This work considers the possibility of the fabrication of a nanocapillary electrochemical biosensor for glucose determination. The principle of glucose determination is based on the reaction of glucose decomposition into glucolactone and hydrogen peroxide. Glucose oxidase is used as an enzyme. Electrodes based on glass nanocapillaries are used as biosensors for the determination of various analytes due to their ease of fabrication, high sensitivity, selectivity and small size.
Before the fabrication of the nanocapillary sensor, the technique of enzyme immobilization on the mica surface was reproduced. Freshly pierced mica sheets were silanized with 0.33% APS diluted in water and ethanol. The silanized mica was washed in distilled water and immersed for 12 h in 2.5% GA solution in PBS, then washed with distilled water and dried under an Ar atmosphere. The mica samples were then immersed in GOx in PBS solution (2 mg/mL) overnight at room temperature. At each modification step, the surface topography was examined via AFM. Evaluation of the surface topography showed that irregularities in the topography appear during the enzyme immobilization process, which change as the mica surface is modified.
This technique was reproduced to functionalize the inner surface of the nanopipette. At each modification step, cyclic voltammetry waveforms were recorded in HBSS from -800 to 800 mV (400 mV/s) relative to Ag/AgCl. After the reaction of quartz with APS, terminal amino groups were formed on the surface and protonated in the electrolyte solution, and the ionic current at positive potentials increased significantly. Upon crosslinking with glutaric aldehyde, the ionic current decreased as the carbonyl groups were bound to the positively charged groups of APS. After functionalization with glucose oxidase, cyclic voltammetry showed the negative rectification of the current as GOx contains a negative charge.
Conclusion: The possibility of immobilizing glucose oxidase on the nanocapillary surface for glucose detection was demonstrated.
