Selective potentiodynamic detection with PEDOT:PSS based organic electrochemical transistors

Conventional electrochemical sensors rarely exhibit adequate robustness and analytical performances for real life applications, either due to the complexity of the real matrices, the small analytes concentration or the massive presence of interfering compounds. Organic Electrochemical Transistors (OECTs) are devices, recently spread in the field of smart electronics, which are suitable for challenging sensing applications, especially thanks to intrinsic signal amplification. In this contribution, we describe the potentialities of a potentiodynamic technique applied to OECT based sensors to achieve improved analytical performances. When operating the OECT potentiodynamically, a linear scan of potential is applied at the gate (Vg) and the drain current (Id) is recorded, in analogy with the acquisition of transfer characteristics, and the transconductance (gm = ΔId/ΔVg) plot is then obtained. When a redox process involving the analyte affects the redox phenomena ruling the OECT, a peak appears whose position relates to the Vg at which the faradaic process takes place. This approach was exploited to selectively detect dopamine (DA) in a mixture containing uric and ascorbic acid (UA and AA, respectively), with overall performances comparable to those obtained with sophisticated electroanalytical techniques (Fig.1a).1 Furthermore, non-redox active species can be also detected with the potentiodynamic method. For instance, super-Nernstian pH sensing was carried out upon gate electrode functionalisation, and the shift of the gm peak was used as the analytical signal (Fig.1b).2 Among the most challenging analytical applications, vitamins detection in food products is commonly carried out using laboratory facilities like high-performance liquid chromatographs, which guarantee high selectivity and sensitivity. However, they also present several limitations such as time-consuming analysis, expensive equipment and laborious sample preparation. In contrast, electrochemical sensors are simple, cost-effective and easily miniaturized. In this regard, our research group has recently developed an OECT sensor exploiting the potentiodynamic approach to detect and distinguish lipophilic vitamins3. The sensor selectivity was optimized by studying a binary system including Vitamin A and Vitamin E. The device was capable of quantitatively determining Vitamin A concentration in commercial food fortifiers, with no sample pretreatment needed.