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In this work, we reported the synthesis of carbon quantum dots (CQDs) with high fluorescent quantum yield (90.7 %). These nanoparticles were applied in a turn-off/turn-on sensor able to detect cyanide ions. In this sensing strategy, Fe3+ ions were added to the aqueous suspension of CQDs to quench the fluorescence of the system, which was recovered from the presence of cyanide ions. Furthermore, a sensor array was developed using the LDA chemometric tool, to classify different species present in cookie formulations, including gluten. The turn-off/turn-on sensor proved to be sensitive and effective for detecting cyanide ions, with a detection limit of 3.77 ppm. This high sensibility and selectivity allowed quantifying the analyte in a real sample of tap water. [Display omitted] • A fluorescent nanoprobe with ultra-high quantum yield (90.7 %) for sensing of allergens and toxic substances was obtained. • Carbon Quantum Dots (CD-90) synthesized by one-step hydrothermal treatment and showed high fluorescence signal at 440 nm. • CD-90 were used as fluorescent nanoprobes in the construction of a sensor array for detection of gluten in cookies samples. • Fe3+ ions quenched the fluorescence of CD-90, which was recovery by adding CN − ions. • CN − ions were identified in tap water sample with recovery of 94.8 % and RSD of 7.34 %. [ABSTRACT FROM AUTHOR]

Multiple forms of detecting Co2+ are reported in this work to quantify these ions in real blood plasma samples. Carbon Quantum Dots (CQDs) were used as a fluorescent nanoprobe. The CQDs were obtained from a bottom-up approach using a hydrothermal method and choline chloride and branched poly(ethyleneimine) as precursor molecules. Several spectroscopic and structural characterizations were performed. The efficient fluorescence quenching of CQDs related to the Co2+ ion was used for the detection of the analyte, generating a sensing strategy with a limit of detection (LOD) of 0.98 μmol L−1. Furthermore, the interaction between the Co2+ ion with the CQDs resulted in the color change of the solution from colorless to pale yellow. Thus, a colorimetric Co2+ sensor was also developed, since there was an absorption band at 315 nm attributed to the formation of the complex CQD + Co2+. The colorimetric method showed an excellent sensitivity to Co2+, with a LOD of 3.01 μmol L−1. In addition, Principal Component Analysis (PCA) together with Linear Discriminant Analysis (LDA) were used successfully to distinguish different concentrations of Co2+ and different interfering ions present in the solution. Finally, a real sample of blood plasma was properly treated and doped with different concentrations of Co2+, which was successfully quantified via fluorescent method. Therefore, the CQDs obtained in this work are a powerful and versatile Co2+ detection tool. • A fluorescent nanoprobe with high selectivity for multi-way sensing of cobalt was obtained through one-pot synthesis. • N-CD-Ch quantify Co2+ ions by fluorescence quenching and chemometric tools. • Co2+ with N-CD-Ch shows color pale yellow and a colorimetric sensor was developed. • Co2+ was identified in blood plasma sample with recovery of 100.9% and RSD of 0.9%. [ABSTRACT FROM AUTHOR]

In this study, we report the synthesis and application of polyethylenimine, ethylenediamine branched-functionalized carbon quantum dots (CQDs.BPEI) for protein sensing. These carbon-based nanoparticles were found to act as a protein-responsive platform. On this basis, the CQDs.BPEI system was able to detect eight different proteins (four metallic and four non-metallic), even using concentrations in the range of 5–40 nM, depending on the analyte protein. The fluorescence titrations performed at 298 and 310 K displayed fluorescence quenching, which can be explained through a collisional mechanism. It was also possible to conclude that the fluorescence quench comes from the amino acid residues on the surface of the proteins. To further check the potential of the system, we developed a “nose”-based methodology to identify proteins. Using materials, such as copper acetate and ethylenediaminetetraacetic acid, our chemical “nose” approach was able to discriminate 40 nM proteins in phosphate buffered saline (pH 7.4). In this case, the identification accuracy of the random unknown set was 83%. Overall, the results evidence the potential of CQDs.BPEI as a protein-responsive probe to detect and identify proteins. [ABSTRACT FROM AUTHOR]

• Highly fluorescent FM-CDs have shown maximum emission wavelength at 435 nm. • FM-CDs proved to be excellent nanoprobes for analysis of additives in food. • Detection of food additives by FM-CDs and LDA algorithm was successfully performed. • The identification in pickled olives samples was performed with 100 % of accuracy. A robust fluorescence-based sensing strategy was designed considering relevance of analyzing chemical additives in industrialized food. In this study, a sensing approach was developed using fluorescent carbon quantum dots (CQDs) as a chemometric tool. CQDs were synthesized by a simple one-step hydrothermal route using the American natural seed Caelsalpinia pulcherrima , and further characterized regarding their chemical structure. Five food additives were identified, citric acid, lactic acid, ascorbic acid, sodium benzoate and potassium sorbate, which showed a highly sensitive response with a limit of detection (LOD) as low as 252 ng mL−1. The sensing platform was designed using the supervised method for recognizing patterns of linear discriminant analysis (LDA), where we could identify different concentrations of additives, after optimization of experimental parameters. Furthermore, the sensing strategy successfully identified all tested additives in a pickled olives sample with 95 % of confidence, where 100 % of combinations were correctly identified based on classification matrix. Overall, the obtained results evidence the accuracy and potential of CQDs-based fluorescence sensing in the identification of food additives. [ABSTRACT FROM AUTHOR]

• CQD and AgNP were combined to develop a pesticides sensing strategy using FRET phenomenon. • A fast pesticide identification was applied in real samples of rice, carrot, orange and pepper. • The sensibility of the sensing strategy achieved 250 ng.mL−1. In this work, a fluorescent sensing strategy was developed for identification of pesticides in food, which was obtained thought the interaction of carbon quantum dots (CQDs) and silver nanoparticles (AgNPs). The CQDs were synthesized from riboflavin according to an experimental design. On this basis, the most appropriate samples were selected and structurally characterized, where AgNPs efficiently quench the fluorescence of CQDs due a fluorescence resonance energy transfer (FRET). The CQDs was titrationed with AgNPs (Ag@PAA and Ag@bPEI), determining the best concentration of quenching (0.228 and 3.030 pmol.L−1, respectively). Furthermore, a strategy of sensing was developed in order to identify the pesticides propanyl, parathion, dimethoate, chlorpyrifos and pyrimicarb, which were also verified in real samples of rice, carrot, orange and pepper. The results were analyzed by linear discriminant analysis (LDA), obtaining different response patterns against pesticide concentrations, with confidence level of 95%. After that, assays were performed using lower concentrations of the analytes. It was verified that in pepper extract, the sensibility of the sensing strategy was 250 ng.mL−1. Therefore, the CQDs synthesized in this work may be considered a powerful tool to identify pesticides in food samples. [ABSTRACT FROM AUTHOR]