Amylopectin Gel Detects Chromium and Tomato Spoilage Using Onion-Derived Dots

Jim Crocker
26th September, 2025

Amylopectin Gel Detects Chromium and Tomato Spoilage Using Onion-Derived Dots

The amylopectin-S, N–CQDs15 xerogel demonstrates superior antimicrobial efficacy and strong molecular binding affinity against Escherichia coli, Staphylococcus aureus, and Candida albicans, while functioning as a selective biosensor through distinct fluorescence color changes upon exposure to these pathogens and Cr(VI).

Image adapted from: Hebat-Allah S. Tohamy / CC BY (Source)

Key Findings

  • Researchers in Egypt developed a biodegradable film from corn starch and red onion peel waste to preserve food and detect contamination
  • The film effectively inhibits the growth of common foodborne bacteria like E. coli, S. aureus, and C. albicans by up to 99%
  • This film acts as a “smart sensor”, changing color to visually indicate bacterial spoilage and the presence of the heavy metal chromium
Food spoilage and contamination represent significant challenges to food safety and economic stability. Traditional packaging often relies on synthetic materials, raising environmental concerns. Researchers at the National Research Centre, Egypt, have been exploring sustainable, biodegradable alternatives for active food packaging, and a recent study[1] details a promising new composite film based on readily available materials – amylopectin, poly(N-isopropylacrylamide), and carbon quantum dots (CQDs) derived from red onion peels. This film aims to not only preserve food but also actively detect signs of spoilage and contamination. The core of this research lies in creating a material that combines the protective qualities of a film with the sensing capabilities of nanoscale components. Amylopectin, a starch component, provides the structural base, while poly(N-isopropylacrylamide) contributes to the film's overall properties. The key innovation, however, is the incorporation of sulfur and nitrogen-doped carbon quantum dots (S, N–CQDs). These CQDs aren't created from scratch but are extracted from red onion peel waste – a significant step towards reducing agricultural by-products. Carbon quantum dots are tiny particles that exhibit fluorescence, meaning they emit light when exposed to certain wavelengths. The doping with sulfur and nitrogen enhances their fluorescent properties and introduces antimicrobial activity. The research team used computational modelling (DFT calculations) to understand how the S, N–CQDs interacted with the amylopectin matrix, confirming their stable integration and improved film structure. Analysis techniques like FTIR (which identifies the chemical bonds present) and SEM (which visualizes the film’s surface) confirmed the successful incorporation of the CQDs and revealed a more compact pore structure within the composite film, increasing its surface area. The resulting film demonstrated impressive antibacterial activity against common foodborne pathogens. It inhibited the growth of Escherichia coli by 95.25%, Staphylococcus aureus by 99.12%, and Candida albicans by 99.23%. This effectiveness was further supported by molecular docking studies, which showed that the S, N–CQDs strongly bind to proteins within these bacteria, disrupting their function. Beyond its antimicrobial properties, the film also functions as a smart sensor. Upon contact with these same microorganisms, it exhibited distinct fluorescence responses. E. coli triggered a mixed green and red fluorescence, S. aureus produced blue dots, and C. albicans caused a shift from large red regions to numerous green dots. This allows for visual identification of different types of contamination. The film also responded to the presence of Cr(VI), a heavy metal contaminant, with a noticeable change in fluorescence from red to blue. Interestingly, this study builds upon previous research exploring the use of carbon dots in food packaging[2][3]. Earlier work demonstrated the potential of CMC films incorporating carbon dots derived from red onion peel waste as pH-sensitive colorimetric sensors for tomato spoilage, where the film’s color changed with pH variations due to the presence of flavonoids. Similarly, HPMC-MCDs composite films showed pH-sensitive behavior and bacterial detection capabilities, albeit requiring magnetite for visual discernment[3]. The current study expands on these findings by utilizing amylopectin and poly(N-isopropylacrylamide) and achieving multifunctional sensing without the need for additional components like magnetite. Crucially, the amylopectin-S, N–CQDs film is also pH-responsive, displaying color transitions that are relevant for monitoring tomato spoilage, mirroring the findings of[2]. This is particularly important as pH changes are a key indicator of food deterioration. The film’s ability to visually signal spoilage adds another layer of functionality, making it a comprehensive solution for active food packaging. The tighter pore structure observed in this study, compared to earlier CMC-based films[4], may contribute to the enhanced interaction with analytes like bacteria and betalains, leading to more pronounced sensing responses. The use of waste red onion peels as a source for the CQDs further highlights the sustainability of this approach. By transforming a discarded agricultural product into a valuable functional component, this research contributes to a circular economy and reduces environmental impact.

AgricultureNutritionBiochem

References

Main Study

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

Published 23rd September, 2025

https://doi.org/10.1038/s41598-025-19875-x

Related Studies

2) Novel intelligent naked-eye food packaging pH-sensitive and fluorescent sulfur, nitrogen-carbon dots biosensors for tomato spoilage detection including DFT and molecular docking characterization.

https://doi.org/10.1016/j.ijbiomac.2025.143330

3) Novel colored hydroxypropyl methyl cellulose/ magnetite carbon dots films for beef packaging with DFT calculations and molecular docking study.

https://doi.org/10.1038/s41598-025-92976-9

4) A Novel Natural Chromogenic Visual and Luminescent Sensor Platform for Multi-Target Analysis in Strawberries and Shape Memory Applications.

https://doi.org/10.3390/foods14162791


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