Heteroatom-doped carbon dot (CD)-reinforced flexible, antioxidant, and UV-resistant polymeric thin films have been fabricated by a facile physical compounding strategy associated with the ‘cast and peel’ technique. The prepared CDs were found to be stable in aqueous media because of their zeta potential value (−5.85 mV). There was no significant change in the zeta potential values during 7 days of storage, indicating the long-term stability of CPCDs. CD-reinforced thermoplastic starch (TPS)/κ-carrageenan hybrid films have been developed as antioxidants to improve the shelf-life of agro-products. Besides this, they also qualified for mechanical strength (>40 MPa), transparency (∼77%), nondeteriorative dimensional integrity at a high relative humidity (∼97%), and UV-resistant properties. For assessing the food preservation behavior, the leaching of CDs also has been studied by time-dependent sustained release in different food simulant media, where it showed a gradual alteration of entrapment efficacy in high-polarity gradient environments. The mechanism of CD release has been obtained from the non-Fickian fittings of the initial preplateaued kinetic data. Surprisingly, when these nanodots were arrested inside the polymer matrix, the film also showed excellent water vapor impermeability, low moisture retention, sufficient toughness, and superficial compliance to external flexing and stretching. Also, CD-based TPS/κ-carrageenan films exhibited strong antioxidant activity, as determined by 1,1-diphenyl-2-picrylhydrazyl (>85%) and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid assays (>90%). Thus, these hybrid films could be promoted as ideal alternatives for food packaging with their thin, flexible, tough, antioxidant, and moisture-impermeable properties.

Hospital-acquired (nosocomial) infections account for the majority of adverse health effects during care delivery, placing an immense financial strain on healthcare systems around the world. For the first time, the present article provides evidence of a straightforward pollution-free technique to fabricate a heteroatom-doped carbon dot immobilized fluorescent biopolymer composite for the development of functional textiles with antioxidant and antimicrobial properties. A simple, facile, and ecofriendly approach was devised to prepare heteroatom-doped carbon dots from waste green tea and a biopolymer. The carbon dots showed an excitation-dependent emission behavior, and the XPS data unveiled that they are co-doped with nitrogen and sulfur. A facile physical compounding strategy was adopted to fabricate a carbon dot reinforced biopolymeric composite followed by immobilization onto the textile. The composite textiles revealed excellent antioxidant activity, determined by 1,1-diphenyl-2picrylhydrazyl (>80%) and 2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid assays (>90%). The results of the disc diffusion assay indicated that the composite textiles substantially inhibited the growth of both tested bacteria Escherichia coli and Bacillus subtilis with increasing coating cycles. The time-dependent antibacterial experiments revealed that the nanocomposite can inhibit significant bacterial growth within a few hours. The present study could open up the possibility for the commercialization of inexpensive smart textile substrates for the prevention of microbial contamination used for the medical and healthcare field.

The concentration of thiocyanate (SCN-) in bodily fluids is a good indicator of potential and severe health issues such as nasal bleeding, goiters, vertigo, unconsciousness, several inflammatory diseases, and cystic fibrosis. Herein, a visual SCN- sensing method has been developed using the enzyme-like nature of positively charged gold quantum dots (Au QDs) mixed with 3,3′,5,5′-tetramethylbenzidine (TMB) and hydrogen peroxide (H2O2). This research also reports a new method of synthesizing positively charged Au QDs directly from gold nanoparticles through a hydrothermal process. Microscopic imaging has showed that the Au QDs were 3–5 nm in size, and the emission wavelength was at 438 nm. Au QDs did not display any enzyme-like nature while mixed up with TMB and H2O2. However, the nanozymatic activity of Au QDs appeared when SCN- was included, leading to a very low detection limit (LOD) of 8 nM and 99–105% recovery in complex media. The steady-state kinetic reaction of Au QDs showed that Au QDs had a lower Michaelis–Menten constant (Km) toward H2O2 and TMB, which indicates that the Au QDs had a higher affinity for H2O2 and TMB than horseradish peroxidase (HRP). A mechanism study has revealed that the scavenging ability of hydroxyl (•OH) radicals by the SCN- group plays an important role in enhancing the sensitivity in this study. The proposed nanozymatic “Off–On” SCN- sensor was also successfully validated in commercial milk samples.

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