Nitrogen and copper (Ⅱ) co-doped carbon dots as multi-functional fluorescent probes for Fe3+ ions and tetracycline

Fe-doped carbon dots with enhanced fluorescence: Facilitating Cu2+ detection and urea electro-oxidation

In this work, Fe-doped carbon dots (Fe-CDs) were synthesized using o-phenylenediamine as a precursor and FeCl3·6H2O as a metal dopant by a one-step hydrothermal method. Notably, Fe-doping not only enhances the fluorescence of CDs, but also causes a red-shift in the emission wavelength. More importantly, Fe-CDs exhibit responsive fluorescence quenching to Cu2+ with high selectivity, sensitivity and anti-interference ability, enabling the sensor to achieve a detection limit of 0.23 μM for Cu2+. The quenching mechanism is triggered by the synergistic sensing process of dynamic and static quenching. Additionally, doping Fe into CDs can effectively regulate the electron density distribution and energy gap of the CDs, significantly altering their surface active sites. This coupling effect further augments the activity of the urea oxidation reaction (UOR). When utilized to catalyze UOR, Fe-CDs can achieve a battery voltage of 1.39 V at a current density of 100 mA cm-2 and demonstrate excellent 24-h stability. Therefore, Fe-CDs are a promising catalyst and have great significance in related fields such as energy conversion and urea treatment.

Multivariate Analysis of pH-Dependent Carbon Dots Sensitivity for Fe3⁺ Ions Detection Using UV-VIS Spectroscopy

Fluorescent carbon dots (CDs) have become a potent and adaptable nanomaterial in recent years for the sensitive and specific detection of heavy metal ions. Ferric ion (Fe3+) is one of the most damaging metal ions that can infiltrate the human body and the environment. In this study, blue-emitting carbon dots (CDs) were successfully synthesized from lemon juice using a hydrothermal process. The sensitivity of CDs to Fe3+ ions was examined using various concentrations of Fe3+ (0-400 µM) under different pH conditions (3, 5, 7, 9, 11, and 13) by measuring UV-Vis absorbance at 200-700 nm. The findings showed that the interaction between CDs and Fe3+ is significantly influenced by pH, resulting in varying absorbance enhancement responses. To get more profound insights into this pH-dependent performance, multivariate analysis techniques, including principal component analysis (PCA), linear discriminant analysis (LDA), and partial least squares regression (PLSR) were utilized. By combining these techniques with experimental data, significant correlations between pH levels, π - π ∗ and n - π ∗ electronic transitions of CDs, and Fe3⁺ sensing performance were identified. According to the PLSR model, pH 7 is ideal for real-world uses since it offers the optimum balance between Fe3⁺ solubility and CDs sensing capabilities, closely matching environmental and physiological conditions. This work contributes to the knowledge of CDs-based sensing mechanisms and emphasizes the value of multivariate analysis in boosting material performance for real-world applications in the biochemical and environmental domains.

A novel functionalized nitrogen- and sulfur-co-doped nanocarbon dots for the fluorescence detection and photocatalysis degradation of tetracycline antibiotics

Monitoring and eliminating pollutants are critical for environmental remediation. In this study, nitrogen- and sulfur-co-doped nanocarbon dots (NS-NCDs) were synthesized via a hydrothermal method using ascorbic acid and thiosemicarbazide as precursors. The introduction of nitrogen and sulfur atoms through doping altered the electron configuration and nanostructure of the carbon dots, resulting in strong blue fluorescence (quantum yield: 11.32 %). These NS-NCDs functioned as dual-functional agents for both detecting and degrading tetracycline antibiotics (TCs). Under UV light, the fluorescence color of the NS-NCDs transitioned from blue to colorless with increasing TCs concentration. Fluorescence quenching of NS-NCDs by TCs was mediated synergistically by the inner filter effect (IFE) and electron transfer, with IFE contributing 76 %, 75 %, and 71 % of the total quenching efficiency for tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC), respectively. This dual-mechanism enabled ultrasensitive detection of TCs, achieving limits of detection (LODs) as low as 0.21 μM (TC), 0.28 μM (OTC), and 0.16 μM (CTC), which are well below regulatory thresholds for environmental antibiotic residues. The NS-NCDs probe also exhibited high selectivity and anti-interference performance in complex matrices. Furthermore, NS-NCDs serve as a catalyst to rapidly activate peroxymonosulfate (PMS) under sunlight for the degradation of TCs, achieving degradation rates exceeding 90 % within 60 min. TCs degradation is driven by the oxidation of free radicals and electron transfer from TCs to PMS, facilitated by NS-NCDs. This study demonstrates the bifunctional role of NS-NCDs in real-time monitoring and photocatalytic degradation of TCs, providing an innovative strategy to combat antibiotic contamination.

Application of polyamide 56 nanofiber membrane loaded with coffee grounds carbon dots in Fe3+ detection

One novel nanofiber membrane was fabricated which could detect Fe3+ with the help of either fluorescence spectrometer or smartphone. Coffee grounds carbon dots (CCDs) were prepared by the solvent-thermal method, followed by the fabrication of CCDs/polyamide 56 (PA56) composite nanofiber membrane through electrospinning process. The 4 % CCDs/PA56 composite nanofiber membrane (FNM4) maintained good fluorescence performance (λem = 554 nm, λex = 470 nm) even after 5-runs quenching-recovery cycles. Its fluorescence could be quenched by Fe3+ with the limit of detection (LOD) of 0.74 μM when the fluorescence spectrometer was used. In addition, FNM4 could also detect Fe3+ by reading its RGB values using one smartphone and the lowest LOD was 4.31 μM when one Apple smartphone was used. The second method is portable to operate and eliminates the constraints of bulky laboratory equipment.

Recent progress in lanthanide-based fluorescent nanomaterials for tetracycline detection and removal

Tetracycline (TC) has been widely used in clinical medicine and animal growth promotion due to its broad-spectrum antibacterial properties and affordable prices. Unfortunately, the high toxicity and difficult degradation rate of TC molecules make them easy to accumulate in the environment, which breaks the ecological balance and seriously threatens human health. Rapid and accurate detection of TC residue levels is important for ensuring water quality and food safety. Recently, fluorescence detection technology of TC residues has developed rapidly. Lanthanide nanomaterials, based on the high luminescence properties of lanthanide ions and the high matching with TC energy levels, are favored in the real-time trace detection of TC due to their advantages of high sensitivity, rapidity, and high selectivity. Therefore, they are considered potential substitutes for traditional detection methods. This review summarizes the synthesis strategy, TC response mechanism, removal mechanism, and applications in intelligent sensing. Finally, the development of lanthanide nanomaterials for TC fluorescence detection and removal is reasonably summarized and prospected. This review provides a reference for the establishment of a method for the accurate determination of TC content in complex food matrices.

Selective detection of ionic liquid fluorescence probes for visual colorimetry of different metal ions

At present, the fast distinction of different metal ions in pure water media is not only a great challenge, but also drives the protection of water quality in environmental water bodies. In this paper, a novel ionic liquid fluorescent probe Glycolic Acid-L-Arginine (GA-L-Arg) was rationally created and designed through an in-depth study of ionic liquids. It is also used as an innovative multi-ion fluorescent probe for colorimetric detection and separate identification of Fe3+ and Co2+ in aqueous solutions of various metal ions. GA-L-Arg has excellent water solubility due to the strong hydrophilicity of Glycolic Acid and L-Arginine. The probe showed high sensitivity, extremely significant selectivity, and great pH stability for Fe3+ and Co2+ in pure water. The GA-L-Arg structure and the mechanism of Fe3+ and Co2+ detection were analyzed by infrared spectroscopic characterization and quantum chemical calculations. More importantly, the distinct colorimetric partitioning of Fe3+ and Co2+ was performed by the unique extraction of Fe3+ in the presence of the fluorescent probe and buffer solution.

Synthesis of high quantum yield rhenium-doped carbonized polymer dots for dual sensing of Fe3+ and Mo6+ and anti-counterfeit ink applications

The bottom-up approach serves as an efficacious and noteworthy method for the synthesis of carbonized polymer dots (CPDs). In the present investigation, rhenium-doped CPDs (Re-CPDs) were successfully synthesized via a hydrothermal technique employing citric acid, urea, and NH4ReO4. Subsequent to a comprehensive series of characterizations, Re-CPDs demonstrated an average particle size of 2.67 nm, excitation/emission maxima of 377/461 nm, and an elevated quantum yield of 45.36% at 377 nm excitation. Through the selectivity analysis involving various metal ions, Re-CPDs displayed sensitivity towards Fe3+ and Mo6+ ions, with limits of detection (LODs) of 0.02 μM and 0.48 μM, respectively. Furthermore, Re-CPDs exhibited multi-chromatic fluorescence (450-550 nm) under excitation wavelengths (375-430 nm). As a result, by amalgamating Re-CPDs with sucrose, detection patterns capable of generating multi-chromatic fluorescence at excitation wavelengths of 375, 395, and 430 nm, respectively, were successfully devised. In summary, Re-CPDs hold considerable potential as a material for the detection of Fe3+ and Mo6+ ions, as well as for anti-counterfeiting ink applications.

Copper nanoclusters stabilized by D-penicillamine for ultrasensitive and visual detection of oxytetracycline

Copper nanoclusters (DPA@CuNCs) with red fluorescence were successfully synthesized by a one-step method based on D-penicillamine (DPA), which acted not only as a reducing agent but also as a stabilizer. The products were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, particle-size analysis, ultraviolet-visible spectrophotometry, and fluorescence spectrometry. When the excitation wavelength was 280 nm, DPA@CuNCs emitted bright red fluorescence at 640 nm with a fluorescence quantum yield of 5.8 %. Due to the inner filter effect, oxytetracycline (OTC) effectively quenched the fluorescence of DPA@CuNCs, and then DPA@CuNCs were applied to the trace detection of OTC. The method showed a good linear range for OTC from 5 to 60 μmol/L, with a detection limit of 0.026 μmol/L and a correlation coefficient R² of 0.9983. Moreover, a paper-based sensor for the visual detection of OTC has been developed, which can conveniently and rapidly distinguish the concentration ranges of OTC through the color changes of the test papers.

Two Stable Cd-MOFs as Dual-Functional Materials with Luminescent Sensing of Antibiotics and Proton Conduction

Construction and investigation of dual-functional metal-organic frameworks (MOFs) with luminescent sensing and proton conduction provide widespread applications in clean energy and environmental monitoring fields. By selecting a phosphonic acid ligand 4-pyridyl-CH₂N(CH₂PO₃H₂)₂ (H₄L) and coligand 2,2'-biimidazole (H₂biim), two cadmium-based MOFs [Cd_1.5(HL)(H₂biim)_0.5] (1) and (H₄biim)_0.5·[Cd₂(L)(H₂biim)Cl] (2) with different structures and properties have been hydrothermally synthesized by controlling reaction temperature. Based on the excellent thermal and chemical stabilities, and good luminescent stabilities in water solution, 1 and 2 can serve as luminescent sensors of chloramphenicol (CAP) with different quenching constant (K_SV) values and detection limits (LODs) in water, simulated environmental system, and real fish water system. Meanwhile, different sensing effects and possible sensing mechanisms are analyzed in detail. Moreover, 1 and 2 can also serve as good proton-conducting materials. The proton conductivities can reach up to 1.41 × 10^-4 S cm^-1 for 1 and 1.02 × 10^-3 S cm^-1 for 2 at 368 K and 95% relative humidity (RH). Among them, 2 shows better luminescent sensing and proton conduction performance than 1, which indicates that different crystal structures have a great impact on the properties of MOFs. Through the discussion of the relationship between structures and properties in detail, the possible reasons for the differences in properties are obtained, which can provide theoretical guidance for the rational design of this kind of dual-functional MOFs in the future.

Optical Dynamics of Copper-Doped Cadmium Sulfide (CdS) and Zinc Sulfide (ZnS) Quantum-Dots Core/Shell Nanocrystals

Recently, quantum-dot-based core/shell structures have gained significance due to their optical, optoelectronic, and magnetic attributes. Controlling the fluorescence lifetime of QDs shells is imperative for various applications, including light-emitting diodes and single-photon sources. In this work, novel Cu-doped CdS/ZnS shell structures were developed to enhance the photoluminescence properties. The objective was to materialize the Cu-doped CdS/ZnS shells by the adaptation of a two-stage high-temperature doping technique. The developed nanostructures were examined with relevant characterization techniques such as transmission electron microscopy (TEM) and ultraviolet–visible (UV–vis) emission/absorption spectroscopy. Studying fluorescence, we witnessed a sharp emission peak at a wavelength of 440 nm and another emission peak at a wavelength of 620 nm, related to the fabricated Cu-doped CdS/ZnS core/shell QDs. Our experimental results revealed that Cu-doped ZnS shells adopted the crystal structure of CdS due to its larger bandgap. Consequently, this minimized lattice mismatch and offered better passivation to any surface defects, resulting in increased photoluminescence. Our developed core/shells are highly appropriate for the development of efficient light-emitting diodes.

Recent progress of carbon dot fluorescent probes for tetracycline detection

We made a detailed discussion about TCs and CDs, including the synthetic methods, doping strategies and promising prospects.