We report the finding of the presence of carbon nanoparticles (CNPs) in different carbohydrate based food caramels, viz. bread, jaggery, sugar caramel, corn flakes and biscuits, where the preparation involves heating of the starting material. The CNPs were amorphous in nature; the particles were spherical having sizes in the range of 4–30 nm, depending upon the source of extraction. The results also indicated that particles formed at higher temperature were smaller than those formed at lower temperature. Excitation tuneable photoluminescence was observed for all the samples with quantum yield (QY) 1.2, 0.55 and 0.63%, for CNPs from bread, jaggery and sugar caramels respectively. The present discovery suggests potential usefulness of CNPs for various biological applications, as the sources of extraction are regular food items, some of which have been consumed by humans for centuries, and thus they can be considered as safe.

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The classical chemistry of sodium thiosulfate was applied to synthesize luminescent Sdots where elemental sulfur produced in situ was etched with NaOH. This method notably reduces the synthesis time of Sdots in comparison to the previously reported etching technique of bulk sulfur. The assynthesized Sdots exhibited excitation dependent photoluminescence with a QY of 2.5%, photostabality under UV light irradiation, excellent dispersibility in aqueous medium, and also the stability even after several weeks. Notably, no emission was observed due to the oxidation of PEG-400 during the course of reaction. The Sdots was then employed as a dual function probe for the sensing of metal ions. Using fluorimetric method, Sdots showed preferential selectivity toward the Co 2+ metal ions. However, a single probe Sdots can colorimetrically distinguish multiple metal ions such as Co 2+ , Cr 6+ , and Pb 2+ by displaying color change on the immediate addition of analytes. Furthermore, the color change of Sdots is demonstrated with the help of hue images and hue spectra (or histogram) that will help in the development of Sdots based portable device. The present study contributes to the further advancement of this emerging field as a promising single-element nanomaterial an alternative to luminescent metallic nanomaterials.

We report the conducting nature of carbon dots (Cdots) synthesized from citric acid and ethylene diamine. Chemically synthesized conducting nanocomposite consisting of Cdots and polypyrrole (PPy) is further reported, which showed higher electrical conductiviy in comparison to the components i.e., Cdots or PPy. The conductive film of the composite material was used for highly sensitive and selective detection of picric acid in water as well as in soil. To the best of our knowledge, this is the first report on the conductivity based sensing application of Cdot nanocomposite contrary to the traditional fluorescence based sensing approaches.

The present review article focuses on novel findings corresponding to the structural and photophysical properties of carbon dots. The article also highlights unique characteristics of crystalline dots that offer new chemistry and thus new application potential.

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A mechanochemical synthesis of luminescent sulfur quantum dots (Sdots) is demonstrated for the first time to reduce the synthesis reaction time. Structural characterization using X-ray photoelectron spectroscopy, transmission electron microscopy, and Raman spectroscopy confirmed the formation of Sdots. The present method produced Sdots through a short-chain polymerization of sulfur and features an excitation-dependent photoluminescence with a quantum yield of 4.8%, high photostability, excellent hydrophilicity, and low toxicity. Further, Sdots were seen to cause a low toxicity in both normal and cancer cells, which makes this a promising candidate for bioimaging and biolabeling.

Herein, different surface charged carbon dots (Cdots) were synthesized by using diethylene glycol as a carbon source with various amine containing surface passivating agents. The synthesis method is very simple and fast microwave oven-based, that results in almost similar sized positive, negative and uncharged fluorescent Cdots which has been confirmed by zeta potential analysis in our case. The formation of Cdots was confirmed by characterization using fluorescence spectroscopy, transmission electron microscopy, XRD, FT-IR, and XPS spectroscopy. To find out relative bactericidal activity of these Cdots, green fluorescence protein expressing recombinant E. coli bacteria were taken as a model system. Time-dependent bacterial growth and FACS study demonstrated that both uncharged Cdots and positively charged Cdots were showing better bactericidal activity as compared to negative charged Cdots. The Cdots caused elevation of reactive oxygen species level, which is possibly leading to bacterial cell death.