Colorimetric detection of Cr in dietary supplements using a smartphone based on EDTA and tannic acid-modified silver nanoparticles.

A simplistic, portable and low-cost method for the rapid detection of Cr was developed based on a smartphone readout and a co-functionalized silver nanoparticles (AgNPs) system for use as an on-site device in resource-poor areas. The presence of Cr induced aggregation of AgNPs through coordinated complex formation between Cr and stabilizing agents on the NPs surface, resulted in a bright yellow of an AgNPs solution turned to wine red along with a SPR band was red-shifted from 429 nm to 625 nm. A smartphone with an available free application, called "PhotoMetrix" was used to measure the RGB (red, green, blue) values of the color intensities in the AgNPs system and convert into Cr concentration by using univariate calibration curves in less than 60s. This smartphone-based detection system showed a high selectivity of AgNPs with Cr and gave a positive coefficient correlation (R = 0.9878) between the intensity of channel R and the Cr concentration, with a linear range of 2.0-5.0 mg L, and a detection limit of 1.52 mg L. Furthermore, the proposed method has been successfully applied for quantification of Cr in dietary supplement samples. The results obtained were in close agreement with those obtained in FAAS (Flame Atomic Absorption Spectrometry). The developed colorimetric system based on a smartphone readout device exhibits feasibility and reliability for on-site Cr detection in the real samples.