Microwave-assisted green synthesis of carbon dots derived from wild lemon (Citrus pennivesiculata) leaves as a fluorescent probe for tetracycline sensing in water

Highly efficient and sensitive detection of tetracycline in environmental water: Insights into the synergistic mechanism of biomass-derived carbon dots and N-methyl pyrrolidone solvent

The tetracycline (TC) residue in water environment has caused serious public safety issue. Thus, efficient sensing of TC is highly desirable for environmental protection. Herein, biomass-derived nitrogen-doped carbon dots (N-CDs) synthesized from natural Ophiopogon japonicus f. nanus (O. japonicus) were used for TC detection. The unique solvent synergism efficiently enhanced detection sensitivity, and the detailed sensing mechanism was deeply investigated. The blue fluorescence of N-CDs was quenched by TC via static quenching and inner filter effect. Moreover, the enhancement of green fluorescence from deprotonated TC was firstly proposed and sufficiently verified. The solvent effect of N-methyl pyrrolidone (NMP) and the fluorescence resonance energy transfer (FRET) with N-CDs achieved an instantaneous enhancement of the green emission by 64-fold. Accordingly, a ratiometric fluorescence method was constructed for rapid and sensitive sensing of TC with a low detection limit of 6.3 nM within 60 s. The synergistic effect of N-CDs and solvent assistance significantly improved the sensitivity by 7-fold compared to that in water. Remarkably, the biomass-derived N-CDs displayed low cost, good solubility, and desired stability. The deep insights into the synergism with solvent can provide prospects for the utilization of biomass-based materials and broaden the development of advanced sensors with promising applications.

Application of carbon quantum dots as fluorescent probes in the detection of antibiotics and heavy metals

Carbon quantum dots (CQDs) are ideal fluorescent probes for rapid detection. This paper reviews the synthesis methods of CQDs, their application in the rapid detection of antibiotics and heavy metals in the environment and food, and the underlying detection mechanisms. The hydrothermal method is the most commonly used for synthesis, and CQDs doped with heteroatoms (such as N, P and S) exhibit superior fluorescence performance. In the presence of antibiotics and heavy metals, the fluorescence of CQDs can be quenched or enhanced. Single-signal and dual-signal probes can be developed using the fluorescence, phosphorescence and absorbance of CQDs, enabling rapid detection of various antibiotics (e.g., tetracycline, quinolone and beta-lactam antibiotics) and heavy metals (e.g., Cd2+, Cr6+, Fe3+, Hg2+, and Pb2+). With the combination of smartphones and fluorescent probe test strips developed based on CQDs, on-the-spot rapid detection can be realized. This review offers new insights into the rapid detection of CQDs.

N-Doped Carbon Dots for Selective Detection of Fe3+ and Degradation of Fe3+/Basic Red 9 Complexes in Water Samples

In this work, the eco-friendly N-doped carbon dots KF-CDs and A-CDs were derived from kiwifruit by a simple one-step hydrothermal strategy at 180 °C for 6 h. KF-CDs have a high fluorescence quantum yield (27.85%), it is obviously rapid quenched by Fe3+, and have a good linear relationship from 1 to 8.26 µM (the detection limit was 0.077 µM). Basic red 9 is extensively used in biological, environmental and industry. Although it makes a great contribution to the economy, its toxicity should be taken seriously, especially with harmful metal ions. Within 2 h, A-CDs could degrade basic red 9 with degradation efficiency 89.6%, even though there was a stable compound formed with Fe3+ that the degradation efficiency was up to 88.3%. The results complement the research blank of carbon dots in catalytic degradation of basic red 9.

A review on green synthesis, biological applications of carbon dots in the field of drug delivery, biosensors, and bioimaging

Since the beginning of nanoscience and nanotechnology, carbon dots (CDs) have been the foundational idea and have dominated the growth of the nano-field. CDs are an intriguing platform for utilization in biology, technology, catalysis, and other fields thanks to their numerous distinctive structural, physicochemical, and photochemical characteristics. Since several carbon dots have already been created, they have been assessed based on their synthesis process, and luminescence characteristics. Due to their biocompatibility, less toxic effects, and most significantly their fluorescent features in contrast to other carbon nanostructures, CDs have several benefits. This review focuses on the most recent advancements in the characterization, applications, and synthesis techniques used for CDs made from natural sources. It will also direct scientists in the creation of a synthesis technique for adjustable carbon dots that is more practical, effective, and environmentally benign. With low toxicity and low cost, CDs are meeting the new era's requirements for more selectivity and sensitivity in the detection and sensing of various things, such as biomaterial sensing, enzymes, chemical contamination, and temperature sensing. Its variety of properties, such as optical properties, chemiluminescence, and morphological analysis, make it a good option to use in bioimaging, drug delivery, biosensors, and cancer diagnosis.

Microwave-assisted preparation of yellow fluorescent graphitic carbon nitride quantum dots for trace tetracycline-specific detection

Tetracycline (TC) is extensively utilized in livestock breeding, aquaculture, and medical industry. TC residues seriously harm food security, the environment, and human health. There is an urgent need to exploit a highly efficient and sensitive testing method to monitor TC residue levels in aquatic environments. In this study, graphitic carbon nitride quantum dots (g-CNQDs) were successfully synthesized by a one-step microwave-assisted method using citric acid and urea as precursors. The as-prepared g-CNQDs with size of 1.25-3.75 nm exhibited bright yellow fluorescence at 523 nm when excited at 397 nm. Interestingly, this characteristic fluorescence emission of g-CNQDs could be selectively and efficiently quenched by TC. Based on this phenomenon, for TC detection was successfully explored and applied in real water samples. Wide linear scope of 7-100 μM, low detection limit (LOD) of 0.48 μM, satisfactory recovery of 97.77%-103.4%, and good relative standard deviation (RSD) of 1.05-5.87% were obtained. Mechanism investigations revealed that the static quenching and the inner filter effect (IFE) were responsible for this fluorescence quenching between g-CNQDs and TC. This work not only provided a facile approach for g-CNQDs synthesis but also constructed a g-CNQDs-based fluorescent sensor platform for the highly sensitive and selective detection of TC in aquatic environments.

A new fabricated hetero-atom doped carbon quantum dots as a fluorescent probe for metronidazole determination using garlic and red lentils with microwave assistance

Biocompatible and highly fluorescent phosphorus, nitrogen and sulfur carbon quantum dots (P,N,S-CQDs) were synthesized using a quick and ecologically friendly process inspired from plant sources. Garlic and red lentils were utilized as natural and inexpensive sources for efficient synthesis of the carbon-based quantum dots using green microwave-irradiation, which provides an ultrafast route for carbonization of the organic biomass and subsequent fabrication of P,N,S-CQDs within only 3 min. The formed P,N,S-CQDs showed excellent blue fluorescence at λem = 412 nm when excited at 325 nm with a quantum yield up to 26.4%. These fluorescent dots were used as a nano-sensor for the determination of the commonly used antibacterial and antiprotozoal drug, metronidazole (MTR). As MTR lacked native fluorescence and prior published techniques had several limitations, the proposed methodology became increasingly relevant. This approach affords sensitive detection with a wide linear range of 0.5-100.0 μM and LOD and LOQ values of 0.14 μM and 0.42 μM, respectively. As well as, it is cost-effective and ecologically benign. The MTT test was used to evaluate the in-vitro cytotoxicity of the fabricated P,N,S-CQDs. The findings supported a minimally cytotoxic impact and good biocompatibility, which provide a future perspective for the applicability of these CQDs in biomedical applications.

A novel fluorescence platform for specific detection of tetracycline antibiotics based on [MQDA-Eu3+] system

Tetracycline antibiotics (TCs) are extensively used in clinical medicine, animal husbandry, and aquaculture because of their cost-effectiveness and high antibacterial efficacy. However, the presence of TCs residues in the environment poses risks to humans. In this study, an inner filter effect (IFE) fluorescent probe, 2,2'-(ethane-1,2-diylbis((2-((2-methylquinolin-8-yl)amino)-2-oxoethyl)azanediyl))diacetic acid (MQDA), was developed for the rapid detection of Eu3+ within 30 s. And its complex [MQDA-Eu3+] was successfully used for the detection of TCs. Upon coordination of a carboxyl of MQDA with Eu3+ to form a [MQDA-Eu3+] complex, the carboxyl served as an antenna ligand for the effective detection of Eu3+ to intensify the emission intensity of MQDA via "antenna effect", the process was the energy absorbed by TCs via UV excitation was effectively transferred to Eu3+. Fluorescence quenching of the [MQDA-Eu3+] complex was caused by the IFE in multicolor fluorescence systems. The limits of detection of [MQDA-Eu3+] for oxytetracycline, chlorotetracycline hydrochloride, and tetracycline were 0.80, 0.93, and 1.7 μM in DMSO/HEPES (7:3, v/v, pH = 7.0), respectively. [MQDA-Eu3+] demonstrated sensitive detection of TCs in environmental and food samples with satisfactory recoveries and exhibited excellent imaging capabilities for TCs in living cells and zebrafish with low cytotoxicity. The proposed approach demonstrated considerable potential for the quantitative detection of TCs.

Recent advancements and prospects in carbon-based nanomaterials derived from biomass for environmental remediation applications

The conversion of waste biomass into a value-added carbonaceous nanomaterial highlights the appealing power of biomass valorization. The advantages of using sustainable and cheap biomass precursors exhibit the tremendous opportunity for boosting energy production and their application in environmental remediation processes. This review emphasis the development and production of carbon-based nanomaterials derived from biomass, which possess favourable characteristics such as biocompatibility and photoluminescence. The advantages and limitations of various nanomaterials synthesised from different precursors were also discussed with insights into their physicochemical properties. The surface morphology of the porous nanomaterials is also explored along with their characteristic properties like regenerative nature, non-toxicity, ecofriendly nature, unique surface area, etc. The incorporation of various functional groups confers superiority of these materials, resulting in unique and advanced functional properties. Further, the use of these biomass derived nanomaterials was also explored in different applications like adsorption, photocatalysis and sensing of hazardous pollutants, etc. The challenges and outcomes obtained from different carbon-based nanomaterials are briefly outlined and discussed in this review.

Fluorescence sensor based on optimized quantum yield manganese-carbon polymer dots and smartphone-integrated sensing platform for tetracycline detection

The one-step synthesis of Mn-doped carbon quantum dots (Mn-CPDs) with a high quantum yield (QY = 45%) is reported using the microwave-assisted method. Subsequently, Mn-CPDs were successfully combined with Eu3+ ions to construct an Eu3+@Mn-CPDs fluorescence sensor. The presence of tetracycline (TC) induced a transition of fluorescence emission from blue (434 nm) to red (618 nm), and a robust linear relationship was observed between the ratio of F618 nm / F434 nm and the TC concentration (5 - 50 nmol/L), with a limit of detection (LOD) of 5.76 nmol/L. The underlying mechanism of Eu3+@Mn-CPDs and TC sensing is unveiled as a synergistic effect involving inner filter effect (IFE) and concurrent interactions. Notably, the smartphone-integrated sensing platform based on Eu3+@Mn-CPDs enables rapid and quantitative TC detection within a short time (< 30 s) by monitoring fluorescence color changes, achieving high-detection sensitivities (with a LOD of 6.18 nmol/L). This versatile and efficient sensing platform demonstrates its potential for the determination of TC concentrations in milk, honey, and tap water samples.

Pharmaceutical pollution fingerprinting and waterbodies remediation using waste-derived carbon dots as sustainable advanced nanomaterials

The conversion of biomass waste into high-value nanomaterials such as carbon dots might represent a great advancement towards a circular economy system. Biomass wastes are an excellent choice as carbon precursors because of their wide availability, abundance, chemical composition, and eco-friendly nature. Moreover, their use as a raw material might decrease the total cost of the synthesis processes and reduce the environmental impacts. In addition, the complex composition of biomass leads to carbon dots with abundant functional groups, which in turn enhances water dispersibility and photoluminescence properties. In this manner, the effective transformation of biomass wastes into carbon dots reduces environmental pollution through the inadequate management of waste while producing carbon dots with enhanced performances. Therefore, this review describes biomass wastes as potential candidates for the synthesis of carbon dots through different synthesis methods. In addition, we have analyzed the great potential of biomass-derived carbon dots (CDs) for the degradation and detection of emerging pharmaceutical pollutants by promoting a circular economy approach. Finally, we identified current challenges to propose possible research directions for the large-scale and sustainable synthesis of high-quality biomass-derived CDs.

Turning food waste into value-added carbon dots for sustainable food packaging application: A review

Carbon dots (CDs) are a recent addition to the nanocarbon family, encompassing both crystalline and amorphous phases. They have sparked significant research interest due to their unique electrical and optical properties, remarkable biocompatibility, outstanding mechanical characteristics, customizable surface chemistry, and negligible cytotoxicity. Their current applications are mainly limited to flexible photonic and biomedical devices, but they have also garnered attention for their potential use in intelligent packaging. The conversion of food waste into CDs further contributes to the concept of the circular economy. It provides a comprehensive overview of emerging green technologies, energy-saving reactions, and cost-effective starting materials involved in the synthesis of CDs. It also highlights the unique properties of biomass-derived CDs, focusing on their structural performance, cellular toxicity, and functional characteristics. The application of CDs in the food industry, including food packaging, is summarized in a concise manner. This paper sheds light on the current challenges and prospects of utilizing CDs in the packaging industry. It aims to provide researchers with a roadmap to tailor the properties of CDs to suit specific applications in the food industry, particularly in food packaging.

Green and rapid synthesis of biomass carbon dot-based fluorescence sensing for the sensitive determination of oxytetracycline

Eco-friendly biomass carbon dots (CDs) with blue fluorescence emission were rapidly synthesized by a microwave method. Based on the inner filter effect (IFE) between oxytetracycline (OTC) and CDs, the fluorescence of CDs could be selectively quenched by OTC. Therefore, a simple and time-saving fluorescence sensing system for the detection of OTC was established. Under optimal experimental conditions, the concentration of OTC showed a good linear relationship with fluorescence quenching values (ΔF) in the range of 4.0-100.0 μmol L^-1, a corresponding correlation coefficient (r) of 0.9975, and a detection limit of 0.12 μmol L^-1. The method has the advantages of low cost, time-saving, and green synthesis that could be used for the determination of OTC. Moreover, possessing high sensitivity and specificity, this fluorescence sensing method was successfully applied for detecting OTC in milk, indicating its potential applications in food safety.

Natural Nitrogen-Doped Carbon Dots Obtained from Hydrothermal Carbonization of Chebulic Myrobalan and Their Sensing Ability toward Heavy Metal Ions

Chebulic Myrobalan is the main ingredient in the Ayurvedic formulation Triphala, which is used for kidney and liver dysfunctions. Herein, natural nitrogen-doped carbon dots (NN-CDs) were prepared from the hydrothermal carbonization of Chebulic Myrobalan and were demonstrated to sense heavy metal ions in an aqueous medium. Briefly, the NN-CDs were developed from Chebulic Myrobalan by a single-step hydrothermal carbonization approach under a mild temperature (200 °C) without any capping and passivation agents. They were then thoroughly characterized to confirm their structural and optical properties. The resulting NN-CDs had small particles (average diameter: 2.5 ± 0.5 nm) with a narrow size distribution (1-4 nm) and a relatable degree of graphitization. They possessed bright and durable fluorescence with excitation-dependent emission behaviors. Further, the as-synthesized NN-CDs were a good fluorometric sensor for the detection of heavy metal ions in an aqueous medium. The NN-CDs showed sensitive and selective sensing platforms for Fe3+ ions; the detection limit was calculated to be 0.86 μM in the dynamic range of 5-25 μM of the ferric (Fe3+) ion concentration. Moreover, these NN-CDs could expand their application as a potential candidate for biomedical applications and offer a new method of hydrothermally carbonizing waste biomass.

Sustainable Synthesis of Bright Fluorescent Nitrogen-Doped Carbon Dots from Terminalia chebula for In Vitro Imaging

In this study, sustainable, low-cost, and environmentally friendly biomass (Terminalia chebula) was employed as a precursor for the formation of nitrogen-doped carbon dots (N-CDs). The hydrothermally assisted Terminalia chebula fruit-derived N-CDs (TC-CDs) emitted different bright fluorescent colors under various excitation wavelengths. The prepared TC-CDs showed a spherical morphology with a narrow size distribution and excellent water dispensability due to their abundant functionalities, such as oxygen- and nitrogen-bearing molecules on the surfaces of the TC-CDs. Additionally, these TC-CDs exhibited high photostability, good biocompatibility, very low toxicity, and excellent cell permeability against HCT-116 human colon carcinoma cells. The cell viability of HCT-116 human colon carcinoma cells in the presence of TC-CDs aqueous solution was calculated by MTT assay, and cell viability was higher than 95%, even at a higher concentration of 200 μg mL^-1 after 24 h incubation time. Finally, the uptake of TC-CDs by HCT-116 human colon carcinoma cells displayed distinguished blue, green, and red colors during in vitro imaging when excited by three filters with different wavelengths under a laser scanning confocal microscope. Thus, TC-CDs could be used as a potential candidate for various biomedical applications. Moreover, the conversion of low-cost/waste natural biomass into products of value promotes the sustainable development of the economy and human society.