Vitamin B 6 Cofactor‐Conjugated Polyethyleneimine‐Passivated Silver Nanoclusters for Fluorescent Sensing of Zn 2+ and Cd 2+ Using Chemically Modified Cellulose Strips

This work presents the fluorescent turn‐on sensing of Zn 2+ and Cd 2+ by using a nano‐assembly designed by the surface modification of the blue fluorescent polyethyleneimine (PEI) passivated silver nanoclusters (PEI‐AgNCs) with the vitamin B 6 cofactor pyridoxal 5‘‐phosphate (PLP) in aqueous medium. The cofactor PLP was conjugated through the Schiff base condensation between the ‐CHO group of PLP and the free –NH 2 present in PEI‐AgNCs. The formation of nano‐assembly PLP_PEI‐AgNCs was ascertained from various characterization along with the fluorescent color change from blue to yellow. Upon addition of Zn 2+ and Cd 2+ , the yellow fluorescent of PLP_PEI‐AgNCs instantaneously and selectively changed to bluish‐green with a significant fluorescence enhancement at 475 nm. The developed nanoprobe shows the detection limit down to 50.5 x 10 −8 M for Zn 2+ and 59.0 x 10 −8 M for Cd 2+ without any interference from other tested metal ions and was applied for the recognition of Zn 2+ and Cd 2+ in various environmental and biological fluids with good recovery %. Also, the PLP conjugated PEI‐AgNCs was covalently anchored over the cellulose paper strips, characterized and then applied for the detection of Zn 2+ and Cd 2+ . In addition, the developed system has been employed for the qualitative detection of intracellular Zn 2+ in live HeLa cells by fluorescence imaging.