbon nanoelectrodes in the sub-micron range were modified with an enzyme cascade immobilized in a spatially separated polymer double layer system for the detection of glutamate at the cellular level. The enzyme cascade consists of glutamate oxidase (GlutOx) that was immobilized in a hydrophilic redox silent polymer on top of a horseradish peroxidase (HRP)/redox polymer layer. In the presence of O2, glutamate was oxidized under concomitant reduction of O2 to H2O2 at GlutOx. H2O2 is further reduced to water by means of HRP and electrons are shuttled via the redox polymer matrix that wires the HRP to the electrode surface, hence delivering a current response proportional to the glutamate concentration. The nanometer-sized sensors could be successfully used to measure glutamate release from primary mouse astrocytes in 10 mM HEPES buffer.