Highly fluorescent nitrogen-doped carbon dots with excellent thermal and photo stability applied as invisible ink for loading important information and anti-counterfeiting

Nanodroplets Engineered with Folate Carbon Dots for Enhanced Cancer Cell Uptake toward Theranostic Application

The research in nanotherapeutics is rapidly advancing, particularly in the realm of nanoconstructs for drug delivery. This study introduces folate-based carbon dot-decorated nanodroplets (f-Dnm), synthesized from a binary mixture of negatively charged folic acid carbon dots (f-CDs) and cationic-branched polyethylenimine (PEI). The uniformly spherical nanodroplets with an average diameter of 115 ± 15 nm exhibit notable photoluminescence. Surface potential analysis reveals a significant change upon coacervation, attributed to strong electrostatic interactions between f-CD and PEI. The engineered nanodroplets show excellent colloidal and photostability even after 6 months of storage at room temperature. The pH-dependent self-assembly and disassembly properties of f-Dnm are explored for drug loading and release studies using doxorubicin (DOX) as a model anticancer drug. Moreover, the f-Dnm nanocarrier demonstrates significantly higher drug loading capabilities (∼90%). In vitro release studies of doxorubicin-loaded f-Dnm [f-Dnm(DOX)] reveal 5 times higher drug release at lysosomal pH 5.4 compared to that at physiological blood pH 7.4. Cytocompatibility assessments using the MTT assay on HeLa, A549, and NIH-3T3 cells confirm the nontoxic nature of f-Dnm, even at high concentrations. Additionally, f-Dnm(DOX) exhibits higher cytotoxicity in HeLa cells compared to f-CD(DOX) at similar DOX concentrations. Cellular uptake studies show an increased uptake of f-Dnm in folate receptor-positive HeLa and MDA-MB 231 cells. Hemolysis assay validated the biocompatibility of the developed formulation. Overall, these engineered nanodroplets represent a class of nontoxic nanocarriers that offer promising potential as nanotherapeutics for folate receptor-positive cells.

Construction of fluorescent sensor array with nitrogen-doped carbon dots for sensing Sudan Orange G and identification of various azo compounds

In this study, nitrogen-doped carbon dots (N-CDs) were facilely fabricated by one-pot hydrothermal method with levulinic acid and triethanolamine. A fluorescent sensor array was established for identifying azo compounds including Sudan Orange G (SOG), p-diaminoazobenzene, p-aminoazobenzene, azobenzene and quantitative detection of SOG. Experimental results revealed that azo compounds could quench the fluorescent intensity of N-CDs. Owing to various azo compounds showing different affinities to N-CDs, the sensor array exhibited different fluorescence quenching changes, which were further analyzed with principal component analysis to discriminate azo compounds. The sensor array was able to differentiate and recognize diverse concentrations of azo compounds from 0.25 to 2 mg/L. Simultaneously, a variety of factors affecting the detection of SOG were optimized. Under the optimized conditions, the sensor showed excellent stability and sensitivity. The sensor possessed marvelous linearity in the range of 0.1-1 mg/L and 1-4 mg/L and the detection limit was 27.82 μg/L. Spiked recoveries of 90.8-98.2 % were attained at spiked levels of 0.2 mg/L and 1 mg/L, demonstrating that the constructed fluorescence sensor was dependable and feasible for sensing SOG in environmental water samples.

Carbon Dots and Their Polymeric Nanocomposites: Insight into Their Synthesis, Photoluminescence Mechanisms, and Recent Trends in Sensing Applications

Carbon dots (CDs), a novel class of carbon-based nanoparticles, have received a lot of interest recently due to their exceptional mechanical, chemical, and fluorescent properties, as well as their excellent photostability and biocompatibility. CDs' emission properties have already found a variety of potential applications, in which bioimaging and sensing are major highlights. It is widely acknowledged that CDs' fluorescence and surface conditions are closely linked. However, due to the structural complexity of CDs, the specific underlying process of their fluorescence is uncertain and yet to be explained. Because of their low toxicity, robust and wide optical absorption, high chemical stability, rapid transfer characteristics, and ease of modification, CDs have been recognized as promising carbon nanomaterials for a variety of sensing applications. Thus, following such outstanding properties of CDs, they have been mixed and imprinted onto different polymeric components to achieve a highly efficient nanocomposite with improved functional groups and properties. Here, in this review, various approaches and techniques for the preparation of polymer/CDs nanocomposites have been elaborated along with the individual characteristics of CDs. CDs/polymer nanocomposites recently have been highly demanded for sensor applications. The insights from this review are detailed sensor applications of polymer/CDs nanocomposites especially for detection of different chemical and biological analytes such as metal ions, small organic molecules, and several contaminants.

Aldehyde modified nanocellulose-based fluorescent hydrogel toward multistage data security encryption

In view of the insecurity of encode information storage based on fluorescence switch single-stage encryption, a fluorescent hydrogel for multistage data security encryption were proposed, named as polyvinyl alcohol/dialdehyde cellulose nanofibrils/carbon quantum dots hydrogel. Herein, the interpenetrating network was formed by chemically crosslinking between polyvinyl alcohol (PVA) and dialdehyde cellulose nanofibrils (DACNF). Additionally, nitrogen-doped carbon quantum dots (CDs) synthesized by one-step hydrothermal method were introduced into the above hydrogel system by hydrogen bonds. The resultant fluorescent hydrogels possessed high stretchability up to 530 %, good strength of 0.96 MPa, Fe3+-responsive fluorescence quenching, fluorescence recovery triggered by ascorbic acid and borax-triggered shape memory. Moreover, various complex 3D hydrogel geometries were fabricated by folding/assembling 2D fluorescent hydrogel sheets, extending data encryption capability from 2D plane to 3D space. More remarkably, the 3D data encryption-erasing process of fluorescent hydrogel was realized by the strategy of alternating treatment of Fe3+ solution and ascorbic acid solution. This work provided a facile and general strategy for constructing high security important information encryption and protection.

Zero Thermal Quenching Phenomenon of Green Emitting Carbon Dots with High Biocompatibility and Stable Multicolor Biological Imaging in a Hot Environment

Carbon dots are emerging fluorescent nanomaterials with unique physical and chemical properties and a wide range of applications. Herein, we have designed and successfully synthesized thermally stable green emissive nitrogen-doped carbon dots (NCDs) with a photoluminescent quantum yield of 11.32% through facile solvent-free carbonization. NCDs demonstrated zero thermal quenching upon various temperatures modulating from 20 to 80 °C. The green emissive NCDs perform very stably even after heating them at 80 °C for 1 h. The thermal stability mechanism demonstrates that C═O and C═N functional groups control the particle aggregation and protect the fluorescent hub from photo-oxidation and thermal oxidation. Highly biocompatible CDs exhibit bright, stable, and multicolor emissions in T-ca cells under hot circumstances (25-45 °C). Additionally, NCDs offer long-term stability in the biosystem, as evidenced by the fact that the cell retains its brightness about 70% after prolonging the incubation time to 8 days. Furthermore, the fluorescent NCDs are utilized as in vivo imaging agents in the hot environment as they display bright and thermally stable imaging (27-45 °C) under 488 nm excitation. The results confirmed that the produced thermally stable NCDs could be used in biology and related medical fields that require hot environment imaging.

Stability of carbon quantum dots: a critical review

Carbon quantum dots (CQDs) are fluorescent carbon nanomaterials with unique optical and structural properties that have drawn extensive attention from researchers in the past few decades. Environmental friendliness, biocompatibility and cost effectiveness of CQDs have made them very renowned in countless applications including solar cells, white light-emitting diodes, bio-imaging, chemical sensing, drug delivery, environmental monitoring, electrocatalysis, photocatalysis and other related areas. This review is explicitly dedicated to the stability of CQDs under different ambient conditions. Stability of CQDs is very important for every possible application and no review has been put forth to date that emphasises it, to the best of our knowledge. This review's primary goal is to make the readers cognizant of the importance of stability, ways to assess it, factors that affect it and proposed ways to enhance the stability for making CQDs suitable for commercial applications.

Carbon-Based Stimuli-Responsive Nanomaterials: Classification and Application

Carbon-based nanomaterials, including carbon nanotubes, carbon nanospheres, and carbon nanofibers, are becoming a research hotspot due to their unique structure and good mechanical, thermal, electrical, optical, and chemical properties. With the development of material synthesis technology, they can be functionalized and used in various fields such as energy, environment, and biomedicine. In particular, stimuli-responsive carbon-based nanomaterials have stood out in recent years because of their smart behavior. Researchers have applied carbon-based nanomaterials to different disease treatments based on their stimulus-response properties. In this paper, based on stimuli-responsive carbon-based nanomaterials' morphology, we categorize them into carbon nanotubes, carbon nanospheres, and carbon nanofibers according to their morphology. Then, their applications in probes, bioimaging, tumor therapy, and other fields are discussed. Finally, we address the advantages and disadvantages of carbon-based stimuli-responsive nanomaterials and discuss their future perspective.

A versatile platform for colorimetric, fluorescence and photothermal multi-mode glyphosate sensing by carbon dots anchoring ferrocene metal-organic framework nanosheet

Concerns regarding pesticide residues have driven attempts to exploit accurate, prompt and straightforward approaches for food safety pre-warning. Herein, a nanozyme-mediated versatile platform with multiplex signal response (colorimetric, fluorescence and temperature) was proposed for visual, sensitive and portable detection of glyphosate (GLP). The platform was constructed based on a N-CDs/FMOF-Zr nanosensor that prepared by in situ anchoring nitrogen-doped carbon dots onto zirconium-based ferrocene metal-organic framework nanosheets. The N-CDs/FMOF-Zr possessed excellent peroxidase (POD)-like activity and thus could oxide colorless 3, 3', 5, 5'-tetramethylbenzidine (TMB) into a blue oxidized TMB (oxTMB) in presence of H₂O₂. Intriguingly, owing to the blocking effect triggered by multiple interaction between GLP and N-CDs/FMOF-Zr, its POD-like activity of the latter was remarkably suppressed, which can modulate the transformation of TMB into oxTMB, generating tri-signal responses of fluorescence enhancement, absorbance and temperature decrease. More significantly, the temperature mode can be facilely realized by a portable home-made mini-photothermal device and handheld thermometers. The proposed multimodal sensing was capable of providing sensitive results by fluorescence mode and simultaneously realized visual/portable testing by colorimetric and photothermal channels. Consequently, it exhibited more adaptability for practical applications, which can satisfy different testing requirements according to sensitivity and available instruments/meters, presenting a new horizon for exploiting multifunctional sensors.

Cellulose as an Eco-Friendly and Sustainable Material for Optical Anticounterfeiting Applications: An Up-to-Date Appraisal

The falsification of documents, currency, pharmaceuticals, branded goods, clothing, food products, and packaging leads to severe consequences. Counterfeited products can not only pose health risks to consumers but also cause substantial economic losses that can negatively impact the global markets. Unfortunately, most anticounterfeiting strategies are easily duplicated due to rapid technological advancements. Therefore, innovative and cost-effective antiforgery techniques that can offer superior multilevel security features are continuously sought after. Due to the ever-growing global awareness of environmental pollution, renewable and eco-friendly native biopolymers are garnering wide attention in anticounterfeiting applications. This review highlights the potential use of cellulose-based eco-friendly materials to combat the counterfeiting of goods. The initial section of the review focuses on the structure, properties, and chemical modifications of cellulose as a sustainable biomaterial. Further, the topical developments reported on cellulose and nanocellulose-based materials used as fluorescent security inks, films, and papers for achieving protection against counterfeiting are presented. The studies suggest the convenient use of celluose and modified cellulose materials for promising optical antiforgery applications. Furthermore, the scope for future research developments is also discussed based on the current critical challenges in the fabrication of cellulose-based materials and their anticounterfeit applications.

Synthesis of N-doped carbon dots for highly selective and sensitive detection of metronidazole in real samples and its cytotoxicity studies

The current investigation reports the synthesis of N-CDs using glucosamine, ascorbic acid, and ethylenediamine precursors by a simple hydrothermal technique. The formation of N-CDs was proved by various characterisation techniques such as X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and Fourier-Transform Infrared Spectrophotometer (FT-IR). The optical properties were investigated by fluorescence and UV-vis spectrophotometer. Also, N-CDs showed high selectivity in detecting the MTZ compared to several other analytes. However, the metronidazole serves as an antibiotic against several microbial diseases but also a genotoxic, carcinogenic to the human when used in excessive dosage. The synthesised N-CDs showed high selectivity in detecting the MTZ compared to several other analytes. Besides, the cytotoxicity of the N-CDs was studied to evaluate its toxicity against the HeLa cancer cells. It showed 65.6% cell viability and 34.3% toxicity against the cancerous cells, and similarly 71% of cells viability against H9C2 cells. Thus, the current investigation explores the promising selective sensing of N-CDs against MTZ, along with that, it proved its cytotoxicity against HeLa cancerous cells and non-toxicity against H9C2 cells. The synthesised CDs can be better MTZ sensors and anti-cancer agents on further development at the industrial scale.

Dye Plants Derived Carbon Dots for Flexible Secure Printing

Carbon dots (C-dots) are fluorescent nanomaterials, exhibiting excellent structure-dependent optical properties for various types of optical and electrical applications. Although many precursors were used for C-dots production, it is still a challenge to produce high-quality C-dots using environmentally-friendly natural precursors. In this work, multiple-colored colloidal C-dots were synthesized via a heating reaction using natural plant dyes as precursors, for example, Indigo, Carcuma longa, and Sophora japonica L. The as-prepared C-dots have absorption in the UV range of 220 to 450 nm with the typical emission ranging from 350 to 600 nm. The as-obtained C-dots have a quantum yield as high as 3.8% in an aqueous solution. As a proof-of-concept, we used the as-prepared C-dots as fluorescence inks for textile secure printing. The printed patterns are almost invisible under daylight and have distinct and clear patterns under 365 and 395 nm light, proving the great potential in optical anti-counterfeiting. This work demonstrates the advanced strategy for high-performance C-dots production from natural dyes and their potential application in flexible secure printing systems.

ZnO/CQDs Nanocomposites for Visible Light Photodegradation of Organic Pollutants

Currently, carbon quantum dots (CQDs) have been widely investigated as an enhancing photocatalytic component of various nanocomposites. In this study, hetero-structures containing carbon quantum dots (CQDs) associated to zinc oxide were prepared following two one-pot procedures: (i) a hydrothermal approach in which commercial ZnO was used as carrier for CQDs; and (ii) an approach in which the ZnO/CQDs samples were produced in situ by adding zinc acetate to an aqueous suspension of CQDs. CQDs were prepared in advance by a low-temperature hydrothermal (LHT) treatment of useless humins wastes produced by the glucose dehydration in an acidic medium. These samples were characterized by several techniques such asadsorption-desorption isotherms of liquid nitrogen at 77K, X-ray diffraction (XRD), infrared diffuse reflectance with Fourier transform (DRIFT) and UV-vis spectroscopy. The photocatalytic behavior of these materials was investigated in the degradation of methylene blue (MB). The obtained results revealed electronic interactions between CQDs and ZnO which have as an effect an enhancement of the charge separation and diminution of the charge recombination. In accordance, a correlation between the photocatalytic activity and the intrinsic properties of ZnO/CQDs has been evidenced. The highest photocatalytic activity corresponded to the heterostructure containing highly dispersed narrow sized CQDs onto ZnO. Under visible light irradiation and after 180 min of irradiation, MB was degraded by as much as 97.6%.

A Review on Carbon Quantum Dots: Synthesis, Photoluminescence Mechanisms and Applications

Carbon quantum dots (CQDs), having outstanding biocompatibility, attractive catalytic performance, excellent optical properties, and valuable environment friendliness, are emerging as a new paradigm to design luminescent devices and show great potential in application fields such as biomedical sensors, optical and photonic devices. And CQDs are known as one of the most promising carbon based nanomaterials in the 21st century. Therefore, it has attracted a lot of attention since it was first discovered in 2004. In this review, we explain the accepted photoluminescence mechanism of CQDs, including fluorescence and phosphorescence. There are two main types of synthesis strategies: top-down approach and bottom-up approach. At the same time, the main application fields, including ion detection, anti-counterfeiting, biological imaging, food safety, sensors, lubrication additives, are reviewed. Finally, the existing bottlenecks, pending problems and prospects for the future of CQDs are discussed.

Uracil-Appended Fluorescent Sensor for Cu2+ and Hg2+ Ions: Real-Life Utilities Including Recognition of Vitamin B2 (Riboflavin) in Milk Products and Invisible Ink Applications

A simple uracil-appended fluorescent sensor (1) has been developed by one pot reaction and characterized by using common spectroscopic methods such as UV-vis, Fluorescence, HRMS and FT-IR analyses. Upon addition of various metal ions to the CH₃CN solution of sensor 1, the fluorescence was quenched in the presence of Cu²⁺ / Hg²⁺ ions. The limit of detection for Cu²⁺ and Hg²⁺ was calculated to be 3.31 and 0.316 µM, respectively. Further, the sensor was applied for real-life applications in the determination of Vitamin B₂ (riboflavin) and its presence in milk products. With the incorporation of different sources of vitamin-B to acetonitrile solution of it, there was discernible fluorescence enhancement only in the presence of vitamin B₂. Also, it has been successfully applied for the detection of Vitamin B₂ (riboflavin) in milk and curd. Moreover, based on the fluorescent color changes, the sensor was utilized for invisible ink applications.

Facile preparation of aqueous-soluble fluorescent polyethylene glycol functionalized carbon dots from palm waste by one-pot hydrothermal carbonization for colon cancer nanotheranostics

Carbon dots (CDs) are categorized as an emerging class of zero-dimension nanomaterials having high biocompatibility, photoluminescence, tunable surface, and hydrophilic property. CDs, therefore, are currently of interest for bio-imaging and nano-medicine applications. In this work, polyethylene glycol functionalized CDs (CD-PEG) were prepared from oil palm empty fruit bunch by a one-pot hydrothermal technique. PEG was chosen as a passivating agent for the enhancement of functionality and photoluminescence properties of CDs. To prepare the CDs-PEG, the effects of temperature, time, and concentration of PEG were investigated on the properties of CDs. The as-prepared CDs-PEG were characterized by several techniques including dynamic light scattering, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, fluorescence spectroscopy, Raman spectroscopy, Fourier-transform infrared spectroscopy and Thermogravimetric analysis. The as-prepared CDs under hydrothermal condition at 220 °C for 6 h had spherical morphology with an average diameter of 4.47 nm. Upon modification, CDs-PEG were photo-responsive with excellent photoluminescence property. The CDs-PEG was subsequently used as a drug carrier for doxorubicin [DOX] delivery to CaCo-2, colon cancer cells in vitro. DOX was successfully loaded onto CDs-PEG surface confirmed by FT-IR and Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometer (MALDI-TOF/MS) patterns. The selective treatment of CDs-PEG-DOX against the colorectal cancer cells, , relative to normal human fibroblast cells was succesfully demonstrated.

Zn-assisted modification of the chemical structure of N-doped carbon dots and their enhanced quantum yield and photostability

This article presents the Zn-assisted synthesis of N-doped carbon dots (N-CDs) with an enhanced quantum yield (QY) and photostability. There have been intensive studies to improve or tune the optical properties of carbon dots (CDs) to meet the demand for luminescent materials in various fields, including energy conversion, photocatalysis, bioimaging, and phototherapy. For these applications, the photostability of the CDs is also a critical factor, but the related studies are relatively less common. The Zn-assisted N-CDs (denoted as Zn:N-CDs) obtained by the addition of Zn(OAc)₂ to the precursors during the synthesis of N-CDs not only exhibited an enhanced quantum yield but also improved photostability compared to those of N-CDs. A comprehensive study of the chemical composition of Zn:N-CD and N-CD using X-ray photoelectron spectroscopy indicated a correlation between their chemical structure and photostability. Zn(OAc)₂, which acts as a catalytic reagent, induced the modification of chemical structures at the edges of carbogenic sp² domains, without being doped in N-CD, and the heteroatom-carbon bonds in Zn:N-CD seemed to be more resistant to light compared to those in N-CDs. The increased QY and photostability of Zn:N-CDs make them more suitable as an optical probe and they could be used in fingerprint identification. With Zn:N-CDs, the microstructure of fingerprints was confirmed clearly for a long duration effectively.

Background color dependent photonic multilayer films for anti-counterfeiting labeling

A new concept for anti-counterfeiting security films that utilize the humidity from human breath to reveal a QR code on color-tunable one-dimensional (1D) PC films is presented. The 1D PC film was fabricated on a transparent polyethylene terephthalate (PET) substrate via sequential alternate layer deposition of photo-crosslinkable poly(2-vinylnaphthalene-co-benzophenone acrylate) (P(2VN-co-BPA)) and quaternized poly(4-vinylpyridine-co-benzophenone acrylate) (P(4VP-co-BPA)) (P4QP-51%). The films exhibited remarkable color transitions with reliable reversibility and reproducibility. Films placed on a black background exhibited the full visible spectrum color in a high humidity environment. Additionally, films placed on a white background displayed three different composite colors, including yellow, magenta, and cyan. These films with vivid color transitions in a high humidity environment can be applied as anti-counterfeiting films. A hidden QR code was also laser printed on the initial PC film to enhance the film's anti-counterfeiting security capabilities. These colorimetric 1D PC films can be used as anti-counterfeiting labels and for information storage.

Highly Photostable Carbon Dots from Citric Acid for Bioimaging

Bioimaging supported by nanoparticles requires low cost, highly emissive and photostable systems with low cytotoxicity. Carbon dots (C-dots) offer a possible solution, even if controlling their properties is not always straightforward, not to mention their potentially simple synthesis and the fact that they do not exhibit long-term photostability in general. In the present work, we synthesized two C-dots starting from citric acid and tris (hydroxymethyl)-aminomethane (tris) or arginine methyl ester dihydrochloride. Cellular uptake and bioimaging were tested in vitro using murine neuroblastoma and ovine fibroblast cells. The C-dots are highly biocompatible, and after 24 h of incubation with the cells, 100% viability was still observed. Furthermore, the C-dots synthesized using tris have an average dimension of 2 nm, a quantum yield of 37%, high photostability and a zeta potential (ζ) around −12 mV. These properties favor cellular uptake without damaging cells and allow for very effective bioimaging.

Structural evolution of carbon dots during low temperature pyrolysis

Carbon dots (CDs) are an emerging class of photoluminescent material. Their unique optical properties arise from the discrete energy levels in their electronic states, which directly relate to their crystalline and chemical structure. It is expected that when CDs go through structural changes via chemical reduction or thermal annealing, their energy levels will be altered, inducing unique optoelectronic properties such as solid-state photoluminescence (PL). However, the detailed structural evolution and how the optoelectronic characteristics of CDs are affected remain unclear. Therefore, it is of fundamental interest to understand how the structure of CDs prepared by hydrothermal carbonisation (HTC) rearranges from a highly functionalised disordered structure into a more ordered graphitic structure. In this paper, detailed structural characterisation and in situ TEM were conducted to reveal the structural evolution of CDs during the carbonisation process, which have demonstrated a growth in aromatic domains and reduction in oxidation sites. These structural features are correlated with their near-infrared (NIR) solid-state PL properties, which may find a lot of practical applications such as temperature sensing, solid-state display lighting and anti-counterfeit security inks.

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.

Carbon dot/inorganic nanomaterial composites

The preparation methods, formation mechanism, properties and applications of carbon dot/inorganic nanohybrid materials are reported.

Design and engineering of a dual-mode absorption/emission molecular switch for all-optical encryption

Photochemical reactions that produce a detectable change in the spectroscopic properties of organic chromophores can be exploited to harness the principles of Boolean algebra and design molecule-based logic circuits. Moreover, the logic processing capabilities of these photoactive molecules can be directed to protect, encode, and conceal information at the molecular level. We have designed a photochemical strategy to read, write and encrypt data in the form of optical signals. We have synthesized a supramolecular system based on the known dye resazurin, and investigated a series of photochemical transformations that can be used to regulate its absorption and emission properties upon illumination with ultraviolet or visible light. We have then examined the logic behaviour of the photochemistry involved, and illustrated its potential application in data encryption.

Fluorescent Carbon Dots an Effective Nano-Thermometer in Vitro Applications

Fluorescent sensing of temperature in nanoscale regions has many advantages and applications in the biological field. Herein, blue emitting carbon dots (CDs) are designed and successfully developed using a one step hydrothermal method. As synthesized CDs exhibit temperature dependent photoluminescent (PL) intensity and PL decay lifetime over the physiological temperature ranging from room temperature (RT) to 70 °C. The PL intensity and PL decay lifetime of the obtained CDs correlate linearly to temperature (RT-70 °C) with correlation coefficient of 0.997 and 0.996, respectively. Additionally, dual mode thermal sensing (PL intensity/lifetime) make these CDs a promising optical nanothermometer over alternative semiconductors quantum dots and CD-based quantum dots. Moreover, the resultant aqueous CDs demonstrate excitation-independent blue emission, and the PL quantum yield (QY) is reached at 44.5%. The obtained CDs illustrate stable performance to high ionic environments and photobleaching even after keeping them for 2 h under continues UV irradiation. Furthermore, blue emitting CDs have low cytotoxicity for T-ca. cells and illuminate deep blue fluorescence under the excitation of 406 nm. As a result, high thermal sensitivity of these fluorescent CDs has potential to detect temperature in living cells in the range of 25-40 °C.

Magnetic perovskite nanoparticles for latent fingerprint detection

Fingerprints form when fingers touch a solid surfaceand are considered the best way for individual identification. However, the current latent fingerprint (LFP) developing methods cannot meet the demand for high sensitivity and being convenient and healthy. Herein, bifunctional Fe3O4@SiO2-CsPbBr3 powders have been designed and fabricated and exhibit good magnetic and strong fluorescent properties. The magnetism of Fe3O4 can avoid dust flying, while the fluorescence of CsPbBr3 ensures the high definition of LFPs. Clear fingerprints have been detected on various solid substrates using the Fe3O4@SiO2-CsPbBr3 powders instead of eikonogen. Detailed characterization studies suggest that the ammonium cationic groups on the surface of nanoparticles (NPs) have strong adhesive interactions with the residues of fingerprints because of the electrostatic attraction between them. Therefore, the convenient operation and excellent resolution offer great opportunity in the practical application of fingerprint detection and other areas.

Leftover Kiwi Fruit Peel-Derived Carbon Dots as a Highly Selective Fluorescent Sensor for Detection of Ferric Ion

Recently, the use of natural products for the synthesis of carbon dots (CDs) has received much attention. Herein, leftover kiwi (Actinidia Deliciosa) fruit peels were successfully turned into beneficial fluorescent carbon dots (KN-CDs) via the hydrothermal-carbonization route. KN-CDs 1 and KN-CDs 2 were prepared without and with ammonium hydroxide, respectively. KN-CDs 1 and KN-CDs 2 were systematically characterized by various analytical techniques. Synthesized KN-CDs showed spherical-shaped morphology with narrow size distribution and excellent optical properties with excitation-independent behaviors. The quantum yields of KN-CDs 1 and KN-CDs 2 were calculated as 14 and 19%, respectively. Additionally, the KN-CDs possess excellent prolonging and photostability. Because of the excellent optical properties of KN-CDs, they were utilized as fluorescent sensors. The strong fluorescence of the KN-CDs was selectively quenched by Fe3+ ion, and quenching behavior showed a linear correlation with the concentrations of Fe3+ ion. KN-CDs 1 and KN-CDs 2 showed the detection of Fe3+ ions within the concentration range of 5–25 µM with the detection limit of 0.95 and 0.85 µM, respectively. Based on the turn-off sensing by the detection of Fe3+ ions, KN-CDs would be a promising candidate as a selective and sensitive fluorescent sensor.

Ultra-high quantum yield nitrogen-doped carbon quantum dots and their versatile application in fluorescence sensing, bioimaging and anti-counterfeiting

The exploration of carbon quantum dots (CQDs) with ultra-high quantum yield, simple synthesis path, and satisfying output to facilitate their wide applications in numerous fields are always the research focus. In this work, nitrogen-doped carbon quantum dots (N-CQDs) with strong blue fluorescence were synthesized with a simple one-step hydrothermal method using citric acid and o-phenylenediamine as raw materials, and the absolute quantum yield was as high as 92.1%. The detailed research results demonstrate that the N-CQDs have outstanding fluorescence stability, high selectivity, and anti-interference in Hg²⁺ detection. The obtained N-CQDs also possess excellent biocompatibility, which can also be successfully applied in cell imaging and intracellular Hg²⁺ detection. Most importantly, due to their high quantum yield and excellent dispersibility, the N-CQDs solution can be used as a quick-drying fluorescent ink for ink-jet printing. Therefore, the as-prepared N-CQDs have great potential in fluorescence sensing, biomedical diagnosis, data encryption, and anti-counterfeiting.

An advanced color tunable persistent luminescent NaCa2GeO4F:Tb3+ phosphor for multicolor anti-counterfeiting

Luminescent materials play an important role in anticounterfeiting applications due to their superior properties of visual convenience and high concealment. However, traditional luminescent materials usually exhibit monochromatic emission and are easily counterfeited. Therefore, in this work, we report a multicolor long persistent luminescence (PersL) material, NaCa2GeO4F:Tb3+ (abbreviated as NCGOF:Tb3+), where the color of PersL can be tuned from blue to cyan and bright green by changing the concentration of Tb3+, and the afterglow (concentration) can last for 5.62 h (0.1%), 8.52 h (0.4%) and 7.14 h (0.8%) at the corresponding concentrations of Tb3+, respectively. Investigation revealed that the multicolor PersL is essentially associated with the opportune traps and cross-relaxation effect of Tb3+ in NCGOF. Based on the unique features of PersL, anticounterfeiting devices have been fabricated, and the results indicate that their multicolor features can be easily detected using a portable ultraviolet lamp, and that they are impossible to counterfeit using any substitute so far, meaning that they provide a high level of security for use in practical applications.

Carbon Nanodots as a Multifunctional Fluorescent Sensing Platform for Ratiometric Determination of Vitamin B2 and "Turn-Off" Detection of pH

In this work, we synthesized carbon nanodots (CNDs) by a one-pot hydrothermal method to carbonize precursors of dry carnation petals and polyethylenimine. The obtained CNDs possess favorable photostability, good biocompatibility, and excellent water solubility, which can serve as a dual-responsive nanosensor for the determination of vitamin B₂ (VB₂) and pH. A unique ratiometric fluorescence resonance energy transfer probe was developed through a strong interaction between VB₂ and surface moieties of CNDs. CNDs emitted at 470 nm; however, in the presence of VB₂, an enhanced emission peak was clearly observed at 532 nm. The value of I₅₃₂/I₄₇₀ exhibits a stable response to the VB₂ concentration from 0.35 to 35.9 μM with a detection limit of 37.2 nM, which has been used for VB₂ detection in food and medicine samples and ratiometric imaging of VB₂ in living cells with satisfying performance. In addition, the proposed CNDs also displayed pH-sensitive behavior and can be a turn-off fluorescent sensor to monitor pH. The fluorescent intensity at 470 nm is a good linear response against pH values from 3.6 to 8, affording the capability as a single-emissive nanoprobe for intracellular pH sensing.

Water-soluble green-emitting carbon nanodots with enhanced thermal stability for biological applications

High stability and water solubility of fluorescent nanomaterials are considered key factors to evaluate their feasibility for fundamental applications. Herein, water-soluble and thermally stable, green-emitting carbon nanodots (CNDs) have been synthesized via a facile hydrothermal method with an average size of 1.9 nm. CNDs showed green emission centered at 544 nm with the photo-luminescence quantum yield (PLQY) of up to 10.1% under the excitation of 400 nm. The obtained CNDs demonstrated high resistance towards photo-bleaching and an ionic (KCl) environment. Moreover, the aqueous solution of CNDs exhibited excellent stability under harsh thermal conditions from 10 °C to 80 °C. The as-prepared CNDs showed stable performance at high temperatures, even after keeping them at 80 °C for 30 min. Furthermore, the green emissive CNDs were incubated in T-ca cancer cells for bio-imaging applications. The results indicated that CNDs can served as an effective thermally-stable bio-imaging agent in T-ca cells at the physiological temperature range of 25 °C-45 °C. Green emission and excellent thermal stability make these CNDs promising fluorescent materials for potential applications in the medical field, which requires long-wavelength fluorescence and high-temperature imaging.

Preparation, characterization and in vitro anticancer performance of nanoconjugate based on carbon quantum dots and 5-Fluorouracil

This study is focused on the development of a nanodevice for loading and release of 5-Fluorouracil (5-FU) with a view to improving its therapeutic efficiency, using as strategy the fabrication of a nanoconjugate through drug anchorage on the surface of carbon quantum dots (CQD). Several physicochemical and analytical techniques were employed to obtain information about materials morphology, structure, and optical properties. The results indicated that the interactions between both entities resulted in good physicochemical properties and photostability. Acid pH favored drug release, indicating a tendency to release 5-FU from 5-FU-CQD into the tumor microenvironment. The cytotoxicity of CQD and 5-FU-CQD nanoconjugate was evaluated against normal human lung fibroblast (GM07492A) and human breast cancer (MCF-7) cell lines. The CQD was non-toxic, indicating that these materials are biocompatible and can be used as a nanocarrier for 5-FU in biological systems. For the 5-FU-CQD nanoconjugate, it was observed a reduction in toxicity for normal cells compared to free 5-FU, suggesting that drug anchoring in CQD reduced drug-associated toxicity, while for cancer cells exhibited an antitumor effect equivalent to that of the free drug, opening perspectives for the application of this material in anticancer therapy.

Polymerization-Driven Photoluminescence in Alkanolamine-Based C-Dots

Carbonized polymer dots (CPDs), a peculiar type of carbon dots, show extremely high quantum yields, making them very attractive nanostructures for application in optics and biophotonics. The origin of the strong photoluminescence of CPDs resides in a complicated interplay of several radiative mechanisms. To understand the correlation between CPD processing and properties, the early stage formation of carbonized polymer dots has been studied. In the synthesis, citric acid monohydrate and 2-amino-2-(hydroxymethyl)propane-1,3-diol have been thermally degraded at 180 °C. The use of an oil bath instead of a more traditional hydrothermal reactor has allowed the CPD properties to be monitored at different reactions times. Transmission electron microscopy, time-resolved photoluminescence, nuclear magnetic resonance, infrared, and Raman spectroscopy have revealed the formation of polymeric species with amide and ester bonds. Quantum chemistry calculations have been employed to investigate the origin of CPD electronic transitions. At short reaction times, amorphous C-dots with 80 % quantum yield, have been obtained.

Color-switchable hybrid dots/hydroxyethyl cellulose ink for anti-counterfeiting applications

Many anti-counterfeiting inks have been explored recently, most of them are commonly involved in weak fastness, high cost and long-term toxicity, impeding their real-life applications. Herein, an environment-friendly and inexpensive anti-counterfeiting ink with excellent fastness is reported. The untifake ink is developed by combining hybrid dots (silicon/carbon) with hydroxyethyl cellulose (HEC) binder. Interestingly, the HEC binder can effectively prevent from aggregation-induced quenching of hybrid dots. Subsequently, the customized patterns are successfully transferred onto different surfaces of various substrates including cotton fabric, cellulosic paper, glass, metal, silicon wafer and PET film, using the as-prepared ink by screen-printing technique, exhibiting that the hybrid dots/HEC ink possesses widespread practicability. Notably, fluorescent color of these patterns can be switchable by adjusting environmental pH-value, further imparting the as-prepared ink with excellent covert performance. This new fluorescent hybrid dots/HEC ink will be promising candidates for high-level anti-counterfeiting applications including food packaging, apparel and documents.

Recent advances in luminescent materials for super-resolution imaging via stimulated emission depletion nanoscopy

Recent progress on STED fluorophores for super-resolution imaging and also their characteristics are outlined here, thus providing some guidelines to select proper probes and even develop new materials for super-resolution imaging via STED nanoscopy.

Hydrothermal synthesis of fluorescent carbon dots from gardenia fruit for sensitive on-off-on detection of Hg2+ and cysteine

Nitrogen and sulfur co-doped carbon dots (N/S-CDs) were prepared by a simple hydrothermal method using gardenia fruit as precursor. The N/S-CDs are nearly spherical particles with a size of 2.1 nm and possess excellent fluorescence stability in a wide pH range and high NaCl concentrations, as well as under UV light irradiation. The absolute quantum yield (QY) without any surface modification reaches up to 10.7%. Meanwhile, the N/S-CDs can be quenched by Hg²⁺ (turn-off), while the quenched fluorescence can be recovered (turn-on) by introducing cysteine (Cys), with linear ranges of 2-20 μM for Hg²⁺and 0.1-2.0 μM for Cys. On the basis of the on-off-on sensing mode, the N/S-CDs can be used to detect Hg²⁺ and Cys. Hence, the N/S-CDs would be a promising sensor in environmental and biological analysis.