Abstract A recyclable polymeric film was designed and prepared for the consecutive colorimetric detection of cysteine and mercury (II) ions. A target random terpolymer (P1) of N,N-dimethylacrylamide (DMA), (E)-2-((4-((4-formylphenyl)diazenyl)phenyl)(methyl)amino) ethyl acrylate (FPDEA, M1), and N-(4-benzoylphenyl)acrylamide (BPAm) was synthesized via free radical polymerization (FRP). The average molecular weight (Mn) of [p(DMA-co-FPDEA-co-BPAm), P1] was 39,300, and the molecular weight distribution (Mw/Mn) was 1.6. P1 exhibited excellent sensitivity and selectivity towards cysteine in the aqueous media. A simple reaction between the aldehyde groups of P1 and cysteine led to the formation of P2 with five-membered rings, accompanied by the color change from orange to yellow. The in situ generated P2 after cysteine detection responded selectively to mercury (II) ions in which the five-membered rings of P2 dissociated into P1 with CHO groups and cysteine. For further film study to demonstrate the reversiblity of the system, P1 was immobilized on a quartz slide by the spin-coating, followed by the exposure to UV light. The resulting film was successfully used for the consecutive colorimetric detection of cysteine and mercury (II) ions, demonstrating its reusability even after multiple cycles. Highlights Azoaniline-based polymeric probe was synthesized and characterized. Selective and colorimetric sensing for cysteine in water. Excellent selectivity and colorimetric sensing for mercury(II) ions in water. Consecutive sensing by using a single component. Reusable polymeric film for detection of cysteine and mercury (II) ions. Graphical abstract [DISPLAY OMISSION] Aldehyde-functionalized azo-containing polymer was synthesized and characterized. Consecutive sensing of cysteine and mercury (II) ions was checked in water with high selectivity and sensitivity. After immobilizing the polymer on the surface, the successive colorimetric detection of cysteine and mercury (II) ions was repeatable over several cycles, demonstrating the whole system to be reversible, and this polymeric film can be reused.
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