Novel Wax Valves To Improve Distance-Based Analyte Detection in Paper Microfluidics

Microfluidic paper-based analytical devices (μPADs) have been extensively studied for disease diagnostics, food quality control, and environmental monitoring due to the advantages of low cost, portability, and simplicity. The lack of flow controllability has triggered the development of valves for such devices. This paper reports the μPADs integrating novel wax valves for distance-based detection. The valves are printed on paper and can be manually opened by organic solvents within seconds. The opened valve does not influence the flow. The μPADs with wax valves were then applied in the distance-based detection of potassium iodate and glucose. The valves allow mixing of reagents and subsequent incubation in the loading zone, resulting in a shorter detection time and larger linear detection range. This study has demonstrated a linear detection range of 0.05-0.5 mM for potassium iodate, while linear ranges of 1-5 and 2.5-80 mg/dL are achieved for glucose when total detection time is 15 and 25 min, respectively. The lower detection limit is only 1/11 of that in a previous study. The detection ranges of iodate and glucose assays cover the concentrations of iodate in salt/milk and glucose in human saliva, respectively. Due to the simplicity, reliability, and ability for high-density integration, the μPADs with wax valves are of great potential in point-of-care (sampling) applications.