Colorimetric detection of Cr3+ 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 Cr3+ 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 Cr3+ induced aggregation of AgNPs through coordinated complex formation between Cr3+ 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 Cr3+ concentration by using univariate calibration curves in less than 60s. This smartphone-based detection system showed a high selectivity of AgNPs with Cr3+ and gave a positive coefficient correlation (R2 = 0.9878) between the intensity of channel R and the Cr3+ concentration, with a linear range of 2.0-5.0 mg L-1, and a detection limit of 1.52 mg L-1. Furthermore, the proposed method has been successfully applied for quantification of Cr3+ 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 Cr3+ detection in the real samples.