A Printable OECT for Simple Integration in Nitrocellulose-Based Assays

Paper-based biosensors hold significant promise for point-of-care (POC) diagnostic applications. Among these, lateral flow assays (LFAs) are particularly appealing due to their ease of use, portability, and low cost. However, their limited sensitivity and qualitative output set drawbacks on their reliability and widespread application. In response to the growing need for rapid and consistent diagnostic and monitoring tools, Organic Electrochemical Transistors (OECTs) have emerged as powerful devices in biochemical sensing applications because of their high sensitivity, low operating voltage, and compatibility with a biological environment. In this work, we developed a printable OECT for biochemical sensing on a commercial cellulose membrane, commonly used as a detection substrate in LFA-based rapid tests. Constituting a self-standing, passive microfluidic platform, the system was designed to transport and interact with liquid samples, while ensuring a contamination-free zone for the active components. Inside a dry area delimited by a hydrophobic barrier, the OECT components include dispense-printed silver electrodes, a polystyrenesulfonate-doped poly(3,4-ethylenedioxy-thiophene) (PEDOT:PSS) channel and gate, and a solid-state electrolyte (SSE) layer. Outside the dry area, a PEDOT:PSS extended gate alone interacts with the analyte in the liquid sample, preventing channel contamination and enhancing the system stability. We investigated the effect of dopamine (DA) oxidation at the extended gate interface on the device response and observed variations in the transfer characteristics, transconductance and I_on/I_off ratio, obtaining a limit of detection of 0.01 mM. With a maximum transconductance of approximately 4 mS, our system shows potential for the integration of an easy-to-fabricate device into an affordable biochemical assay, providing quantitative results at the point-of-care site to complement and reinforce the typical colorimetric response of LFAs.