Improving the reading accuracy of distance-readout microfluidic paper-based analytical device through laser grayscale printing.

Distance-readout microfluidic paper-based analytical devices(μPADs)offer great promise for applications in environmental monitoring, food safety, and point-of-care diagnostics owing to their low-cost, portability, and intuitive visual readout. However, the shear resistance near the hydrophobic boundary can cause uneven liquid flow in the paper channel, presenting a faster center and slower edges, which limit the accuracy of signal-readout and quantification.To address this issue, a strategy using laser grayscale printing to adjust the uniformity of the liquid flow was proposed. By precisely controlling the toner coverageto adjust the local porosity r(y) and contact angleθ(y), an ideal capillary resistance gradient can be generated to compensate for velocity differences. The Gaussian bell-shaped grayscale distribution reduces the maximum flow front deviation from approximately 6.32 mm to 0.06 mm, suppressing the convex flow front by spatially balancing permeability and flow resistance, resulting in an exceptionally flat flow interface.By using ascorbic acidas the model analyte, a strong linear correlation (R2 = 0.987) was obtained between the bleaching distance and ascorbic acid concentration, with a detection limit of 0.72 mM. More importantly, grayscale modulation reduced the relative standard deviation from 7.37% to 3.87% compared with the untreated channels, demonstrating significantly superior signal reading consistency.Overall, it is believed that thisone-step, flexible, universaland in expensive strategy will pave the way for improving the quantitative accuracy and expanding the wide application of Distance-Readout μPADs.