Novel N-doped carbon dots prepared via citric acid and benzoylurea by green synthesis for high selectivity Fe(III) sensing and imaging in living cells

Facile Synthesis of Polyethylene Glycol Passivated N-doping CQDs as Fluorescent Probe for Multi-Target Simultaneous Detection in Heavy-Metals Solution

In order to quickly and conveniently detect multiple heavy metal ions in aqueous phase simultaneously, a polyethylene glycol passivated N-doping carbon quantum (p-N-CQDs) was synthesized by a hydrothermal method with citric acid (carbon source), urea (nitrogen source) and polyethylene glycol (passivator). The as-prepared p-N-CQDs could be evenly dispersed in deionized water, and the average diameter was 1.83 nm, resulting in 18.72% of fluorescence quantum yield. As a sensor, the fluorescence of p-N-CQDs would be significantly quenched with Fe3+ or Cu2+ under the different maximum emission wavelength of 452 nm and 448 nm, respectively. Therefore, a method for simultaneously detecting multiple heavy metal ions was proposed by discriminative fitting of the fluorescence emission peaks after metal ion quenching. Upon the experiments, two linear calibration curves between resolving fluorescence intensities of p-N-CQDs and concentration of the metal ions were obtained within a range of 10 to 1000 µM of Cu2+ and 40 to 800 µM of Fe3+. And a limit of detection (LOD) of 0.032 µM was attained after resolving the curves based on the emission wavelength of 448 nm for Cu2+ and 452 nm for Fe3+ by a peak splitting software. In addition, the stability, selectivity and anti-interference of the proposal senor was confirmed.

Facile One-Pot Microwave-Assisted Synthesis and Ultrafast Spectroscopic Characterization of Nitrogen-Sulfur-Codoped Carbon Quantum Dots

We report an eco-friendly, cost-effective, one-pot microwave-assisted synthesis of nitrogen and sulfur co-doped carbon quantum dots (N,S-CQDs) using citric acid and thiourea in formamide without surface passivation. The N,S-CQDs were characterized by HRTEM, FE-SEM, XRD, EDX, FTIR, Raman, and XPS, confirming monodispersed spherical particles of 4.8 nm with an amorphous carbon phase containing oxygen, nitrogen, and sulfur. The comprehensive photophysical studies of N,S-CQD employed by steady state and different time-resolved spectroscopic techniques (TCSPC, Ultrafast Time-Resolved Fluorescence Up-Conversion and Femtosecond Transient Absorption techniques). These N,S-CQDs show broad UV-visible to near-infrared absorption with peaks near 300 and 400 nm and emit strong blue photoluminescence at 360 nm excitation, with a quantum yield of ~8.4%. Time-resolved spectroscopy (TCSPC, fluorescence up-conversion, transient absorption) reveals multiexponential carrier relaxation with time constants from 0.5 ps to > 500 ps, including a 360 ps rise component and three distinct decay components, indicating complex fluorescence driven by surface defects. Ultrafast decay components correspond to thermal cooling of hot excitons, while later decays relate to carrier trapping at surface states. The tunable optical properties and carrier dynamics make N,S-CQDs promising for optoelectronic applications such as LEDs, sensors, and photodetectors, with further enhancement possible through surface engineering and defect control.

Highly-fluorescent extracts from Pterocarpus wood for Fe3+ ion detection

At present, excessive Fe3+ in daily water has become a threat to human health. Among the conventional detection methods for Fe3+, fluorescent probes have been applied on a large scale due to their simplicity and efficiency. However, the currently available fluorescent probes are difficult to synthesize, costly and environmentally unfriendly, limiting their applications. In this work, a fluorescent extract of Pterocarpus wood was successfully obtained, and the structure of some coumarin-based molecules in this extract was determined by 2D-NMR. Subsequently, the intensity of this fluorescence was optimized using response surface methodology (RSM), resulting in a high-intensity fluorescent probe. The probe was sensitive to the concentrations of Fe3+ and MnO4-, and could efficiently detects Fe3+ in the range of 2.7 μM-8.0 μM, with LOD and LOQ reaching 1.06 μM and 3.20 μM, respectively. Moreover, based on the strong complexation property of EDTA on Fe3+, this work designed the "switch-on" fluorescent probes. The experiment shows that both static and dynamic quenching exist in this system. The mechanism of complexation and oxidation of fluorescent molecules by the quencher is interpreted in the quenching reaction. In addition, the fluorescent probe has a high yield and low cost, it also performs well in actual water sample tests. This method is expected to be developed as a new way on Fe3+ detection.

Biomass-derived carbon dots as emerging visual platforms for fluorescent sensing

Biomass-derived carbon dots (CDs) are non-toxic and fluorescently stable, making them suitable for extensive application in fluorescence sensing. The use of cheap and renewable materials not only improves the utilization rate of waste resources, but it is also drawing increasing attention to and interest in the production of biomass-derived CDs. Visual fluorescence detection based on CDs is the focus of current research. This method offers high sensitivity and accuracy and can be used for rapid and accurate determination under complex conditions. This paper describes the biomass precursors of CDs, including plants, animal remains and microorganisms. The factors affecting the use of CDs as fluorescent probes are also discussed, and a brief overview of enhancements made to the preparation process of CDs is provided. In addition, the application prospects and challenges related to biomass-derived CDs are demonstrated.

N-Doping CQDs as an Efficient Fluorescence Probe Based on Dynamic Quenching for Determination of Copper Ions and Alcohol Sensing in Baijiu

To address an accurate detection of heavy metal ions in Baijiu production, a nitrogen-doping carbon quantum dots (N-CQDs) was prepared by hydrothermal method from citric acid and urea. The as-prepared N-CQDs had an average particle size of 2.74 nm, and a large number of functional groups (amino, carbonyl group, etc.) attached on its surface, which obtained a 9.6% of quantum yield (QY) with relatively high and stable fluorescence performance. As a fluorescent sensor, the fluorescence of N-CQDs at 380 nm excitation wavelength could be quenched quantitatively by adding Cu2+, due to the dynamic quenching of electron transfer caused by the binding of amine groups and Cu2+, which showed excellent sensitivity and selectivity to Cu2+ in the range of 0.5-5 μM with a detection limit (LOD) of 0.032 μM. In addition, the N-CQDs as well as could be applied to quantitative determine alcohol content in the range of 10-80 V/V% depending on the fluorescence enhancement. Upon the experiment, the fluorescent mechanism was studied by Molecular dynamics (MD) simulations, which demonstrated that solvent effect played an influential role on sensing alcohol content in Baijiu. Overall, the work provided a theoretically guide for the design of fluorescence sensors to monitor heavy metal ion in liquid drinks and sense alcohol content.

Carbon Dots based Tissue Equivalent Dosimeter as an Ionizing Radiation Sensor

This work explores the potential of carbon dots as a fluorescent probe in the determination of heavy ions and as an electrochemical biosensor. It also discusses how carbon dots can be introduced into the Fricke solution to potentially serve as an ionizing radiation sensor. The study presents a novel tissue equivalent dosimeter carbon dots-based as an ionizing radiation sensor. The methodology for the synthesis of Nitrogen-doped Carbon Dots N-CDs and the characterization of the material are described. The results show that the N-CDs have a high sensitivity to ionizing radiation and can be used as a dosimeter for radiation detection. The study also discusses the limitations and challenges of using carbon dots as a dosimeter for ionizing radiation. Overall, this study provides valuable insights into the potential applications of carbon dots in different fields and highlights the importance of further research in this area.

An optical and visual multi-mode sensing platform base on nitrogen, sulfur, boron co-doped carbon dots for rapid and simple determination of ferric ions in water

Abnormal iron ions levels may lead to some diseases and serious environmental pollution. Herein, optical and visual detection strategies of Fe3+ in water based on co-doped carbon dots (CDs) were established in the present study. Firstly, a one-pot synthetic strategy for the preparation of the N, S, B co-doped CDs with a home microwave oven was developed. Secondly, the optical properties, chemical structures, and morphology of CDs were further characterized by fluorescence spectroscopy, Uv-vis absorption spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscope. Finally, the results indicated that the fluorescence of the co-doped CDs was quenched by ferric ions via the static mechanism and the aggregation of CDs, accompanied by the increased red color. The multi-mode sensing strategies of Fe3+ with fluorescence photometer, UV-visible spectrophotometer, portable colorimeter and smartphone had the advantages of good selectivity, excellent stability and high sensitivity. Fluorophotometry based on co-doped CDs was a powerful probe platform for measuring lower concentrations of Fe3+ due to its higher sensitivity, better linear relationship, lower limit of detection (0.27 μM) and limit of quantitation (0.91 μM). In addition, the visual detection methods with a portable colorimeter and smartphone had been proven to be very suitable for rapid and simple sensing of higher concentrations of Fe3+. Moreover, the co-doped CDs utilized for Fe3+ probes in tap water and boiler water obtained satisfactory results. Consequently, the efficient, versatile optical and visual multi-mode sensing platform could be extended to apply such a visual analysis of ferric ions in the biological, chemical and other fields.

Polyethylenimine-functionalized nitrogen and sulfur co-doped carbon dots as effective fluorescent probes for detection of Hg2+ ions

Surface modification of nitrogen and sulfur co-doped carbon quantum dots (N, S-CDs) were performed using cysteine and polyethylenimine as raw materials. The prepared N, S-CDs exhibited excitation-independent in the range of 300-380 nm. Furthermore, mercury(II) ions (Hg²⁺) can effectively quench the fluorescence intensity of the N, S-CDs. Based on this, we developed a fluorescence sensor with high sensitivity and selectivity to detect Hg²⁺. Under optimized conditions, the sensor showed good linearity in the range of 0-500 nM, and the limit of detection is 9.2 nM. Further, the sensor showed high sensitivity to Hg²⁺ in lake water and rice samples. The recovery of the Hg²⁺ in lake water and rice samples ranged between 98.2 % and 109.5 % with a relative standard deviation below 5.8 %. With outstanding sensitivity and selectivity, the fluorescence sensor provides a promising platform for monitoring Hg²⁺ in real samples.

Multi-applications of carbon dots and polydopamine-coated carbon dots for Fe3+ detection, bioimaging, dopamine assay and photothermal therapy

Carbon dots (CDs) or CDs/polymer composites have been applied in numerous fields. Here, novel CDs were synthesized by carbonization of egg yolk, and characterized by TEM, FTIR, XPS and photoluminescence spectra. The CDs were found to be approximate sphere in shape with an average size of 4.46 ± 1.17 nm, and emitted bright blue photoluminescence under UV irradiation. The photoluminescence of CDs was found selectively quenched by Fe³⁺ in a linear manner in the range of 0.05-0.45 mM, meaning they could be applied for Fe³⁺ detection in solution. Moreover, the CDs could be uptaken by HepG2 cells to exhibit bright blue photoluminescence. The intensity could reflect the level of intracellular Fe³⁺, indicating they could be further used for cell imaging and intracellular Fe³⁺ monitoring. Next, dopamine was polymerized on the surface of CDs to obtain the polydopamine (PDA)-coated CDs (CDs@PDA). We found PDA coating could quench the photoluminescence of CDs via inner filter effect, and the degree of quenching was linearly related to the logarithm of DA concentration (Log C_DA). Also, the selectivity experiment indicated the method had a high selectivity for DA over a number of possible interfering species. This indicated the CDs in combination with Tris buffer could be potentially applied as the assay kit of dopamine. At last, the CDs@PDA exhibited excellent photothermal conversion capability, and they could efficiently kill HepG2 cells under NIR laser irradiation. Overall, the CDs and CDs@PDA in this work exhibited many excellent advantages, and could be potentially used for multi-applications, such as Fe³⁺ sensor in solution and cellular, cell imaging, dopamine assay kit, as well as photothermal agents for cancer therapy.

Dual-mode detection sensor based on nitrogen-doped carbon dots from pine needles for the determination of Fe3+ and folic acid

In this study, nitrogen-doped carbon dots (N-CDs) from pine needles were obtained by one-step hydrothermal synthesis without any chemical reagents. The fluorescence quenching and absorbance enhancement of N-CDs occurred when Fe³⁺ and folic acid (FA) were added. Based on this, the dual-mode detection sensor by fluorescence and ultraviolet-visible (UV-Vis) spectrophotometry for the determination of Fe³⁺ and FA was established. Detected by the dual-mode detection sensor under the optimized condition, the linear range of Fe³⁺ was 0.1-540 μM and FA was 0.1-165 μM. At the same time, the two inputs "NOR" and "OR" logic gates are constructed successfully according to the dual-mode sensor signals. The proposed dual-mode detection sensor is simple, efficient and stable; it can be applied to determinate Fe³⁺ and FA in practical samples successfully and the results are satisfactory.

Flexible and Stretchable Carbon-Based Sensors and Actuators for Soft Robots

In recent years, the emergence of low-dimensional carbon-based materials, such as carbon dots, carbon nanotubes, and graphene, together with the advances in materials science, have greatly enriched the variety of flexible and stretchable electronic devices. Compared with conventional rigid devices, these soft robotic sensors and actuators exhibit remarkable advantages in terms of their biocompatibility, portability, power efficiency, and wearability, thus creating myriad possibilities of novel wearable and implantable tactile sensors, as well as micro-/nano-soft actuation systems. Interestingly, not only are carbon-based materials ideal constituents for photodetectors, gas, thermal, triboelectric sensors due to their geometry and extraordinary sensitivity to various external stimuli, but they also provide significantly more precise manipulation of the actuators than conventional centimeter-scale pneumatic and hydraulic robotic actuators, at a molecular level. In this review, we summarize recent progress on state-of-the-art flexible and stretchable carbon-based sensors and actuators that have creatively added to the development of biomedicine, nanoscience, materials science, as well as soft robotics. In the end, we propose the future potential of carbon-based materials for biomedical and soft robotic applications.

Preparation of Multicolour Solid Fluorescent Carbon Dots for Light-Emitting Diodes Using Phenylethylamine as a Co-Carbonization Agent

Carbon dots (CDs), as a new type of photoluminescent nanomaterial, have attracted extensive attention in various fields because of their unique luminescence properties. However, CDs will exhibit fluorescence quenching in the solid state or aggregate state, which limits their application. In this paper, a unique strategy is proposed to regulate solutions to achieve multicolour fluorescence of CDs in the solid state. We report the successful preparation of orange, green and blue solid fluorescent CDs using citric acid, urea and phenylethylamine as precursors and methanol, ethanol and water as solvents, respectively. The solid-state fluorescence of CDs may be caused by the linkage of the phenylethyl structure to the surface of CDs during formation, which effectively disperses the CDs and prevents π-π interactions between graphitized nuclei. Meanwhile, multicolour solid fluorescent CDs are realized by adjusting the solvent in the preparation process. Based on the excellent fluorescence properties of CDs, orange, green and blue light-emitting diodes (LEDs) are prepared. A white LED (WLED) can be obtained by mixing the three colours of solid fluorescent CDs, which shows the application potential of CDs in display lighting equipment.

Carbon dots-based nanomaterials for fluorescent sensing of toxic elements in environmental samples: Strategies for enhanced performance

Rapid industrialization and manufacturing expansion have caused heavy metal pollution, which is a critical environmental issue faced by global population. In addition, the disadvantages presented by conventional detection methods such as the requirement of sophisticated instruments and qualified personnel have led to the development of novel nanosensors. Recently, carbon dots (CDs) have been presented as a multifunctional nanomaterial alternative for the accurate detection of heavy metal ions in water systems. The capacity of CDs to detect contaminants in wastewater -including heavy metals- can be found in the literature; however, to the best of our knowledge, none of them discusses the most recent strategies to enhance their performance. Therefore, in this review, beyond presenting successful examples of the use of CDs for the detection of metal ions, we further discuss the strategies to enhance their photoluminescence properties and their performance for environmental monitoring. In this manner, strategies such as heteroatom-doping and surface passivation are reviewed in detail, as well as describing the mechanisms and the effect of precursors and synthesis methods. Finally, the current challenges are described in detail to propose some recommendations for further research.

Green-emitting silicon nanoparticles as a fluorescent probe for highly-sensitive crocin detection and pH sensing

Novel green fluorescent silicon nanoparticles were synthesized via a one-pot hydrothermal method and utilized as a fluorescent probe for highly sensitive and accurate detection of crocin and pH sensing.

A lysosome-targeting fluorescent probe to visualize endogenous and exogenous methylglyoxal in live cells and zebrafish

The first fluorescent probe targeting MGO in lysosomes was developed for the detection of intracellular and extracellular sources of methylglyoxal.

A facile fluorescent sensor based on nitrogen-doped carbon dots derived from Listeria monocytogenes for highly selective and visual detection of iodide and pH

Listeria monocytogenes-derived nitrogen-doped carbon dots served as a facile fluorescent sensor with excellent sensing performances for iodide with low detection limit of 20 nmol L−1 and wide pH range from 1.81 to 11.82.