A universal facile synthesis of nitrogen and sulfur co-doped carbon dots from cellulose-based biowaste for fluorescent detection of Fe3+ ions and intracellular bioimaging

Carbon dots as versatile nanomaterials in sensing and imaging: Efficiency and beyond

Carbon dots (CDs) have emerged as a versatile and promising carbon-based nanomaterial with exceptional optical properties, including tunable emission wavelengths, high quantum yield, and photostability. CDs are appropriate for various applications with many benefits, such as biocompatibility, low toxicity, and simplicity of surface modification. Thanks to their tunable optical properties and great sensitivity, CDs have been used in sensing as fluorescent probes for detecting pH, heavy metal ions, and other analytes. In addition, CDs have demonstrated potential as luminescence converters for white organic light-emitting diodes and light emitters in optoelectronic devices due to their superior optical qualities and exciton-independent emission. CDs have been used for drug administration and bioimaging in the biomedical field due to their biocompatibility, low cytotoxicity, and ease of functionalization. Additionally, due to their stability, efficient charge separation, and low recombination rate, CDs have shown interesting uses in energy systems, such as photocatalysis and energy conversion. This article highlights the growing possibilities and potential of CDs as adaptable nanomaterials in a variety of interdisciplinary areas related to sensing and imaging, at the same time addressing the major challenges involved in the current research and proposing scientific solutions to apply CDs in the development of a super smart society.

Carbon dots-adorned silver nanoparticles as a straightforward sustainable colorimetric sensor for the rapid detection of ketotifen in eye drops and aqueous humor

The rapid and accurate detection of drug molecules in pharmaceutical formulations and biological samples is of paramount importance. In this research article, we present a novel colorimetric sensor based on carbon dots decorated silver nanoparticles (CDs/AgNPs) for the rapid detection of ketotifen (KTF), a widely used antihistamine drug. The CDs were synthesized via a facile one-step microwave-assisted method and subsequently conjugated onto AgNPs through a simple adsorption process, forming a stable CDs/AgNPs composite. The resulting composite exhibited unique optical properties, including a strong absorption peak at 410 nm with remarkable intensity reduction and color changes upon the addition of KTF. The developed colorimetric sensor exhibited a wide linear range of 3.0-40.0 µg mL-1 (R2 = 0.9996), with a %RSD of 2.41, and a low limit of detection (LOD) of 0.981 µg mL-1. Furthermore, the sensor's practical applicability was evaluated by successfully detecting KTF in eye drops and artificial aqueous humor, demonstrating a remarkable percentage recovery exceeding 96.0 %. Finally, a comprehensive evaluation of the greenness and blueness of the method was performed using analytical eco-scale, GAPI, AGREEprep, and BAGI tools. The results of these assessments indicate its exceptional sustainability. Overall, the proposed method holds significant potential for applications in pharmaceutical quality control and therapeutic monitoring, contributing to improved patient care and drug safety in the field of ophthalmology.

Electrostatically induced Furfural-Derived carbon Dots-CdS hybrid for solar Light-Driven hydrogen production

Carbon dots (CDs) exhibit distinctive optical, electronic, and physicochemical properties, rendering them effective cocatalysts to enhance the photocatalytic performance of light-absorbing materials. The interplay between CDs and substrates is pivotal in manipulating photogenerated charge separation, transfer, and redistribution, significantly influencing overall photocatalytic efficiency. This study introduces a novel electrostatic interaction strategy to interface positively charged CdS nanorods (CdS NRs) with negatively charged furfural-derived CDs. The resulting optimized composite (25-CDs@CdS NRs), showcases photocatalytic hydrogen production at a rate of 1076 μmol g-1h-1. Experimental analyses and theoretical simulations offer insights into the structure-activity relationship, underscoring the crucial role of enhanced electrostatic interaction between CDs and CdS NRs in facilitating efficient charge transfer, activating reaction sites, and improving reaction kinetics. This research establishes an adaptable strategy for integrating CDs with metal-based semiconductors, opening new avenues for developing photocatalytic hybrid assemblies.

o-phenylenediamine Derived Fluorescent Carbon Quantum dots for Detection of Hg(II) in Environmental Water

With the expansion of human activities, the consequent influx of mercury (Hg) into the food chain and the environment is seriously threatening human life. Herein, nitrogen and sulfur co-doped fluorescent carbon quantum dots (yCQDs) were prepared via a hydrothermal method using o-phenylenediamine (OPD) and taurine as precursors. The morphological characteristics as well as spectral features of yCQDs indicated that the photoluminescence mechanism should be the molecular state fluorophores of 2, 3-diaminophenothiazine (oxOPD), which is the oxide of OPD. The as-synthesized yCQDs exhibited sensitive recognition of Hg2+. According to the investigation in combination of UV-Vis absorption spectra, time-resolved fluorescence spectra and quantum chemical calculations, the abundant functional groups on the surface of yCQDs allowed Hg2+ to bind with yCQDs through various interactions, and the formed complexes significantly inhibited the absorption of excitation light, resulting in the static fluorescence quenching of yCQDs. The proposed yCQDs was utilized for Hg2+ sensing with the limit of detection calculated to be 4.50 × 10- 8 M. Furthermore, the recognition ability of yCQDs for Hg2+ was estimated in tap water, lake water and bottled water, and the results indicated that yCQDs have potential applications in monitoring Hg2+.

N, S/P co-doped hemicellulose-based carbon dots with tunable fluorescence for anti-counterfeiting

Based on the status quo of high energy consumption and low utilization of nonfibrous components in traditional pulp and paper industry, a sustainable and facile approach was proceeded to realize the high-value utilization of hemicelluloses from papermaking waste liquor. The hemicellulose waste produced by ethanol precipitation in pre-hydrolysis liquor (PHL), was directly used to fabricate carbon dots (CDs) via a hydrothermal method. The hydrothermal carbonization and heteroatoms doping contributed to the sp2 conjugated domains and surface defect states of CDs, thus creating the bright blue (N-CDs), deep cyan (N/S-CDs), and light cyan (N/P-CDs) fluorescence under UV radiation. The XPS analysis and density functional theory (DFT) calculations demonstrated that the large sp2 conjugated system and the synergistic effect of CO, N-(C)3, CS, and PO groups promoted the narrow of band gap and the red-shift of fluorescence emission. Importantly, the prepared CDs grew in situ on cotton fibers, showed excellent fluorescent performance. The obtained CDs could be also utilized to prepare anti-counterfeiting film and ink due to their excellent optical features, verifying the great potential application as security material. The feasible strategy of the high-value conversion of biomass waste opens a window of opportunity for the practical anti-counterfeiting utilizations.

Alginate based films integrated with nitrogen-functionalized carbon dots and layered clay for active food packaging applications

The applications of alginate derived from seaweed polysaccharide in food packaging are restricted due to their inherent deficient antibacterial, antioxidant and UV barrier properties. In this study, nitrogen-functionalized carbon dots (NCDs) with active functions (0.5-3 %) and layered clay (1 %) with barrier property were introduced to construct alginate based active films via solution casting method. The results showed that the synthesized spherical NCDs had a particle size of 2-3 nm, and the internal structure of NCDs was similar to graphene, with a large number of active groups (-NH2, -OH, etc.) on the surface. Infrared analysis revealed that NCDs could form strong hydrogen bonds with alginate matrix, which slowed down the deterioration of mechanical properties and reduced the surface wettability. With the addition of NCDs, active functions and surface hydrophobicity of the active films were enhanced significantly (P < 0.05). When the amount of NCDs reached 3 %, UV barrier, antioxidant and antibacterial properties of the active films were increased by 50.0 %, 61.1 % and 70.1 %, respectively. The addition of NCDs could enhance the anti-browning ability of alginate based coatings and extend the shelf life of banana significantly. Therefore, a suitable amount of NCDs (1-2 %) and layered clay (1 %) can synergistically improve comprehensive performance of alginate based films and promote their food packaging application used as active films/inner coatings.

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.

Lignocellulosic Biomass-Based Carbon Dots: Synthesis Processes, Properties, and Applications

Carbon dots (CDs), a new type of carbon-based fluorescent nanomaterial, have attracted widespread attention because of their numerous excellent properties. Lignocellulosic biomass is the most abundant renewable natural resource and possesses broad potential to manufacture different composite and smart materials. Numerous studies have explored the potential of using the components (such as cellulose, hemicellulose, and lignin) in lignocellulosic biomass to produce CDs. There are few papers systemically aiming in the review of the state-of-the-art works related to lignocellulosic biomass-derived CDs. In this review, the significant advances in synthesis processes, formation mechanisms, structural characteristics, optical properties, and applications of lignocellulosic biomass-based CDs such as cellulose-based CDs, hemicellulose-based CDs and lignin-based CDs in latest research are reviewed. In addition, future research directions on the improvement of the synthesis technology of CDs using lignocellulosic biomass as raw materials to enhance the properties of CDs are proposed. This review will serve as a road map for scientists engaged in research and exploring more applications of CDs in different science fields to achieve the highest material performance goals of CDs.

One-Pot, Optimized Microwave-Assisted Synthesis of Difunctionalized and B-N Co-Doped Carbon Dots: Structural Characterization

In this work, we employed a novel microwave-assisted synthesis method to produce nitrogen and boron co-doped carbon dots (B-N co-doped CDs). To achieve optimal synthesis, we conducted a comprehensive parameter modulation approach, combining various synthesis temperatures, times, and precursor concentrations, while keeping the power constant at 150 W and pH 5. Using maximum fluorescence emission as our response variable, the best conditions were identified as 120 °C, 3 min, and a precursor concentration of 1 mg/mL. Characterization using field emission scanning electron microscopy revealed these CDs to have a spherical morphology with an average size of 10.9 ± 3.38 nm. Further high-resolution transmission electron microscopy showed an interplanar distance of 0.23 nm, which is in line with prior findings of CDs that present a 0.21 nm distance corresponding to the (100) plane of graphite. Optical properties were ascertained through UV-vis absorption, identifying distinct π-π* and n-π* transitions. Fluorescence spectroscopy highlighted an emission peak at 375 nm when excited at 295 nm, achieving a quantum yield of 56.7%. Fourier-transform infrared spectroscopy and Raman spectroscopy analyses confirmed the boronic acid and amine groups' presence, underscoring the graphitic nature of the core and the co-doping of boron and nitrogen. These empirical observations were compared with theoretical investigations through simulated Raman spectra, proposing a potential structure for the CDs. X-ray photoelectron spectroscopy further endorsed the co-doping of nitrogen and boron, along with the detection of the specified functional groups. All these characteristics could lend this nanomaterial to different types of applications such as fluorescent probes for a broad range of analytes and for fluorescent cell imaging.

Development of biomass waste-based carbon quantum dots and their potential application as non-toxic bioimaging agents

Over recent years, carbon quantum dots (CQDs) have advanced significantly and gained substantial attention for their numerous benefits. These benefits include their simple preparation, cost-effectiveness, small size, biocompatibility, bright luminescence, and low cytotoxicity. As a result, they hold great potential for various fields, including bioimaging. A fascinating aspect of synthesizing CQDs is that it can be accomplished by using biomass waste as the precursor. Furthermore, the synthesis approach allows for control over the physicochemical characteristics. This paper unequivocally examines the production of CQDs from biomass waste and their indispensable application in bioimaging. The synthesis process involves a simple one-pot hydrothermal method that utilizes biomass waste as a carbon source, eliminating the need for expensive and toxic reagents. The resulting CQDs exhibit tunable fluorescence and excellent biocompatibility, making them suitable for bioimaging applications. The successful application of biomass-derived CQDs has been demonstrated through biological evaluation studies in various cell lines, including HeLa, Cardiomyocyte, and iPS, as well as in medaka fish eggs and larvae. Using biomass waste as a precursor for CQDs synthesis provides an environmentally friendly and sustainable alternative to traditional methods. The resulting CQDs have potential applications in various fields, including bioimaging.

Plastic Waste-Derived Carbon Dots: Insights of Recycling Valuable Materials Towards Environmental Sustainability

Carbon dots (CDs) or carbon quantum dots (CQDs) have emerged as rising stars in the carbon family due to their diverse applications in various fields. CDs are spherical particles with a well-distributed size of less than 10 nm. Functional CDs are promising nanomaterials with low toxicity, low cost, and enormous applications in the field of bioimaging, optoelectronics, photocatalysis, and sensing. Plastic is non-biodegradable and hazardous to the environment, however extremely durable and used in abundance. During the COVID-19 pandemic, the use of plastic waste, particularly masks, goggles, face shields, and shoe cover, has increased tremendously. It needs to be recycled in a productive way as plastic wastes take hundreds or thousands of years to degrade naturally. The conversion of plastic waste into magnificent CDs has been reported as one of the key alternatives for environmental sustainability and socio-economic benefits. In this review, synthetic routes for the conversion of plastic wastes into CDs utilizing hydrothermal, solvothermal, pyrolysis, flash joule heating, and characterization of these CDs using different techniques, such as Fourier-transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, and transmission electron microscope, have been discussed. Furthermore, potential applications of these plastic-derived CDs in sensing, catalysis, agronomics, and LED lights are summarized herein.

Heating-free synthesis of red emissive carbon dots through separated processes of polymerization and carbonization

Polymerization and carbonization are believed as two basic processes for the bottom-up synthesis of carbon dots (CDs). Since these two processes usually occur simultaneously due to the high reaction temperature and fast reaction rate, it is still a challenge to separate and control these two processes. In the present work, we reported a new room temperature method, which achieved the separated and controlled polymerization and carbonization processes. The polymerization process is realized by dissolving o-phenylenediamine (OPD) in ethanol at room temperature, and finally obtained polymer dots (PDs) without any lattice with a sphere size of 29.6 nm. The carbonization process begins in a manual way by adding concentrated sulfuric acid. After carbonization, CDs (noted as CPDs in this work) with a size of 3.6 nm and a clear lattice can be obtained. Importantly, the separated polymerization and carbonization make us possible to adjust the composition or interactions of intermediate products during the synthesis process. As a prototype, we added acetic acid (AA) additives into OPD precursors during the polymerization stage. Due to the crosslink enhanced emission (CEE) effect via hydrogen bonds which are produced by the amide groups from AA reaction products with H in the -NH₃⁺ or aromatic ring, the resulted CPDs show improved PLQY from an initial 6.87% (without AA) to 16.47%. The current work realized the separated and controllable polymerization and carbonization processes, opening up the door for tuning the composition and interactions of intermediate products before carbonization.

Carbon dots: Types, preparation, and their boosted antibacterial activity by photoactivation. Current status and future perspectives

Carbon dots (CDs) correspond to carbon-based materials (CBM) with sizes usually below 10 nm. These nanomaterials exhibit attractive properties such us low toxicity, good stability, and high conductivity, which have promoted their thorough study over the past two decades. The current review describes four types of CDs: carbon quantum dots (CQDs), graphene quantum dots (GQDs), carbon nanodots (CNDs), and carbonized polymers dots (CPDs), together with the state of the art of the main routes for their preparation, either by "top-down" or "bottom-up" approaches. Moreover, among the various usages of CDs within biomedicine, we have focused on their application as a novel class of broad-spectrum antibacterial agents, concretely, owing their photoactivation capability that triggers an enhanced antibacterial property. Our work presents the recent advances in this field addressing CDs, their composites and hybrids, applied as photosensitizers (PS), and photothermal agents (PA) within antibacterial strategies such as photodynamic therapy (PDT), photothermal therapy (PTT), and synchronic PDT/PTT. Furthermore, we discuss the prospects for the possible future development of large-scale preparation of CDs, and the potential for these nanomaterials to be employed in applications to combat other pathogens harmful to human health. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Polysaccharide-based C-dots and polysaccharide/C-dot nanocomposites: fabrication strategies and applications

C-dots are a new class of materials with vast applications. The synthesis of bio-based C-dots has attracted increasing attention in recent years. Polysaccharides being the most abundant natural materials with high biodegradability and no toxicity have been the focus of researchers for the synthesis of C-dots. C-dots obtained from polysaccharides are generally fabricated via thermal procedures, carbonization, and microwave pyrolysis. Small size, photo-induced electron transfer (PET), and highly adjustable luminosity behavior are the most important physical and chemical properties of C-dots. However, C-dot/polysaccharide composites can be introduced as a new generation of composites that combine the features of both C-dots and polysaccharides having a wide range of applications in biomedicines, biosensors, drug delivery systems, etc. This review demonstrates the features, raw materials, and methods used for the fabrication of C-dots derived from different polysaccharides. Furthermore, the properties, applications, and synthesis conditions of various C-dot/polysaccharide composites are discussed in detail.

Flexible and Stretchable Carbon-Based Sensors and Actuators for Soft Robots

In recent years, the emergence of low-dimensional carbon-based materials, such as carbon dots, carbon nanotubes, and graphene, together with the advances in materials science, have greatly enriched the variety of flexible and stretchable electronic devices. Compared with conventional rigid devices, these soft robotic sensors and actuators exhibit remarkable advantages in terms of their biocompatibility, portability, power efficiency, and wearability, thus creating myriad possibilities of novel wearable and implantable tactile sensors, as well as micro-/nano-soft actuation systems. Interestingly, not only are carbon-based materials ideal constituents for photodetectors, gas, thermal, triboelectric sensors due to their geometry and extraordinary sensitivity to various external stimuli, but they also provide significantly more precise manipulation of the actuators than conventional centimeter-scale pneumatic and hydraulic robotic actuators, at a molecular level. In this review, we summarize recent progress on state-of-the-art flexible and stretchable carbon-based sensors and actuators that have creatively added to the development of biomedicine, nanoscience, materials science, as well as soft robotics. In the end, we propose the future potential of carbon-based materials for biomedical and soft robotic applications.

Research Progress in the Synthesis of Carbon Dots and Their Application in Food Analysis

Food safety is connected to public health, making it crucial to protecting people's health. Food analysis and detection can assure food quality and effectively reduce the entry of harmful foods into the market. Carbon dots (CDs) are an excellent choice for food analysis and detection attributable to their advantages of good optical properties, water solubility, high chemical stability, easy functionalization, excellent bleaching resistance, low toxicity, and good biocompatibility. This paper focuses on the optical properties, synthesis methods, and applications of CDs in food analysis and detection, including the recent advances in food nutritional composition analysis and food quality detection, such as food additives, heavy metal ions, foodborne pathogens, harmful organic pollutants, and pH value. Moreover, this review also discusses the potentially toxic effects, current challenges, and prospects of CDs in basic research and applications. We hope that this review can provide valuable information to lay a foundation for subsequent research on CDs and promote the exploration of CDs-based sensing for future food detection.

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.

Carbon dots-based nanomaterials for fluorescent sensing of toxic elements in environmental samples: Strategies for enhanced performance

Rapid industrialization and manufacturing expansion have caused heavy metal pollution, which is a critical environmental issue faced by global population. In addition, the disadvantages presented by conventional detection methods such as the requirement of sophisticated instruments and qualified personnel have led to the development of novel nanosensors. Recently, carbon dots (CDs) have been presented as a multifunctional nanomaterial alternative for the accurate detection of heavy metal ions in water systems. The capacity of CDs to detect contaminants in wastewater -including heavy metals- can be found in the literature; however, to the best of our knowledge, none of them discusses the most recent strategies to enhance their performance. Therefore, in this review, beyond presenting successful examples of the use of CDs for the detection of metal ions, we further discuss the strategies to enhance their photoluminescence properties and their performance for environmental monitoring. In this manner, strategies such as heteroatom-doping and surface passivation are reviewed in detail, as well as describing the mechanisms and the effect of precursors and synthesis methods. Finally, the current challenges are described in detail to propose some recommendations for further research.

Preparation, Properties, and Application of Lignocellulosic-Based Fluorescent Carbon Dots

Carbon dots (CDs) are a relatively new type of fluorescent carbon material with excellent performance and widespread application. As the most readily available and widely distributed biomass resource, lignocellulosics are a renewable bioresource with great potential. Research into the preparation of CDs with lignocellulose (LC-CDs) has become the focus of numerous researchers. Compared with other carbon sources, lignocellulose is low cost, rich in structural variety, exhibits excellent biocompatibility,^[1] and the structures of CDs prepared by lignin, cellulose, and hemicellulose are similar. This Review summarized research progress in the preparation of CDs from lignocellulosics in recent years and reviewed traditional and new preparation methods, physical and chemical properties, optical properties, and applications of LC-CDs, providing guidance for the formation and improvement of LC-CDs. In addition, the challenges of synthesizing LC-CDs were also highlighted, including the interaction of different lignocellulose components on the formation of LC-CDs and the nucleation and growth mechanism of LC-CDs; from this, current trends and opportunities of LC-CDs were examined, and some research methods for future research were put forward.

Microwave-Assisted Green Synthesis of Carbon Quantum Dots Derived from Calotropis Gigantea as a Fluorescent Probe for Bioimaging

An eco-friendly, cost-effective, and convenient approach for synthesizing biocompatible fluorescent carbon quantum dots (CQDs) from the leaf extract of the medicinal plant Calotropis gigantea, commonly known as crown flower, has been demonstrated in this work. Fluorescence quantum yields of up to 4.24 percent were observed in as-synthesized CQDs. The size distribution of the as-synthesized CQDs varied from 2.7 to 10.4 nm, with a significant proportion of sp² and sp³ carbon groups verified by nuclear magnetic resonance analysis. The zeta potential of as-synthesized CQDs was measured to be -13.8 mV, indicating the existence of a negatively charged surface with incipient instability in aqueous suspension. Furthermore, as an alternative to organic or synthetic dyes, the development of simple, inexpensive, and non-destructive fluorescence-based staining agents are highly desired. In this regard, as-synthesized CQDs have shown remarkable fluorescent staining capabilities in this work and might be utilised as a suitable probe for optical and bio-imaging of bacteria, fungi, and plant cells.

Carbon Dots Embedded in Cellulose Film: Programmable, Performance-Tunable, and Large-Scale Subtle Fluorescent Patterning by in Situ Laser Writing

Fluorescent patterns with multiple functions enable high-security anti-counterfeiting labels. Complex material synthesis and patterning processes limit the application of multifunctional fluorescent patterns, so the technology of in situ fluorescent patterning with tunable multimodal capabilities is becoming more necessary. In this work, an in situ fluorescent patterning technology was developed using laser direct writing on solid cellulose film at ambient conditions without masks. The fluorescent intensity and surface microstructure of the patterns could be adjusted by programmable varying of the laser parameters simultaneously. During laser direct writing, carbon dots are generated in situ in a cellulose ester polymer matrix, which significantly simplifies the fluorescent patterning process and reduces the manufacturing cost. Interestingly, the tunable fluorescent intensity empowers the fabrication of visual stereoscopic fluorescent patterns with excitation dependence, further improving its anti-counterfeiting performance. The obtained fluorescent patterns still show ultrahigh optical properties after being immersed in an acid/base solution (pH 5-12) over one month. In addition, the anti-UV performance of the obtained laser-patterned film with transmittance around 90% is comparable to that of commercial UV-resistant films. This work provided an advanced and feasible approach to fabricating programmable, performance-tunable, subtle fluorescent patterns in large-scale for industrial application.

Waste tobacco leaves derived carbon dots for tetracycline detection: Improving quantitative accuracy with the aid of chemometric model

The recycling and reutilization of biomass wastes are significant for environmental protection and sustainable development. Recently, there have many studies on utilizing biomass wastes to produce carbon dots. Whereas, the spectrum shift effect that occurs in the quantitative application of carbon dots as fluorescent probes limits the accuracy of the quantitative analysis. In this work, waste tobacco leaves were used as the carbon source for synthesizing a novel carbon dots (CDs(WTL)) through a facile hydrothermal method. The CDs(WTL) possess a series of excellent properties, including good water solubility, well stability, and high fluorescence quantum yield. The fluorescent intensity of the CDs(WTL) can be quenched by tetracycline (TC) obviously, but there is a spectrum shift. In order to use the CDs(WTL) as fluorescent probes to quantify TC with higher accuracy, a quantification fluorescence model (QFM) was introduced to overcome this spectrum shift effect that often occurs. The coefficient of determination (R2) of traditional quantification model (TQ), partial least squares (PLS), and QFM are 0.9672, 0.9834, and 0.9991, respectively; the average relative predictive error (ARPE) of TQ, PLS, and QFM are 8.8%, 4.5%, and 3.9% for the spiked water samples, and 21.9%, 22.0%, and 2.9% for spiked tablet samples, respectively. The obtained results suggest that QFM is more accurate than PLS and TQ for the TC detection. By utilizing QFM, the spike recoveries (mean ± standard deviation) in three kinds of real tablet samples produced by different manufacturers are 98.9 ± 3.6%, 102.5 ± 6.2%, and 98.5 ± 2.7%, respectively; the spike recovery in river water samples is 99.4 ± 5.0%. In addition, high performance liquid chromatography (HPLC) was used as a reference method, the F and t tests suggest that there are no significant differences on the precision and accuracy between QFM and HPLC methods.

Ultrasonic-Assisted Synthesis of N-Doped, Multicolor Carbon Dots toward Fluorescent Inks, Fluorescence Sensors, and Logic Gate Operations

Over past decades, the multicolor carbon dots (M-CDs) have attracted enormous attentions due to their tunable photoluminescence and versatile applications. Herein, the nitrogen-doped (N-doped) M-CDs including green, chartreuse, and pink emissive CDs are successfully synthesized by ultrasonic treatment of kiwifruit juice with different additive reagents such as ethanol, ethylenediamine, and acetone. Owing to their strong fluorescence upon irradiation with 365 nm UV light, the highly water-soluble M-CDs present great potential in the anticounterfeit field as fluorescent inks. Particularly, the resulting green emission CDs (G-CDs) with excellent fluorescence and stability are applied as a label-free probe model for “on–off” detection of Fe3+. The fluorescence of G-CDs is significantly quenched by Fe3+ through static quenching. The nanoprobe demonstrates good selectivity and sensitivity toward Fe3+ with a detection limit of ~0.11 μM. Besides, the quenched fluorescence of G-CDs by Fe3+ can be recovered by the addition of PO43− or ascorbic acid (AA) into the CDs/Fe3+ system to realize the “off–on” fluorescent process. Furthermore, NOT and IMPLICATION logic gates are constructed based on the selection of Fe3+ and PO43− or AA as the inputs, which makes the G-CD-based sensors utilized as various logic gates at molecular level. Therefore, the N-doped M-CDs hold promising prospects as competitive candidates in monitoring the trace species, applications in food chemistry, anticounterfeit uses, and beyond.

Curauá-derived carbon dots: Fluorescent probes for effective Fe(III) ion detection, cellular labeling and bioimaging

This study reports the generation of curauá-derived carbon dots (C-dots) and their suitability for Fe(III) detection, bioimaging and FACS analysis. C-dots were generated from curauá (Ananas erectifolius) fibers by a facile one-step hydrothermal approach. They exhibited graphite-like structure with a mean diameter of 2.4 nm, high water solubility, high levels of carboxyl and hydroxyl functional groups, excitation-dependent multicolor fluorescence emission (in the range 450 nm - 560 nm) and superior photostability. C-dots were highly selective and effective for the detection of ferric Fe(III) ion in an aqueous medium with a detection limit of 0.77 μM in the linear range of 0-30 μM, a value much lower than the guideline limits proposed by the World Health Organization (WHO). In biological cell systems, C-dots were very well tolerated by B16F1 mouse melanoma and J774.A1 mouse macrophages cell lines, both of which effectively internalized C-dots in their cytoplasmic compartment. Finally, C-dots were effective probes for long-term live cell imaging experiments and multi-channel flow cytometry analysis. Collectively, our findings demonstrate that curauá-derived C-dots serve as versatile and effective natural products for Fe(III) ion sensing, labeling and bioimaging of various cell types. This study adds novel C-dots to the library of carbon-based probes and paves the way towards a sustainable conversion of a most abundant biomass waste into value-added products.

Recent studies on cellulose-based fluorescent smart materials and their applications: A comprehensive review

The progress of bio-based fluorescent smart materials and their multifunctional applications have attained increasing interest in the recent decades. Cellulose is among the cheapest and widespread raw material on earth which can be modified into diverse useful materials. This review summarizes the chemical modification of cellulose into smart fluorescent materials. This further highlights on the fabrication of the prepared fluorescent materials into films, fibers, paper strips, carbon dots, hydrogels and solutions which are applied for the sensing of toxic metals and anions, pH, bioimaging, common organic solvents, aliphatic and aromatic amines, nitroaromatics, fluorescent printing, coating, and anti-counterfeiting applications. Finally, the discussion about the upcoming investigations, challenges, and options open for the cellulose-based luminescence sensors are communicated. We believe that this review will appeal more and more attention and curiosity for the chemists, biochemists, and chemical engineers working with the synthesis of cellulose-based fluorescent materials for widespread applications.

Microwave-assisted green synthesis of fluorescent carbon quantum dots from Mexican Mint extract for Fe3+ detection and bio-imaging applications

Biomass-derived carbon quantum dots have drawn special interest owing to their admirable photostability, biocompatibility, fluorescence, high solubility, sensitivity and environmentally friendly properties. In the present work, the Carbon Quantum Dots (CQDs) was synthesized from the Plectranthus amboinicus (Mexican Mint) leaves via the microwave-assisted reflux method. The strong absorption peaks observed from UV-vis spectra at 291 and 330 nm corresponds to the π-π* and n-π* transitions, respectively, reveal the formation of CQDs. The synthesized CQDs showed bright blue fluorescence under UV irradiation with a fluorescence quantum yield of 17% and a maximum emission of 436 nm in the blue region at an excitation wavelength of 340 nm. The HRTEM analysis elucidates that the synthesized CQDs were crystalline and spherical in shape with a particle size of 2.43 ± 0.02 nm. The FT-IR spectroscopy confirms the presence of the different functional groups such as -OH, -CH, CO and C-O. The chemical composition of CQD was revealed through XPS analysis. The synthesized CQDs were used as a fluorescent probe to detect different metal ions, where high selectivity was obtained for Fe³⁺ ions through quenching phenomenon. The emission intensity of CQD showed a good linear relationship with R² = 0.9111 with the concentration of Fe³⁺ ions in the range of 0-15 μM. The fluorescence emission of CQD was turned OFF upon the binding of Fe³⁺ ions and turned - ON with the addition of ascorbic acid. With this fluorescent turn ON-OFF behaviour of CQD, the NOT and IMPLICATION logic gates were constructed and studied for different input conditions. The biocompatibility of CQD was tested via MTT assay using MCF7 breast cancer cell line, which revealed that CQD synthesized from the Mexican Mint leaves possess less cytotoxicity. Further, the prepared CQD was applied effectively as fluorescent probes in a cell imaging application.

Biocompatible sulfur nitrogen co-doped carbon quantum dots for highly sensitive and selective detection of dopamine

In this work, sulfur and nitrogen co-doped carbon quantum dots (S,N-CQDs) were prepared via one-pot hydrothermal treatment of EDTA disodium and sodium sulfide. The prepared S,N-CQDs were characterized by TEM, XRD, FT-IR, XPS, UV-vis absorption and fluorescence spectra to characterize their morphology, crystal structure, functional groups, elemental composition, and optical properties. It was found that S and N elements were successfully doped into the CQDs and the morphology was approximately spherical with an average particle size of 2.16 nm, in which the excitation/emission wavelengths were 350 and 420 nm, respectively. Compared with single element doped CQDs, double element doped CQDs have a higher quantum yield and excellent optical stability. Cell experiments showed that S,N-CQDs had good biocompatibility because they had no obvious toxicity on both normal cell lines and cancer cell lines. More importantly, based on the synergy of static quenching and dynamic quenching, the S,N-CQDs were used as effective fluorescent probes for sensitive detection of DA, with high anti-interference and low limit of detection. Based on the good biocompatibility of S,N-CQDs, the detection of dopamine in actual serum samples were carried out and the results showed an excellent recovery rate. Therefore, this work provides a dopamine sensor with a practical application prospect.

Doped-carbon dots: Recent advances in their biosensing, bioimaging and therapy applications

As a fascinating class of fluorescent carbon dots (CDs), doped-CDs are now sparked intense research interest, particularly in the diverse fields of biomedical applications due to their unique advantages, including low toxicity, physicochemical, photostability, excellent biocompatibility, and so on. In this review, we have summarized the most recent developments in the literature regarding the employment of doped-CDs for pharmaceutical and medical applications, which are published over approximately the past five years. Accordingly, we discuss the toxicity and optical properties of these nanomaterials. Beyond the presentation of successful examples of the application of these multifunctional nanoparticles in photothermal therapy, photodynamic therapy, and antibacterial activity, we further highlight their application in the cellular labeling, dual imaging, and in vitro and in vivo bioimaging by use of fluorescent-, photoacoustic-, magnetic-, and computed tomography (CT)-imaging. The potency of doped-CDs was also described in the biosensing of ions, small molecules, and drugs in biological samples or inside the cells. Finally, the advantages, disadvantages, and common limitations of doped-CD technologies are reviewed, along with the future prospects in biomedical research. Therefore, this review provides a concise insight into the current developments and challenges in the field of doped-CDs, especially for biological and biomedical researchers.

Highly Fluorescent N-Doped Carbon Quantum Dots Derived from Bamboo Stems for Selective Detection of Fe3+ Ions in Biological Systems

The establishment of sensing platform for trace analysis of Fe³⁺ in biological systems is meaningful for health monitoring. Herein, a Fe³⁺ sensitive fluorescent nanoprobe was constructed based on highly fluorescent N-doped carbon quantum dots (NCQDs) derived from bamboo stems through a hydrothermal method employing ethylenediamine as the nitrogen dopant. The prepared NCQDs had a uniformly distributed size and their mean size was around 2.43 nm. Abundant functional groups (C=N, N-H, C=O, and carboxyl) anchored on NCQDs demonstrated successful doping of N in CQDs. The obtained NCQDs possessed a high fluorescence quantum yield of 20.02% and outstanding fluorescence stability over a wide pH range and at high ionic strengths. Moreover, Fe³⁺ ions presented a specific fluorescent quenching effect to the as-prepared NCQDs. The calibration curve for fluorescence quenching degree corresponding to Fe³⁺ concentration showed a linear response in a range of 0.01-10 µM, and detection limit was 0.486 µM, which indicated that the NCQDs had high sensitivity to Fe³⁺ ions. Ascribed to these unique properties, the NCQDs were selected as luminescent probes for trace amount of Fe³⁺ ions in human serum. These results demonstrated their promising use in clinical diagnostics and other biologically relevant studies.

Facile synthesis and performance of pH/temperature dual-response hydrogel containing lignin-based carbon dots

This study demonstrated a facile method to synthesize lignin-based carbon dots (L-CDs) first. Results indicated that the L-CDs had a diameter of 2-5 nm and a graphene-like crystalline structure. It was found that under the optimal synthesis conditions, the fluorescence lifetime of L-CDs was about 12 ns. Within the range of pH 1-10, the fluorescence intensity of the L-CDs and pH value followed a linear relationship. With the contribution of L-CDs, pH/temperature dual responsive hydrogel was synthesized. The elastic modulus G' of hydrogel was much higher than viscous modulus G″. When the PVA content was larger than 10 wt%, the temperature sensitivity and water retention rate gradually decreased. The skeleton of hydrogels had a typical porous honeycomb structure, which made it possible to control its internal pore size by adjusting the content of PVA. There was a linear relationship between the fluorescence intensity of hydrogels and pH value in the range of pH 1-7. Therefore, the pH/temperature dual responsive hydrogel presented a new route for designing tissue engineering scaffolds and drug carriers.

Carbon Dots: An Emerging Smart Material for Analytical Applications

Carbon dots (CDs) are optically active carbon-based nanomaterials. These nanomaterials can change their light emission properties in response to various external stimuli such as pH, temperature, pressure, and light. The CD's remarkable stimuli-responsive smart material properties have recently stimulated massive research interest for their exploitation to develop various sensor platforms. Herein, an effort has been made to review the major advances made on CDs, focusing mainly on its smart material attributes and linked applications. Since the CD's material properties are largely linked to their synthesis approaches, various synthesis methods, including surface passivation and functionalization of CDs and the mechanisms reported so far in their photophysical properties, are also delineated in this review. Finally, the challenges of using CDs and the scope for their further improvement as an optical signal transducer to expand their application horizon for developing analytical platforms have been discussed.

One-step synthesis of M13 phage-based nanoparticles and their fluorescence properties

Fluorescent carbon nanoparticles have been gaining more attention in recent years for their excellent fluorescence properties and simple synthesis routes. Different carbon sources have been reported for fluorescent carbon nanoparticle synthesis but the use of virus particles as a carbon source is scarce. Herein, we report the utilization of M13 bacteriophage particles as the carbon source to synthesize phage-based nanoparticles through facile, one-step microwave heating. M13 bacteriophage is a nanosized filamentous virus particle with a single-stranded DNA genome encapsulated by a large number of coat proteins. These amino acid rich building blocks provide a substantial amount of carbon source for the synthesis of fluorescent nanoparticles. The resulting nanoparticles from M13 bacteriophage showed good water solubility and exhibited bright blue luminescence. The selectivity and sensitivity of the phage-based nanoparticles towards Fe(iii) ions showed a quenching effect with a linear correlation and a detection limit of 8.0 μM. This process highlights the potential application of virus particles as a source for the synthesis of fluorescent carbon nanoparticles and the sensing application.

Comparison of the effects of synthesis methods of B, N, S, and P-doped carbon dots with high photoluminescence properties on HeLa tumor cells

Although heteroatom doping is widely used to promote the optical properties of carbon dots for biological applications, the synthesis process still has problems such as multi-step process, complicating the setting of instrument along with uncontrolled products. In the present study, some elements such as boron, nitrogen, sulfur, and phosphor were intentionally doped into citric acid-based carbon dots by furnace- and microwave-assisted direct and simple carbonization processes. The process produced nanoparticles with an average diameter of 5-9 nm with heteroatoms (B, N, S, and P) placed on the core and surface of carbon dots. Among the doped carbon dots prepared, boron-doped carbon dots obtained by the microwave-assisted (B-CDs2) process showed the highest photoluminescence intensity with a quantum yield (QY) of about 32.96%. All obtained carbon dots exhibit good stability (at pH 6-12 and high ionic strength concentrations up to 0.5 M), whereas cytotoxicity analysis showed that all doped carbon dots are low-toxic with an average cell viability percentage above 80% up to 500 μg mL-1. It can be observed from the CLSM image of all doped carbon dots that the doping process not only increases the QY percentage, but also might accelerate the HeLa uptake on it and produce strong carbon dot emission at the cytoplasm of the cell. Thus, the proposed synthesis process is promising for high-potency bioimaging of HeLa cancer cells.

A Review of Carbon Dots Produced from Biomass Wastes

The fluorescent carbon dot is a novel type of carbon nanomaterial. In comparison with semiconductor quantum dots and fluorescence organic agents, it possesses significant advantages such as excellent photostability and biocompatibility, low cytotoxicity and easy surface functionalization, which endow it a wide application prospect in fields of bioimaging, chemical sensing, environmental monitoring, disease diagnosis and photocatalysis as well. Biomass waste is a good choice for the production of carbon dots owing to its abundance, wide availability, eco-friendly nature and a source of low cost renewable raw materials such as cellulose, hemicellulose, lignin, carbohydrates and proteins, etc. This paper reviews the main sources of biomass waste, the feasibility and superiority of adopting biomass waste as a carbon source for the synthesis of carbon dots, the synthetic approaches of carbon dots from biomass waste and their applications. The advantages and deficiencies of carbon dots from biomass waste and the major influencing factors on their photoluminescence characteristics are summarized and discussed. The challenges and perspectives in the synthesis of carbon dots from biomass wastes are also briefly outlined.

A minireview on doped carbon dots for photocatalytic and electrocatalytic applications

To date, carbon dots (CDs) or carbon quantum dots (CQDs), considered as alternatives to conventional fluorescent materials such as organic dyes and semiconductor quantum dots (QDs), have drawn significant attention from relevant researchers due to their superior properties, including nontoxicity, biocompatibility, low cost and facile synthesis, and high photoluminescence. In particular, doping heteroatoms with CDs can not only dramatically enhance the fluorescence but also greatly improve the electronic structure and doped CDs have been successfully applied in various technological fields. Herein, this minireview summarizes recent advances on the synthesis and optical properties of doped CDs and their promising applications for photocatalysis and electrocatalysis. Finally, some challenging issues as well as future perspectives of this exciting material are discussed.

Preparation of Biomass-Based Carbon Dots with Aggregation Luminescence Enhancement from Hydrogenated Rosin for Biological Imaging and Detection of Fe3

Fluorescent carbon dots (CDs) have numerous important applications, but enhancing the fluorescence emission and overcoming fluorescence quenching are still big challenges. Here, fluorescence-enhanced carbon dots (named hr-CDs) were prepared from sustainable hydrogenated rosin, using a simple hydrothermal method in a water solvent. The hr-CDs were mainly composed of graphitized carbon cores with surface functional groups. With the increase in the concentration to hr-CDs aqueous solutions, the distance between the carbon cores decreased, which resulted in the formation of J aggregates and the enhanced blue fluorescence emission. Even in the solid state, the hr-CDs show fluorescence emission because the surface functional groups could prevent π-π stacking interactions between the carbon cores. The hr-CDs show excellent resistance to photobleaching under intense ultraviolet light (200 mW/cm²). Vibrations and rotations of graphitized carbon core are restricted by low temperature and high viscosity, leading to increased radiative transition and thus increase in fluorescence intensity. The pH value in the range of 3.99-9.87 and anions have little effect on the fluorescence emission of hr-CDs. The fluorescence emission of the hr-CDs was selectively quenched by Fe³⁺ and can thus be used to detect Fe³⁺. The hr-CDs also have good biocompatibility and show the same ability in cell nuclear staining as 4',6-diamidino-2-phenylindole (DAPI).

Cane Molasses Graphene Quantum Dots Passivated by PEG Functionalization for Detection of Metal Ions

Poly(ethylene glycol) passivated graphene quantum dots (PEG-GQDs) were synthesized based on a green and effective strategy of the hydrothermal treatment of cane molasses. The prepared PEG-GQDs, with an average size of 2.5 nm, exhibit a brighter blue fluorescence and a higher quantum yield (QY) (up to approximately 21.32%) than the QY of GQDs without surface passivation (QY = 10.44%). The PEG-GQDs can be used to detect and quantify paramagnetic transition-metal ions including Fe3+, Cu2+, Co2+, Ni2+, Pb2+, and Mn2+. In the case of ethylenediaminetetraacetic acid (EDTA) solution as a masking agent, Fe3+ ions can be well selectively determined in a transition-metal ion mixture, following the lowest limit of detection (LOD) of 5.77 μM. The quenching mechanism of Fe3+ on PEG-GQDs belongs to dynamic quenching. Furthermore, Fe3+ in human serum can be successfully detected by the PEG-GQDs, indicating that the green prepared PEG-GQDs can be applied as a promising candidate for the selective detection of Fe3+ in clinics.

Recent Advancements in Doped/Co-Doped Carbon Quantum Dots for Multi-Potential Applications

Carbon quantum dots (CQDs)/carbon nanodots are a new class of fluorescent carbon nanomaterials having an approximate size in the range of 2–10 nm. The majority of the reported review articles have discussed about the development of the CQDs (via simple and cost-effective synthesis methods) for use in bio-imaging and chemical-/biological-sensing applications. However, there is a severe lack of consolidated studies on the recently developed CQDs (especially doped/co-doped) that are utilized in different areas of application. Hence, in this review, we have extensively discussed about the recent development in doped and co-doped CQDs (using elements/heteroatoms—e.g., boron (B), fluorine (F), nitrogen (N), sulphur (S), and phosphorous (P)), along with their synthesis method, reaction conditions, and/or quantum yield (QY), and their emerging multi-potential applications including electrical/electronics (such as light emitting diode (LED) and solar cells), fluorescent ink for anti-counterfeiting, optical sensors (for detection of metal ions, drugs, and pesticides/fungicides), gene delivery, and temperature probing.