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Nitrogen, boron co-doped carbon quantum dots (gCQDs), and a coloration probe (PPD-NPs) with response to cobalt ions (Co2+) were prepared by using 4-hydroxyphenylboric acid as the common precursor, with ethylenediamine and p-phenylenediamine (PPD) adopted as nitrogen-doped reagents, respectively. A noticeable brown-to-purple color change can be observed with the addition of Co2+, and a broad absorption band emerges at 535 nm. At the same time, gCQDs, which is introduced as the fluorescence signal source, will be significantly quenched due to the enhanced inner filtration effect, induced by the overlap between the emission spectrum of gCQDs and the emerging absorption band. Therefore, a colorimetric/fluorescent dual-mode sensing probe for Co2+ is constructed by combining the recognition unit PPD-NPs and the fluorescent gCQDs into PPD-NP/gCQD. Under the optimized experimental conditions, the calculated limits of detection are 1.51 × 10−7 M and 3.75 × 10−7 M for the colorimetric mode and the fluorescence mode, respectively, well qualified for the determination of Co2+ maximum permitted level in drinking water. The feasibility of the proposed method has been verified in tap water, lake water, and black tea samples. [ABSTRACT FROM AUTHOR]

With the expansion of human activities, the consequent influx of mercury (Hg) into the food chain and the environment is seriously threatening human life. Herein, nitrogen and sulfur co-doped fluorescent carbon quantum dots (yCQDs) were prepared via a hydrothermal method using o-phenylenediamine (OPD) and taurine as precursors. The morphological characteristics as well as spectral features of yCQDs indicated that the photoluminescence mechanism should be the molecular state fluorophores of 2, 3-diaminophenothiazine (oxOPD), which is the oxide of OPD. The as-synthesized yCQDs exhibited sensitive recognition of Hg2+. According to the investigation in combination of UV-Vis absorption spectra, time-resolved fluorescence spectra and quantum chemical calculations, the abundant functional groups on the surface of yCQDs allowed Hg2+ to bind with yCQDs through various interactions, and the formed complexes significantly inhibited the absorption of excitation light, resulting in the static fluorescence quenching of yCQDs. The proposed yCQDs was utilized for Hg2+ sensing with the limit of detection calculated to be 4.50 × 10− 8 M. Furthermore, the recognition ability of yCQDs for Hg2+ was estimated in tap water, lake water and bottled water, and the results indicated that yCQDs have potential applications in monitoring Hg2+. [ABSTRACT FROM AUTHOR]

Amaranth red is usually used as a food colorant in carbonated drinks, but long-term excess consumption of amaranth red in carbonated drinks may lead to the loss of zinc in the human body, thus causing kidney dysfunction. In this study, we developed a simple method to combine cysteamine (Cys) and silver nanoparticles (AgNPs), the surface of AgNPs was modified with Cys at room temperature, and then the amino-functionalized SERS substrate was obtained, which was applied to the determination of amaranth red in carbonated drinks. The characteristic peak in Raman spectra of amaranth red showed obvious SERS enhancement at 1570 cm−1, whose intensity had a good linear relationship with the concentration of amaranth red in carbonated drinks. The limits of detection (LOD) in water and carbonated drinks were calculated to be 1.49 μg/L and 4.13 μg/L, and the adjusted correlation coefficients (R2) were 0.992 and 0.990, respectively. In addition, the average recovery rate of amaranth red in carbonated drinks was 95.11–105.48%, and the relative standard deviation (RSD) was 4.37–8.09%. This work provides a simple and fast method for detecting amaranth red in carbonated drinks. [ABSTRACT FROM AUTHOR]

[Display omitted] • This is the first time that carbon dots have been synthesized using ammonium citrate and glutamic acid as precursors. • The fluorescence stability of carbon dots is fully explored, facilitating their use in real-world environments. • This method achieves high selectivity and sensitivity in the trace detection range. • Monitoring Cd2+ ions in tap water and lake water. In this study, fluorescent carbon dots were synthesized for the first time using ammonium citrate and glutamic acid as precursors via a one-pot hydrothermal method. The synthesized carbon dots emit blue fluorescence at 436 nm (excited at 320 nm) and demonstrate excellent photobleaching resistance and fluorescence stability in high salt environments. Within the range of 1–25 μM, the fluorescence of CDs gradually increases with the increasing concentration of Cd2+, reaching a limit of detection as low as 13 nM. This phenomenon could be ascribed to the chelation-enhanced fluorescence, a result of Cd2+ forming complexes with the abundant surface functional groups such as CN–, –COOH, –OH, –NH 2 in CDs. Furthermore, this turn-on fluorescent probe has been successfully used for the detection of Cd2+ in tap water and lake water, providing an efficient and sensitive method for the analysis of environmental metals. [ABSTRACT FROM AUTHOR]

In this paper, fluorescent carbon dots were prepared by hydrothermal method using 3,5-dihydroxybenzoic acid and l -Arginine as precursors. The synthesized CDs have excitation-dependent emission with emission peaks at 354 nm and 460 nm, corresponding to the optimal excitation wavelengths of 295 nm and 330 nm, respectively. CDs have good dispersion and resistance to photobleaching in aqueous solution, and can maintain stable fluorescence in highly concentrated salt environment. Based on the inner filter effect, Cr(VI) with strong absorption can shield the excitation light of CDs at 295 nm and absorb the emission fluorescence at 354 nm simultaneously. Due to the intermolecular electrostatic interaction, Hg(II) can coordinate with CDs surface groups and cause static quenching, which significantly reduces the fluorescence intensity of CDs emitted at 460 nm. The linear ranges were 0.1–2 μM and 0.4–5 μM for Cr(VI) and Hg(II) detection, respectively, and limits of detection were 0.024 μM and 0.084 μM. Additionally, the probe was successfully applied to tap water and lake water samples. With high sensitivity and spectral selectivity, this sensing strategy realized the detection of two heavy metal ions by a single fluorescent probe, demonstrating its great potential in the field of environmental metal analysis. [Display omitted] • First synthesis of carbon dots with spectral selectivity using 3,5-dihydroxybenzoic acid and l -arginine as precursors. • Separate detection of Cr(VI) and Hg(II) ions using the same carbon dots under different excitations. • This method achieves high selectivity and sensitivity in the trace detection range. • Monitoring Cr(VI) and Hg(II) ions in tap water and lake water. [ABSTRACT FROM AUTHOR]

[Display omitted] • This is the first time that carbon dots were synthesized using cysteine and ethylenediamine as precursors. The synthesis method is green and simple, and the prepared N -CDs have good fluorescence stability. • The developed experimental conditions for the detection of Fe3+ using nitrogen-doped carbon dots as fluorescent probes have been fully optimized to significantly improve the sensitivity. • The method is simple, sensitive and highly feasible, with LOD as low as 0.069 μM in deionized water. And, linear models were also constructed in tap water and lake water with LOD of 0.21 μM and 0.59 μM, respectively. In this study, we synthesized stable nitrogen-doped carbon dots by a simple and economical one-step hydrothermal method using l -cysteine and anhydrous ethylenediamine as precursors. The prepared carbon dots have bright and stable blue light emission near 383 nm and can be used as fluorescent probes to detect the concentration of Fe3+ in environmental waters. It was demonstrated that due to intermolecular electrostatic interaction, a non-fluorescent complex N -CDs/Fe3+ is formed by coordination of Fe3+ with amino and carboxyl functional groups on the surface of carbon dots. Therefore, in combination with internal filtration effect, the fluorescence of carbon dots can be quenched in the presence of Fe3+, and the degree of quenching is linearly related to the concentration of Fe3+. The limit of detection in deionized water was as low as 0.069 μM with R2 of 0.998 and a linear range of 0.3 to 20 μM. In addition, satisfactory recoveries were achieved for the determination of Fe3+ in environmental water samples. The method is reliable, with highly sensitivity and selectivity, and has potential for practical applications in environmental metal analysis. [ABSTRACT FROM AUTHOR]