Diamond-Like Carbon Thin Film Electrodes for Microfluidic Bioelectrochemical Sensing Platforms

This work aims to utilize diamond-like carbon (DLC) thin films for bioreceptor immobilization and amperometric biosensing in a microfluidic platform. A specific RF-PECVD method was employed to prepare DLC thin film electrodes with desirable surface and bulk properties. The films possessed a relatively high sp² fraction, a moderate electrical conductivity (7.75 × 10^-3 S cm^-1), and an optical band gap of 1.67 eV. X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy revealed a presence of oxygen-containing functional groups on the DLC surface. The DLC electrodes were integrated into polydimethylsiloxane (PDMS) microfluidic electrochemical cells with the channel volume of 2.24 μL. Glucose oxidase (GOx) was chosen as a model bioreceptor to validate the employment of DLC electrodes for bioelectrochemical sensing. In-channel immobilization of glucose oxidase (GOx) at the DLC surface was realized through carbodiimide covalent linkages. Enzyme bound DLC electrode was confirmed with the redox potential at around -79 mV vs NHE in 0.1 M phosphate buffer pH 7.4. Amperometric flow-injection glucose sensing at a potential of -0.45 V vs Ag in the absence of standard redox mediators showed the increase of current response upon increasing the glucose concentration. The sensing mechanism is based on the reduction process of H₂O₂ liberated from the enzymatic activity. The proposed model for the catalytic H₂O₂ reduction to H₂O on DLC electrodes was attributed to the dissociation of C-O bonds at the DLC surface.