In situ synthesis of NIR-light emitting carbon dots derived from spinach for bio-imaging applications

A novel red fluorescent and dynamic nanocomposite hydrogel based on chitosan and alginate doped with inclusion complex of carbon dots

Red fluorescent hydrogels possessing injectable and self-healing properties have widespread potential in biomedical field. It is still a challenge to achieve a biomacromolecules based dynamic hydrogels simultaneously combining with excellent red fluorescence, good mechanical properties, and biocompatibility. Here we first explore hydrophilic inclusion complex of (R-CDs@α-CD) derived from hydrophobic red fluorescent carbon dots (R-CDs) and α-cyclodextrin (α-CD), and then achieved a red fluorescent and dynamic polysaccharide R-CDs@α-CD/CEC-l-OSA hydrogel. The nanocomposite hydrogel can be fabricated through controlled doping of red fluorescent R-CDs@α-CD into dynamic polymer networks, taking reversibly crosslinked N-carboxyethyl chitosan (CEC) and oxidized sodium alginate (OSA) as an example. The versatile red fluorescent hydrogel simultaneously combines the features of injection, biocompatibility, and augmented mechanical properties and self-healing behavior, especially in rapid self-recovery even after integration. The R-CDs@α-CD uniformly dispersed into dynamic hydrogel played the role of killing two birds with one stone, that is, endowing red emission of a hydrophilic fluorescent substance, and improving mechanical and self-healing properties as a dynamic nano-crosslinker, via forming hydrogen bonds as reversible crosslinkings. The novel red fluorescent and dynamic hydrogel based on polysaccharides is promising for using as biomaterials in biomedical field.

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

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

Full-color biomass carbon dots for high-level information encryption and multi-color light emitting diode applications

Six biomass carbon dots (BCDs) with adjustable emission from 450 to 680 nm under a single wavelength excitation were successfully synthesized from spinach via solvent control strategy. The obtained BCDs show blue, green, yellow, violet, pink, and red emission with high photoluminescence quantum yield (PLQY = 12.68 ~ 30.77%). Detailed characterizations disclose that the tunable-emission mechanism is caused by the synergistic effect of carbon conjugate and surface oxidation degree. Meanwhile, full-color photoluminescence BCDs/PVP powder and BCDs/PVP/PVA films were fabricated by utilizing the prepared BCDs combined with polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA), respectively, which presented excellent high-level information encryption application. Importantly, multi-color and white light-emitting diode (LED) with Commission Internationale de L' Eclairage (CIE) of blue (0.25, 0.29); green (0.25, 0.31); yellow (0.42, 0.45); red (0.52, 0.31); and white (0.32, 0.31) were achieved by only using our prepared BCDs. This work provides a valuable strategy of preparing multi-color BCDs using readily available biomass materials and paves a way for high-level information encryption and LED applications.

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

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

Microwave Synthesis of Carbon Quantum Dots from Arabica Coffee Ground for Fluorescence Detection of Fe3+, Pb2+, and Cr3

In this study, carbon quantum dots (CQDs), which were synthesized from arabica coffee ground-derived activated carbon, have been successfully employed as a fluorescence sensor to detect Fe3+ ions. CQDs were fabricated using microwave heating for 5-10 min, which emitted vibrant blue light at 455 nm when exposed to excitation at 365 nm. Dynamic light scattering (DLS) analysis revealed that the average size of CQDs was 10.12 nm with a quantum yield of 6.01%. Fluorescence detection was developed for sensing Fe3+, Pb2+, and Cr3+ ions. The addition of the three metal ions resulted in a decrease in the fluorescence (FL) intensity of the CQDs, with the addition of Fe3+ ions demonstrating a more significant decrease in FL compared to the addition of both Cr3+ and Pb2+ ions. The results indicated that the CQDs synthesized from activated carbon of arabica coffee waste performed as a selective fluorescent detector for Fe3+ ions, with a detection limit of 0.27 μM.

Sleep deprivation boosts O2·- levels in the brains of mice as visualized by a Golgi apparatus-targeted ratiometric fluorescence nanosensor

Sleep deprivation (SD) is highly prevalent in the modern technological world. Emerging evidence shows that sleep deprivation is associated with oxidative stress. At the organelle level, the Golgi apparatus actively participates in the stress response. In this study, to determine whether SD and Golgi apparatus stress are correlated, we rationally designed and fabricated a novel Golgi apparatus-targeted ratiometric nanoprobe called Golgi dots for O2·- detection. This probe exhibits high sensitivity and selectivity in cells and brain slices of sleep-deprived mice. Golgi dots can be readily synthesized by coprecipitation of Golgi-F127, an amphiphilic polymer F127 modified with a Golgi apparatus targeting moiety, caffeic acid (CA), the responsive unit for O2·-, and red emissive carbon nanodots (CDs), which act as the reference signal. The fluorescence emission spectrum of the developed nanoprobe showed an intense peak at 674 nm, accompanied by a shoulder peak at 485 nm. As O2·- was gradually added, the fluorescence at 485 nm continuously increased; in contrast, the emission intensity at 674 nm assigned to the CDs remained constant, resulting in the ratiometric sensing of O2·-. The present ratiometric nanoprobe showed high selectivity for O2·- monitoring due to the specific recognition of O2·- by CA. Moreover, the Golgi dots exhibited good linearity with respect to the O2·- concentration within 5 to 40 μM, and the limit of detection (LOD) was ~ 0.13 μM. Additionally, the Golgi dots showed low cytotoxicity and an ability to target the Golgi apparatus. Inspired by these excellent properties, we then applied the Golgi dots to successfully monitor exogenous and endogenous O2·- levels within the Golgi apparatus. Importantly, with the help of Golgi dots, we determined that SD substantially elevated O2·- levels in the brain.

Biomass carbon and Ti2C3MXene quantum dots as ratiometric fluorescent probes for sensitive detecting malachite green in fish sample

A visual detection method for malachite green (MG) in food was established based on 'double-response-OFF' ratiometric fluorescent paper-based sensor. Biomass carbon quantum dots (BCQDs) using broad bean shell, and Ti3C2MXene quantum (MQDs) dots modified by ethylenediamine were synthesized by solvothermal method. The MG and two kinds of quantum dots could undergo static quenching, and the fluorescence color of two kinds of quantum dots gradually changed from red to blue, eventually the fluorescence was quenched, and the pattern had a two-stage linear relationship using fluorescent spectrofluorometer in the range of 0.1-140.0μM and the detection limit of 0.07μM. On this basis, a BCQDs/MQDs ratiometric fluorescence paper-based sensor was constructed and applied to fish sample. Through mobile phone software-Color recognizer, RGB values of fluorescent paper-based sensor at various concentrations of MG were extracted. The results showed that MG concentration was linearly correlated withR' value of RGB in the range of 20.0-140.0μM with 16.5μM detection limit. The method had been applied to the determination of canned fish and fresh basa fish samples, and the recovery rates were 97.33%-108.93% and 96.04%-117.97%, respectively. It proved that the ratiometric fluorescent paper-based sensor could be used for the rapid visual quantitative detecting MG in real samples.

Microwave-Assisted Synthesis of Functionalized Carbon Nanospheres Using Banana Peels: pH-Dependent Synthesis, Characterization, and Selective Sensing Applications

This work presents a microwave-based green synthesis method for producing carbon nanospheres (CNSs) and investigates the impact of presynthesis pH on their size and assembly. The resulting CNSs are monodispersed, averaging 35 nm in size, and exhibit notable characteristics including high water solubility, photostability, and a narrow size distribution, achieved within a synthesis time of 15 min. The synthesized CNS features functional groups such as -OH, -COOH, -NH, -C-O-C, =C-H, and -CH. This diversity empowers the CNS for various applications including sensing. The CNS exhibits a distinct UV peak at 282 nm and emits intense fluorescence at 430 nm upon excitation at 350 nm. These functionalized CNSs enable selective and specific sensing of Cu2+ ions and the amino acid tryptophan (Trp) in aqueous solutions. In the presence of Cu2+ ions, static-based quenching of CNS fluorescence was observed due to the chelation-enhanced quenching (CHEQ) effect. Notably, Cu2+ ions induce a substantial change in UV spectra alongside a red-shift in the peak position. The limits of detection and quantification for Cu2+ ions with CNS are determined as 0.73 and 2.45 μg/mL, respectively. Additionally, on interaction with tryptophan, the UV spectra of CNS display a marked increase in the peak at 282 nm, accompanied by a red-shift phenomenon. The limits of detection and quantification for l-tryptophan are 4.510 × 10-3 and 1.50 × 10-2 μg/mL, respectively, indicating its significant potential for biological applications. Furthermore, the practical applicability of CNSs is demonstrated by their successful implementation in analyzing real water samples and filter paper-based examination, showcasing their effectiveness for on-site sensing.

Manganese Amplifies Photoinduced ROS in Toluidine Blue Carbon Dots to Boost MRI Guided Chemo/Photodynamic Therapy

The contrast agents and tumor treatments currently used in clinical practice are far from satisfactory, due to the specificity of the tumor microenvironment (TME). Identification of diagnostic and therapeutic reagents with strong contrast and therapeutic effect remains a great challenge. Herein, a novel carbon dot nanozyme (Mn-CD) is synthesized for the first time using toluidine blue (TB) and manganese as raw materials. As expected, the enhanced magnetic resonance (MR) imaging capability of Mn-CDs is realized in response to the TME (acidity and glutathione), and r1 and r2 relaxation rates are enhanced by 224% and 249%, respectively. In addition, the photostability of Mn-CDs is also improved, and show an efficient singlet oxygen (1 O2 ) yield of 1.68. Moreover, Mn-CDs can also perform high-efficiency peroxidase (POD)-like activity and catalyze hydrogen peroxide to hydroxyl radicals, which is greatly improved under the light condition. The results both in vitro and in vivo demonstrate that the Mn-CDs are able to achieve real-time MR imaging of TME responsiveness through aggregation of the enhanced permeability and retention effect at tumor sites and facilitate light-enhanced chemodynamic and photodynamic combination therapies. This work opens a new perspective in terms of the role of carbon nanomaterials in integrated diagnosis and treatment of diseases.

An Overview of the Potential of Food-Based Carbon Dots for Biomedical Applications

Food-based carbon dots (CDs) hold significant importance across various fields, ranging from biomedical applications to environmental and food industries. These CDs offer unique advantages over traditional carbon nanomaterials, including affordability, biodegradability, ease of operation, and multiple bioactivities. This work aims to provide a comprehensive overview of recent developments in food-based CDs, focusing on their characteristics, properties, therapeutic applications in biomedicine, and safety assessment methods. The review highlights the potential of food-based CDs in biomedical applications, including antibacterial, antifungal, antivirus, anticancer, and anti-immune hyperactivity. Furthermore, current strategies employed for evaluating the safety of food-based CDs have also been reported. In conclusion, this review offers valuable insights into their potential across diverse sectors and underscores the significance of safety assessment measures to facilitate their continued advancement and application.

Green synthesis of N,S-doped carbon dots for tartrazine detection and their antibacterial activities

A simple, green and low-cost method was developed for the synthesis of highly fluorescent N,S-doped carbon dots (N,S-CDs) via the hydrothermal treatment of Gandha Prasarini (GP) leaves as a natural source of carbon, nitrogen and sulfur. The as-prepared N,S-CDs exhibited excitation-dependent green fluorescence emission (λex = 450 nm, λem = 525 nm) with excellent stability, and were used as a fluorescent probe for the selective detection of tartrazine with a limit of detection of 0.18 μM. The fluorescence quenching of N,S-CDs was due to the inner filter effect. The developed method has been employed for the determination of tartrazine in honey and soft drinks with satisfactory recovery ranging from 92 to 110.2%. In addition, the antibacterial activity of the N,S-CDs was explored against both Gram-negative bacteria, Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa), and Gram-positive bacteria, Staphylococcus aureus (S. aureus). The antibacterial mechanism of the N,S-CDs was investigated. The results indicated that the antibacterial activity was due to the membrane damage of the bacteria by the N,S-CDs. Besides, the N,S-CDs showed negligible lytic effects on human erythrocytes. These findings will inspire further exploitation of CD-based nano-bactericides in biomedical applications.

Comprehensive advances in the synthesis, fluorescence mechanism and multifunctional applications of red-emitting carbon nanomaterials

Red emitting fluorescent carbon nanomaterials have drawn significant scientific interest in recent years due to their high quantum yield, water-dispersibility, photostability, biocompatibility, ease of surface functionalization, low cost and eco-friendliness. The red emissive characteristics of fluorescent carbon nanomaterials generally depend on the carbon source, reaction time, synthetic approach/methodology, surface functional groups, average size, and other reaction environments, which directly or indirectly help to achieve red emission. The importance of several factors to achieve red fluorescent carbon nanomaterials is highlighted in this review. Numerous plausible theories have been explained in detail to understand the origin of red fluorescence and tunable emission in these carbon-based nanostructures. The above advantages and fluorescence in the red region make them a potential candidate for multifunctional applications in various current fields. Therefore, this review focused on the recent advances in the synthesis approach, mechanism of fluorescence, and electronic and optical properties of red-emitting fluorescent carbon nanomaterials. This review also explains the several innovative applications of red-emitting fluorescent carbon nanomaterials such as biomedicine, light-emitting devices, sensing, photocatalysis, energy, anticounterfeiting, fluorescent silk, artificial photosynthesis, etc. It is hoped that by choosing appropriate methods, the present review can inspire and guide future research on the design of red emissive fluorescent carbon nanomaterials for potential advancements in multifunctional applications.

Ultra-Narrow-Bandwidth Deep-Red Electroluminescence Based on Green Plant-Derived Carbon Dots

Deep-red light-emitting diodes (DR-LEDs, >660 nm) with high color-purity and narrow-bandwidth emission are promising for full-color displays and solid-state lighting applications. Currently, the DR-LEDs are mainly based on conventional emitters such as organic materials and heavy-metal based quantum dots (QDs) and perovskites. However, the organic materials always suffer from the complicated synthesis, inferior color purity with full-width at half-maximum (FWHM) more than 40 nm, and the QDs and perovskites still suffer from serious problems related to toxicity. Herein, this work reports the synthesis of efficient and high color-purity deep-red carbon dots (CDs) with a record narrow FWHM of 21 nm and a high quantum yield of more than 50% from readily available green plants. Moreover, an exciplex host is further established using a polymer and small molecular blend, which has been shown to be an efficient strategy for producing high color-purity monochrome emission from deep-red CDs via Förster energy transfer (FET). The deep-red CD-LEDs display high color-purity with Commission Internationale de l'Eclairage (CIE) coordinates of (0.692, 0.307). To the best of the knowledge, this is the first report of high color-purity CD-LEDs in the deep-red region, opening the door for the application of CDs in the development of high-resolution light-emitting display technologies.

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.

A novel AIE fluorescence probe featuring with high quantum yield for high-fidelity lysosomal targeting and tracking

High-fidelity imaging and long-term visualization of lysosomes are pivotal factors in the functional assessment of lysosomes, which perform an instrumental role in the physiological activity of cells. However, commercial probes have great limitations in lysosome exploration resulting from the aggregation-caused quenching effect as well as photobleaching instability and small Stokes shift. Therefore, we constructed a novel probe named TTAM with triphenylamine as the matrix and morpholine ring as the targeting group. In contrast with commonly accessible Lyso-tracker Red, TTAM has the merits of aggregation-induced emission effect, extremely high quantum yields (51.57 % solid-state) as well as fluorescence intensity, significant photostability, and high resolution. These properties make it ideal for imaging and activity monitoring lysosomes, which provides a powerful condition for bio-imaging.

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.

Green Carbon Dots: Applications in Development of Electrochemical Sensors, Assessment of Toxicity as Well as Anticancer Properties

Carbon dots are one of the most promising nanomaterials which exhibit a wide range of applications in the field of bioimaging, sensing and biomedicine due to their ultra-small size, high photostability, tunable fluorescence, electrical properties, etc. However, green carbon dots synthesized from several natural and renewable sources show some additional advantages, such as favorable biocompatibility, wide sources, low cost of production and ecofriendly nature. In this review, we will provide an update on the latest research of green carbon dots regarding their applications in cancer therapy and in the development of electrochemical sensors. Besides, the toxicity assessment of carbon dots as well as the challenges and future direction of research on their anticancer and sensing applications will be discussed.

Preparation of Multicolor Biomass Carbon Dots Based on Solvent Control and Their Application in Cr(VI) Detection and Advanced Anti-Counterfeiting

Multicolor fluorescent carbon dots (CDs) have received widespread attention due to their excellent fluorescence performance and promising prospects in anti-counterfeiting and sensing detection. To date, most of the multicolor CDs synthesized are derived from chemical reagents; however, the overuse of chemical reagents during the synthesis process will pollute the environment and limit their application. Herein, multicolor fluorescent biomass CDs (BCDs) were prepared by a one-pot ecofriendly solvothermal method, with spinach as the raw material based on solvent control. The as-obtained BCDs can emit blue, crimson, grayish white, and red luminescence, and their quantum yields (QYs) are 8.9, 12.3, 10.8, and 14.4%, respectively. The results of the characterization of BCDs reveal that the regulating mechanism for multicolor luminescence is mainly ascribed to the change of the boiling point and polarity of solvents, which changes the carbonization process of polysaccharides and chlorophyll in spinach, resulting in the altered particle size, surface functional groups, and porphyrin luminescence properties. Further research reveals that blue BCDs (BCD1) show an excellent sensitive and selective response to Cr(VI) in a concentration scale of 0-220 μM with a detection limit (LOD) of 0.242 μM. More importantly, the intraday and interday relative standard deviation (RSD) values were less than 2.99%. The recovery rate of the Cr(VI) sensor for tap water and river water is 101.52-107.51%, which indicates that the sensor has the advantages of high sensitivity, selectivity, rapidity, and reproducibility. Consequently, different multicolor patterns are obtained by using the obtained four BCDs as fluorescent inks, which exhibit beautiful landscape and advanced anti-counterfeiting effects. This study provides a low-cost and facile green synthesis strategy for multicolor luminescent BCDs and proves that BCDs have broad application prospects in ion detection and advanced anti-counterfeiting.

Down/up-conversion dual-mode ratiometric fluorescence imprinted sensor embedded with metal-organic frameworks for dual-channel multi-emission multiplexed visual detection of thiamphenicol

The establishment of a fluorescence sensing system for sensitive and selective visual detection of trace antibiotics is of great significance to food safety and human health risk assessment. A simple and rapid one-pot strategy was developed successfully to synthesize a down/up-conversion dual-excitation multi-emission fluorescence imprinted sensor for dual-channel thiamphenicol (TAP) detection. In this strategy, the metal-organic frameworks were in situ incorporated into the fluorescence imprinted sensor, guiding the coordination induced emission of abiotic carbon dots and signal-amplification effect of fluorescence sensing. Under dual-excitation (370 nm and 780 nm), the fluorescence imprinted sensor exhibited a dual-channel fluorescence response toward TAP with two-part linear ranges of 5.0 nM-6.0 μM and 6.0 μM-26.0 μM. Significantly, the fluorescence color ranged from blue to purple to red can be observed with the naked eye. The results of the dual-channel TAP determination in actual samples by the fluorescence imprinted sensor indicated that the fluorescence imprinted sensor provided a sensitive, selective, and multiplexed visual detection of TAP in complex sample.

Endoplasmic reticulum-targeted polymer dots encapsulated with ultrasonic synthesized near-infrared carbon nanodots and their application for in vivo monitoring of Cu2

Endoplasmic reticulum (ER) is the largest organelle in eukaryotic cells and plays a variety of functions in living cells include protein folding, calcium homeostasis, and lipid biosynthesis. Normal function of ER is crucial for cell survival, while disequilibrium of ER can cause misfolding of proteins and ER stress, leading to many serious diseases. It has been documented that ER stress is closely related to the metabolism of Cu²⁺, as ER is the main intracellular accumulation space of Cu²⁺ and toxic reactive oxygen species can be generated by Cu²⁺ via Fenton and Haber-Weiss reactions. In this context, developing a powerful tool capable of selective and sensitive monitoring of Cu²⁺ in ER and investigating its role in physiological and pathological processes is of great importance. Herein, we report the first ER targeted near infrared (NIR) nanosensor, polymer dots encapsulated with NIR hydrophobic carbon nanodots, for detecting Cu²⁺ in biosystems. This nanosensor with stable fluorescence showed a fast response toward Cu²⁺ (120 s) and can be used for the quantification of Cu²⁺ in a linear range covering from 0.25 to 9.0 μM with a detection limit of 13 nM. In addition, the fluorescence variations of the nanosensor are remarkably specific to Cu²⁺ in comparison with the other metal ions and amino acids. Moreover, the developed nanosensor exhibited low cytotoxicity, good biocompatibility, and ER targeting ability. Because of these excellent spectroscopic features, the nanosensor was successfully utilized for visualizing Cu²⁺ fluctuations at the living cell, zebrafish and mouse levels, which further proved its potential application in biological systems.

Progress on carbon dots and hydroxyapatite based biocompatible luminescent nanomaterials for cancer theranostics

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Biocompatible carbon dots (CDs) and nanohydroxyapatite (nHA) have attracted much attention for the development of optical imaging probes.

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This review discusses the development of CD and nHA based nanomaterials as multifunctional agents for cancer theranostics.

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The effect of synthesis strategies and doping on photoluminescent properties along with tuning of emission in biological window has been briefly reviewed.

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The cancer targeting strategies, biocompatibility and biodistribution of CDs and nHA based luminescent probes is discussed.

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A summary of current challenges and future perspectives is provided.

Despite the significant advancement in cancer diagnosis and therapy, a huge burden remains. Consequently, much research has been diverted on the development of multifunctional nanomaterials for improvement in conventional diagnosis and therapy. Luminescent nanomaterials offer a versatile platform for the development of such materials as their intrinsic photoluminescence (PL) property offers convergence of diagnosis as well as therapy at the same time. However, the clinical translation of nanomaterials faces various challenges, including biocompatibility and cost-effective scale up production. Thus, luminescent materials with facile synthesis approach along with intrinsic biocompatibility and anticancerous activity hold significant importance. As a result, carbon dots (CDs) and nanohydroxyapatite (nHA) have attracted much attention for the development of optical imaging probes. CDs are the newest members of the carbonaceous nanomaterials family that possess intrinsic luminescent and therapeutic properties, making them a promising candidate for cancer theranostic. Additionally, nHA is an excellent bioactive material due to its compositional similarity to the human bone matrix. The nHA crystal can efficiently host rare-earth elements to attain luminescent property, which can further be implemented for cancer theranostic applications. Herein, the development of CDs and nHA based nanomaterials as multifunctional agents for cancer has been briefly discussed. The emphasis has been given to different synthesis strategies leading to different morphologies and tunable PL spectra, followed by their diverse applications as biocompatible theranostic agents. Finally, the review has been summarized with the current challenges and future perspectives.

Research Progress of Photothermal Nanomaterials in Multimodal Tumor Therapy

The aggressive growth of cancer cells brings extreme challenges to cancer therapy while triggering the exploration of the application of multimodal therapy methods. Multimodal tumor therapy based on photothermal nanomaterials is a new technology to realize tumor cell thermal ablation through near-infrared light irradiation with a specific wavelength, which has the advantages of high efficiency, less adverse reactions, and effective inhibition of tumor metastasis compared with traditional treatment methods such as surgical resection, chemotherapy, and radiotherapy. Photothermal nanomaterials have gained increasing interest due to their potential applications, remarkable properties, and advantages for tumor therapy. In this review, recent advances and the common applications of photothermal nanomaterials in multimodal tumor therapy are summarized, with a focus on the different types of photothermal nanomaterials and their application in multimodal tumor therapy. Moreover, the challenges and future applications have also been speculated.

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.

Dual Fluorescence in Glutathione-Derived Carbon Dots Revisited

Dual-fluorescence carbon dots have great potential as nanosensors in life and materials sciences. Such carbon dots can be obtained via a solvothermal synthesis route with glutathione and formamide. In this work, we show that the dual-fluorescence emission of the synthesis products does not originate from a single carbon dot emitter, but rather from a mixture of physically separate compounds. We characterized the synthesis products with UV-vis, Raman, infrared, and fluorescence spectroscopy, and identified blue-emissive carbon dots and red-emissive porphyrin. We demonstrate an easy way to separate the two compounds without the need for time-consuming dialysis. Understanding the nature of the system, we can now steer the synthesis toward the desired product, which paves the way for a cheap and environmentally friendly synthesis route toward carbon dots, water-soluble porphyrin, and mixed systems.

Bay Leaf Extract-Based Near-Infrared Fluorescent Probe for Tissue and Cellular Imaging

The development of fluorescence dyes for near-infrared (NIR) fluorescence imaging has been a significant interest for deep tissue imaging. Among many imaging fluoroprobes, indocyanine green (ICG) and its analogues have been used in oncology and other medical applications. However, these imaging agents still experience poor imaging capabilities due to low tumor targetability, photostability, and sensitivity in the biological milieu. Thus, developing a biocompatible NIR imaging dye from natural resources holds the potential of facilitating cancer cell/tissue imaging. Chlorophyll (Chl) has been demonstrated to be a potential candidate for imaging purposes due to its natural NIR absorption qualities and its wide availability in plants and green vegetables. Therefore, it was our aim to assess the fluorescence characteristics of twelve dietary leaves as well as the fluorescence of their Chl extractions. Bay leaf extract, a high-fluorescence agent that showed the highest levels of fluorescence, was further evaluated for its tissue contrast and cellular imaging properties. Overall, this study confirms bay-leaf-associated dye as a NIR fluorescence imaging agent that may have important implications for cellular imaging and image-guided cancer surgery.

Red-emitting carbon nanoparticles with unprecedented singlet oxygen generation efficiency for cancer theranostics

Fluorescent Red-emitting carbon nanoparticles (RCNPs) are produced by an economical and green hydrothermal method using Eucalyptus leaves as a precursor. This is the first report of its kind demonstrating RCNPs in combined PDT-Chemo combination therapy, as RCNPs bind with mitoxantrone (MTO) electrostatically. The synthesized RCNPs before and after conjugation of MTO are characterised using DLS, SEM, TEM, UV-Vis, Fluorescence, FTIR, and ¹H NMR Spectroscopy. FTIR and ¹H NMR confirm the interaction between -NH proton of MTO with carboxylic acid oxygen of RCNPs. RCNPs are demonstrated as brightly fluorescent, type II photosensitizer (PS) with an extraordinary ¹O₂ quantum yield of 0.96, when triggered with a red laser at 660 nm. Moreover, the biocompatibility of RCNPs and RCNPs-MTO are examined and confirmed by performing a cytotoxicity assay on MCF-7 cell lines. Subsequently, to explore the internalization process of the RCNPs as a function of concentration, confocal imaging study is also carried out. The cell viability and the apoptosis assay indicates that RCNPs-MTO can achieve the PDT-Chemo synergistic cancer therapy. To the best of our knowledge, this is the first time that Eucalyptus leaves, a natural source of great abundance, is used as raw material and applied for combined PDT-chemotherapy.

Near-infrared emitting dual-stimuli-responsive carbon dots from endogenous bile pigments

Carbon dots are biocompatible nanoparticles suitable for a variety of biomedical applications. Careful selection of carbon dot precursors and surface modification techniques has allowed for the development of carbon dots with strong near-infrared fluorescence emission. However, carbon dots that provide strong fluorescence contrast would prove even more useful if they were also responsive to stimuli. In this work, endogenous bile pigments bilirubin (BR) and biliverdin (BV) were used for the first time to synthesize stimuli-responsive carbon dots (BR-CDots and BV-CDots respectively). The precursor choice lends these carbon dots spectroscopic characteristics that are enzyme-responsive and pH-responsive without the need for surface modifications post-synthesis. Both BV- and BR-CDots are water-dispersible and provide fluorescence contrast, while retaining the stimuli-responsive behaviors intrinsic to their precursors. Nanoparticle Tracking Analysis revealed that the hydrodynamic size of the BR-CDots and BV-CDots decreased with exposure to bilirubin oxidase and biliverdin reductase, respectively, indicating potential enzyme-responsive degradation of the carbon dots. Fluorescence spectroscopic data demonstrate that both BR-CDots and BV-CDots exhibit changes in their fluorescence spectra in response to changes in pH, indicating that these carbon dots have potential applications in pH sensing. In addition, BR-CDots are biocompatible and provide near-infrared fluorescence emission when excited with light at wavelengths of 600 nm or higher. This work demonstrates the use of rationally selected carbon sources for obtaining near-infrared fluorescence and stimuli-responsive behavior in carbon dots that also provide strong fluorescence contrast.

Towards Red Emissive Systems Based on Carbon Dots

Carbon dots (C-dots) represent an emerging class of nontoxic nanoemitters that show excitation wavelength-dependent photoluminescence (PL) with high quantum yield (QY) and minimal photobleaching. The vast majority of studies focus on C-dots that exhibit the strongest PL emissions in the blue/green region of the spectrum, while longer wavelength emissions are ideal for applications such as bioimaging, photothermal and photodynamic therapy and light-emitting diodes. Effective strategies to modulate the PL emission of C-dot-based systems towards the red end of the spectrum rely on extensive conjugation of sp2 domains, heteroatom doping, solvatochromism, surface functionalization and passivation. Those approaches are systematically presented in this review, while emphasis is given on important applications of red-emissive suspensions, nanopowders and polymer nanocomposites.

Carbon Dots-Mediated Fluorescent Scaffolds: Recent Trends in Image-Guided Tissue Engineering Applications

Regeneration of damaged tissues or organs is one of the significant challenges in tissue engineering and regenerative medicine. Many researchers have fabricated various scaffolds to accelerate the tissue regeneration process. However, most of the scaffolds are limited in clinical trials due to scaffold inconsistency, non-biodegradability, and lack of non-invasive techniques to monitor tissue regeneration after implantation. Recently, carbon dots (CDs) mediated fluorescent scaffolds are widely explored for the application of image-guided tissue engineering due to their controlled architecture, light-emitting ability, higher chemical and photostability, excellent biocompatibility, and biodegradability. In this review, we provide an overview of the recent advancement of CDs in terms of their different synthesis methods, tunable physicochemical, mechanical, and optical properties, and their application in tissue engineering. Finally, this review concludes the further research directions that can be explored to apply CDs in tissue engineering.

An Improved Synthesis of Water-Soluble Dual Fluorescence Emission Carbon Dots from Holly Leaves for Accurate Detection of Mercury Ions in Living Cells

Background

Carbon dots (CDs) emitting near-infrared fluorescence were recently synthesized from green leaves. However, the Hg²⁺ detection of CDs was limited because of the insufficient water solubility, low fluorescence and poor stability.

Methods

Dual fluorescence emission water-soluble CD (Dual-CD) was prepared through a solvothermal method from holly leaves and low toxic PEI_1.8k. PEG was further grafted onto the surface to improve the water solubility and stability.

Results

The Dual-CD solution can emit 487 nm and 676 nm fluorescence under single excitation and exhibit high quantum yield of 16.8%. The fluorescence at 678 nm decreased remarkably while the emission at 470 nm was slightly affected by the addition of Hg²⁺. The ratiometric Hg²⁺ detection had a wide linear range of 0–100 μM and low detection limit of 14.0 nM. In A549 cells, there was a good linear relation between F₄₈₇/F₆₇₆ and the concentration of Hg²⁺ in the range of 0–60 μM; the detection limit was 477 nM. Furthermore, Dual-CD showed visual fluorescence change under Hg²⁺.

Conclusion

Dual-CD has ratiometric responsiveness to Hg²⁺ and can be applied for quantitative Hg²⁺ detection in living cells.

In-situ synthesis of carbon dots-embedded europium metal-organic frameworks for ratiometric fluorescence detection of Hg2+ in aqueous environment

A novel dual-emission ratiometric fluorescent sensor (CDs@Eu-MOFs) has been synthesized successfully by encapsulating water-soluble fluorescent CDs into the chambers of Eu-MOFs via a simple one-pot hydrothermal method, which can be used for the detection of Hg²⁺ in environmental water samples. The synthesized CDs@Eu-MOFs inherited simultaneously the excellent luminescence performance of Eu³⁺ and CDs and exhibited good structural and fluorescence stability in aqueous solution. The presence of Hg²⁺ changed the fluorescence intensity of CDs, while the fluorescence intensity of Eu-MOFs hardly changed, which could be used as the recognition part and the reference part respectively to construct the ratiometric fluorescence sensor. The obtained Hg²⁺ fluorescent probe showed a wide linear range (0-300 μM) and a low detection limit (0.12 nM). The developed method can be used as a multi-functional fluorescent sensor with high sensitivity and good selectivity for the determination of Hg²⁺ in actual water samples.

Dual-emissive carbon dots for dual-channel ratiometric fluorometric determination of pH and mercury ion and intracellular imaging

Dual-emissive carbon dots (CDs) were fabricated for dual-channel ratiometric fluorometric determination of pH and mercury ion (Hg²⁺) and intracellular imaging. Dual-emissive CDs were synthesized by one-pot solvothermal treatment of cabbage. The CDs exhibited two distinctive fluorescence emissions at 500 and 678 nm under single excitation at 410 nm. The green emission (500 nm) had reversible linear response to pH (7.0-12.0) due to deprotonation and protonation of surface functional groups and their non-covalent interactions. On the other hand, the red emission (678 nm) had efficient and selective fluorescence response to Hg²⁺ by formation of non-emission complex between CDs and Hg²⁺. The limit of detection (LOD) and limit of quantification (LOQ) for Hg²⁺ were 6.25 and 20.63 nM, respectively. The CDs have been successfully applied for label-free ratiometric fluorometric determination of pH and Hg²⁺ in fish and human serum samples with good recoveries (92.0-108.3%). In addition, the CDs had excellent photostability, low cytotoxicity, and good biocompatibility for intracellular imaging. All in all, the system was multi-functional in determination, high in sensitivity, and excellent in selectivity, which demonstrated wide and promising applicability for biosensing and bioimaging in the future. Graphical abstract Schematic presentation of dual-emission carbon dots (CDs) synthesized by solvothermal treatment of cabbage for dual-channel determination of pH and Hg²⁺.

Visible-Light-Excited Room Temperature Phosphorescent Carbon Dots

Carbon dots (CDs) with a room temperature phosphorescent (RTP) feature have attracted considerable interest in recent years due to their fundamental importance and promising applications. However, the reported matrix-free RTP CDs only show short-wavelength (green to yellow) emissions and have to be triggered by ultraviolet (UV) light (below 400 nm), limiting their applications in certain fields. Herein, visible-light-excited matrix-free RTP CDs (named AA-CDs) with a long-wavelength (orange) emission are reported for the first time. The AA-CDs can be facilely prepared via a microwave heating treatment of L-aspartic acid (AA) in the presence of ammonia and they emit unique orange RTP in the solid state with visible light (420 nm) excitation just being switched off. Through the studies of the carbonization process, the C=O and C=N containing moieties in the AA-CDs are confirmed to be responsible for the observed RTP emission. Finally, the applications of AA-CDs in information encryption and anti-counterfeiting were preliminarily demonstrated.

White pepper-derived ratiometric carbon dots for highly selective detection and imaging of coenzyme A

A new-style white pepper derived dual-emission carbon dots (CDs) with a quantum yield of 10.4% was designed and facile constructed with one-pot solvothermal method. The green emission (520 nm) had an efficient and special "turn-on" fluorescence sensing of coenzyme A (CoA) with the aid of Cu²⁺, while red emission (668 nm) barely changed and worked as reference. In the concentration range (0-150 µM), relative fluorescence intensity ratios (F₅₂₀/F₆₆₈) showed excellent linear correlation with concentrations of CoA, and detection limit was as low as 8.75 nm. Moreover, the strategy has been successfully applied for label-free detection of CoA in real pig liver samples with good recoveries (93.3-108.0%). Notably, the synthesized CDs had durable fluorescence, low cytotoxicity, and good biocompatibility for cellular imaging, which demonstrated wide and promising applicability for biosensing and bioimaging in the future.

Luminescent carbon dots with concentration-dependent emission in solution and yellow emission in solid state

Carbon dots (CDs) is a class of zero-dimensional carbon nanomaterials with favorable stability and optical properties. However, CDs in solid state often suffer from fluorescence quenching due to π-π stacking of conjugated systems, like most small molecules or organic dyes. Herein, we prepared the CDs that generate bright yellow luminescence in solid state without any additional matrix, meanwhile the solid CDs are inclined to assembly into spherical structure. While the CDs are dissolved in aqueous solution, the photoluminescence (PL) emission from blue to green can be realized by regulating the concentration of CDs. With the concentration increasing, the self-assembly behavior of CDs is observed in solution, which leads to the bathochromic shift of photoluminescence. Besides, the mechanism of PL conversion in this process was proposed based on the characterization results, that with the concentration of CDs rising in solution, π-π interaction was restrained while electron redistribution was induced. Consequently, a localized state II caused by electron rearrangement gradually becomes the predominant emission state, resulting in the PL emission shifting to long-wavelength region. Moreover, CDs have shown favorable potentials in the field of anti-counterfeit and multicolor bioimaging, making the CDs highly attractive for a wide variety of applications.

Novel single excitation dual-emission carbon dots for colorimetric and ratiometric fluorescent dual mode detection of Cu2+ and Al3+ ions

In this study, dual-emission carbon dots (D-CDs) are synthesized via a simple one-step solvothermal treatment of red tea. The obtained D-CDs are characterized by XPS, IR, TEM, XRD, fluorescence and UV-vis spectroscopy techniques. It is found that D-CDs present a strong red fluorescence emission peak at 671 nm and weak blue fluorescence emission peak at 478 nm under the excitation wavelength of 410 nm. The unique dual-emission properties of D-CDs provide great opportunities in ratiometric fluorescence sensing applications. The results show that Cu2+ ions can quench the fluorescence of the red emission band of D-CDs effectively, resulting in the disappearance of red fluorescence ultimately. Upon the addition of Al3+ ions, the fluorescence of blue emission band at 478 nm grows apparently, and the fluorescence color transforms gradually from red to orange, then to yellow-green. Based on these findings, a novel ratiometric fluorescence and colorimetric dual mode nanosensor is developed for simultaneous detection of Cu2+ and Al3+ ions. Regarding Cu2+ ions, the fluorescent detection linear range is 0.1-50 μM with detection limit of 0.1 μM, and the colorimetric detection limit is estimated as 25 μM. With regard to Al3+ ions, the fluorescent detection linear range is 0-20 μM and 25-100 μM with detection limit of 0.5 μM, and the colorimetric detection limit is 20 μM. Furthermore, the fluorescence response mechanisms of Cu2+ and Al3+ ions were discussed detailed. To the best of our current knowledge, this will be the first research work on the simultaneous determination of Cu2+ and Al3+ using D-CDs as fluorescent probes.

Nucleolus-Targeted Red Emissive Carbon Dots with Polarity-Sensitive and Excitation-Independent Fluorescence Emission: High-Resolution Cell Imaging and in Vivo Tracking

Red-emitting carbon dots (CDs) have attracted tremendous attention due to their wide applications in areas including imaging, sensing, drug delivery, and cancer therapy. However, it is still highly challenging for red-emitting CDs to simultaneously achieve high quantum yields (QYs), nucleus targeting, and super-resolution fluorescence imaging (especially the stimulated emission depletion (STED) imaging). Here, it is found that the addition of varied metal ions during the hydrothermal treatment of p-phenylenediamine (pPDA) leads to the formation of fluorescent CDs with emission wavelengths up to 700 nm. Strikingly, although metal ions play a crucial role in the synthesis of CDs with varied QYs, they are absent in the formed CDs, that is, the obtained CDs are metal-free, and the metal ions play a role similar to a "catalyst" during the CD formation. Besides, using pPDA and nickel ions (Ni²⁺) as raw materials, we prepare Ni-pPCDs which have the highest QY and exhibit various excellent fluorescence properties including excitation-independent emission (at ∼605 nm), good photostability, polarity sensitivity, and ribonucleic acid responsiveness. In vitro and in vivo experiments demonstrate that Ni-pPCDs are highly biocompatible and can realize real-time, wash-free, and high-resolution imaging of cell nuclei and high-contrast imaging of tumor-bearing mice and zebrafish. In summary, the present work may hold great promise in the synthesis and applications of red emissive CDs.

Efficient Red/Near-Infrared-Emissive Carbon Nanodots with Multiphoton Excited Upconversion Fluorescence

Red/near-infrared (NIR) emissive carbon nanodots (CNDs) with photoluminescence (PL) quantum yield (QY) of 57% are prepared via an in situ solvent-free carbonization strategy for the first time. 1-Photon and 2-photon cellular imaging is demonstrated by using the CNDs as red/NIR fluorescence agent due to the high PL QY and low biotoxicity. Further study shows that the red/NIR CNDs exhibit multiphoton excited (MPE) upconversion fluorescence under excitation of 800-2000 nm, which involves three NIR windows (NIR-I, 650-950 nm; NIR-II, 1100-1350; NIR-III, 1600-1870 nm). 2-Photon, 3-photon, and 4-photon excited fluorescence of the CNDs under excitation of different wavelengths is achieved. This study develops an in situ solvent-free carbonization method for efficient red/NIR emissive CNDs with MPE upconversion fluorescence, which may push forward the application of the CNDs in bioimaging.

Pheophytin Derived Near-Infrared-Light Responsive Carbon Dot Assembly as a New Phototheranotic Agent for Bioimaging and Photodynamic Therapy

Carbon dots (CDs), a kind of phototheranostic agent with the capability of simultaneous bioimaging and phototherapy [i.e., photodynamic therapy (PDT) or photothermal therapy (PTT)], have received considerable attention because of their remarkable properties, including flexibility for surface modification, high biocompatibility, low toxicity and photo-induced activity for malignant tumor cells. Among numerous carbon sources, it has been found that natural biomass are good candidates for the preparation of CD phototheranostic agents. In this study, pheophytin, a type of Mg-free chlorophyll derivative and also a natural product with low toxicity, was used as a raw carbon source for the synthesis of CDs by using a microwave method. The obtained hydrophobic CDs exhibited a maximum near-infrared (NIR) emission peak at approximately 680 nm, and high singlet oxygen (¹ O₂ ) generation with a quantum yield of 0.62. The self-assembled CDs from the as-prepared CDs with DSPE-mPEG2000 retained efficient ¹ O₂ generation. The obtained carbon dot assembly was not only an efficient fluorescence (FL) imaging agent but also a smart PDT agent. Our studies indicated that the obtained hydrophilic CD assembly holds great potential as a new phototheranostic agent for cancer therapy. This work provides a new route for synthesis of CDs and proposes a readily available candidate for tumor treatment.