Rapid electrochemical flow analysis of urinary creatinine on paper: unleashing the potential of two-electrode detection

The development of low-cost, disposable electrochemical sensors is an essential step in moving traditionally inaccessible quantitative diagnostic assays towards the point of need. However, a major remaining limitation of current technologies is the reliance on standardized reference electrode materials. Integrating these reference electrodes considerably restricts the choice of electrode substrate and drastically increases fabrication costs. Herein, we demonstrate that adoption of two-electron detection systems can circumvent these limitations and allow the development of low-cost, paper-based devices. We showcase the power of this approach by developing a continuous flow assay for urinary creatinine, enabled by an embedded graphenic two-electrode detector. The detection system not only simplifies sensor fabrication and readout hardware but also provides robust sensing performance with high detection efficiencies. In addition to enabling high-throughput analysis of clinical urine samples, our two-electrode sensors provide unprecedented insights into the fundamental mechanism of the ferricyanide-mediated creatinine reaction. Finally, we develop a simplified circuitry to drive the detector. This forms the basis of a smart reader that guides the user through the measurement process. This study showcases the potential of affordable capillary-driven cartridges for clinical analysis within primary care settings.