Rapid, simple and highly selective determination of Chromium(III) in aqueous samples by a microfluidic cell coupled to a smartphone-based colorimetric-sensing detector

In this study, citrate-modified Ag (AgNPs@Cit) plasmonic nanoparticles were synthesized and characterized using UV–visible spectrophotometry and transmission electron microscopy (TEM). Subsequently, a microfluidic kit was developed for the colorimetric point of care (POC) detection of Cr³⁺ based on the color change of AgNPs@Cit solution from yellow to red in the presence of Cr³⁺ ions. The experimental parameters were optimized using a central composite experimental design, and the interactions between operational factors were thoroughly examined. Under optimum conditions (flow rate: 0.04 mL/min, flow path length: 9.65 cm, and pH = 7.6), a linear relationship was established between the red component of RGB pixels of the analyzed images captured by a smartphone and the concentration of Cr³⁺ within the range of 1.00–35.00 µmol L⁻¹. The proposed method exhibited a detection limit of 0.33 µmol L⁻¹. The selectivity of the developed microfluidic kit was evaluated, and no significant interference was observed. Furthermore, the applicability of the suggested microfluidic kit for the determination of Cr³⁺ in five different drinking water samples was successfully demonstrated, with calculated recovery values falling within the range of 96.2–106.4%.