Guoqiang Xiang

In this study, N, S‐co‐doped carbon dots (N, S‐CDs) with high fluorescence quantum yield (36.6%) were successfully prepared by H ₂ O ₂ mediated self‐exothermic reaction under alkaline conditions using Eriocaulon buergerianum as a carbon source and ethylenediamine (EDA) as a surface modifier. The synthesized N, S‐CDs have a uniform size distribution (1–4.5 nm) and exhibit double emission peaks (389 and 410 nm) under 310 nm excitation. It was found that the N, S‐CDs exhibited highly selective and sensitive fluorescence response to Pd ²⁺ in aqueous solution, and the fluorescence intensity decreased significantly with the increase of Pd ²⁺ concentration (0.05–3.5 μg mL ⁻¹ ). The detection limit was as low as 5.51 ng mL ⁻¹ , and the relative standard deviation (RSD) was 1.56%. The study of quenching mechanism showed that the mixed static‐dynamic quenching interaction between Pd ²⁺ and N, S‐CDs resulted in fluorescence quenching. In addition, the probe showed good detection performance in lake water, river water, and synthetic water samples, and the recovery rate met the analysis requirements. This study not only provides a green and economical fluorescence sensing strategy for the efficient detection of Pd ²⁺ but also opens up a new way for the application of natural plant resources in the preparation of functional nanomaterials.

In this study, nitrogen-doped carbon dots (N-CDs) were successfully synthesized through a facile one-step hydrothermal approach using honeysuckle and ethylenediamine (EDA) as carbon and nitrogen sources, respectively. The obtained N-CDs displayed intense blue fluorescence emission at 420 nm upon excitation at 350 nm, along with an exceptional fluorescence quantum yield of 60.53%. Systematic characterization experiments employing transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) revealed the morphological features, surface functional groups, and elemental composition of the N-CDs. Remarkably, in HCl medium, chloride ion-catalyzed bromate oxidation led to pronounced fluorescence quenching of the N-CDs. A highly linear correlation (R² = 0.9965) was found between bromate concentration (64–1024 ng·mL^− 1) and fluorescence quenching efficiency, as quantified by the equation log(I₀/I) = 3.86685C + 0.00557, with an impressive detection limit of 14 ng·mL^− 1 (S/N = 3). The practical application of this sensing platform to bromate determination in flour-based food products and tap water samples yielded satisfactory recoveries, ranging from 87.4 to 104.4%, with relative standard deviations below 3.5%. These findings highlight the great potential of the as-synthesized N-CDs as a reliable fluorescent nanoprobe for sensitive and selective bromate detection in complex food and environmental samples.

In this study, multi-element doped carbon dots (DXM-CDs) were synthesized via a one-step hydrothermal method, utilizing dexamethasone sodium phosphate (DXM) injection as a precursor. The synthesized DXM-CDs exhibited ultraviolet fluorescence emission at 380 nm, with a fluorescence quantum yield (QY) of 19.7%. The fluorescence intensity of DXM-CDs was quenched via oxidative degradation using KBrO₃ in H₃PO₄ medium. The presence of Ir⁴⁺ ion catalyzed the oxidation of DXM-CDs using KBrO₃, resulting in an accelerated fluorescence quenching. Based on this catalytic oxidation reaction, a kinetic fluorimetric method for the quantification of Ir⁴⁺ ions was developed. The optimum conditions obtained are 0.4 M H₃PO₄, 2.0 mg mL^− 1 of DXM-CDs, 1.0 mM KBrO₃, reaction temperature of 100 °C, and reaction time of 20 min. Under optimized conditions, the method achieved a detection limit (3σ) of 14 pg mL^− 1 and linear response was observed in the concentration range of 0.2 to 20 ng mL^− 1. The developed method was successfully applied to the determination of Ir⁴⁺ ions in water samples, yielding accurate and precise results.

Nitrogen-doped carbon dots (N-CDs) were prepared by self-exothermic procedure using grasshopper powder as a single precursor. The prepared N-CDs not only have excellent fluorescence properties, but also can catalyze and enhance the ultra-weak chemiluminescence of NaHCO₃-H₂O₂. The reaction conditions of NaHCO₃-H₂O₂-N-CDs CL were optimized. Under the optimal experimental conditions, when AA was added to the NaHCO₃-H₂O₂-N-CDs CL system, AA had a significant inhibitory effect on the CL intensity of NaHCO₃-H₂O₂-N-CDs. There was a good linear relationship between the calculated lg(I0/I) and the concentration of AA (C), and the calibration curve equation was lg(I₀/I) = 0.03667 C-0.00708 (µM). The established CL analysis method has a detection limit of 0.12 µM for AA and a linear range of 0–50 µM. The selectivity of CL method was evaluated, and the method was successfully applied to the determination of AA in vegetable and fruit samples. The spiked recoveries were between 88.9% and 118.9%, which indicated that the method was simple, rapid, and sensitive, and had great potential in the determination of AA in foods.

A selective and sensitive fluorometric assay was developed for specific determination of curcumin (Cur) based on fluorescence resonance energy transfer (FRET) between molybdenum disulfide quantum dots (MoS₂ QDs) and Cur. The MoS₂ QDs were prepared via a one-step hydrothermal protocol using sodium molybdate dihydrate, L-cysteine (Cys) as precursors, and sodium cholate (SC) as a modification agent. The as-prepared MoS₂ QDs possessed maximum fluorescence emission at 460 nm with a 20% of fluorescence quantum yield (FQY). It was found that the fluorescence of MoS₂ QDs could be quantitatively quenched by Cur through FRET mechanism. Therefore, Cur could be detected in the range of 0.1–20 µg mL^− 1 with a detection limit of 5 ng mL^− 1. Additionally, the developed MoS₂ QDs based fluorescent assay has been successfully applied for real food sample analysis with satisfactory results.

Rapid, green and high yield synthesis of nitrogen doped carbon dots(N-CDs) through exothermic decomposition reaction of H₂O₂ using grasshopper powder as precursor and polyethyleneimine (PEI) as a surface passivation reagent. Water-soluble fluorescent N-CDs can be obtained by reacting 5 minutes and purified N-CDs were obtained after an activated carbon adsorption separation procedure with a product yield of 53.3%. TEM, FT-IR, XPS, fluorescence and UV-vis spectra were used to investigate the morphology, elemental information and optical properties of N-CDs. The results indicated that the fluorescence emission of N-CDs is typical excitation wavelength dependent with a strongest emission peak at 417 nm under 330 nm excitation wavelength. There is a good linear response between the fluorescence intensity of N-CDs and temperature, which makes N-CDs a potential nanothermometer to monitor temperature. The great spectral overlap between the blue emission peak (417 nm) of N-CDs and the absorption peak (430 nm) of tartrazine (TAR) leads to an effectively fluorescence quenching phenomenon by TAR through inner filter effect (IFE) and the fluorescence quenching degree (lg(I₀/I)) was linearly response to the TAR concentration in the range of 1-100 µM. The detection limit of developed method is 54.3 nM for TAR, and the relative standard deviation (RSD) is 1.14% (n=7, c=10 μM). The N-CDs came from an exothermic reaction is a highly selective and sensitive fluorescent probe for TAR, and it was successfully applied to the determination of TAR in food samples with satisfactory results.