A highly efficient indigenous portable optical sensor for measurement of total chromium concentration in environmental and biological samples: Design, development, and validation with spectroscopic results

The development of a portable, selective, and digital optical sensor named E-Eye for sensing chromium in environmental and biological samples is reported in this article. Colorimetric sensing of the analyte +has been established, akin to the spectrophotometric absorption principle, without engaging the high-end instruments and critical synthesis techniques. Chromium in the sample is measured from the absorbance of a purple-colored complex resulting from the 1,5-diphnylcarbazide reaction. The absorbance of the complex of the different chromium concentrations was differentiated based on the working principle of the LED-LDR (Light Emitting Diode − Light-dependent Resistor) coupling, where LDR’s resistance is analogous to absorbance. The pH of the reaction mixture was also optimized to enhance the sensor performance in terms of the Limit of Detection (LOD) and Quantification (LOQ) being 10.78 µg L−1 (ppb) and 32.7 µg L−1 (ppb), respectively, which are the lowest reported values in the colorimetric route to date. This was achieved without the assistance of a nanoparticle route and high-end equipment. The chromium sensor’s efficacy was tested against 80 field samples collected from various environmental and biological sources, and the results were compared with the UV–vis spectroscopy and Atomic absorption Spectroscopy (AAS) reading. It reports good accuracy for all types of samples. The average absolute percentage error ranges from 2.75 % to 10.31 % w.r.t. UV–vis spectroscopy measurement and 0.6 % to 1.5 % w.r.t. AAS results. This prototype can be converted to a user-friendly, handheld POCT device, which senses and quantifies chromium selectively.