A cobalt-based bifunctional metal organic framework-mediated fluorescent bio-sensing system for the hypersensitive detection of Ag+ ions through catalytic hairpin assembly

Abstract

Silver is often used as a water disinfectant in healthcare institutions as well as in potable water purifiers. Even though there are no strict regulations regarding the amount of silver in water, harmful impacts such as argyria and respiratory system irritation, have been linked to excessive silver consumption. Hence, herein, a rapid and sensitive fluorescent biosensor for Ag⁺ detection was developed using a cobalt-based bi-functional metal–organic framework (Co-BFMOF) as a fluorescence quencher and target-induced catalytic hairpin assembly (CHA). Three identical fluorophore (FAM)-labeled metastable hairpin aptamer probes (FAM-FAM-HAPs: FAM-HAP-1, FAM-HAP-2 and FAM-HAP-3) can be thoroughly adsorbed on the Co-BFMOF surface to quench the fluorescence signal (Turn-off mode). The presence of Ag⁺ ions was used to trigger the CHA of hairpin aptamer probes with the assistance of a helper aptamer. Finally, the hybridized robust triangle-shaped DNA structure containing duplex DNA was harder. Therefore, it was desorbed from the Co-BFMOF surface and generated an effective fluorescence signal (Turn-on mode). Under optimum conditions, the peak intensity of fluorescence increased with the increase in Ag⁺ with a wide dynamic working range from 0 nM to 0.8 nM with a detection limit down to 45 pM. The advanced sensing method provides good selectivity toward the target over other challenging metal ions and the ability to identify spiked Ag⁺ in real water samples.