Polymer/enzyme-modified HF-etched carbon nanoelectrodes for single-cell analysis.

Carbon-based nanoelectrodes fabricated by means of pyrolysis of an alkane precursor gas purged through a glass capillary and subsequently etched with HF were modified with redox polymer/enzyme films for the detection of glucose at the single-cell level. Glucose oxidase (GOx) was immobilized and electrically wired by means of an Os-complex-modified redox polymer in a sequential dip coating process. For the synthesis of the redox polymer matrix, a poly(1-vinylimidazole-co-acrylamide)-based backbone was used that was first modified with the electron transfer mediator [Os(bpy)2Cl]+ (bpy = 2,2'-bipyridine) followed by the conversion of the amide groups within the acrylamide monomer into hydrazide groups in a polymer-analogue reaction. The hydrazide groups react readily with bifunctional epoxide-based crosslinkers ensuring high film stability. Insertion of the nanometre-sized polymer/enzyme modified electrodes into adherently growing single NG108-15 cells resulted in a positive current response correlating with the intracellular glucose concentration. Moreover, the nanosensors showed a stable current output without significant loss in performance after intracellular measurements.

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.