An electrochemically modulated single-walled carbon nanotube network for the development of a transparent flexible sensor for dopamine

Transparent and flexible single-walled carbon nanotube (SWCNT) network electrodes were used for the determination of neurotransmitters. The surface of SWCNT network film was oxidised by multiple electrochemical anodic scans, thereby the electronic structure of SWCNTs network film was modulated with p-typed doping. Herein, we analysed the electronic structure in-depth by resonant Raman spectroscopy with two different wavelength lasers (514 and 633 nm) and UV-vis-NIR absorption spectroscopy. From this analysis, it is found that the electrochemical oxidation process selectively occurred on metallic SWCNTs surface in the mixture of metallic and semiconducting SWCNTs. Interestingly, after electrochemical oxidation, the charge transfer resistance was observed to have decreased by 52%, compared to that of a SWCNT network electrode before treatment (4.7 kΩ). This is probably due to the suppression of Schottky barrier of junctions between metallic and semiconducting SWCNT bundles. The enhanced electrocatalytic activity of a SWCNT network film by electrochemical doping (Eox-SWCNT network film) has enabled discrimination of dopamine (DA) from a mixture with ascorbic acid (AA) and uric acid (UA). The limit of detection was estimated to be 0.51 μM DA in the presence of 100 μM AA and 10 μM UA, and the DA sensing activity was not significantly affected even using a bent configuration of Eox-SWCNT network film. The simple and eco-friendly electrochemical doping with multiple cyclic voltammetric scans can be a powerful tool to modulate the electronic energy in the band structure of carbon-related materials.