Deep eutectic solvent-assisted chemosensing of Fe(iii), V(iii), C(ii), and P(ii) ions using a paper-based micro-array...

Heavy metal pollution has become one of the most serious environmental and industrial challenges today. This is because of their toxicity, tendency to bioaccumulate in living organisms, and persistence in the environment. In recent years, various techniques have been developed to detect and quantify heavy metal contaminants. In this study, an innovative paper-based chemosensor (PCS) was constructed for the specific colorimetric recognition of Fe(iii), V(iii), Co(ii), and Pd(ii) ions in the presence of deep eutectic solvent (DES). This micro-array of PCS, mounted on fiberglass with a diameter of 5 mm for each zone of reaction. Thus, a miniaturized ion sensing substrate was proposed for low-cost, rapid, sensitive, and selective ion detection in real samples using a smartphone, with silver nanoparticles (AgNPrs) with a prism structure that serves as an optical probe. The DES-PCS combined with silver nanoparticles showed excellent performance in both semi-quantitative and quantitative analysis of Fe(iii), V(iii), Co(ii), and Pd(ii). Furthermore, an RGB-based absorbance method was used to estimate ion concentrations through digital image analysis with a color-picker app installed on a Samsung Galaxy A54 smartphone. High linearity was achieved for all analytes (R ² > 0.975), with a low limit of quantification (LLOQ) ranging from 50 ng ml^-1 to 1 µg ml^-1. The use of the developed DES-PCS confirmed that it is easy to detect Fe(iii), V(iii), Co(ii), and Pd(ii) in human biofluids, with results aligning well with those from standard solutions. Additionally, the DES-PCS demonstrated selective, sensitive, and stable responses without needing sample manipulation, making it suitable for on-site monitoring of ions in both occupational and environmental contexts.