Amylopectin xerogel with onion based sulfur nitrogen doped carbon quantum dots as a chemosensor for chromium and biosensor for microbial spoilage in tomatoes

Abstract

Abstract This study presents the development of a multifunctional, biodegradable xerogel film based on amylopectin and poly(N-isopropylacrylamide) (poly(NIPAm)) incorporating sulfur and nitrogen-doped carbon quantum dots (S, N–CQDs) derived from red onion peels (ROP). The formation mechanism and stability of the composite film were investigated using DFT calculations, revealing enhanced interactions and stability in the S, N–CQDs-containing film (amylopectin-S, N–CQDs15). FTIR and SEM analyses confirmed the successful incorporation of S, N–CQDs and revealed a tighter pore structure in the composite film, leading to increased surface area. The amylopectin-S, N–CQDs15 film exhibited significantly improved antibacterial activity, with inhibition rates of 95.25% against Escherichia coli, 99.12% against Staphylococcus aureus, and 99.23% against Candida albicans. These findings were supported by molecular docking studies indicating strong binding affinities. Furthermore, the film demonstrated its potential as a smart sensor through distinct fluorescence responses to these microorganisms: it showed mixed green and red fluorescence with E. coli, blue dots with S. aureus, and a change from large red regions to numerous green dots with C. albicans. The film also exhibited a fluorescence shift from red to blue upon exposure to Cr(VI). Notably, the film displayed pH-responsive color transitions relevant to monitoring tomato spoilage. These findings highlight the potential of this bio-based composite film, prepared from a waste resource, as a sustainable and effective solution for active food packaging, offering antimicrobial properties and detection of spoilage and contamination.