Cost effective paper-based colorimetric devices for a simple assay of dopamine in pharmaceutical formulations using 3,3',5,5'-tetramethylbenzidine- silver nitrate as a chromogenic reagent

Paper-based devices using smartphone-based detection have been widely used for colorimetric analysis due to their simplicity, ease of operation, and handheld capability. Herein, we demonstrate simple colorimetric measurement of dopamine on paper-based devices, which were fabricated in the 96-well plate shape using wax printing technique. The detection reaction was based on the 3,3',5,5'-tetramethylbenzidine (TMB)-silver nitrate redox reaction. The oxidized TMB possessed the blue color which could be observed by naked eyes. In the presence of dopamine, the blue color of the oxidized TMB decreased according to the reduction of the oxidized TMB. In optimal condition, the responses were fit to the logarithmic curve with r² of 0.9932. The method showed good precision (%RSD < 6.6%), and recoveries (92.8 - 106.2%) with the detection limit of < 0.6 mM. Moreover, the results were well agreeing with those obtained from the conventional UV-Vis spectrophotometry, which were not statistically difference (P > 0.05). The developed method did not require any complex or time-consuming preparation and was successfully employed for the determination of dopamine injections.