Rapid, in-field speciation of Cr(VI) in aqueous samples using photoluminescent MoS₂ quantum dots and portable fluorimetry with digital image analysis

This study explores a novel approach for in-field speciation of Cr(VI) in various aqueous samples employing nontoxic, MoS₂ quantum dots (QDs) as a fluorescent probe. The proposed fluorimetric method, compatible with commercial instruments, utilizes a portable custom-built fluorimeter equipped with a multi-wavelength LED array. The method seamlessly incorporates digital image analysis, with fluorescence signals recorded by a smartphone for detection and signal analysis. Digital image analysis decomposes fluorescence intensity into RGB components, enabling rapid analysis and instantaneous sharing of results. The optimized method yielded a linear calibration graph ranging from 50 to 5000 μg L^-1, with a correlation coefficient of 0.98. The relative standard deviation for determination of 500 μg L^-1 Cr(VI) was 0.52% for five replicate measurements. Successfully applied to wastewater and river water samples, this method combines efficiency, portability, and versatility for in-field Cr(VI) speciation and provides an accessible environmental monitoring tool for less developed countries facing budget and skilled workforce limitations.