Facile and green synthesis of N, Cl-dual-doped carbon dots as a label-free fluorescent probe for hematin and temperature sensing

Low-energy-consumption rapid synthesis of carbon dots at room temperature from combusted food waste with versatile analytical applications

In this study, we developed a low-energy-consumption green method for synthesising carbon dots (CD) at room temperature using watermelon rind as the carbon source through a cutting process based on NaCl crystals. The synthesis process was rapid (<5 min) and facile. The synthesised CD were characterised using photoluminescence (PL) spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy. The results revealed that the synthesised dots exhibited robust adsorption, a spherical shape and a uniform size distribution. The PL intensity of the quantum dots decrease due to the temperature rising, metal ions and ponceau 4R added. In contrast with PH, PL intensity increase, so these CD can serve as multifunctional sensing materials. Overall, this study presents an environmentally friendly method for the rapid synthesis of CD that are suitable for temperature, pH, metal ion and food sensing applications.

Facile and green synthesis of chlorophyll-derived multi-color fluorescent carbonized polymer dots and their use for sensitive detection of hemin

Due to the very important role in physiological process, a simple and sensitive hemin detection method is necessarily required. Biomass-based carbonized polymer dots (CPDs) have been widely studied especially as fluorescence probe owing to the advantages of low toxicity and the variety of fluorescence color, yet there are still challenges in developing their multi-color emission property from the same raw materials. In this work, red, white and blue emissive CPDs derived from chlorophyll have been synthesized via hydrothermal method. Then white-emitted CPDs (white-CPDs) with the Commission International d'Eclairage (CIE) coordinates at (0.34, 0.32) were used to develop a fluorescence quenched sensing system for hemin determination. There is a good linear relationship between (F0-F)/F0 and concentration of hemin in the range of 0.1-0.95 μM with a detection limit of 0.043 μM, and the quenching mechanism was considered to be caused by inner filter effect (IFE). Moreover, it has been successfully used for hemin detection in serum and also for visual determination, which indicating great potential in applications of disease diagnoses and trace identification.

Water-soluble long afterglow carbon dots/silica composites for dual-channel detection of alkaline phosphatase and multi-level information anti-counterfeiting

Water-soluble carbon dots/silica (CDs/SiO₂) composites with an ultra-long lifetime of 846.9 ms and an ultra-high afterglow quantum yield of 12.1% were successfully obtained by incorporating CDs into a SiO₂ network. Within the aqueous solution, the SiO₂ layer isolates CDs from the surrounding oxygen. Meanwhile, hydrogen bonds and covalent bonds are formed between the CDs and SiO₂, and these bonds restrict the movement and vibration of the CDs. Accordingly, the non-radiative inactivation rate of the triplet excitons of the CDs is reduced, thereby enhancing the room-temperature phosphorescence of the CDs and triggering thermally activated delayed fluorescence. The multiple properties of the material effectively protect the CDs from the external environment, making CDs/SiO₂ emit a long afterglow in the solid and liquid phases. The prepared CDs/SiO₂ composites have exceptional stability against strong oxidants, acids, bases, and polar solvents. The composites were successfully used in the dual-optical mode detection of alkaline phosphatase, as an anti-counterfeiting ink, and in multi-level information anti-counterfeiting and encryption.

Highly efficient red-emitting carbon dots as a "turn-on" temperature probe in living cells

Nanothermometers, which can precisely detect the intracellular temperature changes, have great potential to solve questions concerning the cellular processes. Thus, the temperature sensors that provide fluorescent "turn-on" signals in the biological transparency window are of highly desirable. To meet these criteria, this work reported a new "turn-on" carbon dot (CD)-based fluorescent nanothermometry device for sensing temperature in living cells. The CDs that emit bright red fluorescence (R-CDs; λ_max = 610 nm in water) were synthesized with o-phenylenediamine as carbon precursor via a facile solvothermal method. The R-CDs in water were almost nonfluorescent at 15 °C. As the temperature increased, the fluorescence intensity of R-CDs exhibited a gradual increase and the final enhancement factor was greater than 21-fold. The fluorescence intensity exhibited a linear response to temperature and a high-sensitive variation of ≈13.3 % °C^-1 was detected within a broad temperature range of 28-60 °C. Moreover, the R-CD thermal sensors also exhibited high storage stability, excellent response reversibility and superior photo- and thermo-stability. Due to its good biocompatibility and "intelligent" response to external temperature, the nanothermometer could be applied for sensing temperature changes in biological media.

Fluorescence Thermometer: Intermediation of the Fontal Temperature and Light

The rapid advance of thermal materials and fluorescence spectroscopy has extensively promoted micro-scale fluorescence thermometry development in recent years. Based on the advantages of fast response, high sensitivity, simple operation,...

N,Cl-Codoped Carbon Dots from Impatiens balsamina L. Stems and a Deep Eutectic Solvent and Their Applications for Gram-Positive Bacteria Identification, Antibacterial Activity, Cell Imaging, and ClO- Sensing

In this study, we first synthesized metal-free N,Cl-doped carbon dots (N,Cl-CDs) using Impatiens balsamina L. stems as green precursors in a deep eutectic solvent (DES). The obtained N,Cl-CDs were characterized through transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, fluorescence (FL) spectroscopy, and ultraviolet (UV) spectroscopy. In addition to the common features of carbon dots (CDs), such as high light stability, small size, low toxicity, good aqueous solubility, and favorable biocompatibility, these N,Cl-CDs exhibited excellent recognition and selectivity for Gram-positive bacteria by doping with N and Cl elements using DES. The N,Cl-CDs with positive charge cannot only differentiate Gram-positive bacteria by selective fluorescence imaging but also have antibacterial effects on Gram-positive bacteria. Through potential, ROS, and morphological analyses of bacteria before and after treatment with N,Cl-CDs, the antibacterial mechanisms of bacteriostasis, Enterococcus faecium, Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, and Salmonella were explored. In addition, N,Cl-CDs demonstrated low cytotoxicity and good cell imaging ability in cancer and normal cells. Moreover, they can be used as a fluorescence sensor for the detection of ClO^- with a detection range from 100 nM to 40 μM and a limit of detection (LOD) of 30 nM. In summary, the prepared N,Cl-CDs could be applied as environmentally friendly Gram-positive bacterial identification and antibacterial agents. Additionally, their cell imaging and ClO^- detection abilities were outstanding.

Dual-excitation and dual-emission carbon dots for Fe3+ detection, temperature sensing, and lysosome targeting

Dual-excitation and dual-emission carbon dots (CDs) have been prepared by simple one-step hydrothermal treatment of p-phenylenediamine and 5-aminosalicylic acid. The as-prepared CDs emit bright green fluorescence under excitation at 320-400 nm and bright orange fluorescence under excitation at 490-560 nm. Interestingly, the CDs can be employed as a dual-excitation and dual-emission fluorescent probe for Fe³⁺ detection in aqueous solution and living cells. Furthermore, the obtained CDs can function as a promising dual-excitation and dual-emission temperature sensor. Additionally, the CDs can be utilized for lysosomal targeting.

Multifunctional N-Doped Carbon Dots for Bimodal Detection of Bilirubin and Vitamin B12, Living Cell Imaging, and Fluorescent Ink

A N-doped carbon dot (NCD) has been synthesized via a simplistic one-step hydrothermal technique using l-aspartic acid and 3,6-diaminoacridine hydrochloride. The NCDs exhibit a high quantum yield (22.7%) and excellent optical stability in aqueous media. Additionally, NCDs display good solid-state yellowish-green emission and are suitable for security ink applications. The remarkable fluorescence (FL) properties of NCDs are further applied to develop a multifunctional sensor for bilirubin (BR) and vitamin B₁₂ (VB12) via fluorescence quenching. We have systematically studied the FL quenching mechanisms of the two analytes. The primary quenching mechanism of BR is via the Förster resonant energy transfer (FRET) pathway facilitated by the H-bonding network between the hydrophilic moieties existing at the surface of BR and NCDs. In contrast, the inner filter effect (IFE) is mainly responsible for the recognition of VB12. The practicability of the nanoprobe NCDs is further tested in real-sample analysis for BR (human serum and urine samples) and VB12 (VB12 tablets, human serum, and energy drink) with a satisfactory outcome. The in vitro competency is also verified in the human cervical cancer cell line (HeLa cell) with negligible cytotoxicity and significant biocompatibility. This result facilitates the application of NCDs for bioimaging and recognition of VB12 in a living organism.

An "on-off-on" selective fluorescent probe based on nitrogen and sulfur co-doped carbon dots for detecting Cu2+ and GSH in living cells

The abnormal level of Cu²⁺ or GSH can cause variety of neurodegenerative diseases in humans. Thus, the selective and sensitive detection of Cu²⁺ and GSH has inspired intensive research efforts in biological sample analysis fields. Herein, an "on-off-on" fluorescent probe based on nitrogen and sulfur co-doped carbon dots (N,S-CDs) has been successfully prepared for the detection of Cu²⁺ and GSH. The "turn-off" process of fluorescence in the presence of Cu²⁺ ions was induced by forming a non-luminescent ground state complex due to the interaction between surface groups of the probe and Cu²⁺ ions. Moreover, the strong coordination between GSH and Cu²⁺ could destroy the structure of the complex and restore the fluorescence to "turn-on". This fluorescent probe had excellent selectivity and high sensitivity toward Cu²⁺ and GSH with the limits of detection (LODs) of 38 nM and 41 nM. More importantly, the as-prepared N,S-CDs served as an efficient fluorescent probe for not only detecting Cu²⁺ ions in lake water and tap water, and GSH in BSA solution, but also sensing Cu²⁺ and GSH in living cells. Therefore, these N,S-CDs could be considered as a promising fluorescence probe candidate for environmental monitoring and biological imaging.

Carbon Dots as New Generation Materials for Nanothermometer: Review

Highly sensitive non-contact mode temperature sensing is substantial for studying fundamental chemical reactions, biological processes, and applications in medical diagnostics. Nanoscale-based thermometers are guaranteeing non-invasive probes for sensitive and precise temperature sensing with subcellular resolution. Fluorescence-based temperature sensors have shown great capacity since they operate as "non-contact" mode and offer the dual functions of cellular imaging and sensing the temperature at the molecular level. Advancements in nanomaterials and nanotechnology have led to the development of novel sensors, such as nanothermometers (novel temperature-sensing materials with a high spatial resolution at the nanoscale). Such nanothermometers have been developed using different platforms such as fluorescent proteins, organic compounds, metal nanoparticles, rare-earth-doped nanoparticles, and semiconductor quantum dots. Carbon dots (CDs) have attracted interest in many research fields because of outstanding properties such as strong fluorescence, photobleaching resistance, chemical stability, low-cost precursors, low toxicity, and biocompatibility. Recent reports showed the thermal-sensing behavior of some CDs that make them an alternative to other nanomaterials-based thermometers. This kind of luminescent-based thermometer is promising for nanocavity temperature sensing and thermal mapping to grasp a better understanding of biological processes. With CDs still in its early stages as nanoscale-based material for thermal sensing, in this review, we provide a comprehensive understanding of this novel nanothermometer, methods of functionalization to enhance thermal sensitivity and resolution, and mechanism of the thermal sensing behavior.