Portable paper-based microfluidic devices based on CuS@Ag2S nanocomposites for colorimetric/electrochemical dual-mode detection of dopamine.

The development of integrated multiple signal outputs within a single platform is highly significant for efficient and accurate on-site biomarker detection. Herein, colorimetric/electrochemical dual-mode microfluidic paper-based analytical devices (μPADs) were designed for portable, visual and accurate dopamine (DA) detection. The dual-mode μPADs, featuring folded structure, integrate a colorimetric layer and an electrochemical layer using wax printing and laser-induced graphene (LIG) pyrolysis techniques, allowing the vertical flow of analyte solution. Copper sulfide @ silver sulfide (CuS@Ag2S) nanocomposites, with excellent laccase-like and electrocatalytic performance, were modified onto the detection zones as colorimetric/electrochemical sensing substrates for dual-mode DA recognition. In the colorimetric detection zones, the obvious violet-colored signals were generated based on the enhanced laccase-like oxidation reaction induced. Further, amplified electrical response signals toward DA were collected in electrochemical detection zone due to the epitaxial heterostructure of silver sulfide (Ag2S). Consequently, the developed CuS@Ag2S-incorporated μPADs exhibit linear responses for colorimetric and electrochemical DA detection in ranges of 2-50 μM and 0.5-70 μM, respectively, with the limit of detection (LOD) of 0.675 μM and 0.086 μM. This work integrates multiple detection modes into μPADs, providing the portable, reliable and visual alternative to traditional detection methods of DA for POCT.