Description
In 2003, the World Health Organization summarized key requirements for diagnostic tests through the ASSURED criteria (affordable, sensitive, specific, user-friendly, rapid, equipment-free, delivered), which continue to guide the design of accessible, reliable point-of-care (POC) technologies. Advances in microfluidics and portable instrumentation have accelerated the adoption of POC technologies in clinical care, supporting faster diagnosis and disease monitoring, as well as in food safety and low-income contexts where laboratory access and long turnaround times can limit effective access to healthcare.
Microfluidic “labs-on-a-chip” enable precise handling of microliter-scale samples under laminar flow and reduce reagent consumption, making them attractive for a wide range of POC applications, where efficient fluid management is crucial for delivering reliable results and minimizing sample volume. Although the silicon polymer PDMS has long dominated microfluidic fabrication, limitations in scalability and fabrication costs motivate a transition toward alternative substrates that are more compatible with scalable production and have lower environmental impact.
Paper and nitrocellulose are particularly attractive for POC solutions, since they are low-cost, disposable, and intrinsically microfluidic via capillary flow. Nitrocellulose-based lateral flow assays (LFAs) are widely used rapid tests, yet traditional colorimetric readouts suffer from limited sensitivity and subjective interpretation, especially at low analyte concentrations. Signal-enhancement approaches using nanolabels can improve sensitivity and provide quantifiable outputs in LFAs, but often increase assay complexity and costs.
Organic electrochemical transistors have stood out as highly sensitive analytical devices for biosensing, owing to their operation at low voltages and their intrinsic compatibility with aqueous environments. Among organic mixed ionic-electronic conductors employed as OECTs active materials, PEDOT:PSS is extensively adopted because of its high performance and suitability for solution-based processing. In parallel, advances in additive manufacturing and increasing attention to scalable and sustainable fabrication have guided the search for alternatives to conventional fabrication routes. Dispense printing is a non-contact printing strategy that has recently been applied to rapid prototyping of printed electronics, including sensors and OECTs on flexible polymeric substrates. Despite this progress, nitrocellulose and lateral flow assay membranes have not yet been investigated as OECT substrates, likely due to their porosity and mechanical fragility.
Motivated by the need for affordable quantitative sensing integrated with cellulose microfluidics, we developed a printable organic electrochemical transistor (OECT) on nitrocellulose, enabling straightforward integration of an analytical transistor into cellulose-based biochemical assays. By combining hydrophobic barriers with a solid-state electrolyte interface, the device separates a wet sensing region from a protected dry active area, enabling capillary-driven sample delivery while preserving transistor stability. With a maximum transconductance of approximately 4 mS, the device exhibits a LOD of 0.01 mM for dopamine when integrated into a capillary-driven nitrocellulose strip. Requiring low operating voltage and consequently reducing power requirements, the system supports integration into portable diagnostic platforms, while the generated currents in the milliampere range simplify signal acquisition and processing. The proposed strategy aims to complement capillary-driven, paper-based POC platforms with an electronic output, supporting scalable, low-cost POC diagnostics aligned with ASSURED principles.