Facile synthesis of N-doped carbon dots for direct/indirect detection of heavy metal ions and cell imaging

Multifunctional Fluorescent Material Based Red-emitting Carbon Dots for Cell Imaging and Photodynamic Sterilization

In this paper, a new carbon dot (R1-CDs) was prepared by one-pot hydrothermal method by using 1,8-diaminonaphthalene and o-phthalic acid (o-PA) as precursors. Due to the high purity of R1-CDs, NMR analysis was performed to identify the types of H and C atoms in their graphene sheets. From our research findings, three important information was disclosed such as (1) five types H atoms are presented in R1-CDs; (2) 18 kinds of C atoms in the graphene sheets are observed, and 8 kinds of them are quaternary atoms, and 10 kinds of carbon atoms as tertiary one; (3) functional groups of -COOH and -NH2 from precursors cannot be inherited into the edges or defect sites of graphene sheet. Obviously, our research findings for the first time revealed the more details of chemical structures of CDs. We believe that our works can supply a general concept to fabricate CDs by selecting specific precursors, also can encourage CDs' development in a more "chemistry" way by employing NMR as a powerful method.

Fluorescent carbon quantum dots for heavy metal sensing

Many heavy metals pose significant threats to the environment and human health. Traditional methods for detecting heavy metals are often limited by complex procedures, high costs, and challenges in field monitoring. Carbon quantum dots (CQDs), a novel class of fluorescent carbon nanomaterials, have garnered significant interest due to their excellent biocompatibility, low cost, and minimal toxicity. This paper reviews the primary synthesis methods, luminescence mechanisms, and fluorescence quenching mechanisms of CQDs, as well as their recent applications in detecting heavy metals. In heavy metal sensing applications, the simplest hydrothermal method is commonly employed for the one-step synthesis and surface modification of CQDs. Various green reagents and biomass materials, such as citric acid, glutathione, orange peel, and bagasse, can be used for CQDs' preparation. Quantum confinement effects and surface defects give CQDs their distinctive luminescence properties, enabling the detection of heavy metals through fluorescence quenching or enhancement. Additionally, CQDs can be applied in biological imaging and smart detection, and when combined with adsorption materials, they can offer multifunctional capabilities. This review also discusses the future development prospects of CQDs.

Orange Pomace-Derived Fluorescent Carbon Quantum Dots: Detection of Dual Analytes in the Nanomolar Range

Green-emissive carbon quantum dots (CQDs) with exclusive chemosensing aspects were synthesized from orange pomace as a biomass-based precursor via a facile microwave method without using any chemicals. The synthesis of highly fluorescent CQDs with inherent nitrogen was confirmed through X-ray diffraction, X-ray photoelectron, Fourier transform infrared, Raman, and transmission electron microscopic techniques. The average size of the synthesized CQDs was found to be 7.5 nm. These fabricated CQDs displayed excellent photostability, water solubility, and outstanding fluorescent quantum yield, i.e., 54.26%. The synthesized CQDs showed promising results for the detection of Cr⁶⁺ ions and 4-nitrophenol (4-NP). The sensitivity of CQDs toward Cr⁶⁺ and 4-NP was found up to the nanomolar range with the limit of detection values of 59.6 and 14 nM, respectively. Several analytical performances were thoroughly studied for high precision of dual analytes of the proposed nanosensor. Various photophysical parameters of CQDs (quenching efficiency, binding constant, etc.) were analyzed in the presence of dual analytes to gain more insights into the sensing mechanism. The synthesized CQDs exhibited fluorescence quenching toward incrementing the quencher concentration, which was rationalized by the inner filter effect through time-correlated single-photon counting measurements. The CQDs fabricated in the current work exhibited a lower detection limit and a wide linear range through the simple, eco-friendly, and rapid detection of Cr⁶⁺ and 4-NP ions. To evaluate the feasibility of the detection approach, real sample analysis was conducted, demonstrating satisfactory recovery rates and relative standard deviations toward the developed probes. This research paves the way for developing CQDs with superior characteristics utilizing orange pomace (biowaste precursor).

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.

Quick and hassle-free smartphone's RGB-based color to photocatalytic degradation rate assessment of malachite green dye in water by fluorescent Zr-N-S co-doped carbon dots

Sunlight active blue emissive zirconium, nitrogen, and sulfur co-doped carbon dots (Zr-N-S-CDs) have been synthesized by microwave-induced pyrolysis for achieving efficient photocatalytic degradation of pollutant malachite green dye (MG) in water. Surface morphology studies using high-resolution transmission electron microscopy confirmed the formation of spherical-shaped CDs with an absorbance peak at 350 nm and emission peak at 437 nm in UV-vis and fluorescence spectroscopy, respectively. Surface functional groups, elemental composition, and metal/non-metal co-doping were confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. To understand the photocatalytic performance of Zr-N-S-CDs, various parameters, such as the source of energy, concentration of dye, catalyst dosage, and change in pH, were investigated. MG dye (20 ppm) at a pH 7 with 0.5 mg/mL of Zr-N-S-CDs could be photodegraded efficiently in 90 min under sunlight (99%) compared to dark and artificial light conditions. Moreover, real-time analysis of degradation rate could be conveniently calculated by integrating the colorimetric responses of MG dye with RGB values obtained by the "Color Picker" app of a smartphone. The degradation rate obtained using a smartphone (97.89%) was found to be in agreement with the UV-vis spectroscopy (99%), thus, providing a new, handy, and instrument-free route for speedy and quantitative estimation of the degradation of hazardous MG dye by Zr-N-S-CDs.

Carbon dot composites for bioapplications: a review

Carbon dots (CDs) have received extensive attention in the last decade for their excellent optical, chemical and biological properties. In recent years, CD composites have also received significant attention due to their ability to improve the intrinsic properties and expand the application scope of CDs. In this article, the synthesis processes of four types of CD composites (metal-CD, nonmetallic inorganics-CD, and organics-CD as well as multi-components-CD composites) are systematically summarized first. Then the recent advancements in the bioapplications (bioimaging, drug delivery and biosensing) of these composites are also highlighted and discussed. Last, the current challenges and future trends of CD composites in biomedical fields are discussed.

Versatile Fluorescent Carbon Dots from Citric Acid and Cysteine with Antimicrobial, Anti-biofilm, Antioxidant, and AChE Enzyme Inhibition Capabilities

Nanostructured fluorescent particles derived from natural molecules were prepared by a green synthesis technique employing a microwave method. The precursors citric acid (CA) and cysteine (Cys) were used in the preparation of S- and N-doped Cys carbon dots (Cys CDs). Synthesis was completed in 3 min. The graphitic structure revealed by XRD analysis of Cys CDs dots had good water dispersity, with diameters in the range of 2-20 nm determined by TEM analysis. The isoelectric point of the S, N-doped CDs was pH value for 5.2. The prepared Cys CDs displayed excellent fluorescence intensity with a high quantum yield of 75.6 ± 2.1%. Strong antimicrobial capability of Cys CDs was observed with 12.5 mg/mL minimum bactericidal concentration (MBC) against gram-positive and gram-negative bacteria with the highest antimicrobial activity obtained against Staphylococcus aureus. Furthermore, Cys CDs provided total biofilm eradication and inhibition abilities against Pseudomonas aeruginosa at 25 mg/mL concentration. Cys CDs are promising antioxidant materials with 1.3 ± 0.1 μmol Trolox equivalent/g antioxidant capacity. Finally, Cys CDs were also shown to inhibit the acetylcholinesterase (AChE) enzyme, which is used in the treatment of Alzheimer's disease, even at the low concentration of 100 μg/mL.