A novel fluorescent receptor L was synthesized by Schiff base condensation of 1-pyrenemethylamine with the vitamin B cofactor pyridoxal. The receptor L is highly selective and sensitive towards Zn ions among other tested metal ions. Upon interaction with Zn, the receptor L showed a distinct fluorescence enhancement at 485 nm due to the excimer formation leading to the fluorescent colour change from blue to bluish-green. Subsequently, when the in situ generated ZnL complex interacted with various anions and amino acids, the addition of HPO and cysteine reinstated the fluorescence of the receptor L due to the demetalation of Zn from the ZnL complex. Accordingly, the receptor L was developed for the highly selective, specific and sensitive detection of three important bioactive analytes, i.e., Zn, HPO and cysteine with a detection limit down to 2.3 × 10 M, 2.18 × 10 M and 1.59 × 10 M, respectively. Additionally, the receptor L was applied to the detection of intracellular Zn ions in live HeLa cells.

This work presents the fluorescent turn‐on sensing of Zn2+ and Cd2+ by using a nano‐assembly designed by the surface modification of the blue fluorescent polyethyleneimine (PEI) passivated silver nanoclusters (PEI‐AgNCs) with the vitamin B6 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 –NH2 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 Zn2+ and Cd2+, 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 Zn2+ and 59.0 x 10−8 M for Cd2+ without any interference from other tested metal ions and was applied for the recognition of Zn2+ and Cd2+ 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 Zn2+ and Cd2+. In addition, the developed system has been employed for the qualitative detection of intracellular Zn2+ in live HeLa cells by fluorescence imaging.

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A new fluorescence receptor (E)‐2‐amino‐N′‐((3‐hydroxy‐5‐(hydroxymethyl)‐2‐methylpyridin‐4‐yl)methylene)benzohydrazide (1) was synthesized by reacting vitamin B6 cofactor pyridoxal with 2‐aminobenzohydrazide, and characterized by various spectral (FT‐IR, 1H NMR, 13C NMR and ESI‐MS) data. It shows high selectivity and sensitivity towards Zn2+ and CN− ions among the other tested metal ions (Cu2+, Co2+, Ni2+, Mn2+, Mg2+, Fe3+, Fe2+, Cd2+, Hg2+, Pb2+, Al3+ and Cr3+) and anions (F−, Cl−, Br−, I−, NO3−, N3−, HSO4−, H2PO4−, ClO4− and AcO−). With the addition of Zn2+ and CN−, the receptor 1 displays a drastic fluorescence enhancement around 475–480 nm without any interference from other tested cations/anions. Receptor 1 shows the detection limit down to 3.20 ×10−7 M and 1.53×10−7 M for Zn2+ and CN− ions, respectively. In addition, the receptor 1 shows selective response towards CN− by giving a new absorption band around 431 nm. The recognition mechanism was proposed through 1H NMR and DFT results. Finally, the receptor 1 was applied for the detection of bioactive Zn2+ ions in live HeLa cells.

A novel anion selective chromogenic and fluorogenic chemosensor (L) bearing catechol and phenol groups was developed. The sensorLwas tested for live breast cancer cell imaging and can be applied to the breast tumour diagnosis.