Ensuring high selectivity for preconcentration and detection of ultra-trace cadmium using a phage-functionalized metal–organic framework

Metal-organic frameworks functionalized with Cd(ii) binding phages were for the first time fabricated for the isolation and preconcentration of ultra-trace cadmium. Highly specific Cd(ii) binding phages were screened through biological panning from a phage display peptide library. Thereafter, chloroauric acid (HAuCl₄) was reduced by the phages to provide phage-stabilized gold nanoparticles (AuNPs). The phage-AuNP networks were then assembled onto the metal-organic framework UiO66-NH₂ to serve as an affinity probe for the selective recognition and isolation of ultra-trace cadmium. 2.0 μg L^-1 Cd²⁺ was selectively captured by the derived UiO66-NH₂@phage composite with an adsorption efficiency of 100%. UiO66-NH₂@phage exhibits favorable anti-interference capability against the coexisting species. It ensures highly selective and sensitive quantification of ultra-trace cadmium with detection by graphite furnace atomic absorption spectrometry (GFAAS). An enrichment factor of 17.4 was obtained along with a limit of detection (LOD) of 3.9 ng L^-1 within a linear range of 0.01-0.35 μg L^-1. The procedure was further validated by analyzing cadmium content in a certified reference material (CRM, simulated water, GBW08608) and a series of environmental water samples. In general, the present study provides a new protocol for the development of novel adsorbents toward the target by biopanning to regulate the selectivity.