Pyrrole-modified gold nanoparticle structure for dual UV-vis and smartphone-based colorimetric detection of hexavalent chromium in food and environmental samples.

As a potent, human-carcinogenic toxin, hexavalent chromium, Cr(vi), causes aggressive cancers and severe organ failure. It poses a major environmental threat due to its mobility in water and easy cellular penetration. Therefore, sensitive detection methods are essential for monitoring and managing Cr(vi) levels in food, soil, water, and cosmetics. Herein, a gold nanoparticles-pyrrole (AuNPs@pyrrole) based novel colorimetric sensing platform is developed for the rapid quantification of Cr(vi). The mechanism of the developed sensor is driven by the bridging effect of Cr(vi) ions. By binding to the pyrrole on distinct gold nanoparticles, the ions link the particles together, triggering aggregation and an observable color change. The colorimetric response was quantitatively analyzed using UV-vis spectroscopy and a smartphone RGB detector, providing a portable and user-friendly Cr(vi) monitoring approach, with a detection limit of 0.01 ppm over a linear range of 0.1-100 ppm. Furthermore, the developed sensor exhibited outstanding specificity toward Cr(vi). The detection process remained immune to the presence of competing aqueous metal ions, notably Fe(ii), Cd(ii), As(iii), Pb(ii), Cr(iii), Hg(ii), and Fe(iii). The efficiency of the proposed sensing platform was validated against a reference coupled plasma optical emission spectrometry (ICP-OES) scheme, demonstrating the detector's high precision and robustness. The practical utility of the AuNPs@pyrrole structure was confirmed through the successful detection of Cr(vi) in food and environmental water samples. These findings emphasize the potential of the developed sensing platform as an intuitive, user-friendly colorimetric sensor for on-site pollution monitoring, providing a cost-effective and dependable solution for both environmental and industrial applications.