Carbon quantum dots with blue/near infrared emissions for ratiometric fluorescent lornoxicam sensing and bio-imaging

Carbon quantum dots in spectrofluorimetric analysis: A comprehensive review of synthesis, mechanisms and multifunctional applications

Carbon quantum dots (CQDs), as a representative nanomaterial, have demonstrated promising applications in fluorescence analysis owing to their unique optical properties, low cytotoxicity and exceptional biocompatibility. This review systematically summarizes recent advances in synthesis strategies, detection mechanisms and applications of CQDs for sensing metal ions (e.g., Hg2+, Fe3+, Cu2+), small molecules (e.g., biomolecules, pharmaceuticals, azo dyes) and proteins. Hybridization of CQDs with functional materials has been shown to significantly enhance their photoluminescence properties while optimizing detection sensitivity and selectivity. The article critically examines fundamental detection mechanisms, especially fluorescence quenching and further outlines design strategies for fluorescence probes based on "on-off" switching or ratio signaling. Moreover, current challenges are analyzed, such as the need for synthetic protocol standardization, in-depth exploration of heteroatom-doped CQDs, expansion of detectable analytes and rational design of fluorescence turn-on probes. Future prospects in environmental monitoring, biomedical diagnostics and pharmaceutical analysis are also highlighted. This comprehensive review offers critical insights to guide the rational design and application of advanced CQD-based hybrid systems.

Solid-Phase Pyrolysis Synthesis of Amino Acid-Based Nitrogen-Doped Carbon Dots as an "On-Off-On" Fluorescent Probe for the Detection of Copper Ions and Glutathione

This study introduces the synthesis of amino acid-based nitrogen-doped carbon dots (N-L-Ser-CDs) from L-serine (L-Ser) and urea through a straightforward and economical one-step solid-phase pyrolysis process. The incorporation of nitrogen into the carbon dots resulted in a remarkable 27.6-fold increase in fluorescence intensity, featuring a peak emission at 405 nm when excited at 330 nm and a significant fluorescence quantum yield of 22.5%. These N-L-Ser-CDs displayed a specific binding affinity for Cu2+, leading to a pronounced fluorescence quenching effect. However, upon interaction with glutathione (GSH), the fluorescence of the N-L-Ser-CDs + Cu2+ complex was selectively restored. This restoration was attributed to the displacement of Cu2+ from the surface of the N-L-Ser-CDs due to the strong interaction between GSH and Cu2+. The mechanism underlying this fluorescence quenching was elucidated as an electron transfer process from the excited state of the N-L-Ser-CDs to Cu2+. Additionally, the sensor developed in this study exhibited a linear detection range of 0-90 µM for Cu2+ with a detection limit of 3 µM, and a linear detection range of 0-120 µM with a detection limit of 3 µM for GSH. By integrating the detection capabilities for both Cu2+ and GSH, a successful "on-off-on" fluorescent probe was developed. Most importantly, this proposed method offers simplicity, affordability, and ease of use, while also showing potential for practical GSH detection in real urine samples.

Detection of Tetracycline in Farm Wastewater by Nitrogen-doped Carbon Quantum Dots

The detection of tetracycline antibiotics in environmental waters is crucial due to their widespread use, persistence, and potential toxicity. Herein, a method for the specific detection of tetracycline in aquaculture wastewater using a nitrogen-doped carbon quantum dots fluorescence probe is reported. Nitrogen-doped carbon quantum dots (N-CQDs) were synthesized in one step via a hydrothermal method, employing citric acid as the carbon source and diethylenetriamine as the nitrogen source. The resulting N-CQDs exhibit excellent stability, solubility and fluorescence properties. Upon the introduction of tetracycline, a fluorescence burst can be observed, indicating that the N-CQDs function as a ratio fluorescence probe. The fluorescence burst phenomenon is primarily due to the internal filtering effect. In the case of N-CQDs, this burst is attributed to the overlap between the absorption spectrum of tetracycline and the emission spectrum of the carbon quantum dots, which results in internal filtering. The linear range for tetracycline detection spans from 54.2 nM to 0.8 μM, with a detection limit of 54.2 nM. The developed fluorescence probe shows potential for application in detecting tetracycline in real water samples.

Carbon quantum dot with co-doped nitrogen and phosphorus for tazettine ratiometric fluorescent sensing

An overdose of tazettine (TZ) has toxic side effects, which makes it extremely important to rapidly and subtly determine the TZ. In this study, double-emitting, nitrogen-phosphorus co-doped carbon quantum dots (N,P-CQDs) were prepared using cis-butenedioic acid, phosphoric acid, and p-phenylenediamine. An effective inner filter effect (IFE) can occur between TZ and N,P-CQDs, resulting in their fluorescence quench. Therefore, a ratio fluorescent probe was constructed for detecting the TZ was constructed. After optimizing the experimental conditions, the quenching efficiency showed a strong linear connection with the TZ concentration in the range of 0.01-30 µmol/L, with the detection limit of 0.002 µmol/L. This method could be satisfactorily applied to detect TZ in mouse plasma samples.