Selective Heavy Atom Effect-Promoted Photosensitization Colorimetric Detection of Ag⁺ in Silver Ore Samples

Analytical methods capable of facile screening of silver ore samples are of vital importance for resource exploration and ore mining. Due to its extreme simplicity, colorimetric detection is desired for silver ore screening, but the analytical sensitivity of existing approaches is typically not sufficient. Here, an Ag⁺-selective heavy atom effect-promoted photosensitization colorimetric assay was developed. Specifically, Ag⁺ and dsDNA-staining dye (photosensitizer) were spatially adjoined in close proximity in dsDNA bearing several cytosine (C) mismatches, leading to enhanced ¹O₂ generation for photosensitized oxidation of chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB). Due to the stable C-Ag(I)-C metallo-base pair, the C-C mismatches in dsDNA can selectively capture Ag⁺, thus allowing highly selective colorimetric detection of Ag⁺ with a visual limit of quantification (LOQ) as low as 0.2 ng/mL. For ore sample analysis, the visual LOQ was about 2 g/t, which was suitable for colorimetric screening analysis of ores of different values. The accuracy of the proposed method was verified through analyzing both certified reference material and real ore samples, the results of which agreed well with those obtained by electrothermal atomic absorption spectrometry (ET-AAS). To facilitate field silver ore screening, acid leaching of the samples was also adopted, and satisfactory analytical accuracy was also obtained at a rough leaching efficiency of 20%.