Novel ionic liquid-functionalized carbon quantum dots (IL-CDs) were prepared by hydrothermal method, and characterized with FT-IR, TEM and XPS. The IL-CDs exhibited narrower particle size distribution with more uniform dispersion and the surface potential changes from negative to positive due to the function of IL. IL-CDs could be quenched (“turned off”) after adding ascorbic acid (AA), and as an “on–off”, fluorescent probe could be established for direct analysis AA. The linear range of AA was 0.34–30.00 μg/mL and the LOD was 0.11 μg/mL. The method was successfully applied to the determination of AA in real samples with satisfactory results.

Since soil salinization imposes various adverse effects on plants, research on how to relieve salt stress from plants is extremely urgent. We synthesized a new type of cerium-doped carbon quantum dots by a hydrothermal synthesis method. Characterization shows that the carbon quantum dots have a small and uniform particle size, high stability, high water solubility and biocompatibility. Mung bean seeds were soaked in CDs:Ce solutions under a concentration gradient (0.25, 0.5, 1, 2, 3 mg/ mL) and germinated under salt stress (150 mM NaCl). Compared with salt stress, the addition of CDs solutions effectively enhanced the ability of plants to relieve salt stress. The relieving effect on mung bean plants was the most significant after treatment with 2 mg/mL CDs:Ce, and the main root length, plant height and leaf length in comparison with the case of salt stress increased by 83%, 80%, and 60%, respectively. Chlorophyll content, peroxidase activity, superoxide dismutase activity and catalase activity, total protein content increased by 90%, 77%, 76%, 77% and 76%, respectively, malondialdehyde and proline The content decreased by 83% and 77%. Inductively coupled plasma mass spectroscopy proved mung bean plants absorbed CDs:Ce, but the absorption of NaCl decreased by 21.8%. Fluorescence imaging showed CDs:Ce was absorbed by roots, and transferred from the vascular system and apoplastic pathways to stems and leaf veins, and mainly aggregated in intercellular gaps, the vascular system, leaf veins, cilia and stomata. Stereomicroscopy showed that CDs:Ce induction increased the stomatal opening by 15.7%, and improved metabolic efficiency and NaCl excretion from the plants. Hence, CDs:Ce shows great potential in protecting crops from abiotic stress.

Food toxins are regarded as a major source of health risks, serious illnesses susceptible to even death. These dangerous pathogens may lead to significant economic impact worldwide. The food production chain undergoes different stages like harvesting, processing, storage, packaging, distribution, and lastly preparation, and consumption. Therefore, each step is susceptible to risks of environmental contamination. Nowadays, the carbon quantum dots (CDs) are regarded as one of the most widely used hybrid carbon nanomaterials due to their different magical physical and chemical properties. The CDs have a size below 10 nm and show the fluorescent property. The CDs find vast applications in different fields like sensing, food safety, drug delivery, bioimaging, catalyst, energy conversion, etc. Compared to other available methods, the fluorescence detection techniques have low cost, easy handling, and safe operating system. There is a need for a review to compile the fluorescence properties of carbon nanodots used to detect food pathogens. This brief review is addressed in that direction and mostly focused on the synthesis of carbon dots-based fluorescence sensors for detecting pathogens and toxins in foods and beverages. The detailed mechanisms and origin of fluorescence properties of carbon quantum dots are also highlighted herewith.

Herein, a facile bottom–up approach for producing nitrogen-doped carbon quantum dots (N-CQDs) was carried out by the hydrothermal treatment of microcrystalline cellulose, in the presence of different nitrogen sources (blank/urea/ammonia water/ethanediamine(EDA)/Hexamethylenetetramine). The result showed that the fluorescence intensity and quantum yields (QYs) of N-CQDs with different nitrogen sources are all higher than that without nitrogen source. Compared with the other three nitrogen sources, N-CQDs prepared by EDA not only have the highest fluorescence intensity but also the largest QYs of 51.39%. Therefore, EDA was chosen as the nitrogen source to prepare N-CQDs. The obtained N-CQDs are uniform spherical particles with a diameter of 2.76 nm. The N-CQDs also exhibit excitation-dependent and long-wave emission properties. The emission range of N-CQDs is 470–540 nm. Moreover, N-CQDs as fluorescent agents successfully acted on purple LEDs (λem = 365 nm) to achieve white LEDs light emission. At the same time, a fluorescent thin layer chromatography plate was successfully prepared using N-CQDs, silica gel G and Sodium carboxymethylcellulose as raw materials. The separation trajectory of mixed sample of Sudan red III and kerosene on the fluorescent TLC plate is obviously clearer than that of the TLC plate.

An extract of fresh guava leaves (Psidium guajava) was used as a green carbon precursor to fabricate blue fluorescent carbon quantum dots (GCQDs) by hydrothermal process. The GCQDs show bright blue fluorescence emission under UV light with an excitation wavelength of 350 nm and emission at 450 nm. The physical structure of GCQDs was characterized by Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), High-resolution transmission electron microscope (HR-TEM) and atomic force microscopy (AFM). GCQDs 80 μg inhibited the growth of waterborne pathogens Escherichia coli and Salmonella typhi. We also investigated the catalytic activity of the GCQDs on the removal of two azo dyes, namely Congo red and bromophenol blue, with and without NaBH4. The GCQDs showed an excellent reduction of color intensity of both dyes without NaBH4 within 30 min of treatment.

In the present study, a novel electrochemical sensor for acetaminophen (AMP) which included quantum graphitic carbon nitride dots, g-C3N4QDs, was designed and conducted with molecular imprinted polymer (MIP). First, bulk g-C3N4 was generated with direct thermal polycondensation of melamine. After the treatment of the acidic solution containing H2SO4: HNO3 (1:1, v:v), the heating treatment at 200 °C on the dispersion provided g-C3N4QDs. In this respect, for nanomaterial characterization, some spectroscopic approaches were performed including Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) as well as electroanalytical methods such as electrochemical impedance (EIS) and cyclic voltammetry (CV). In accordance with the aims of the study, AMP imprinted electrode was formed after high electrocatalytic performance and linear range of 1.0 × 10– 11–2.0 × 10– 8 M and the LODs of 2.0 × 10– 12 was achieved. Eventually, an AMP-printed sensor was also used for AMP identification in pharmaceutical samples.

Highly luminescent carbon quantum dots (CQDs) are developed as fluorescent probes for selective detection of the heavy-ion Fe3+, where the CQDs exhibit excellent nontoxicity, functionalizability, sensitivity, and selectivity. Biomass-based CQDs and nitrogen-doped CQDs (N-CQDs) are synthesized for the selective detection of Fe3+ by using H2O2 as an oxidant and polyetherimide (PEI) as a nitrogen precursor by a green hydrothermal synthesis method. The prepared CQDs and N-CQDs exhibit an elliptical morphology and with an average particle size of 7 and 4 nm, respectively, and emit blue photoluminescence at 445 and 468 nm under excitation at 367 and 343 nm, respectively. The CQDs and N-CQDs exhibit good water solubility because of the abundant hydroxyl and carboxyl/carbonyl groups and graphic/pyrrolic/pyridinic nitrogen on the surfaces, giving rise to a quantum yield of about 24.2% and 30.7%, respectively. Notably, the Matrimony vine-PEI-based CQDs exhibit excellent Fe3+ selectivity and sensitivity relative to the Matrimony vine-based CQDs due to complexation of the numerous phenolic hydroxyl groups and nitrogen-containing groups with Fe3+, leading to increased fluorescence quenching, which greatly improves the sensitivity of detection. The minimum detection limit was 2.22 μmol L− 1 with a complexation constant of 44.7.

Nanostructured ZnO materials have been studied extensively because of their functional properties. This paper presents a composite material of zinc oxide quantum dots (ZnO QDs) and porous carbon using a one-step carbonization process. The direct carbonization of a metal–organic complex generates mesostructured porous carbon with a homogeneous distribution of ZnO QDs. The structural and morphological properties are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The resulting ZnO QDs@porous carbon composite delivers a high specific capacity of 990 mAh g−1 at 100 mA g−1, 357 mAh g−1 at 2 A g−1, and high reversibility when evaluated as an anode for lithium ion batteries.