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A simple, effective, and highly sensitive analytical approach was created and applied in this study for the accurate measurement of three β2-agonist residues (clenbuterol, salbutamol, and ractopamine) in meat samples. In the course of the experiment, new adsorbent molecular sieves (ZMS)@nitrogen-doped carbon quantum dots (N-CQDs) composite materials were synthesized with the aid of hydrothermal synthesis. The composite adsorbent materials were prepared and characterized through scanning electron microscopy, transmission electron microscope, X-ray photoelectron spectroscopy, fluorescence, and zeta potential. Four determinants affecting the extraction and elution’s efficiency, such as the amount of adsorbent, the extraction time, desorption time, and the amount of extraction salt, were substantially optimized. The analytes were quantified by gas chromatography–mass spectrometry. Final results of the methodological validation reflected that the ZMS@N-CQDs composite materials were able to adsorb three β2-agonist residues well and had good reproducibility. In the meantime, all analytes indicated good linearity with coefficient of determination R2 ≥ 0.9908. The limit of detection was 0.7–2.0 ng·g−1, the limit of quantification varied from 2.4 to 5.0 ng·g−1, the precision was lower than 11.9%, and the spiked recoveries were in the range of 79.5–97.8%. To sum up, the proposed approach was quite effective, reliable, and convenient for the simultaneous analysis of multiple β2-agonist residues. Consequently, this kind of approach was successfully applied for the analysis of such compounds in meat samples.

One of the most promising drugs recently approved for the treatment of various types of cancer is dacomitinib, which belongs to the tyrosine kinase inhibitor class. The US Food and Drugs Administration (FDA) has recently approved dacomitinib as a first-line treatment for patients suffering from non-small cell lung cancer (NSCLC) with epidermal growth factor receptor (EGFR) mutations. The current study proposes the design of a novel spectrofluorimetric method for determining dacomitinib based on newly synthesized nitrogen-doped carbon quantum dots (N-CQDs) as fluorescent probes. The proposed method is simple and does not require pretreatment or preliminary procedures. Since the studied drug does not have any fluorescent properties, the importance of the current study is magnified. When excited at 325 nm, N-CQDs exhibited native fluorescence at 417 nm, which was quantitatively and selectively quenched by the increasing concentrations of dacomitinib. The developed method involved the simple and green microwave-assisted synthesis of N-CQDs, using orange juice as a carbon source and urea as a nitrogen source. The characterization of the prepared quantum dots was performed using different spectroscopic and microscopic techniques. The synthesized dots had consistently spherical shapes and a narrow size distribution and demonstrated optimal characteristics, including a high stability and a high fluorescence quantum yield (25.3%). When assessing the effectiveness of the proposed method, several optimization factors were considered. The experiments demonstrated highly linear quenching behavior across the concentration range of 1.0−20.0 μg/mL with a correlation coefficient (r) of 0.999. The recovery percentages were found to be in the range of 98.50–100.83% and the corresponding relative standard deviation (%RSD) was 0.984. The proposed method was shown to be highly sensitive with a limit of detection (LOD) as low as 0.11 μg/mL. The type of mechanism by which quenching took place was also investigated by different means and was found to be static with a complementary inner filter effect. For quality purposes, the assessment of the validation criteria adhered to the ICHQ2(R1) recommendations. Finally, the proposed method was applied to a pharmaceutical dosage form of the drug (Vizimpro® Tablets) and the obtained results were satisfactory. Considering the eco-friendly aspect of the suggested methodology, using natural materials to synthesize N-CQDs and water as a diluting solvent added to its greenness profile.

The aim of this study was to establish a rapid detection method of rutin in food based on nitrogen-doped carbon quantum dots (N-CDs) as the fluorescent probe. N-CDs were prepared via a single-step hydrothermal process using citric acid as the carbon source and thiourea as the nitrogen source. The optical properties of N-CDs were characterized using an electron transmission microscope, X-ray diffractometer, Fourier-transform infrared spectrometer, and nanoparticle size potential analyzer. The UV/Vis absorption property and fluorescence intensity of N-CDs were also characterized using the respective spectroscopy techniques. On this basis, the optimal conditions for the detection of rutin by N-CDs fluorescent probes were also explored. The synthesized N-CDs were amorphous carbon structures with good water solubility and optical properties, and the quantum yield was 24.1%. In phosphate-buffered solution at pH = 7.0, Rutin had a strong fluorescence-quenching effect on N-CDs, and the method showed good linearity (R2 = 0.9996) when the concentration of Rutin was in the range of 0.1–400 μg/mL, with a detection limit of 0.033 μg/mL. The spiked recoveries in black buckwheat tea and wolfberry were in the range of 93.98–104.92%, the relative standard deviations (RSD) were in the range of 0.35–4.11%. The proposed method is simple, rapid, and sensitive, and it can be used for the rapid determination of rutin in food.

The knowledge of the ways in which post-synthesis treatments may influence the properties of carbon quantum dots (CDs) is of paramount importance for their employment in biosensors. It enables the definition of the mechanism of sensing, which is essential for the application of the suited design strategy of the device. In the present work, we studied the ways in which post-synthesis thermal treatments influence the optical and electrochemical properties of Nitrogen-doped CDs (N-CDs). Blue-emitting, N-CDs for application in biosensors were synthesized through the hydrothermal route, starting from citric acid and urea as bio-synthesizable and low-cost precursors. The CDs samples were thermally post-treated and then characterized through a combination of spectroscopic, structural, and electrochemical techniques. We observed that the post-synthesis thermal treatments show an oxidative effect on CDs graphitic N-atoms. They cause their partially oxidation with the formation of mixed valence state systems, [CDs]0+, which could be further oxidized into the graphitic N-oxide forms. We also observed that thermal treatments cause the decomposition of the CDs external ammonium ions into ammonia and protons, which protonate their pyridinic N-atoms. Photoluminescence (PL) emission is quenched.

Nitrogen-doped carbon quantum dots (N-CQDs) with strong fluorescence were prepared by a one-step hydrothermal method using natural biomass waste. Two efficient fluorescent probes were constructed for selective and sensitive detection of oxytetracycline (OTC). The synthesized N-CQDs were characterized by UV-visible absorption spectra, fluorescence spectra, Fourier transform infrared spectroscopy (FT-IR), X-ray photon spectroscopy (XPS), atomic force microscopy (AFM), and high-resolution transmission electron microscopy (HRTEM), which proved that the synthesized N-CQDs surface were functionalized and had stable fluorescence performance. The basis of N-CQDs detection of OTC was discussed, and various reaction conditions were studied. Under optimized conditions, orange peel carbon quantum dots (ON-CQDs) and watermelon peel carbon quantum dots (WN-CQDs) have a good linear relationship with OTC concentrations in the range of 2–100 µmol L−1 and 0.25–100 µmol L−1, respectively. ON-CQDs and WN-CQDs were both successfully applied in detecting the OTC in pretreated tap water, lake water, and soil, with the recovery rate at 91.724–103.206%, and the relative standard deviation was less than 5.35%. The results showed that the proposed N-CQDs proved to be green and simple, greatly reducing the detection time for OTC in the determination environment.

Dye-sensitized solar cells are regarded as promising candidates to resolve the energy and environmental issues in recent years, arising from their solution-processable fabrication technology and high power conversion efficiency. However, there are still several problems regarding how to accelerate the development of this type of photovoltaics, including the limited light-harvesting ability and high-production cost of molecular dye. In the current work, we have systematically studied the role of nitrogen-doped carbon quantum dots (N-CQDs) as co-sensitizers in traditional dye sensitized solar cells. A series of N-CQDs have been prepared by employing chitosan as a precursor via one-pot hydrothermal technology for various times, demonstrating a maximized efficiency as high as 0.089% for an only N-CQDs-based device. Moreover, the co-sensitized solar cell based on N719 dye (C58H86N8O8RuS2) and optimized N-CQDs shows significantly enhanced performance, yielding a solar-to-electric conversion efficiency of up to 9.15% under one standard sun (AM 1.5G) irradiation, which is much higher than the 8.5%-efficiency of the controlled device without N-CQDs. The matched characteristics of energy level, excellent up-convention, and FRET (Förster resonance energy transfer) abilities of N-CQDs are responsible for their improved power conversion efficiency.

Nitrites are the upstream precursors of the carcinogenic nitrosamines, which are widely found in the natural environment and many food products. It is important to develop a simple and sensitive sensor for detecting nitrites. In this work, a fluorescence probe based on nitrogen-doped carbon quantum dots (N-CQDs) was developed for the sensitive and selective determination of nitrites. At pH 2, the fluorescence of N-CQDs can be selectively quenched by nitrite due to the fact N-nitroso compounds can be formed in the reaction of amide groups with nitrous acid, which results in fluorescence static quenching. Under optimal conditions, fluorescence intensity quenching upon addition of nitrite gives a satisfactory linear relationship covering the linear range of 0.2–20 μM, and the limit of detection (LOD) is 40 nM. Moreover, this method has been successfully applied to the determination of nitrites in tap water, which indicates its great potential for monitoring of nitrites in environmental samples.