Exploring roles of chitosan, collagen, and semisynthetic polymer in optical-catalytic-electrochemical properties of hybrid opto-electronic system: multimodal sensing and electro-oxidation of Hg(II) in real solutions.

The unusual formation of Hg(III)-coordinated polymer at room temperature offers a unique electro-optical platform to explore the rare high-valent electronic properties of mercury, surpassing conventional redox boundaries. In this work, Hg(III) reduction is restricted through its encapsulation within the donor pockets of supramolecular hybrid semisynthetic polymer system composed of chitosan, collagen, synthetic 2-acrylamido-2-methylpropane sulfonic acid (AAMPS), and in-situ generated 2-methyl-2-(3-(N-(2-methyl-1-sulfopropan-2-yl)acrylamido)propanamido)propane-1-sulfonic acid (MMSPAPPSA). The -C(=O)N<, -C(=O)NH-, -C(=N)OH, -C(O) = N+<, -NH2, -CH2OH, >CHOH, -CH2SH, and -SO3H functionalities of the constituent matrices form donor pockets to coordinate and stabilize Hg(III). Therefore, semisynthetic opto-electroactive polymers (SOEPs) are synthesized through grafting of chitosan in the matrix of AAMPS and MMSPAPPSA. In SOEPs, chitosan manifests dual emission and higher conductivity compared to that of poly(AAMPS-co-MMSPAPPSA). However, to further increase the fluorescence intensity, open circuit potential, and conductivity, SOEP2 (optimized composition) is modified with different amounts of collagen to fabricate hybrid opto-electroactive polymers (HOEPs). The opto-electrochemically optimized HOEP2 shows high selectivity toward Hg(II). In the cyclic voltammetry, Hg(II) → Hg(III) oxidation by HOEP-modified Pt electrode is confirmed from the anodic signal at 0.27 V (Hg(II)/Hg(III)), supported by the spectroscopic analyses of Hg(II/ III)-HOEP2 prepared from electrolyzed product and HOEP2 at the room temperature. Indeed, chitosan-collagen-synthetic polymer system promotes Hg(II) oxidation through electron-rich functionalities and stabilizes Hg(III) through their robust coordination microenvironments, collectively generating Hg(III) within the semisynthetic polymer framework. Additionally, HOEP2 is employed for fluorometric, voltammetric, and impedimetric sensing of Hg(II) in distilled, tap, and pond water with high selectivity, reversibility, reproducibility, and low limits of detection.