This paper describes the development and use of a handheld and lightweight stamp for the production of microfluidic paper-based analytical devices (μPADs). We also chemically modified the paper surface for improved colorimetric measurements. The design of the microfluidic structure has been patterned in a stamp, machined in stainless steel. Prior to stamping, the paper surface was oxidized to promote the conversion of hydroxyl into aldehyde groups, which were then chemically activated for covalent coupling of enzymes. Then, a filter paper sheet was impregnated with paraffin and sandwiched with a native paper (n-paper) sheet, previously oxidized. The metal stamp was preheated at 150 °C and then brought in contact with the paraffined paper (p-paper) to enable the thermal transfer of the paraffin to the n-paper, thus forming the hydrophobic barriers under the application of a pressure of ca. 0.1 MPa for 2 s. The channel and barrier widths measured in 50 independent μPADs exhibited values of 2.6 ± 0.1 and 1.4 ± 0.1 mm, respectively. The chemical modification for covalent coupling of enzymes on the paper surface also led to improvements in the colour uniformity generated inside the sensing area, a known bottleneck in this technology. The relative standard deviation (RSD) values for glucose and uric acid (UA) assays decreased from 40 to 10% and from 20 to 8%, respectively. Bioassays related to the detection of glucose, UA, bovine serum albumin (BSA), and nitrite were successfully performed in concentration ranges useful for clinical assays. The semi-quantitative analysis of all four analytes in artificial urine samples revealed an error smaller than 4%. The disposability of μPADs, the low instrumental requirements of the stamp-based fabrication, and the improved colour uniformity enable the use of the proposed devices for the point-of-care diagnostics or in limited resources settlements.

This paper describes the modification of microfluidic paper-based analytical devices (μPADs) with chitosan to improve the analytical performance of colorimetric measurements associated with enzymatic bioassays.

A systematic investigation was conducted to study the effect of paper type on the analytical performance of a series of microfluidic paper-based analytical devices (μPADs) fabricated using a CO₂ laser engraver.

The modification of μPADs with SiO ₂ NPs provides enhanced color intensity and minimal color gradient.