A Novel Two-Electrode Nonenzymatic Electrochemical Glucose Sensor Based on Vertically Aligned Carbon Nanotube Arrays

We report the fabrication of a novel nonenzymatic two-electrode glucose sensor. Interdigitated Ni electrodes deposited on a Si/SiO₂ substrate were used as growth seeds for vertically aligned multiwalled carbon nanotubes (CNTs) in a plasma-enhanced chemical vapor deposition method. The small separation distance of 12 μm between the two opposite electrodes allowed tests with high signal/noise (≍59) ratio in distilled water. We have shown that by using distilled water, as opposed to a concentrated NaOH solution typically used in electrochemical three-electrode potentiostat setups, the sensor itself is not greatly oxidized during tests. This implies that the sensor could be used repeatedly, without showing response variations and that the tests can be done without a third reference electrode. It is shown that under dc voltage bias, the sensor shows a very high sensitivity of 24200 mA/μMcm⁻² to glucose and a relatively low detection limit of 0.1 μM for glucose in distilled water. Although dc measurements showed selective sensitivity to glucose, easily oxidizable ascorbic acid (AA) was seen to interfere with measurements. However, ac impedance tests showed clear selectivity between the two substances. Amperometric tests were then repeated with an ac modulated dc voltage, which completely removed the response of the otherwise interfering AA, making the introduced sensor an exciting new step in biological sensor development.