Aldoxime-Derived Water-Soluble Polymer for the Multiple Analyte Sensing: Consecutive and Selective Detection of Hg2+, Ag+, ClO–, and Cysteine in Aqueous Media

A simple tailor-made aldoxime-functionalized water-soluble polymeric probe (P-Oxime) for the consecutive colorimetric sensing of multiple analytes, including Hg 2+, Ag +, ClO –, and cysteine, was designed and synthesized. A reaction between the aldehyde groups of the side chain in the polymer (P-CHO) and hydroxylamine in ethanol led to the target polymer, P-Oxime. This water-soluble polymeric probe exhibited excellent sensitivity and selectivity toward Hg 2+ ions under pH = 5 in water due to the formation of strong electron-withdrawing nitrile groups (P-CN) via Hg 2+ -promoted dehydration reaction. The high selectivity and sensitivity of P-Oxime toward ClO – over other reactive oxygen species at pH = 9.5 in water were also observed. After the addition of ClO –, the color of the P-Oxime solution turned from pale yellow to red due to the formation of an aldehyde group. By taking advantage of the formation of functional groups during the Hg 2+ and ClO – sensing process, the consecutive sensing/binding studies toward the different analytes were further investigated. The in situ generated P-CN species after Hg 2+ detection responded selectively to Ag + ions with an 18 nm blue-shift in which the nitrile groups of P-CN interacted with the Ag + ions to form a coordination complex. Similarly, only cysteine and homocysteine among various amino acids showed a remarkable blue-shift upon in situ addition into the obtained P-CHO solutions after ClO – detection via the formation of a thiazolidine ring.