Evolution of wax-on-plastic microfluidics for sub-microliter flow dynamics and its application in distance-based assay

Plastic substrates are known for their flexibility, optical clearance, toughness, heat resistance, and nonabsorbent properties. Here, we introduce new wax-on-plastic microfluidic platforms, which are responsive to liquid types and concentrations in sub-microliter volume regime based on their flow behavior. Fabrication of the wax-on-plastic microfluidic platforms do not require heating to create stable hydrophobic barriers and liquids can move with a capillary flow down to 0.25 μL volume in the microchannels having 10 μm height. The flow dynamics of the studied fluids in these channels followed the Darcy’s theoretical model, which can be correlated with their flow velocity and viscosity. The flow velocity of the liquid flow was used to estimate glucose in simulated urine within ~ 40 s run-time. The distance-based assay involving relying on flow velocities was used to establish a dynamic range of the glucose in simulated urine with limit of quantitation of 0.018%, which is almost 3× lower than the lower limit of glucose quantity normally present in diabetic patients, i.e., 0.05–0.1%. Moreover, these microchannels can also work distinctly with various biofluids, such as sweat, urine, and fat-free milk.