A Smartphone-Interfaced, Flexible Electrochemical Biosensor Based on Graphene Ink for Selective Detection of Dopamine

This study reports the fabrication of flexible electrochemical dopamine sensors using a facile, low temperature (300°C) process based on spin-coating of commercially available graphene ink onto a polyimide (PI) substrate. The electrochemical testing and surface characterization were achieved using cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The graphene-ink based biosensor demonstrated a limit of detection (LoD) of 100 nM of dopamine in PBS and a dynamic concentration range up to 1 mM, with excellent specificity against uric acid and ascorbic acid. The sensor is also resilient against mechanical deformation (< 12% change in peak currents during maximum bending). Furthermore, we demonstrated that a subsequent solution-phase treatment of graphene ink in copper sulfate (CuSO4) followed by annealing in air at 200°C improves the sensor LoD from $1~\mu \text{m}$ to 5 nM in artificial sweat. Wireless data transfer via Wi-Fi in tandem with an on-chip sensor integrated with an in-house built potentiostat is also developed to demonstrate the applicability of the platform for point-of-care applications.