Green route for synthesis of multifunctional fluorescent carbon dots from Tulsi leaves and its application as Cr(VI) sensors, bio-imaging and patterning agents

Progress and obstacles in employing carbon quantum dots for sustainable wastewater treatment

We explored the potential of carbon quantum dots (CQDs) as novel materials for wastewater treatment and their role towards environmental sustainability. The advantages of CQDs over other carbon-based materials, when synthesized using the same precursor material and for the same contaminant are discussed, enabling future researchers to choose the appropriate material. CQDs have demonstrated exceptional adaptability in various wastewater treatment, acting as efficient adsorbents for contaminants, exhibiting excellent photocatalytic properties for degradation of organic pollutants, and functioning as highly sensitive sensors for water quality monitoring. We found that bottom-up approach has better control over particle size (resulting CQDs: 1-4 nm), whereas top-down synthesis approach (resulting CQDs: 2-10 nm) have more potential for large scale applications and tunability. Transmission electron microscopy (TEM) remains the most expensive characterization technique, which provides the best resolution of the CQD's surface. The study emphasizes on the environmental impact and safety considerations pertaining to CQDs by emphasizing the need for thorough toxicity evaluation, and necessary environmental precautions. The study also identifies the lacunae pertaining to critical challenges in practical implementation of CQDs, such as scalability, competition of co-existing contaminants, and stability. Finally, future research directions are proposed, advocating green synthesis approaches, tailored surface functionalization, and, lowering the overall cost for analysis, synthesis and application of CQDs.

Cellulose-based yellow-green emitting carbon dots with large Stokes shift as effective "turn off-on" fluorescence platforms for Cr (VI) and AA dual efficacy detection

BACKGROUND

Hexavalent chromium (Cr (VI)) is highly carcinogenic to humans. Ascorbic acid (AA) deficiency can be hazardous to health. And the dual-effect fluorescence detection of them is an important research topic. Carbon dots (CDs) based on cellulose are excellent candidates for the fluorescence probes due to their low cost and environmental friendliness. But most of them exhibit shortwave emission, small Stokes shift and poor fluorescence performance, all of which limit their use. Therefore, there is an urgent need for cellulose CDs with longer emission wavelengths and larger Stokes shifts in dual-effect fluorescence detection of Cr (VI) and AA.

RESULTS

Under optimal conditions (180 °C, 12 h), we prepared cellulose-based nitrogen-doped carbon dots (N-CDs) by a simple one-step hydrothermal process, which display longer emission wavelengths (ex: 370 nm, em: 510 nm), larger Stokes shifts (140 nm) and high fluorescence quantum yield (QY: 19.27 %). The continuous "turn-off" and "turn-off-on" fluorescence detection platforms were constructed based on the internal filtering effect (IFE) between Cr6+ and N-CDs, and Cr6+ reduced to Cr3+ by AA at pH = 6. The platform has been successfully simultaneous detect Cr (VI) and AA with a wide range of 0.01-40 μM and 0.1-100 μM. And the lowest limits of detection (LOD) are 0.0303 μM and 0.072 μM, respectively. In the presence of some other metals, non-metal ions and water-soluble acids in the fruits, this fluorescent platform can demonstrate a high level of interference immunity.

SIGNIFICANCE AND NOVELTY

This represents the first yellow-green cellulose-based N-CDs with large Stokes shift for dual-effect detection of Cr (VI) and AA in real water samples and fresh fruits. The fluorescence detection platform has the advantage of low volume detection. Less than 2 mL of sample is required for testing and results are available in <5 min. This method is rare and supply a novel idea for the quantitative monitoring of Cr (VI) and AA.

Current nanocomposite advances for biomedical and environmental application diversity

Nanocomposite materials are emerging as key players in addressing critical challenges in healthcare, energy storage, and environmental remediation. These innovative systems hold great promise in engineering effective solutions for complex problems. Nanocomposites have demonstrated various advantages such as simplicity, versatility, lightweight, and potential cost-effectiveness. By reinforcing synthetic and natural polymers with nanomaterials, a range of nanocomposites have exhibited unique physicochemical properties, biocompatibility, and biodegradability. Current research on nanocomposites has demonstrated promising clinical and translational applications. Over the past decade, the production of nanocomposites has emerged as a critical nano-structuring methodology due to their adaptability and controllable surface structure. This comprehensive review article systematically addresses two principal domains. A comprehensive survey of metallic and nonmetallic nanomaterials (nanofillers), elucidating their efficacy as reinforcing agents in polymeric matrices. Emphasis is placed on the methodical design and engineering principles governing the development of functional nanocomposites. Additionally, the review provides an exhaustive examination of recent noteworthy advancements in industrial, environmental, biomedical, and clinical applications within the realms of nanocomposite materials. Finally, the review concludes by highlighting the ongoing challenges facing nanocomposites in a wide range of applications.

l-cysteine capped MoS2 QDs for dual-channel imaging and superior Fe3+ ion sensing in biological systems

MoS2 quantum dots (MQDs) with an average size of 1.9 ± 0.7 nm were synthesized using a microwave-assisted method. Absorbance studies confirmed characteristic transitions of MoS2, with absorption humps at 260-280 nm and 300-330 nm, and a band gap of 3.6 ± 0.1 eV. Fluorescence emission studies showed dominant blue and some green emissions under 315 nm excitation, with an absolute quantum yield of ∼9%. The MQDs exhibited fluorescence stability over time after repeated quenching cycles across various pH and media systems. In vitro toxicity tests indicated cytocompatibility, with around 80% cell survival at 1000 mg L-1. Confocal imaging demonstrated significant uptake and vibrant fluorescence in cancerous and non-cancerous cell lines. The MQDs showed strong selectivity towards Fe3+ ions, with a detection limit of 27.61 ± 0.25 nM. Recovery rates for Fe3+ in phosphate buffer saline (PBS) and simulated body fluid (SBF) systems were >97% and >98%, respectively, with a relative standard deviation (RSD) within 3%, indicating precision. These findings suggest that MQDs have high potential for diagnostic applications involving Fe3+ detection due to their fluorescence stability, robustness, enhanced cell viability, and dual-channel imaging properties.

Exploring the potential of eco-friendly carbon dots in monitoring and remediation of environmental pollutants

Photoluminescent carbon dots (CDs) have garnered significant interest owing to their distinctive optical and electronic properties. In contrast to semiconductor quantum dots, which incorporated toxic elements in their composition, CDs have emerged as a promising alternative, rendering them suitable for both environmental and biological applications. CDs exhibit astonishing features, including photoluminescence, charge transfer, quantum confinement effect, and biocompatibility. Recently, CDs derived from green sources have drawn a lot of attention due to their strong photostability, reduced toxicity, better biocompatibility, enhanced fluorescence, and simplicity. These attributes have shown great promise in the areas of LED technology, bioimaging, photocatalysis, drug delivery, biosensing, and antibacterial activity. In contrast, this review offers a comprehensive overview of various green sources utilized to produce CDs and methodologies, along with their merits and demerits, with a notable emphasis on physiochemical properties. Additionally, the paper provides insight into the bibliometric analysis and recent advancements of CDs in sensing, photocatalysis, and antibacterial activity. In this field, extensive research is underway, and a total of 7,438 articles have been identified. Among these, 4242 articles are dedicated to sensing applications, while 1518 and 1678 focus on adsorption and degradation. Carbon dots demonstrate exceptional sensing capabilities within the nanomolar range with a selectivity of up to 95% for pollutants. They exhibit excellent degradation efficiency exceeding 90% within 10-130 min and possess an adsorption capacity from 100 to 800 mg/g. These fascinating qualities render them suitable for diverse applications.

El Hamd M, Alshehri S, Helmy MI. Bioinspired Carbon Dots-Based Fluorescent Sensor for the Selective Determination of a Potent Anti-Inflammatory Drug in the Presence of Its Photodegradation Products

Herein, we synthesized biogenic carbon dots (CDs) with blue-shifted maximum excitation (λex/λem of 320/404 nm) from largely wasted tangerine seeds for the first time via a one-step hydrothermal method. The biogenic CDs exhibit a maximum excitation wavelength that overlaps with the absorption spectrum of ketorolac tromethamine (KETO) at 320 nm. The developed CDs serve as a turn-off fluorescent probe via an inner filter effect (IFE) quenching mechanism. The resulting CDs have high quantum yield (QY) (39% ± 2.89%, n = 5) and exhibited great performance toward KETO over a concentration range of 0.50-16.00 μg/mL with a limit of detection (LOD) = 0.17 μg/mL. The nanoprobe achieved a high % recovery in assaying KETO in tablet dosage form and had not been significantly affected by various interferents including co-formulated and co-administered drugs. The nanoprobe shows selectivity toward KETO, even in the presence of its photocatalytic degradation products. It can effectively investigate the elimination of KETO from aquatic systems and test its stability in pharmaceutical preparations. The developed nanoprobe underwent a comprehensive evaluation of its environmental impact using analytical eco-scale (AES), complex green analytical procedure index (Complex GAPI), and the Analytical GREEnness calculator (AGREE). The sustainability of the developed nano sensor was assessed and compared to the reported metal-based quantum dots probe for KETO using the innovative RGB 12 model, considering 12 white analytical chemistry (WAC) perspectives.

Fluorescent Carbon Dots: Aggregation-Induced Emission Enhancement, Application as Probe for CN- and Cr2O7-2, Sensing Strips and Bio-imaging Agent

Fluorescent carbon dots (Trp-CDs) were prepared using tryptophan as precursor and were characterized on the basis of elemental analysis, powder-XRD, IR, Raman spectroscopy, 13C-NMR, UV-Vis, fluorescence and TEM. Trp-CDs exhibit poor fluorescence in 100% water but showed strong Aggregation Induced Emission (AIE) in ethanol and higher alcohols. The anion sensing study of Trp-CD revealed that it selectively detects CN- and Cr2O7-2 and from fluorescence quenching titration study, quenching constant, LOD and range of detection were evaluated. The emission life-time of Trp-CD before and after addition of CN- and Cr2O7-2 were measured, the decay curve before addition of anion was best fitted with a bi-exponential function with life-time of τ1 2.79 ns (10.74%) and τ2 18.93 ns (89.26%). The mechanistic study revealed that for CN-, the fluorescence quenching is due to its interaction with protons attached to surface functional groups and for Cr2O7-2, it is due to inner filter effect (IFE). Sensing strips were prepared by coating Trp-CDs onto various solid surfaces including agarose films and were used for detection of CN- and Cr2O7-. Trp-CD was found to be nontoxic and biocompatible and used as staining agent for Artemia and Bacteria (Bacillus Subtilis, Pseudomonas) and detection of CN- and Cr2O7-.

Manganese dioxide nanosheet-modulated ratiometric fluoroprobe based on carbon quantum dots from okra for selective and sensitive dichlorvos detection in foods

Herein, we developed a ratiometric fluoroprobe by integrating okra-derived carbon quantum dots (CQDs) with amplex red (AR) using manganese dioxide nanosheets (MnO2 NSs) as a medium. Fluorescence intensities (FIs) of CQDs were sharply quenched by MnO2 NSs via an inner-filter effect processes, whereas the FIs of AR were significantly enhanced due to oxidation of AR to AR-ox by the oxidase-mimetic activity of MnO2 NSs. Acetyrylcholinesterase hydrolyzed acetylthiocholine to produce thiocholine, and the decomposition of MnO2 NSs to Mn2+ by thiocholine led to the FI recovery of CQDs, but decreased FIs of AR-ox. Based on the above phenomenon and the inhibitory effect of dichlorvos (DDVP) on acetyrylcholinesterase activity, a novel ratiometric fluoroprobe for DDVP quantification was pioneered. Under optimized conditions, this fluoroprobe gave a wide linear range (4-120 μg/L), low detection limit (1.2 μg/L), and satisfactory fortification recoveries (90.0-110.0%), thereby providing good prospects for routine DDVP monitoring in foods.

Carbon dots as potential candidate for photocatalytic treatment of dye wastewater

Water is the utmost important element for the existence of life. In recent decades, water resources have become highly contaminated by a variety of pollutants, especially toxic dyes that are harmful to both living beings and environment. Hence, there is an urgent need to develop more effective methods than traditional wastewater treatment approaches for treatment of hazardous dyes. Herein, we have addressed the various aspects related to the effective and economically feasible method for photocatalytic degradation of these dyes employing carbon dots. The photocatalysts based on carbon dots including those mediated from biomass have many superiorities over conventional methods such as utilization of economically affordable, non-toxic, rapid reactions, and simple post-processing steps. The current study will also facilitate better insight into the understanding of photocatalytic treatment of dye-polluted wastewater for future wastewater treatment studies. Additionally, the possible mechanistic pathways of photocatalytic dye decontamination, several challenges, and future perspectives have also been summarized.

Biomass derived green carbon dots for sensing applications of effective detection of metallic contaminants in the environment

The rapid consumption of metals and unorganized disposal have led to unprecedented increases in heavy metal ion concentrations in the ecosystem, which disrupts environmental homeostasis and results in agricultural biodiversity loss. Mitigation and remediation plans for heavy metal pollution are largely dependent on the discovery of cost-effective, biocompatible, specific, and robust detectors because conventional methods involve sophisticated electronics and sample preparation procedures. Carbon dots (CDs) have gained significant importance in sensing applications related to environmental sustainability. Fluorescence sensor applications have been enhanced by their distinctive spectral properties and the potential for developing efficient photonic devices. With the recent development of biomass-functionalized carbon dots, a wide spectrum of multivalent and bivalent transition metal ions responsible for water quality degradation can be detected with high efficiency and minimal toxicity. This review explores the various methods of manufacturing carbon dots and the biochemical mechanisms involved in metal detection using green carbon dots for sensing applications involving Cu (II), Fe (III), Hg (II), and Cr (VI) ions in aqueous systems. A detailed discussion of practical challenges and future recommendations is presented to identify feasible design routes.

Synthesis, properties and potential applications of photoluminescent carbon nanoparticles: A review

Photoluminescent-carbon nanoparticles (PL-CNPs) are a new class of materials that received immense interest among researchers due to their distinct characteristics, including photoluminescence, high surface-to-volume ratio, low cost, ease of synthesis, high quantum yield, and biocompatibility. By exploiting these outstanding properties, many studies have been reported on its utility as sensors, photocatalysts, probes for bio-imaging, and optoelectronics applications. From clinical applications to point-of-care test devices, drug loading to tracking of drug delivery, and other research innovations demonstrated PL-CNPs as an emerging material that could substitute conventional approaches. However, some of the PL-CNPs have poor PL properties and selectivity due to the presence of impurities (e.g., molecular fluorophores) and unfavourable surface charges by the passivation molecules, which impede their applications in many fields. To address these issues, many researchers have been paying great attention to developing new PL-CNPs with different composite combinations to achieve high PL properties and selectivity. Herein, we thoroughly discussed the recent development of various synthetic strategies employed to prepare PL-CNPs, doping effects, photostability, biocompatibility, and applications in sensing, bioimaging, and drug delivery fields. Moreover, the review discussed the limitations, future direction, and perspectives of PL-CNPs in possible potential applications.

Progress on the luminescence mechanism and application of carbon quantum dots based on biomass synthesis

With the continuous development of carbon-based materials, a variety of new materials have emerged one after another. Carbon Quantum Dots (CQDs) have succeeded in standing out from the crowd of new materials due to their better optical properties in biomedicine, ion detection, anti-counterfeiting materials and photocatalysis. In recent years, through the continuous exploration of CQDs, research scholars have found that the organic substances or heavy metals contained in traditional ones can cause irreversible harm to people and the environment. Therefore, the application of traditional CQDs in future studies will be gradually limited. Among various new materials, biomass raw materials have the merits of good biocompatibility, lower toxicity and green and environmental protection, which largely overcome the defects of traditional materials and have attracted many scholars to focus on the research and development of various biomass CQDs. This paper summarises the optical properties, fluorescence mechanisms, synthetic methods, functionalisation modulation of biomass CQDs and their relevant research progress in the fields of ion detection, bioimaging, biomedicine, biosensing, solar cells, anti-counterfeit materials, photocatalysis and capacitors. Finally, the paper concludes with some discussion of the challenges and prospects of this exciting and promising field of application.

Facile and Green Synthesis of Novel Fluorescent Carbon Quantum Dots and Their Silver Heterostructure: An In Vitro Anticancer Activity and Imaging on Colorectal Carcinoma

Carbon dots (CQDs) have been widely investigated as prime candidates for developing a tumor theranostic platform due to their tunable fluorescence emission and excitation, high water solubility, good photostability, and biocompatibility. Among the CQDs, natural CQDs are an emerging class of nanomaterials in the carbon family. Herein, highly fluorescent carbon quantum dots (CQDs) were synthesized from orange juice using a one-step hydrothermal method and characterized by different techniques. After that, CQD/Ag heterostructures were synthesized by the reduction of silver salt, in particular silver nitrate (AgNO3) solution using sodium borohydride (NaBH4) in different ratios. The photostability and characterization of CQD/Ag heterostructures were investigated. At last, a comparative cellular toxicity measurement was done to select the superior CQD/Ag heterostructure in the human colorectal carcinoma (HCT 116) cell line along with the imaging property. The detailed cell death signaling was also observed in the HCT 116 cell line via the ROS-dependent mitochondrial-mediated pathway, where Akt (RAC-α serine/threonine-protein kinase) played a important role.

Naturally Derived Carbon Dots In Situ Confined Self-Healing and Breathable Hydrogel Monolith for Anomalous Diffusion-Driven Phytomedicine Release

Fluorescent nanocarbons are well-proficient nanomaterials because of their optical properties and surface engineering. Herein, Apium graveolens-derived carbon dots (ACDs) have been synthesized by a one-step hydrothermal process without using any surplus vigorous chemicals or ligands. ACDs were captured via an in situ gelation reaction to form a semi-interpenetrating polymer network system showing mechanical robustness, fluorescent behavior, and natural adhesivity. ACDs-reinforced hydrogels were tested against robust uniaxial stress, repeated mechanical stretching, thixotropy, low creep, and fast strain recovery, confirming their elastomeric sustainability. Moreover, the room-temperature self-healing behavior was observed for the ACDs-reinforced hydrogels, with a healing efficacy of more than 45%. Water imbibition through hydrogel surfaces was digitally monitored via "breathing" and "accelerated breathing" behaviors. The phytomedicine release from the hydrogels was tuned by the ACDs' microstructure regulatory activity, resulting in better control of the diffusion rate compared to conventional chemical hydrogels. Finally, the phytomedicine-loaded hydrogels were found to be excellent bactericidal materials eradicating more than 85% of Gram-positive and -negative bacteria. The delayed network rupturing, superstretchability, fluorescent self-healing, controlled release, and antibacterial behavior could make this material an excellent alternative to soft biomaterials and soft robotics.

Recent Advances in Nanomaterial-Based Sensing for Food Safety Analysis

The increasing public attention on unceasing food safety incidents prompts the requirements of analytical techniques with high sensitivity, reliability, and reproducibility to timely prevent food safety incidents occurring. Food analysis is critically important for the health of both animals and human beings. Due to their unique physical and chemical properties, nanomaterials provide more opportunities for food quality and safety control. To date, nanomaterials have been widely used in the construction of sensors and biosensors to achieve more accurate, fast, and selective food safety detection. Here, various nanomaterial-based sensors for food analysis are outlined, including optical and electrochemical sensors. The discussion mainly involves the basic sensing principles, current strategies, and novel designs. Additionally, given the trend towards portable devices, various smartphone sensor-based point-of-care (POC) devices for home care testing are discussed.

Recent advances in green carbon dots (2015-2022): synthesis, metal ion sensing, and biological applications

Carbon dots (CDs) show extensive potential in various fields such as sensing, bioimaging, catalysis, medicine, optoelectronics, and drug delivery due to their unique properties, that is, low cytotoxicity, cytocompatibility, water-solubility, multicolor wavelength tuned emission, photo-stability, easy modification, strong chemical inertness, etc. This review article especially focuses on the recent advancement (2015-2022) in the green synthesis of CDs, their application in metal ions sensing and microbial bioimaging, detection, and viability studies as well as their applications in pathogenic control and plant growth promotion.

Green synthesis of carbon quantum dots and their environmental applications

Green synthesis of scalable, high-quality, fluorescent carbon quantum dots (CQDs) from natural biomass remains attractive due to their outstanding environmental application. CQDs are an emerging class of zero-dimensional carbon nanomaterials (<10 nm) that have recently attracted much attention due to their strong optical properties, biocompatibility, nontoxicity, uniform particle size, high photostability, low-cost synthesis, and highly tunable photoluminescence. The unique properties of CQDs possess a broad range of prospective applications in a number of fields such as metal ions detection, photocatalysis, sensing, medical diagnosis, bioimaging, and drug delivery. CQD nanostructures are synthesized using various techniques such as hydrothermal method, laser ablation, microwave irradiation, electrochemical oxidation, reflux method, and ultrasonication. However, this type of fabrication approach requires several chemical reactions including oxidation, carbonization, and pyrolysis. Green synthesis of CQDs has several advantages such as the use of low-cost and non-toxic raw materials, renewable resources, simple operations, and being environment-friendly. This review article will discuss the physicochemical properties of CQDs techniques used in the production of CQDs, and the stability of CQDs along with their applications in wastewater treatment and biomedical fields.

Biocompatible Carbon Dot Decorated α-FeOOH Nanohybrid for an Effective Fluorometric Sensing of Cr (VI) in Wastewater and Living Cells

This article reports the fluorometric detection of toxic hexavalent chromium Cr (VI)) in wastewater and Cr (VI) contaminated living cells using in-situ grown carbon quantum dots into the goethite (α-FeOOH) nano-matrix. The synthesized nano-hybrid shows enormous potential in determining the chromium contamination levels in various types of water samples. This selective fluorometric probe is enormously sensitive (LOD 81 nM) toward hexavalent chromium, which makes it a dedicated chromium sensor. Moreover, the sensing mechanism has been assessed using Stern-Volmer's equation and fluorescence lifetime experiments showing the simultaneous occurrence of photoinduced electron transfer and the inner filter effect. This chromium sensor has also been employed to assess the contamination level in real-life industrial wastewater. The performance of this probe in a real-life wastewater sample is quite commendable. Further, this biocompatible fluorometric probe has been used to demonstrate the in-vitro sensing of Cr (VI) in HeLa cells. The rapid detection mechanism of hexavalent chromium in living cells has been validated using theoretical docking simulations. Henceforth, this fluorometric sensor material could open new avenues not only in wastewater monitoring but also in biomedical applications.

Valorisation of bio-derived fluorescent carbon dots for metal sensing, DNA binding and bioimaging

Carbon dots are quasi-spherical and zero dimensional nanomaterials with unique optical and electronic properties. In this work, a facile and sustainable strategy was employed to synthesise nitrogen doped carbon dots from Terminalia chebula via hydrothermal treatment with a quantum yield of 19.9%. The structural and optical properties of nitrogen doped carbon dots (N-CDs) were studied by UV-Visible absorption and fluorescence spectroscopy. The surface functional groups, average particle size and elemental analysis were assessed with the help of Fourier Transform Infra Red spectroscopy, High Resolution Transmission Electron Microscopy and Energy Dispersive X-ray analysis respectively. The N-CDs exhibited excitation dependent emission upon irradiation with UV light, pH stability over neutral range and excellent photostability. The average particle size of the synthesised N-CDs was found to be 3.56 nm. The fluorescence intensity of the N-CDs quenched linearly with increase in concentration of Fe³⁺ ions. The limit of detection (LOD) of N-CDs with Fe³⁺ ions was calculated to be 4.5 nM using Stern-Volmer plot. The fluorescence was restored by addition of EDTA to Fe³⁺ coordinated N-CD system. Further, the synthesised N-CDs interacted with ct-DNA through intercalative mode and the binding constant calculated using the Benesi Hildebrand plot was 1.78 × 10⁸ mg/mL. The cytotoxicity of N-CDs was evaluated using MTT assay. The excellent biocompatible and less toxic nature of N-CDs was extrapolated to serve as fluorescent probes for imaging E.coli and SKMEL cells. From the results of this work, it is evident that the synthesised N-CDs can be used to develop efficient fluorescent metal sensors. The fluorescent property of N-CDs enables it to find extension as a potential curative drug, an efficient patterning agent and an effective biomarker to image biological cells causing no damage to normal cells.

Fluorescent nanocellulose-based hydrogel incorporating titanate nanofibers for sorption and detection of Cr(VI)

Chromium pollution is a major environmental concern; thus, effective and multifunctional adsorbents for removing the Cr(VI) ion are urgently needed. A fluorescent nanocellulose-based hydrogel (FNH) incorporating titanate nanofibers (TNs) was developed for the sorption and detection of Cr(VI) ion. The chemical and physical structures of the hydrogels, as well as their sorption and detection properties, were studied. The predicted maximum adsorption capacity and the lowest detection limit of FNH were 648.4 mg/g and 0.039 μg/L, respectively. Furthermore, the sorption and detection mechanisms of FNH were discussed in detail. These results showed that the excellent sorption and detection might be mainly attributed to the three-dimensional (3D) porous structure constructed by TNs and cellulose nanocrystals modified with carbon dots, which improved the sorption ability and provided the rapid visual response to Cr(VI). Furthermore, cost analysis showed that FNH was cheaper than activated carbon in removing the Cr(VI) ion. This work established a facile technique in developing low-cost and multifunctional adsorbents.

Sensor Heavy Metal from Natural Resources for a Green Environment: A Review Relation Between Synthesis Method and Luminescence Properties of Carbon Dots

Carbon dots are 10-nm nanomaterial classes as excellent candidates in various applications: physics, biology, chemistry, and food science due to high stable biocompatibility and high surface expansive. Carbon dots (CDs) produced from natural materials have received wide attention due to their unique benefits, easy availabilities, sufficient costs, and harmless to the ecosystem. The various properties of CDs can be obtained from various synthesis methods: hydrothermal, microwave-assisted, and pyrolysis. The CDs have shown enormous potential in metal particle detection, colorimetric sensors, electrochemical sensors, and pesticide sensor. This review provides systematic information on a synthesis method based on natural resources and the application to the environmental sensors for supporting the clean environment. We hopefully this review, useful as a reference source in providing the guidance or roadmap of new researchers to develop new strategy in increasing luminescence properties CDs for multi detection of heavy metal in the environment.

What makes carbon nanoparticle a potent material for biological application?

Carbon materials are generally utilized in the form of carbon allotropes and their characteristics are exploited as such or for improving the thermal, electrical, optical, and mechanical properties of other biomaterials. This has now found a broader share in conventional biomaterial space with the generation of nanodiamond, carbon dot, carbon nanoparticles (CNPs), and so forth. With properties of better biocompatibility, intrinsic optical emission, aqueous suspendability, and easier surface conjugation possibilities made CNPs as one of the fore most choice for biological applications especially for use in intracellular spaces. There are various reports available presenting methods of preparing, characterizing, and using CNPs for various biological applications but a collection of information on what makes CNP a suitable biomaterial to achieve those biological activities is yet to be provided in a significant way. Herein, a series of correlations among synthesis, characterization, and mode of utilization of CNP have been incorporated along with the variations in its use as agent for sensing, imaging, and therapy of different diseases or conditions. It is ensembled that how simplified and optimized methods of synthesis is correlated with specific characteristics of CNPs which were found to be suitable in the specific biological applications. These comparisons and correlations among various CNPs, will surely provide a platform to generate new edition of this nanomaterial with improvised applications and newer methods of evaluating structural, physical, and functional properties. This may ensure the eventual use of CNPs for human being for specific need in near future. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > Biosensing Diagnostic Tools > In Vitro Nanoparticle-Based Sensing Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Green synthesis of multifunctional carbon quantum dots: An approach in cancer theranostics

Carbon quantum dots (CQDs) have gained significant growing attention in the recent past due to their peculiar characteristics including smaller size, high surface area, photoluminescence, chemical stability, facile synthesis and functionalization possibilities. They are carbon nanostructures having less than 10 nm size with fluorescent properties. In recent years, the scientific community is curiously adopting biomass precursors for the preparation of CQDs over the chemical compounds. These biomass sources are sustainable, eco-friendly, inexpensive, widely available and convert waste into valuable materials. Hence in our work the fundamental understating of diverse fabrication methodologies of CQDs, and the types of raw materials employed in recent times, are all examined and correlated comprehensively. Their unique combination of remarkable properties, together with the ease with which they can be fabricated, makes CQDs as promising materials for applications in diverse biomedical fields, in particular for bio-imaging, targeted drug delivery and phototherapy for cancer treatment. The mechanism for luminescence is of considerable significance for leading the synthesis of CQDs with tunable fluorescence emission. Therefore, it is aimed to explore and provide an updated review on (i) the recent progress on the different synthesis methods of biomass-derived CQDs, (ii) the contribution of surface states or functional groups on the luminescence origin and (iii) its potential application for cancer theranostics, concentrating on their fluorescence properties. Finally, we explored the challenges in modification for the synthesis of CQDs from biomass derivatives and the future scope of CQDs in phototherapy for cancer theranostics.

Fluorescent Carbon Dot-Supported Imaging-Based Biomedicine: A Comprehensive Review

Carbon dots (CDs) provide distinctive advantages of strong fluorescence, good photostability, high water solubility, and outstanding biocompatibility, and thus are widely exploited as potential imaging agents for in vitro and in vivo bioimaging. Imaging is absolutely necessary when discovering the structure and function of cells, detecting biomarkers in diagnosis, tracking the progress of ongoing disease, treating various tumors, and monitoring therapeutic efficacy, making it an important approach in modern biomedicine. Numerous investigations of CDs have been intensively studied for utilization in bioimaging-supported medical sciences. However, there is still no article highlighting the potential importance of CD-based bioimaging to support various biomedical applications. Herein, we summarize the development of CDs as fluorescence (FL) nanoprobes with different FL colors for potential bioimaging-based applications in living cells, tissue, and organisms, including the bioimaging of various cell types and targets, bioimaging-supported sensing of metal ions and biomolecules, and FL imaging-guided tumor therapy. Current CD-based microscopic techniques and their advantages are also highlighted. This review discusses the significance of advanced CD-supported imaging-based in vitro and in vivo investigations, suggests the potential of CD-based imaging for biomedicine, and encourages the effective selection and development of superior probes and platforms for further biomedical applications.

Carbon Dots: An Excellent Fluorescent Probe for Contaminant Sensing and Remediation

Pollution-induced degradation of the environment is a serious problem for both developing and developed countries. Existing remediation methods are restricted, necessitating the development of novel remediation technologies. Nanomaterials with unique characteristics have recently been developed for remediation. Quantum dots (QDs) are semiconductor nanoparticles (1-10 nm) with optical and electrical characteristics that differ from bigger particles owing to quantum mechanics, making them intriguing for sensing and remediation applications. Carbon dots (CDs) offer better characteristics than typical QDs, such as, CdSe QDs in terms of contaminant sensing and remediation. Non-toxicity, chemical inertness, photo-induced electron transfer, good biocompatibility, and adjustable photoluminescence behavior are all characteristics of CDs. CDs are frequently made from sustainable raw materials as they are cost-effective, environmentally compactable, and excellent in reducing waste generation. The goal of this review article is to briefly describe CDs fabrication methods, to deeply investigate the criteria and properties of CDs that make them suitable for sensing and remediation of contaminants, and also to highlight recent advances in their use in sensing and remediation of contaminants.

Yeast powder derived carbon quantum dots for dopamine detection and living cell imaging

Dopamine (DA) is an important neurotransmitter in the brain of mammals. There is a critical need for fast and sensitive determination approaches to monitor these potential diseases due to various weaknesses in clinical trials of the existing methods for DA detection. DA can effectively quench the fluorescence of carbon quantum dots (CDs) through the inner filter effect and static quenching. In this work, fluorescent yeast CDs (Y-CDs) were prepared via a simple hydrothermal approach of using yeast powder and regarded as the fluorescent nanoprobe to directly monitor the DA concentration. The as-prepared detection platform exhibited excellent sensitivity and selectivity toward DA with a low detection limit of 30 nM and a wide linear range of 0.05-150 μM. Benefiting from these outstanding features, the developed label-free method has been successfully applied for fast DA detection in human serum samples with satisfactory recoveries. Furthermore, it demonstrated that the Y-CDs were well suitable for live cell imaging and showed low toxicity toward MCF-7 cells. Consequently, this work will facilitate the great potential of the versatile Y-CDs in developing biosensors for clinical diagnosis and other biological applications.

One-Step Green Synthesis of Water-Soluble Fluorescent Carbon Dots and Its Application in the Detection of Cu2

Renewable biowaste-derived carbon dots have garnered immense interest owing to their exceptional optical, fluorescence, chemical, and environmentally friendly attributes, which have been exploited for the detection of metals, non-metals, and organics in the environment. In the present study, water-soluble fluorescent carbon dots (CDs) were synthesized via facile green microwave pyrolysis of pine-cone biomass as precursors, without any chemical additives. The synthesized fluorescent pine-cone carbon dots (PC-CDs) were spherical in shape with a bimodal particle-size distribution (average diameters of 15.2 nm and 42.1 nm) and a broad absorption band of between 280 and 350 nm, attributed to a π-π* and n-π* transition. The synthesized PC-CDs exhibited the highest fluorescent (FL) intensity at an excitation wavelength of 360 nm, with maximum emission of 430 nm. The synthesized PC-CDs were an excellent fluorescent probe for the selective detection of Cu2+ in aqueous solution, amidst the presence of other metal ions. The FL intensity of PC-CDs was exceptionally quenched in the presence of Cu2+ ions, with a low detection limit of 0.005 μg/mL; this was largely ascribed to Cu2+ ion binding interactions with the enriched surface functional groups on the PC-CDs. As-synthesized PC-CDs are an excellent, cost effective, and sensitive probe for detecting and monitoring Cu2+ metal ions in wastewater.

Novel synthesis of fluorescent carbon dots from bio-based Carica Papaya Leaves: Optical and structural properties with antioxidant and anti-inflammatory activities

Fluorescent carbon dots (CDs) are prepared from a natural resource Carica Papaya Leaves, by sand bath method. The as-synthesized CDs optical and structural properties were characterized by UltraViolet-Visible, FT- IR, and fluorescence spectroscopy. Also the size, shape, and particle size distribution was studied using Transmission electron microscopy technique. These CDs were examined for biomedical applications like free radical scavenging activity using DPPH assay, antioxidant activity using phosphomolybdate assay, and in vitro anti-inflammatory activity using membrane stabilization protocol. The CDs exhibited excellent biological activities at lower concentrations and showed notable half-maximal effective concentration (EC₅₀). The EC₅₀ of free radical scavenging activity (27.6 μg/mL), antioxidant activity (23.00 μg/mL), and in vitro anti-inflammatory activity (15.52 μg/mL) signifies that CDs can be potential therapeutic agents.

Heavy metal ion detection using green precursor derived carbon dots

The discovery of carbon dots (CDs) for environmental remediation has gained awareness because of the diverse economically viable and environmental friendly green precursors generated from biowastes and biomass compared to the toxic inorganic quantum dots and CDs prepared from chemical precursors. This review presents the recent progress in green CDs, including their synthesis methods and sensing applications for the detection of heavy metal ions such as Iron (III), Mercury (II), Copper (II), Chromium (VI), Lead (II), Arsenic (III), Cobalt (II), Aluminum (III), Silver (I), and Gold (III) which are prominent environmental pollutants. The comparison based on selectivity, sensitivity, quantum yield, detection limit, linear concentration range, and sensing mechanisms are also reported. This review also covers the performance of doped green CDs using heteroatoms, toward the detection of heavy metal ions. Apart from the future perspectives, this review provides a general guide to use such environmental friendly CDs to detect harmful pollutants.

Microwave-assisted synthesis of nitrogen-doped carbon dots using prickly pear as the carbon source and its application as a highly selective sensor for Cr(VI) and as a patterning agent

Preparation of water-dispersible carbon dots from inexpensive natural carbon precursors and its application for purposes such as sensing, bio-imaging and patterning agents is showing growing interest in recent years. In this study, we have reported the preparation of nitrogen-doped carbon dots (N-CDs) using prickly pear as the carbon source and m-xylylenediamine as the nitrogen source using a one-step microwave-assisted synthetic process. The N-CDs prepared were characterized on the basis of elemental analysis, XPS, powder-XRD, FT-IR, Raman, TEM, UV-vis and fluorescence spectroscopy. Doping of nitrogen in the N-CDs made them highly fluorescent and the study on their ion-recognition property revealed that they detect highly toxic Cr(VI) with high selectivity and sensitivity (LOD, 0.04 μM) and without interference from the other ions used in this study. By immobilizing these N-CDs onto filter paper, sensor strips were prepared for on-site monitoring/field applications and they were successfully used for the detection of Cr(VI) in water. Detailed spectral analysis revealed that the mechanism of Cr(VI) sensing involved a phenomenon called the "inner filter effect" and analysis of the fluorescence lifetime data suggested the "static quenching" of fluorescence intensity. These N-CDs were used to prepare fluorescent carbon ink and were successfully used as patterning agents.

Rosmarinic Acid-Capped Silver Nanoparticles for Colorimetric Detection of CN- and Redox-Modulated Surface Reaction-Aided Detection of Cr(VI) in Water

Rosmarinic acid-capped silver nanoparticles (Ro-AgNPs) were prepared and applied as a probe for selective colorimetric detection of cyanide (CN-) and chromium(VI) [Cr(VI)] under different conditions in aqueous media. The carbon atom of CN- interacts with the AgNPs, and the carbon atom donates electrons from the HOMO to the vacant orbitals of the coordinatively unsaturated surface atom (Ag0). After donating electrons, CN- attached onto the surface of the nanoparticles becomes very reactive and interacts with dissolved oxygen and generates reactive oxygen species (ROS) such as superoxide (O2 -), singlet oxygen (1O2), and so forth. In this process, Ag0 oxidizes to Ag+ and combines with CN- forming water-insoluble AgCN, and the ROS (O2 -) formed reacts with Ag/Ag+ to form Ag2O. The oxidation of Ag0 to Ag+ resulted in dissolution of AgNPs, which causes disappearance of the surface plasmon resonance band and color change from yellow to colorless. For detection of Cr(VI), ascorbic acid and CN- were added first; the ascorbic acid replaced the rosmarinic acid and then reduced the added Cr(VI) to Cr(III), and, in this process, ascorbic acid was oxidized to dehydroascorbic acid, which moved away from the nanoparticles' surface. CN- then interacted with the surface Ag0 atom, got activated, and interacted with dissolved oxygen forming Ag+ and ROS, which then followed the same process as described for CN- to form AgCN and Ag2O with a color change. The limits of detection were found to be 0.01 and 0.03 μM for CN- and Cr(VI), respectively. The material was also used for sensing CN- and Cr(VI) in real samples, and the results obtained were satisfactory. For field application, agarose-based strips were prepared by immobilizing the nanoparticles onto the agarose film and successfully used for the detection of CN- and Cr(VI) in water.

Sulfur-doped carbon dots@polydopamine-functionalized magnetic silver nanocubes for dual-modality detection of norovirus

Synergistic dual-mode optical platforms are up-and-coming detection tools in the diagnosis and management of infectious diseases. Here, novel dual-modality fluorescence (FL) and surface-enhanced Raman scattering (SERS) techniques have been integrated into a single probe for the rapid and ultrasensitive detection of norovirus (NoV). The developed FL-SER-based biosensor relies on the dual-signal enhancements of newly synthesized sulfur-doped agar-derived carbon dots (S-agCDs). The antigen-antibody immunoreaction results in forming a core-satellite immunocomplex between anti-NoV antibody-conjugated S-agCDs and polydopamine-functionalized magnetic silver nanocubes [poly (dop)-MNPs-Ag NCs]. By deploying an immunomagnetic enrichment protocol and performing the SERS modality on a single-layer graphene substrate, norovirus-like particles (NoV-LPs) were detected across a wide range of 1 fg mL^-1 - 10 ng mL^-1 with an excellent limit of detection of 0.1 fg mL^-1. The combined advantage of the dual-signaling properties of the biosensor was demonstrated using FL confocal imaging for "hotspots" tracking prior to SERS detection of clinical NoV in fecal specimen down to ⁓10 RNA copies mL^-1. The proposed dual-modality biosensor's performance increases the prospect of a rapid and low-cost sensitive NoV detection and surveillance option for public health.

Effect of heteroatom-doped carbon quantum dots on the red emission of metal-conjugated phthalocyanines through hybridization

Quantum dots (QDs) are significant fluorescent materials for energy transfer studies with phthalocyanines (Pcs) and phthalocyanine (Pc)-like biomolecules (such as chlorophylls). Carbon-based QDs, especially, have been used in numerous studies concerning energy transfer with chlorophylls, but the numbers of studies concerning energy transfer between phthalocyanines and carbon-based QDs are limited. In this study, peripherally, hydroxythioethyl terminal group substituted metal-free phthalocyanine (H₂ Pc) and zinc phthalocyanine (ZnPc) were noncovalently (electrostatic and/or π-π interaction) attached to carbon QDs containing boron and nitrogen to form QD-Pc nanoconjugates. The QD-Pc conjugates were characterized using different spectroscopic techniques (Fourier transform infrared spectroscopy and transmission electron microscopy). The absorption and fluorescence properties of QD-Pc structures in solution were studied. It was found that the quantum yields of the QDs slightly decreased from 30% to 25% upon doping the QDs with heteroatoms B and N. Förster resonance energy transfer efficiency was calculated as 33% for BCN-QD/ZnPc. For the other conjugates, almost no energy transfer from QDs to Pc cores was observed. It was shown that the energy transfer between QDs to Pc cores was completely different from the energy transfer between QDs and photosynthetic pigments, and therefore we concluded that heteroatom doping in the QD structure and the existence of zinc metal in the phthalocyanine structure is obligatory for an efficient energy transfer.

Chromium (VI) detection by microbial carbon dots: Microwave synthesis and mechanistic study

Functionalized carbon dots (CDs) derived from Citrobacter freundii bacterial cells were used for selective detection of Cr(VI). A microwave-heating-based green synthesis approach is adopted to produce functionalized CDs from C. freundii bacterial cells (CF-CDs). The reaction was carried out in a 500 W microwave digester at 200°C for 20 min. The supernatant was filtered with a 0.2 µm filter and highly monodisperse CDs were obtained. Inherent functionalization of CF-CDs with nitrogen and oxygen-containing functional groups made them extremely selective toward Cr(VI) with a lower limit of detection of ~1.7 ppm. More importantly, CF-CDs could distinguish between Cr(VI) and Cr(III), which is highly desirable for practical applications. The fabricated sensor had a dual linear response range between 0 and 50 µM and 50-250 µM. The synthesized CDs were inherently functionalized which made them highly selective for Cr(VI) detection. CF-CDs also possess high stability over long storage period. This study reports the facile synthesis and characterization of a highly selective sensor for Cr(VI). As opposed to similar CDs sensors reported for Cr(VI), based on inner-filter effect, CF-CDs exhibit a strong, specific interaction toward Cr(VI), indicated by the large binding constant.

Top-Down N-Doped Carbon Quantum Dots for Multiple Purposes: Heavy Metal Detection and Intracellular Fluorescence

In the present study, we successfully synthesized N-doped carbon quantum dots (N-CQDs) using a top-down approach, i.e., hydroxyl radical opening of fullerene with hydrogen peroxide, in basic ambient using ammonia for two different reaction times. The ensuing characterization via dynamic light scattering, SEM, and IR spectroscopy revealed a size control that was dependent on the reaction time, as well as a more pronounced -NH2 functionalization. The N-CQDs were probed for metal ion detection in aqueous solutions and during bioimaging and displayed a Cr3+ and Cu2+ selectivity shift at a higher degree of -NH2 functionalization, as well as HEK-293 cell nuclei marking.

Photophysical Investigation of a Benzimidazole Derivative and Its Applications in Selective Detection of Fe3+, Thermosensing and Logic Gates

The fluorescence based applications such as chemosensing of Fe³⁺ ion, temperature sensing, NOR-gate molecular logic operations, and fluorescent ink were achieved using an expired medicine namely Pantoprazole (sensor1) which is a derivative of benzimidazole class. The phenomenon of quenching was a basic principle used in sensing Fe³⁺. We found that there was a combined effect of dynamic and static processes in quenching of fluorescence of sensor1. To confirm the selectiveness of sensor1, we performed interference experiments with other metal ions. There was no interference between these metal ions and Fe³⁺. The low LOD value of 1.032 µM suggested that the molecule is highly sensitive towards Fe³⁺. A high quantum yield of 8.087% increased the possibility of using sensor1 for light applications. There was a 2:1 stoichiometric ratio between sensor1 and Fe³⁺. The FTIR data analysis confirmed the presence of functional groups S = O, C-O-C, etc. The average particle size found with the DLS method was 130.5 nm. The zeta potential of -12.7 mV indicated that sensor1 is quite stable in solution form. For logic gate application EDTA (Ethylenediaminetetraaceticacid) and Fe³⁺ were considered as inputs and fluorescence intensity was taken as an output. In thermal sensing application, the high value of activation energy i.e. 908 meV and relative sensitivity of 1.2% ⁰C^-1 affirmed that sensor1 can be used for thermal applications. The sensor1 was also apt for fluorescent ink application. Hence this investigation deduced that sensor1 can be a potential candidate for such applications over other conventional synthesized fluorescent probes.

Green synthesis of carbon dots and their applications

Carbon dots (CDs) are nanoparticles with tunable physicochemical and optical properties. Their resistance to photobleaching and relatively low toxicity render them attractive alternatives to fluorescent dyes and heavy metal-based quantum dots in the fields of bioimaging, sensing, catalysis, solar cells, and light-emitting diodes, among others. Moreover, they have garnered considerable attention as they lend themselves to green synthesis methods. Increasingly, one-pot syntheses comprising exclusively of renewable raw materials or renewable refined compounds are gaining favor over traditional approaches that rely on harsh chemicals and energy intensive conditions. The field of green CD synthesis is developing rapidly; however, challenges persist in ensuring the consistency of their properties (e.g., fluorescence quantum yield) relative to conventional preparation methods. This has mostly limited their use to sensing and bioimaging, leaving opportunities for development in optoelectronic applications. Herein, we discuss the most common green CD synthesis and purification methods reported in the literature and the renewable precursors used. The physical, chemical, and optical properties of the resulting green-synthesized CDs are critically reviewed, followed by a detailed description of their applications in sensing, bioimaging, biomedicine, inks, and catalysis. We conclude with an outlook on the future of green CD synthesis. Future research efforts should address the broad knowledge gap between CDs synthesized from renewable versus non-renewable precursors, focusing on discrepancies in their physical, chemical, and optical properties. The development of cost effective, safe, and sustainable green CDs with tunable properties will broaden their implementation in largely untapped applications, which include drug delivery, photovoltaics, catalysis, and more.

A review of the green carbon dot synthesis literature outlining the various precursors used, synthesis and purification methods employed, the resulting physicochemical properties of the carbon dots, and their applications.

Green Route for the Synthesis of Fluorescent Carbon Nanoparticles from Circassian Seeds for Fe(III) Ion Detection

A facile and green strategy was carried out for the preparation of fluorescent carbon nanoparticles (CNp) using non-toxic circassian seeds as carbon precursor (CNp, named ACNp). The surface of amorphous ACNp is latched with different surface moieties such as hydroxyl, carbonyl, ether and amino groups and it is confirmed by FTIR and XPS. These functionalities provide high solubility and stability to ACNp in aqueous medium. The surface of ACNp is highly negatively charged due to the presence of oxygen rich functional groups and it is confirmed by zeta potential. A reasonably good quantum yield (QY) of 5.1% is obtained for ACNp compared to other CNp derived from bioprecursors without any surface passivation. Circassian seeds are self sufficient for the synthesis of N doped CNp. The excitation dependent fluorescence property of ACNp is invariant under ionic and thermal environments. They exhibit good selectivity towards Fe³⁺ ions via static quenching mechanism with detection limit of 32.7 µM.

Natural source of carbon dots from part of a plant and its applications: a review

Carbon dots (CDs) are carbon nanoparticles with a size of less than 10 nm, and are synthesized from various sources; they have been of great interest to scientists worldwide due to their unique optical, electrical, and chemical properties. Sources of carbon are inexpensive and can be classified as a renewable natural resources. Many researchers use CDs because of their low toxicity, better water solubility, high biocompatibility, and stable photoluminescence. The simple methods for producing CDs are hydrothermal and use inexpensive equipment, have low energy consumption, simple manipulation, and one-step preparation. Since the discovery of CDs, researchers have used them in various applications such as sensing, bioimaging, drug delivery, and catalysis. In this review, CDs synthesized from natural resources such as samples from herbs, roots, leaves, flowers, and fruit and some applications are described. This review provides a summary of carbon dots that is expected to provide further information for development of new CDs.

The exploitation of thermophile resources in hot springs: fluorescent carbon dots derived from Ureibacillus thermosphaericus for multicolour cellular imaging and selectivity detection of heavy metals

Microbial biomass, as an environmentally friendly resource, has attracted considerable attention as a green biomaterial for the production of unique and functionalised CDs; however, further exploration is required to characterise CDs derived from bacteria. In this study, a green biomaterial (fluorescence CDs-HS18) was successfully synthesised via a hydrothermal method from Ureibacillus thermosphaericus HS-18 specimens isolated from a hot spring. The prepared CDs-HS18 possess excellent photo-physical properties, outstanding fluorescence capabilities, and high biocompatibility, which make them desirable candidates for multi-mode imaging applications. Our results demonstrate that the prepared CDs can selectively stain the membrane of the biological cells tested and can be rapidly distributed to all parts of the leaf via the veins and intercellular interstitium through transpiration. Additionally, CDs-HS18 are likely to enter the digestive tract of Microworms through ingestion and spread rapidly through the entire body and may finally be excreted through the anus. Furthermore, the rapid and highly selective detection platform based on CDs-HS18 exhibited an excellent linear response for Cr6+ between 0 and 9 μM, with a detection limit of 36 nM. This research will expand the understanding of the characteristics of green biomaterials derived from bacteria and widen the application scope of hot spring resources.

Novel fluorescent nitrogen-doped carbon dots derived from Panax notoginseng for bioimaging and high selectivity detection of Cr6

Carbon dots (CDs) and photoluminescent carbon dots (Pn-CDs) are promising nanomaterials due to their bioimaging applications and have attracted considerable attention because of their excellent stability, good biocompatibility, and low biotoxicity. Here, the Pn-CDs and highly fluorescent nitrogen-doped CDs (Pn N-CDs) derived from Panax notoginseng were successfully synthesized by a simple hydrothermal method. Pn N-CDs exhibit optical properties and stability superior to those of Pn-CDs and can be better used as fluorescent dyes and probes in biological imaging. The obtained Pn N-CDs can be effectively applied to the imaging of bacteria, fungi, plant cells, and protozoa. In addition, Pn N-CDs can perform specific staining on the membranes of all tested cells. The in vivo imaging of mice revealed that Pn N-CDs exhibit nontoxicity and good biocompatibility and biodistribution. Furthermore, Pn N-CDs can be utilized as fluorescent probes for the rapid and highly selective detection of Cr⁶⁺. Hence, a simple, cost-effective, scalable, and green synthetic approach based on traditional Chinese medicine-derived CDs can be used to develop biolabeling, membrane targeting, and optical sensing probes.