Rapid light transmittance measurements in paper-based microfluidic devices

We developed methodology and built a portable reader to assess light transmittance in paper-based microfluidic devices in a highly sensitive, user-friendly and field-appropriate manner. By sandwiching the paper assay between micro-light-emitting diodes and micro-photodetectors, the reader quantifies light transmittance through the paper independent of ambient light conditions. To demonstrate the utility of the reader, we created a single-use paper-based microfluidic assay for measurement of alanine aminotransferase, an indicator of liver health in blood. The paper assay and reader system accurately differentiated alanine aminotransferase levels across the human reference range and demonstrated significant differences at clinically relevant cutoff values. Results were provided within 10 min and were automatically generated without complex image analysis. Performance of this point-of-care diagnostic rivals the accuracy of lab-based spectrometer tests at a fraction of the cost, while matching the timeliness of low-cost portable assays, which have historically shown lower accuracy. This combination of features allows flexible deployment of low cost and quantitative diagnostics to resource-poor settings. Keywords: Paper microfluidics, Colorimetric, Light transmission, Alanine aminotransferase, Enzymatic reactions, Continuous monitoring