N-Doped Graphene Nanoplatelets for Direct Capsaicin Detection in Chili Pepper Samples

In this study, we have designed and fabricated a portable electrochemical sensor for direct detection of capsaicin in chili samples at the point-of-testing. The sensor, shaped like a chili pepper and highly portable, is essentially a disposable electrochemical paper-based analytical device (ePAD) modified with N-doped graphene nanoplatelets (GrNPs). The sensor consists of three components: (i) a small potentiostat device, (ii) an interface allowing connection to a smartphone for monitoring and control, and (iii) the sensor (an N-doped GrNPs/ePAD and detection chamber). The N-doped GrNPs/ePAD shows high conductivity and good electrocatalytic activity in the oxidation and reduction of capsaicin. The measurement of capsaicin was performed directly through differential pulse voltammetry once the parameters influencing capsaicin detection (i.e., pH, buffer ethanol content, N-doped GrNPs loading, accumulation potential, and accumulation time) were optimized. Linearity was obtained in the concentration range 1-100 mu M, and the limit of detection was found to be 0.37 mu M. Furthermore, the preparation of ten N-doped GrNPs/ePAD devices confirmed fabrication reproducibility. The sensor was successfully applied to the determination of capsaicin in chili samples, with recoveries between 89.3 +/- 0.3 and 106 +/- 2%, and the results showed no significant difference to those obtained by UV-vis spectrophotometry. Thus, this platform shows excellent potential for the development of portable sensors for capsaicin and future extension to different analytes.