Deep eutectic solvents-derived carbon dots for detection of mercury (II), photocatalytic antifungal activity and fluorescent labeling for C. albicans

Carbon Dots as Bioactive Antifungal Nanomaterials

Nowadays, the widespread diffusion of infections caused by opportunistic fungi represents a demanding threat for global health security. This phenomenon has also worsened by the emergence of contagious events in hospitalisation environments and by the fact that many fungi have developed harsh and serious resistance mechanisms to the traditional antimycotic drugs. Hence, the design of novel antifungal agents is a key factor to counteract mycotic infections and resistance. Within this context, nanomaterials are gaining increasing attention thanks to their biocidal character. Among these, carbon dots (CDs) represent a class of zero-dimensional, photoluminescent and quasi-spherical nanoparticles which, for their great and tuneable features, have found applications in catalysis, sensing and biomedicine. Nevertheless, only a few works define and recapitulate their antifungal properties. Therefore, we aim to give an overview about the recent advances in the synthesis of CDs active against infective fungi. We described the general features of CDs and fungal cells, by highlighting some of the most common antimycotic mechanisms. Then, we evaluated the effects of CDs, antimicrobial drugs-loaded CDs and CDs-incorporated packaging systems on different fungi and analysed the use of CDs as fluorescent nano-trackers for bioimaging, showing, to all effects, their promising application as antifungal agents.

Asparagus officinalis Herb-Derived Carbon Quantum Dots: Luminescent Probe for Medical Diagnostics

The utilization of natural materials for the synthesis of highly fluorescent carbon quantum dots (CQDs) presents a sustainable approach to overcome the challenges associated with traditional chemical precursors. Here, we report the synthesis of novel S,N-self-doped CQDs (S,N@CQDs) derived from asparagus officinalis herb. These S,N@CQDs exhibit 16.7 % fluorescence quantum yield, demonstrating their potential in medical diagnostics. We demonstrate the efficacy of S,N@CQDs as luminescent probes for the detection of anti-pathogenic medications metronidazole (MTZ) and nitazoxanide (NTZ) over concentration ranges of 0.0-180.0 μM (with a limit of detection (LOD) of 0.064 μM) and 0.25-40.0 μM (LOD of 0.05 μM), respectively. The probes were successfully applied to determine MTZ and NTZ in medicinal samples, real samples, and spiked human plasma, with excellent recovery rates ranging from 99.82 % to 103.03 %. Additionally, S,N@CQDs demonstrate exceptional efficacy as diagnostic luminescent probes for hemoglobin (Hb) detection over a concentration range of 0-900 nM, with a minimal detectability of 9.24 nM, comparable to commercially available medical laboratory diagnostic tests. The eco-friendly synthesis and precise detection limits of S,N@CQDs meet necessary analytical requirements and hold promise for advancing diagnostic capabilities in clinical settings. This research signifies a significant step towards sustainable and efficient fluorescence-based medical diagnostics.

Antifungal molecular details of MNQ-derived novel carbon dots against Penicillium digitatum

It is urgent to develop high-efficiency and low-toxicity natural antifungal agents on green mold caused by Penicillium digitatum. The effect of 2-methoxy-1, 4-naphthoquinone (MNQ) inhibition of P. digitatum was not very satisfactory. MNQ-derived carbon dots (MNQ-CDs) synthesized through a solvothermal route were used as antifungal agents against P. digitatum. The antifungal activity of prepared MNQ-CDswas enhanced compared to MNQ, and the minimum inhibitory concentration was 2.8 μg/mL. A total of 441 genes and 122 metabolites have undergone significant changes. The omics data revealed that MNQ-CDs primarily modified the metabolism of aromatic amino acids and synthesis of the cell membrane in P. digitatum, thereby inhibiting its propagation. Furthermore, compared with MNQ, MNQ-CDs had a better control effect on the green mold of citrus fruits, and could more significantly inhibit the propagation of P. digitatum. This study provides a new idea for the design of new and efficient antifungal materials.

Prosopis juliflora hydrothermal synthesis of high fluorescent carbon dots and its antibacterial and bioimaging applications

Carbon dots have stimulated the curiosity of biomedical researchers due to their unique properties, such as less toxicity and high biocompatibility. The synthesis of carbon dots for biomedical application is a core area in research. In the current research, an eco-friendly hydrothermal technique was employed to synthesize high fluorescent, plant-derived carbon dots from Prosopis juliflora leaves extract (PJ-CDs). The synthesized PJ-CDs were investigated by physicochemical evaluation instruments such as fluorescence spectroscopy, SEM, HR-TEM, EDX, XRD, FTIR, and UV-Vis. The UV-Vis absorption peaks obtained at 270 nm due to carbonyl functional groups shifts of n→π*. In addition, a quantum yield of 7.88 % is achieved. The synthesized PJ-CDs showing the presence of carious functional groups O-H, C-H, C=O, O-H, C-N and the obtained particles in spherical shape with an average size of 8 nm. The fluorescence PJ-CDs showed stability against various environmental factors such as a broad range of ionic strength and pH gradient. The antimicrobial activity of PJ-CDs was tested against a Staphylococcus aureus, and a Escherichia coli. The results suggest that the PJ-CDs could substantially inhibit the growth of Staphylococcus aureus. The findings also indicate that PJ-CDs are effective materials for bio-imaging in Caenorhabditis elegans and they can be also used for pharmaceutical applications.

Dual-Emission Carbon-Dot Ratiometric Fluorescence Sensor for Morphine Recognition in Biological Samples

Herein, a novel nitr[ogen-doped carbon dot (N-CD) fluorescence sensor with a dual emission ratio is developed using the microwave-assisted synthesis of m-phenylenediamine and spermidine. As a result of the fluorescence inner filtration effect (IFE) effect between morphine (MOR) and N-CD, the blue fluorescence of N-CDs at 350 nm was reduced in the presence of MOR, whereas the fluorescence of N-CDs at 456 nm increased substantially. The results demonstrated that the approach has a tremendous potential and that the linear range of MOR detection is 0.25-25 µg/mL, with a 71.8 ng/mL detection limit. Under UV light, the blue fluorescent system is easily visible to the naked eye. More significantly, the sensor proved successful in providing satisfactory results for the speciation measurement of MOR in a variety of biological samples.

Bio-Derived Fluorescent Carbon Dots: Synthesis, Properties and Applications

The transformation of biowaste into products with added value offers a lucrative role in nation-building. The current work describes the synthesis of highly water-soluble, luminous carbon quantum dots (CQDs) in the size range of 5-10 nm from discarded rice straw. The small spherical CQDs that were formed had outstanding optical and luminescent qualities as well as good photostabilities. By performing quantitative multi-assay tests that included antioxidant activities, in vitro stability and colloidal assay investigations as a function of different CQD concentrations, the biocompatibility of CQDs was evaluated. To clearly visualize the type of surface defects and emissive states in produced CQDs, excitation-dependent fluorescence emission experiments have also been carried out. The "waste-to-wealth" strategy that has been devised is a successful step toward the quick and accurate detection of Cu2+ ion in aqueous conditions. The fluorescence-quenching behavior has specified the concentration dependency of the developed sensor in the range of 50 μM to 10 nM, with detection limit value of 0.31 nM. The main advantage of the current research is that it offers a more environmentally friendly, economically viable and scaled-up synthesis of toxicologically screened CQDs for the quick fluorescence detection of Cu2+ ions and opens up new possibilities in wastewater management.

Nanocomposite of Ag nanoparticles and deep eutectic solvent-derived carbon dots with oxidase mimicking activity as synergistic bactericidal agent

A new type of nitrogen and chloride co-doped carbon dots (N/Cl-CDs) based on choline chloride-urea-glycine ternary deep eutectic solvents (DESs) was synthesized using a one-step hydrothermal method. The prepared N/Cl-CDs exhibited oxidase-like activity and excellent antibacterial activity against Escherichia coli, Staphylococcus aureus, and methicillin-resistant staphylococcus aureus (MRSA). The addition of silver nanoparticles (Ag NPs) (i.e., N/Cl-CDs + Ag NPs) to the N/Cl-CDs also significantly enhanced the oxidase and antibacterial activity. The nanocomposite (1.8 mg ml^-1 ) completely inactivated 10⁵ CFU ml^-1 of MRSA in 90 min. E. coli and S. aureus were labeled with the N/Cl-CDs, enabling multicolor fluorescence imaging at different excitation wavelengths. The nanocomposites have high antibacterial efficiency as a new bactericidal agent, as well as application potential with good biocompatibility and low toxicity.

Comparison of Carbon Dots Prepared in Deep Eutectic Solvent and Water/Deep Eutectic Solvent: Study of Fluorescent Detection of Fe3+ and Cetirizine and their Photocatalytic Antibacterial Activity

In this study, two solvents (deep eutectic and water/deep eutectic solvents) were used for N-doped carbon dots (N-CDs) preparation by microwave irradiation. The solvent can influence surface chemical composition, quantum yield, morphology, and fluorescence of CDs. N-CDs synthesized in water/deep eutectic solvent (DES) had better quantum yield (24.5%) with respect to N-CDs synthesized in deep eutectic solvent (17.4%). These carbon dots were used as a rapid and high sensitive "off-on" fluorescent probe for the determination of Fe³⁺ ion and cetirizine. Morphology and structure of the N-CDs were characterized by FT-IR, UV-Vis, XRD and TEM. Linear range and detection limit for N-CDs synthesis in deep eutectic solvent for cetirizine were 0.08-48 µM and 15 nM, respectively and for N-CDs synthesis in water/deep eutectic solvent were 0.03-50 µM and 10 nM, respectively. Applicability of this nanoprobe was tested in cetirizine determination in serum sample. Antibacterial activities of the two synthesized N-CDs were also investigated using agar disk diffusion method.

A glycine-functionalized graphene quantum dots synthesized by a facile post-modification strategy for a sensitive and selective fluorescence sensor of mercury ions

In this work, we have developed a facile method for the synthesis of glycine-functionalized graphene quantum dots (Gly-GQDs) through post-modification of graphene quantum dots with Gly under alkaline conditions. The as-synthesized Gly-GQDs exhibit an excellent blue emission at 444 nm, independent of excitation, as well as a high quantum yield (QY) of 35.7%. The Gly-GQDs have a narrow size distribution with an average size of 5.9 nm. Moreover, the as-prepared Gly-GQDs showed a better selective and sensitive recognition capability towards mercury ion (Hg²⁺) in aqueous solutions with a low detection limit of 8.3 nM, compared with GQDs and other nitrogen-doped GQDs synthesized through the one-step solvent thermal method. Gly-GQDs are successfully applied for the determination of Hg²⁺ in real water samples. This work shows a new promising approach for the design and synthesis of desirable GQDs with a given function.

Upcycling of plastic waste into fluorescent carbon dots: An environmentally viable transformation to biocompatible C-dots with potential prospective in analytical applications

The profitable impact on ecological system made the upcycling of plastic waste as one of the captivating issues in scientific world. The current work highlights the sustainable approach to transform the plastic waste comprises of bottles, used cups and polyethylene bags via simple heating to fluorescent carbon dots (C-dots). The obtained C-dots have displayed the absorption peaks around at 260 nm with size ranging between 5 and 30 nm. The upcycling has produced the structural changes in plastic waste and affected the optical properties of C-dots. The three types of used plastic waste as precursor have displayed excellent emission properties with peak positioned around 422 nm and quantum yield (QY) values ∼62, 65 and 64% for C-dots generated from plastic polybags, cups and bottles (P-CDs, C-CDs and B-CDs) respectively. The toxicity profiling of C-dots has been successfully tested by employing multi-assay biocompatible activities i.e. antibacterial and antifungal activities. The potential prospective of C-dots derived from plastic waste have further been explored in analytical applications involving selective copper metal ion sensing in aqueous media. The outcomes of the current studies have highlighted the potential accomplishment in preserving environment fate and giving response towards the budding social hitch of plastic waste.

Novel N,Cl-doped deep eutectic solvents-based carbon dots as a selective fluorescent probe for determination of morphine in food

In the present study, new N,Cl co-doped carbon dots (N,Cl-CDs) based on deep eutectic solvent (DES) were fabricated by a facile hydrothermal process. This fluorescent probe exhibited a good quantum yield of 14% and was applied for the sensitive and selective quantification of morphine in foods. In addition, the influence of solution pH, interaction time, system temperature, interfering substances and analogues on the determination was also investigated. Under the optimized conditions, the luminescence intensity of carbon dots increased linearly with the addition of morphine in the concentration range of (0.15–280.25) μg mL⁻¹ (R² > 0.9969) and the limit of detection (LOD) of 46.5 ng mL⁻¹. Based on these results, it is suggested that N,Cl-CDs is a promising fluorescent probe for sensitive and selective quantification of morphine in foods.

A schematic illustrating the synthesis and morphine detection of N,Cl-CDs.

Deep eutectic solvent assisted synthesis of carbon dots using Sophora flavescens Aiton modified with polyethyleneimine: Application in myricetin sensing and cell imaging

Here, an efficient method for synthesizing carbon dots (CDs) using a deep eutectic solvent (DES) was developed. To investigate the influence of different DESs on the quantum yield of CDs, different hydrogen-bonding acceptors (HBAs) and hydrogen-bonding donors (HBDs) were used to synthesize the DES and prepare CDs. Using Sophora flavescens Aiton as precursor, CDs were prepared using choline chloride (ChCl)/urea based DES as reaction media and doping agent in the presence of water. The CDs showed strong blue fluorescence and were further modified with polyethyleneimine (CDs@PEI). The fluorescence intensity of CDs@PEI was selectively quenched by myricetin with a limit of detection (LOD) of 10 nM. Furthermore, CDs@PEI was used to analyze myricetin in the extracts that were fluorescent by DES with satisfactory performance of Abelmoschus manihot (Linn.) Medicus flowers, vine teas and blueberries. Finally, the bio-imaging application of CDs@PEI was tested and the results confirmed its potential application in bio-imaging.

Sensitive fluorescence detection of atorvastatin by doped carbon dots synthesized in deep eutectic media

Fluorescence properties of nanoparticles can be influenced by solvent. In this work, carbon dots (CDs) were synthesized in deep eutectic solvent by microwave assisted method. Quantum yield (QY) and size of the synthesized CDs were 41.3% and 2 nm, respectively. N/Cl -doped CDs had excellent sensitivity and selectivity for atorvastatin and detection limit was 0.8 nM. Simple and low-cost synthesis method and excellent sensitivity are advantages of this detection method for atorvastatin. The as-synthesized N/Cl-doped CDs were successfully used to determine atorvastatin in blood serum.

Nanozymes used for antimicrobials and their applications

Bacterial infection-related diseases have been growing year-by-year rapidly and raising health problems globally. The exploitation of novel, high efficiency, and bacteria-binding antibacterial agents are extremely need. As far as now, the most extensive treatment is restricted to antibiotics, which may be overused and misused, leading to increased multidrug resistance. Antibiotics abuse, as well as antibiotic-resistance of bacteria, is a global challenge in the current situation. It is highly recommended and necessary to develop novel bactericide to kill the bacteria effectively without causing further resistance development and biosafety issues. Nanozymes, inorganic nanostructures with intrinsic enzymatic activities, have attracted more and more interest from the researchers owing to their exceptional advantages. Compared to natural enzymes, nanozymes can destroy many Gram-positive, Gram-negative bacteria, which builds an important bridge between biology and nanotechnology. As the potent nanoantibiotics, nanozymes have exciting broad-spectrum antimicrobial properties and negligible biotoxicities. And we summarized and highlighted the recent advances on nanozymes including its antibacterial mechanism and applications. Finally, challenges and limitations for the further improvement of the antibacterial activity are covered to provide future directions for the use of engineered nanozymes with enhanced antibacterial function.

Carbon source self-heating: ultrafast, energy-efficient and room temperature synthesis of highly fluorescent N, S-codoped carbon dots for quantitative detection of Fe(iii) ions in biological samples

In recent years, photoluminescent (PL) carbon dots (CDs) have attracted enormous attention because of their many fascinating properties. However, the traditional synthesis routes of PL CDs usually suffer from relatively low quantum yields (QYs) and require complicated operation processes as well as lots of externally supplied energy. Herein, we report a room temperature, green, ultrafast and energy-efficient route for large scale synthesis of highly PL N, S-codoped CDs without any external energy supply. The N, S-codoped CDs are prepared through a novel carbon source self-heating strategy, using the sole precursor tetraethylenepentamine (TEPA) simultaneously as the carbon, nitrogen and heat source, triggered by the heat initiator sodium persulfate (Na2S2O8). The large amount of heat released from Na2S2O8-triggered oxidation of TEPA could effectively promote the spontaneous polymerization and carbonization of TEPA precursors themselves as well as the in situ co-doping of sulfur, which had marked synergistic effects on the fluorescence enhancement of CDs, eventually leading to the high-yield (58.0%) preparation of highly fluorescent N, S-codoped CDs (QY 26.4%) at room temperature within 2 min. Moreover, the fluorescence of N, S-codoped CDs could be selectively quenched by Fe3+ ions in the presence of EDTA, in an ultra-wide range of 0.2-600 μM, with a detection limit of 0.10 μM. Ultimately, the fluorescent nanoprobe was successfully used for the quantitative detection of Fe3+ in human serum samples, indicating its great potential for sensing and biomedical applications.