Synthesis of novel β-cyclodextrin functionalized S, N codoped carbon dots for selective detection of testosterone

Construction of CDs@β-CD@CCM ratiometric fluorescence probe for FRET-based ClO--sensing

β-Cyclodextrin (β-CD)-functionalized carbon quantum dots (CDs) loaded with curcumin (CCM) were used for ClO-sensing with high sensitivity and selectivity. This fluorescence resonance energy transfer (FRET)-based sensor was created through attaching CCM to the CDs via β-CD linker. CCM could get into the interior of β-CD triggering the FRET from CDs to CCM, providing an 'off' state of the CDs. However, the effect of FRET was weakened by the ClO-, because the o-methoxyphenol structure from CCM was oxidized to be benzoquinone. The fluorescence intensity of CDs@β-CD@CCM at 440 nm can be heightened and 520 nm from CCM can decrease along with the increased ClO-. Therefore, a ratiometric fluorescence probe for ClO-sensing is successfully constructed. It conforms to a polynomial curve equation which is I440/I520= -0.0268 + 0.0315 CClO-+ 0.0055[CClO-]2(R2= 0.9958) between 0 and 18.4μM ClO-. Furthermore, we also obtain excellent results using this spectrophotometric method for ClO--sensing in pure water and commercial disinfectants, which afford potential in the environment monitoring area. We expect this sensing platform could be helpful in other analogous probes in relevant fields.

Research progress of fluorescent composites based on cyclodextrins: Preparation strategies, fluorescence properties and applications in sensing and bioimaging

Fluorescence analysis has been regarded as one of the commonly used analytical methods because of its advantages of simple operation, fast response, low cost and high sensitivity. So far, various fluorescent probes, with noble metal nanoclusters, quantum dots, organic dyes and metal organic frameworks as representatives, have been widely reported. However, single fluorescent probe often suffers from some deficiencies, such as low quantum yield, poor chemical stability, low water solubility and toxicity. To overcome these disadvantages, the introduction of cyclodextrins into fluorescent probes has become a fascinating approach. This review (with 218 references) systematically covers the research progress of fluorescent composites based on cyclodextrins in recent years. Preparation strategies, fluorescence properties, response mechanisms and applications in sensing (ions, organic pollutants, bio-related molecules, temperature, pH) and bioimaging of fluorescent composites based on cyclodextrins are summarized in detail. Finally, the current challenges and future perspectives of these composites in relative research fields are discussed.

Luminescent carbon dots versus quantum dots and gold nanoclusters as sensors

Ultra-small nanoparticles, including quantum dots, gold nanoclusters (AuNCs) and carbon dots (CDs), have emerged as a promising class of fluorescent material because of their molecular-like properties and widespread applications in sensing and imaging. However, the fluorescence properties of ultra-small gold nanoparticles (i.e., AuNCs) and CDs are more complicated and well distinguished from conventional quantum dots or organic dye molecules. At this frontier, we highlight recent developments in the fundamental understanding of the fluorescence emission mechanism of these ultra-small nanoparticles. Moreover, this review carefully analyses the underlying principles of ultra-small nanoparticle sensors. We expect that this information on ultra-small nanoparticles will fuel research aimed at achieving precise control over their fluorescence properties and the broadening of their applications.

Orange peel-derived carbon dots/Cu-MOF nanohybrid for fluorescence determination of l-ascorbic acid and Fe3. Anal Chim Acta 2024;1287:342066. [PMID: 38182373 DOI: 10.1016/j.aca.2023.342066]

Recycling and reuse of biomass waste in synthesis of nanomaterials have recently received much attention as an effective solution for environmental protection and sustainable development. Herein, nitrogen-doped carbon dots (N-CDs) with blue emission were synthesized from the orange peels as a precursor through a simple hydrothermal method and then, modified with ethylenediamine tetraacetic acid (N-CD@EDTA). The N-CD@EDTA was embedded as a fluorophore in Cu-based metal-organic framework (MOF-199) structure (N-CD@EDTA/MOF-199) to construct fluorescence sensor toward l-ascorbic acid (L-AA) determination. The N-CD@EDTA/MOF-199 nanohybrid significantly and selectively turned on toward L-AA determination during the fluorimetric experiments. Under optimal conditions, the probe showed a suitable linear response in the concentration range of 10 nM-100 μM with a low limit of detection (LOD) of 8.6 nM and high sensitivity of 0.201 μM-1. The possible mechanism of recognition and adsorption, including the reduction of Cu 2+ nodes in the MOF-199 structure in the presence of L-AA and the release of trapped N-CD@EDTA into the solution, was explored. Moreover, the N-CD@EDTA/MOF-199/L-AA (100 μM) system was further applied as a fluorescent "on-off" sensor for Fe3+ determination with a LOD of 1.15 μM. The proposed probe was successfully used in orange juice and water samples to determine L-AA and Fe3+ with satisfactory recovery, which displays the promising capability of sensor in real samples. The recoveries obtained by suggested method are consistent with that obtained from high performance liquid chromatography (HPLC) and atomic absorption spectroscopy which confirm the favorable characteristic of the sensor for accurate determination of L-AA and Fe3+ in practical applications.

Facile and Green Synthesis of Carbon Dots from Melia Azedarach Leaves for pH Sensing and Cell Imaging

Carbon dots (CDs) have preeminent application prospects as a new star in the nanomaterials field. In this work, a green and facile method to synthesize the blue-emitting CDs was proposed with Melia azedarach leaves as the carbon precursors. Using nature materials without other expensive reagents and instruments, the processes were simple and environmental-friendly. The CDs had high fluorescence quantum yield (11.8%) and excellent luminescence properties. The size of them were among 1.5-2.5 nm and the emission spectrum exhibited a strong peak at 460 nm when excited at 380 nm. Additionally, the CDs were stable in most ions but sensitive to different pH values. As a result, a pH sensor was established for the detection of pH with a linear range of 3-10 pH. Moreover, it was demonstrated that the synthesized CDs had extremely low cytotoxicity. Due to their low toxicity and good biocompatibility, they entered into the A549 cells successfully for cell imaging.

Fluorometric assay of cyanophoric pyrethroids based on benzothiazole modified carbon quantum dots

A fluorometric assay based on benzothiazole carbon quantum dots (benzothiazole-CDs) was developed for the determination of cyanophoric pyrethroids (CPs, e.g., cypermethrin, deltamethrin and fenpropathrin).

3-Aminophenylboronic acid-functionalized molybdenum disulfide quantum dots for fluorescent determination of hypochlorite

A simple method is reported for hypochlorite determination based on fluorescence 3-aminophenylboronic acid-functionalized molybdenum disulfide quantum dots (B-MoS₂ QDs). B-MoS₂ QDs with strong fluorescence at 380 nm have been successfully synthesized by the amidation reaction between APBA and hydrothermal MoS₂ QDs. Hypochlorite sensing was proposed utilizing the fluorescent quenching effect of 3,3',5,5'-tetramethylbenzidine dihydrochloride (TMB) on B-MoS₂ QDs and the fast redox reaction between hypochlorite and TMB. The fluorescent quenching effect of TMB to B-MoS₂ QDs was proved to be caused by static dynamic quenching and inner filter effect. A good linear relationship was obtained in the hypochlorite concentration range from 1 to 20 μM, and the limit of detection (LOD) was 36.8 nM. The proposed fluorescent detection assay was simple and fast, taking only 5 min at room temperature. Satisfactory results were obtained in the standard spike recovery tests on tap water and milk samples, which indicate high potential in constructing fluorescent bio-detection assays.

Novel β-cyclodextrin doped carbon dots for host-guest recognition-assisted sensing of isoniazid and cell imaging

In the present study, novel β-cyclodextrin doped carbon dots (CCDs) were prepared via a simple one-pot hydrothermal method at a mild temperature (140 °C), using mixtures of β-cyclodextrin and citric acid as precursors. By characterizing the chemical properties of CCDs prepared at 140 °C and 180 °C, the importance of low-temperature reaction for preservation of the specific structure of β-CD was elucidated. The CCDs showed excellent optical properties and were stable to changes in pH, ionic strength and light irradiation. Since the fluorescence of the CCDs could be selectively quenched by isoniazid (INZ) through specific host-guest recognition effects, a convenient isoniazid fluorescence sensor was developed. Under the optimal conditions, the sensor exhibited a relatively low detection limit of 0.140 μg mL^-1 and a wide detection range from 0.2 μg mL^-1 to 50 μg mL^-1 for INZ detection. Furthermore, the sensor was employed successfully for the determination of INZ in urine samples with satisfactory recovery (91.1-109.5%), displaying potential in clinical applications. Finally, low cytotoxicity of the prepared CCDs was confirmed using the CCK-8 method, followed by application in HepG2 cell imaging.

Highly sensitive detection of free testosterone assisted by magnetic nanobeads and gap-enhanced SERS nanotags

The quantitative determination of trace free testosterone (FT) is of great significance for the diagnosis of androgen-related endocrine diseases. Herein, a fascinating detection protocol was developed for highly sensitive FT analysis through a competitive immunoassay mechanism, which was composed of magnetic nanobeads (MNBs) and gap-enhanced surface enhanced Raman scattering (SERS) nanotags. With the MNBs as detection carriers, trace FT could be enriched by simple magnetic separation. The SERS nanotag constructed with silver-gold core-shell nanoparticle was acted as quantitative label, and Raman indicators were located at the interface between silver core and gold shell. It is demonstrated that the as-proposed protocol achieves high detection sensitivity for FT of 12.11 fg mL^-1, and wider linear dynamic detection range (LDR) in the concentration of 100 fg mL^-1 to 100 ng mL^-1 with R² value of 0.979, which is due to the enhanced Raman signal of the gap-enhanced SERS nanotag and the high surface-to-volume ratio of the MNB, respectively. Taking advantages of such sensitivity and accuracy approach, the as-developed powerful strategy presents potential applications for rapid disease diagnosis through analyzing trace levels of FT, and can also provide guidance for the exploitation of analysis project of other analytes.

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

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

Can nanomaterials support the diagnosis and treatment of human infertility? A preliminary review

Human infertilities are disorders that afflict many people all over the world. Both male and female reproductive systems must work together in a precise and coordinated manner and infertility has a wide range of problems for this system. Recent advances in nanomedicine immensely helped design the diagnostic and therapeutic approaches to alleviate human infertility in both sexes. Nanoscience has recently been used by researchers to increase the detection limit of infertility-related biomarkers via fabricating sensitive nanobiosensors for detecting follicle-stimulating hormone (FSH), luteinizing hormone (LH), anti-müllerian hormone (AMH), pregnancy-associated plasma protein-A (PAPP-A), progesterone, and testosterone. At the same time, a variety of nanostructures, including magnetic nanoparticles (i.e., zinc nanoparticles, cerium nanoparticles, gold nanoparticles, silver nanoparticles), nano-vitamins, extracellular vesicles, and spermbots, have shown promising outcomes in the treatment of human infertilities. Despite recent advancements, some nanostructures might have toxic effects on cells, especially germ cells, and must be optimized with the right ingredients, such as antioxidants, nutrients, and vitamins, to obtain the right strategy to treat and detect human infertilities. This review presents recent developments in nanotechnology regarding impairments still faced by human infertility. New perspectives for further use of nanotechnology in reproductive medicine studies are also discussed. In conclusion, nanotechnology, as a tool for reproductive medicine, has been considered to help overcome current impairments.

Advances in the Determination of Anabolic-Androgenic Steroids: From Standard Practices to Tailor-Designed Multidisciplinary Approaches

Anabolic-androgenic steroids (AASs), a group of compounds frequently misused by athletes and, unfortunately, also by the general population, have lately attracted global attention; thus, significant demands for more precise, facile, and rapid AAS detection have arisen. The standard methods ordinarily used for AAS determination include liquid and gas chromatography coupled with mass spectrometry. However, good knowledge of steroid metabolism, pretreatment of samples (such as derivatization), and well-trained operators of the instruments are required, making this procedure expensive, complicated, and not routinely applicable. In the drive to meet current AAS detection demands, the scientific focus has shifted to developing novel, tailor-made approaches leading to time- and cost-effective, routine, and field-portable methods for AAS determination in various matrices, such as biological fluids, food supplements, meat, water, or other environmental components. Therefore, herein, we present a comprehensive review article covering recent advances in AAS determination, with a strong emphasis on the increasingly important role of chemically designed artificial sensors, biosensors, and antibody- and fluorescence-based methods.

Application of nanomaterials decorated with cyclodextrins as sensing elements for environment analysis

Environmental pollution has brought adverse socio-economic consequences. Organic pollutants and heavy metals are the main culprits of environmental pollution. It is of great importance to develop novel, simple, rapid, sensitive, and low-cost detection approaches for sensing trace pollutants in environmental samples. A lot of detection strategies which are based on varieties of nanomaterials have been developed for environmental analysis in past decades. In this review, we retrospect a variety of nanomaterials decorated with cyclodextrins (CDs), including carbon nanomaterials decorated with CDs, noble metal nanomaterials decorated with CDs and other nanomaterials decorated with CDs, and their application in environmental analysis. CDs is a type of ideal modifying molecules which could recognize targets, improve the solubility and dispersibility of corresponding functionalized materials, and enhance the detecting performance of designed sensors. CDs have been widely immobilized to carbon nanomaterials, noble metal nanomaterials, phosphorene (BP) nanocomposites, metal organic framework (MOF), and magnetic nanomaterials, and these nanocomposites have been utilized as the sensing elements for different target analytes. Immobilizing CDs on different nanomaterials could extremely expand the development of new sensing systems for environmental analysis based on these materials, greatly broaden the species of sensing targets, and apparently improve their sensing performance. Herein, the nanomaterials decorated with CDs, as sensing elements for environmental analysis, were reviewed including the types of nanomaterials decorated with CDs and their applications in various sensing strategies for environmental analysis. Finally, the perspectives of the nanomaterials decorated with CDs used as sensing elements were also discussed.

Visible light-induced charge injection and migration in self-assembled carbon dot-DNA-carbon dot nano-dumbbell obtained through controlled stoichiometric conjugation

The potential of carbon dots (CDs) for photonic conversion to charged states, together with the ability of DNA to transport such charge for extensive charge separation, offers an opportunity to control directionality of migration for photo-induced radical cations in CD-DNA based nano-assemblies. This is achieved through engineering the reaction valency of CDs whereby one CD is covalently conjugated with one ssDNA strand. Subsequently, a CD-DNA-CD nano-dumbbell architecture was created through hybridization mediated self-assembly. The time and intensity-dependent transduction of visible light photonic energy to chemical potential in DNA was achieved through irradiation of 1,4-diaminoathraquinone and glyoxal derived CD with 100 W tungsten source and natural sunlight. Following charge injection by CD, the radical cation migration in DNA was perceived through trapping of the hole in repeated GG steps in the DNA. Overall, a breakthrough in visible-light-induced charge transfer by CD into DNA was achieved, potentially applicable to optobioelectronics.

Nitrogen doped graphene quantum dots based on host guest interaction for selective dual readout of dopamine

Herein, yellow emissive nitrogen doped graphene quantum dots (N@GQDs) were prepared by a novel advanced thermal driven oxidation. The N@GQDs was functionalized with β-cyclodextrin (β-CD) to improve its catalytic performance towards dopamine (DA) detection. The β-CD/N@GQDs exhibited strong fluorescence at λ_em. = 550 nm after excitation at 460 nm with a quantum yield of 38.6%. The β-CD/N@GQDs showed good peroxidase like activity via catalyzing the oxidation of tetramethylbenzidine (TMB) in presence of H₂O₂ to form blue colored product at λ_max = 652 nm. In the colorimetric assay of DA, the detection based on the oxidation of TMB by H₂O₂ in presence of β-CD/N@GQDs as a catalyst. Then, the color of the blue oxidized TMB (oxTMB) product was reduced by addition of DA. While the fluorometric detection of DA based on the "inner filter effect" of the overlapped emission spectrum of β-CD/N@GQDs with the absorption spectrum of oxTMB, where, addition of DA reduces oxTMB to TMB and restores the fluorescence intensity of β-CD/N@GQDs. Under the optimized conditions, the colorimetric method achieved linearity range of 0.12-7.5 µM and LOD (S/N = 3) of 0.04 µM, while the fluorometric method achieved linearity range of 0.028-1.5 µM and LOD (S/N = 3) of 0.009 µM. The peroxidase like activity of β-CD/N@GQDs was used to detect DA in human plasma and serum samples with good % recoveries. The colorimetric and fluorometric methods exhibited good sensitivity and selectivity toward DA detection.

Determination of melamine in milk based on β-cyclodextrin modified carbon nanoparticles via host-guest recognition

Illegal addition of melamine (MEL) to milk has caused serious food safety accident. It is urgent to develop a highly sensitive method for detecting MEL in milk. β-Cyclodextrin with inner hydrophobic and outer hydrophilic cavities have been widely used in smart sensors design. In this study, an "ON-OFF-ON" sensor for MEL detection was constructed based on β-cyclodextrin modified carbon nanoparticles (β-CD-CNPs). The sensor is switched "OFF" when Fe³⁺ interacts with β-CD-CNPs and switched "ON" when MEL replaces Fe³⁺. Fluorescence recovery of β-CD-CNPs exhibits good linear correlations with MEL concentration ranging from 10.00 ng/mL ~ 180.00 ng/mL and 180.00 ~ 1000.00 ng/mL, the detection limit is 6.82 ng/mL. The sensor was applied to analysis melamine in milk samples with recovery between 94.80% ~ 102.05%, and RSD bellow 12.61%. The results show that this method can meet the requirements of real sample analysis.

Dual-Emitting N/S-Doped Carbon Dots-Based Ratiometric Fluorescent and Light Scattering Sensor for High Precision Detection of Fe(III) Ions

Precise and rapid sensing of Fe(III) under concerned facile conditions is important in environmental monitoring. Herein, a facile and label-free ratiometric sensor is constructed for selective determination of Fe(III) ions by coupling second-order scattering (SOS) and fluorescence. We were synthesized fluorescent N, S-doped carbon dots (N/S-CDs) via facile one-step hydrothermal treatment with an intensive fluorescence and a weak SOS signal and high quantum yield (32%). The fluorescence of N/S-CDs was quenched whereas the intensity of SOS was relatively increased by Fe(III) ions due to aggregation-induced fluorescence quenching or enhancement. Based on this effect, a novel fluorescent ratiometric probe with the combined fluorescence and SOS is proposed for the sensing of Fe(III) ions, and with the detection limit of 83 nM and linear range of 0.1-10 μM and 10-40 μM, respectively.

Carbon dots-inspired fluorescent cyclodextrins: competitive supramolecular "off-on" (bio)sensors

Chromophore-appended cyclodextrins combine the supramolecular loading capabilities of cyclodextrins (CDs) with the optical properties of the affixed chromophores. Among fluorescent materials, carbon dots (CNDs) are attractive and the feasibility of CND-appended CDs as sensors has been demonstrated by different authors. However, CNDs are intrinsically heterogeneous materials and their ulterior functionalization yields hybrid composites that are not well defined in terms of structure and composition. Inspired by the fluorescence properties of 5-oxo-1,2,3,5-tetrahydroimidazo[1,2-a]pyridine-7-carboxylic acid (IPCA), the most paradigmatic of the molecular fluorophores detected in CNDs, herein we report two highly efficient synthetic chemical strategies for the preparation of IPCA-appended CDs that behave as CND-based CD "turn off-on" biosensors suitable for the analysis of cholesterol and β-galactosidase activity. We have deconstructed the CND-CD systems to demonstrate that (i) the role of CNDs is limited to acting as a support for the molecular fluorophores produced during their synthesis and (ii) the molecular fluorophores suffice for the determination of the enzymatic activity based on the quenching by p-nitrophenol as a sacrificial quencher.

Vinyl Phosphate-Functionalized, Magnetic, Molecularly-Imprinted Polymeric Microspheres' Enrichment and Carbon Dots' Fluorescence-Detection of Organophosphorus Pesticide Residues

The rapid detection of organophosphorus pesticide residues in food is crucial to food safety. One type of novel, magnetic, molecularly-imprinted polymeric microsphere (MMIP) was prepared with vinyl phosphate and 1-octadecene as a collection of dual functional monomers, which were screened by Gaussian09W molecular simulation. MMIPs were used to enrich organic phosphorus, which then detected by fluorescence quenching in vinyl phosphate-modified carbon dots (CDs@VPA) originated from anhydrous citric acid. MMIPs and CDs@VPA were characterized by TEM, particle size analysis, FT-IR, VSM, XPS, adsorption experiments, and fluorescence spectrophotometry in turn. Through the fitting data from experiment and Gaussian quantum chemical calculations, the molecular recognition properties and the mechanism of fluorescence detection between organophosphorus pesticides and CDs@VPA were also investigated. The results indicated that the MMIPs could specifically recognize and enrich triazophos with the saturated adsorption capacity 0.226 mmol g^-1, the imprinting factor 4.59, and the limit of recognition as low as 0.0006 mmol L^-1. Under optimal conditions, the CDs@VPA sensor has shown an extensive fluorescence property with a LOD of 0.0015 mmol L^-1 and the linear range from 0.0035 mmol L^-1 to 0.20 mmol L^-1 (R² = 0.9988) at 390 nm. The mechanism of fluorescence detection of organic phosphorus with CDs@VPA sensor might be attributable to hydrogen bonds formed between heteroatom O, N, S, or P, and the O-H group, which led to fluorescent quenching. Meanwhile, HN-C=O and Si-O groups in CDs@VPA system might contribute to cause excellent blue photoluminescence. The fluorescence sensor was thorough successfully employed to the detection of triazophos in cucumber samples, illustrating its tremendous value towards food sample analysis in complex matrix.

Determination of cholic acid in body fluids by β‑cyclodextrin-modified N-doped carbon dot fluorescent probes

An easy, dependable, and sensitive cholic acid activity experiment was designed based on β‑cyclodextrin-modified carbon dot (β‑CD-CD) nanoprobes with specific host-guest recognizing ability and photoelectron transfer capability. The β‑CD-CD nanoprobes were characterized by infrared, ultraviolet-visible, and fluorescence spectroscopy and transmission electron microscopy. The fluorescence of the probes under optimized conditions linearly responded to cholic acid concentration from 0 to 650 μmol·L^-1 with a detection limit of 25 nmol·L^-1. The probes also performed well in detecting cholic acid in serum and urine samples with an average recovery rate of 97.1%-103.4%. Thus, this study provides a reliable, rapid, and easy method of cholic acid detection in body fluids that can be potentially applied in medical studies.

Bulk-state and single-particle imaging are central to understanding carbon dot photo-physics and elucidating the effects of precursor composition and reaction temperature

Carbon dots have garnered attention for their strong multi-color luminescence properties and unprecedented biocompatibility. Despite significant progress in the recent past, a fundamental understanding of their photoluminescence and structure-properties relationships, especially at the bulk vs. single-particle level, has not been well established. Here we present a comparative study of bulk- and single-particle properties as a function of precursor composition and reaction temperature. The synthesis and characterization of multicolored inherently functionalized carbon dots were achieved from a variety of carbon sources, and at synthesis temperatures of 150 °C and 200 °C. Solvothermal synthesis at 200 °C led to quantum yields as high as 86%, smaller particle sizes, and a narrowed fluorescence emission, while synthesis at 150 °C resulted in a greater UV-visible absorbance, increase in nanoparticle stability, red-shifted fluorescence, and a greater resistance to bulk photobleaching. These results suggest the potential for synthesis temperature to be utilized as a simple tool for modulating carbon dot photophysical properties. Single-particle imaging resolved that particle brightness was determined by both the instantaneous intensity and the on-time duty cycle. Increasing the synthesis temperature caused an enhancement in blinking frequency, which led to an increase in on-time duty cycle in three out of four precursors.

Label-free fluorescence imaging of cytochrome c in living systems and anti-cancer drug screening with nitrogen doped carbon quantum dots

As an important biomarker for the early stage of apoptosis, cytochrome c (Cyt c) has been recognized as a key component of the intrinsic apoptotic pathway. Fluorescence imaging tools enabling detection of Cyt c in apoptotic signaling have been rarely explored, though they are critical for cell biology and clinical theranostics. Here, we designed a novel label-free N-doped carbon dot (N-doped CD)-based nanosensor that enables fluorescence activation imaging of Cyt c release in cell apoptosis. The inner filter effect of Cyt c towards N-doped CDs enabled quantitative Cyt c measurement. The nanosensor exhibited high sensitivity and selectivity, rapid response, good cell-membrane permeability and low cytotoxicity. All these features are favorable for in situ visualization of Cyt c for apoptosis research. Notably, the developed nanosensor was successfully applied to monitor intracellular release of Cyt c, and to visualize Cyt c in living zebrafish for the first time. Moreover, it also provided a viable platform for cell-based screening of apoptosis-inducing compounds. In virtue of these advantages and potential, the developed assay not only holds great significance for the better understanding of certain diseases at the cellular level, but also provides an invaluable platform for apoptotic studies and screening of anti-cancer drugs toward drug development.

Highly sensitive sensing of hydroquinone and catechol based on β-cyclodextrin-modified carbon dots

In the proposed study, an efficient method for a carbon dot@β-cyclodextrin (C-dot@β-CD)-based fluorescent probe was developed for the analyses of catechol (CC) and hydroquinone (HQ) at trace levels in water samples. The properties of C-dot@β-CD nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The sensing behaviors of C-dot@β-CD toward CC and HQ were investigated by fluorescence spectroscopy. Based on the host–guest chemistry between C-dot@β-CD and phenolic compounds, which can quench C-dot@β-CD fluorescence, the prepared C-dot@β-CD nanocomposites could be used for the sensitive and selective detection of CC or HQ across a wide linear range (0.1 to 10 μM) with detection limits of 47.9 and 20.2 nM, respectively. These results showed that the synthesized C-dot@β-CD nanocomposite exhibited strong fluorescence and high degree of water solubility and thus, it is suitable for use as a nanoprobe for detecting CC or HQ in real water samples.

In the proposed study, an efficient method for a carbon dot@β-cyclodextrin (C-dot@β-CD)-based fluorescent probe was developed for the analyses of catechol (CC) and hydroquinone (HQ) at trace levels in water samples.

Preparation of enzyme-functionalized carbon nanotubes and their application in glucose and Fe2+ detection through “turn on” and “turn off” approaches

Herein, we report the preparation of enzyme-conjugated carbon nanotubes for the detection of Fe²⁺ and glucose with enhanced signal intensity.

Functional Carbon Quantum Dots: A Versatile Platform for Chemosensing and Biosensing

Carbon quantum dot has emerged as a new promising fluorescent nanomaterial due to its excellent optical properties, outstanding biocompatibility and accessible fabrication methods, and has shown huge application perspective in a variety of areas, especially in chemosensing and biosensing applications. In this personal account, we give a brief overview of carbon quantum dots from its origin and preparation methods, present some advance on fluorescence origin of carbon quantum dots, and focus on development of chemosensors and biosensors based on functional carbon quantum dots. Comprehensive advances on functional carbon quantum dots as a versatile platform for sensing from our group are included and summarized as well as some typical examples from the other groups. The biosensing applications of functional carbon quantum dots are highlighted from selective assays of enzyme activity to fluorescent identification of cancer cells and bacteria.