Cu-Doped Carbon Dots as Catalysts for the Chemiluminescence Detection of Glucose

Metal-doped carbon dots for biomedical applications: From design to implementation

Carbon dots (CDs), as a new kind of fluorescent nanomaterials, show great potential for application in several fields due to their unique nano-size effect, easy surface functionalization, controllable photoluminescence, and excellent biocompatibility. Conventional preparation methods for CDs typically involve top-down and bottom-up approaches. Doping is a major step forward in CDs design methodology. Chemical doping includes both non-metal and metal doping, in which non-metal doping is an effective strategy for modulating the fluorescence properties of CDs and improving photocatalytic performance in several areas. In recent years, Metal-doped CDs have aroused the interest of academics as a promising nano-doping technique. This approach has led to improvements in the physicochemical and optical properties of CDs by altering their electron density distribution and bandgap capacity. Additionally, the issues of metal toxicity and utilization have been addressed to a large extent. In this review, we categorize metals into two major groups: transition group metals and rare-earth group metals, and an overview of recent advances in biomedical applications of these two categories, respectively. Meanwhile, the prospects and the challenges of metal-doped CDs for biomedical applications are reviewed and concluded. The aim of this paper is to break through the existing deficiencies of metal-doped CDs and fully exploit their potential. I believe that this review will broaden the insight into the synthesis and biomedical applications of metal-doped CDs.

Enhanced peroxidase-like activity of Cu-Cu2O composite film through PtPd immobilization for colorimetric glucose detection

In this study, Cu-Cu2O/PtPd nanocomposites were synthesized and characterized for their peroxidase-like enzyme activity. X-ray diffraction and energy dispersive X-ray spectroscopy analyses confirmed the successful synthesis of the nanocomposites, which exhibited a flower-like morphology and a more uniform dispersion than Cu-Cu2O. The catalytic activity of Cu-Cu2O/PtPd was evaluated using the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB), finding that Cu-Cu2O/PtPd outperformed Cu-Cu2O. The optimal temperature and pH for the catalytic activity of Cu-Cu2O/PtPd were determined to be 40 °C and pH 4.0, respectively. A kinetic analysis revealed that Cu-Cu2O/PtPd followed Michaelis-Menten kinetics and exhibited a higher affinity toward TMB than the horseradish peroxidase enzyme. The catalytic mechanism of Cu-Cu2O/PtPd involved the generation of hydroxyl radicals, which facilitated the oxidation of TMB. Furthermore, the Cu-Cu2O/PtPd nanocomposite was successfully applied for the colorimetric detection of glucose, demonstrating a linear range of 8-90 μM, a detection limit of 2.389 μM, and high selectivity for glucose over other sugars.

The applications of carbon dots in oral health: A scoping review

OBJECTIVES

This scoping review aims to provide an overview of the research and potential applications of carbon dots (CDs) for oral health purposes.

DESIGN

Systematic literature searches were performed on PubMed and Web of Science databases (up to February 2023). Two co-authors selected the published works independently and extracted the data in accordance with the PRISMA statement. Studies with the application of CDs for oral health purposes were included.

RESULTS

Among 152 articles, 19 articles were finally selected. Eight studies investigated the anti-microbial effects of CDs against, for example, oral pathogens, eight studies explored the applicability of CDs in relation to oral cancer, and three studies investigated CDs in relation to cell differentiation and tissue regeneration in oral health. The studies showed the promising potential of CDs in oral health, particularly for inducing bacterial killing by increasing reactive oxygen species, killing oral cancer cells via photodynamic therapeutic effects, and inducing dental pulp and periodontal bone regeneration.

CONCLUSION

The findings show that CDs have the potential to be utilized in the future for various oral health purposes. Besides, these results underline the broad-spectrum applicability of CDs, crossing the borders of oral health.

Silver-coated hollow fiber surface plasmon resonance sensor for glucose detection with enhanced limit of detection

A fiber-optic surface plasmon resonance (SPR) biosensor based on a silver-coated hollow fiber (HF) structure for glucose detection is presented. The sensor surface was immobilized with 4-mercaptophenylboronic acid (PMBA) acting as a glucose recognition monolayer. Then, gold nanoparticles (AuNPs) modified with 2-aminoethanethiol (2-AET) and PMBA were introduced onto the sensor surface after glucose was captured to enhance the wavelength shift of the SPR phenomenon excited by the light transmitted in the wall of the HF sensor. Instead of the conventional one-step sensitization pretreatment commonly used in the deposition process of silver films for fiber-optic SPR sensors, a sensitization-activation two-step activation method was adopted in the fabrication of the proposed sensor. Experiments for glucose detection were performed on the fabricated sensors in the concentration range of 1 nM-1 mM. Results showed that the sensor fabricated by the two-step activation method has a much larger shift of resonance wavelength than the sensor fabricated using the one-step sensitization method. The resonance wavelength shift was found to be linear to the logarithm of the concentration in the range of 1 nM-1 mM. The sensor achieved a limit of detection (LOD) of as low as 1 nM, which is at least an order of magnitude lower than that of other fiber-optic sensors for glucose detection reported previously. The presented HF glucose sensor has the potential for biosensing applications and provides a large reference value in the study of optical fiber SPR sensors for biosensing.

The future of plant based green carbon dots as cancer Nanomedicine: From current progress to future Perspectives and beyond

BACKGROUND

The emergence of carbon dots (CDs) as anticancer agents had sparked a transformation in cancer research and treatment strategies. These fluorescent CDs, initially introduced in the early 2000 s, possess exceptional biocompatibility, tunable fluorescence, and surface modification capabilities, positioning them as promising tools in biomedical applications.

AIM OF REVIEW

The review encapsulates the transformative trajectory of green CDs as future anticancer nanomedicine, poised to redefine the strategies employed in the ongoing fight against cancer.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The versatility of CDs was rooted in their various synthesis approaches and sustainable strategies, enabling their adaptability for diverse therapeutic uses. In vitro studies had showcased CDs' selective cytotoxicity against cancer cells while sparing healthy counterparts, forming the basis for targeted therapeutic potential. This selectivity had been attributed to the reactive oxygen species (ROS) generation, which opened avenues for targeted interventions. The role of CDs in combination therapies, synergizing with chemotherapy, radiotherapy, and targeted approaches was then investigated to heighten their anticancer efficacy. Notably, in vivo studies highlight CDs' remarkable biocompatibility and minimal side effects, endorsing their translational promise. Integration with conventional cancer treatments such as chemotherapy, radiotherapy, and immunotherapy amplified the versatility and effectiveness of CDs. The exploration of CDs' applications in photo-induced treatments further solidified their significance, positioning them as photosensitizers (PS) in photodynamic therapy (PDT) and photothermal agents (PA) in photothermal therapy (PTT). In PDT, CDs triggered the generation of ROS upon light exposure, facilitating cancer cell elimination, while in PTT, they induced localized hyperthermia within cancer cells, enhancing therapeutic outcomes. In vitro and in vivo investigations validated CDs' efficacy in PDT and PTT, affirming their potential for integration into combination therapies. Looking ahead, the future of CDs in anticancer treatment encompasses bioavailability, biocompatibility, synergistic treatments, tumor targeting, artificial intelligence (AI) and robotics integration, personalized medicine, and clinical translation. This transformative odyssey of CDs as future anticancer agents is poised to redefine the paradigm of cancer treatment strategies.

Metal-organic framework (MOF) hybridized gold nanoparticles as a bifunctional nanozyme for glucose sensing

Inspired by natural enzymes that possess multiple catalytic activities, here we develop a bifunctional metal-organic frame-work (MOF) for biosensing applications. Ultrasmall gold nano-particles (AuNPs) are grown in the internal cavities of an iron (Fe) porphyrin-based MOF to produce a hybridized nanozyme, AuNPs@PCN-224(Fe), in which AuNPs and PCN-224(Fe) exhibit the catalytic activity of glucose oxidase (GOx) and horseradish peroxidase (HRP), respectively. We established that the bifunctional nanozyme was capable of a cascade reaction to generate hydrogen peroxide in the presence of d-glucose and oxygen in situ, and subsequently activate a colorimetric or chemiluminescent substrate through HRP-mimicking catalytic activity. The nanozyme was selective over a range of other saccharides, and 93% of the catalytic activity was retained after being recycled five times.

Preparation of Ciprofloxacin-Based Carbon Dots with High Antibacterial Activity

Nowadays, bacterial infections are attracting great attention for the research and development of new antimicrobial agents. As one of the quinolones, ciprofloxacin (CI) has a broad-spectrum, strong antibacterial effect. However, the clinical use of ciprofloxacin is limited by drug resistance. Ciprofloxacin carbon dots (CCDs) with enhanced antibacterial activity and copper-doped ciprofloxacin carbon dots (Cu-CCDs) were synthesized by a simple hydrothermal method. The results of structural analysis and antibacterial experiments show that CCDs and Cu-CCDs have effective antibacterial properties by retaining the active groups of ciprofloxacin (-COOH, C-N, and C-F), and Cu-CCDs doped with copper have a better antibacterial effect. In addition, experiments have shown that Cu-CCDs show excellent antibacterial activity against E. coli and S. aureus and have good biocompatibility, which indicates that they have great prospects in clinical applications. Therefore, novel modified copper CCDs with broad-spectrum antibacterial activity, which can be used as antibacterial nanomaterials for potential applications in the field of antibacterial drugs, were synthesized in this study.

Emerging and Versatile Platforms of Metal-Ion-Doped Carbon Dots for Biosensing, Bioimaging, and Disease Therapy

Metal ions possess abundant electrons and unoccupied orbitals, as well as large atomic radii, whose doping into carbon dots (CDs) is a facile strategy to endow CDs with additional physicochemical characteristics. After being doped with metal ions, CDs reveal obvious changes in their optical, electronic, and magnetic properties by adjustments to their electron density distribution and the energy gaps, leading them to be promising and competitive candidates as labeling probes, imaging agents, catalysts, nanodrugs, and so on. In this review, we summarize the fabrication methods of metal-ion-doped CDs (M-CDs), and highlight their biological applications including biosensing, bioimaging, tumor therapy, and anti-microbial treatment. Finally, the challenging future perspectives of M-CDs are analyzed. We hope this review will provide inspiration for further development of M-CDs in various biological aspects, and help readers who are interested in M-CDs and their biological applications.

Emerging metal doped carbon dots for promising theranostic applications

As a bridge between organic fluorophores and inorganic quantum dots, carbon dots (CDs) have been recognized as emerging nanotheranostics for biomedical applications owing to their distinctive merits such as superior optical properties, flexible modification, adjustable functionalities, and remarkable photoactive therapeutic outcome, etc. Compared to metal free CDs, the introduction of metal ion in CDs endowed metal-doped CDs (MCDs) with tunable optical properties and new intrinsic properties, thereby illustrating its different capabilities from metal-free CDs for bioimaging and therapy. This review aims to summarize the recent progress of photonic MCDs as emerging nanoagent for theranostic application such as disease-related diagnostic (involving biosensing and bioimaging) and cancer therapy. The challenges and potential development of MCDs in nanotheranostic fields are also discussed.

Catalytic nanozyme Zn/Cl-doped carbon quantum dots as ratiometric fluorescent probe for sequential on-off-on detection of riboflavin, Cu2+ and thiamine

A novel metal-doped Zn/Cl carbon quantum dots (Zn/Cl-CQDs) was developed successfully as ratiometric fluorescent probes for the sequential on-off-on detection of riboflavin, Cu²⁺ ion and thiamine. The excellent catalytic performance of the Zn/Cl-CQDs nanozyme serves as an ideal platform for sensitive detection of thiamine. Due to the addition of riboflavin to the Zn/Cl-CQDs, the blue emission peak of Zn/Cl-CQDs at 440 nm remains unaffected and used as an internal reference approach, while the green emission peak of riboflavin at 520 nm appeared and increased remarkably. Following the presence of Cu²⁺, a quenching blue fluorescence signal of Zn/Cl-CQDs was observed which resulted in consequent fluorescent 'turn-off' response toward Cu²⁺ ion. Finally, upon the addition of thiamine to the above solution under alkaline condition, the blue emission of Zn/Cl-CQDs was gradually recovered. The prepared Zn/Cl-CQDs could act as a nanozyme catalyst for directly catalyzing the oxidation of non-fluorescent substrate of thiamine to produce highly fluorescent substrate of thiochrome. As a result, the blue fluorescence emission peak at 440 nm was recovered. Eventually, the sequential detection properties of ratiometric probes for riboflavin, Cu²⁺ ion and thiamine were successfully applied in VB2 tablets, drinking water and VB1 tablet with good recoveries of 96.21%, 98.25% and 98.44%, respectively.

Copper-doped carbon dots with enhanced Fenton reaction activity for rhodamine B degradation

The Fenton reaction has attracted extensive attention due to its potential to be a highly efficient and environmentally friendly wastewater treatment technology. Noble copper-doped carbon dots (CuCDs) are prepared through a simple one-step hydrothermal method with 3,4-dihydroxyhydrocinnamic acid, 2,2'-(ethylenedioxy)bis(ethylamine) and copper chloride, endowing the Fenton reaction with enhanced catalytic activity for rhodamine B (RhB) degradation. The effects of the concentration of CuCDs, temperature, pH, oxygen (O2), metal ions and polymers on the catalytic activity of CuCDs are investigated. It is worth noting that electron transfer happening on the surface of CuCDs plays a vital role in the RhB degradation process. As evidenced by radical scavenger experiments and electron spin resonance (ESR) studies, CuCDs significantly boost the formation of hydroxyl radicals (˙OH) and singlet oxygen (1O2), facilitating the Fenton reaction for RhB degradation. Due to the strong oxidation of ROS generated by the Fe2+ + H2O2 + CuCD system, RhB degradation may involve the cleavage of the chromophore aromatic ring and the de-ethylation process. Additionally, the toxicity of RhB degradation filtrates is assessed in vitro and in vivo. The as-prepared CuCDs may be promising catalytic agents for the enhancement of the Fenton reaction.

Copper Doped Carbon Dots for Addressing Bacterial Biofilm Formation, Wound Infection, and Tooth Staining

Oral infectious diseases and tooth staining, the main challenges of dental healthcare, are inextricably linked to microbial colonization and the formation of pathogenic biofilms. However, dentistry has so far still lacked simple, safe, and universal prophylactic options and therapy. Here, we report copper-doped carbon dots (Cu-CDs) that display enhanced catalytic (catalase-like, peroxidase-like) activity in the oral environment for inhibiting initial bacteria (Streptococcus mutans) adhesion and for subsequent biofilm eradication without impacting the surrounding oral tissues via oxygen (O₂) and reactive oxygen species (ROS) generation. Especially, Cu-CDs exhibit strong affinity for lipopolysaccharides (LPS) and peptidoglycans (PGN), thus conferring them with excellent antibacterial ability against Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli), such that they can prevent wound purulent infection and promoting rapid wound healing. Additionally, the Cu-CDs/H₂O₂ system shows a better performance in tooth whitening, compared with results obtained with other alternatives, e.g., CDs and clinically used H₂O₂, particularly its negligible enamel and dentin destruction. It is anticipated that the biocompatible Cu-CDs presented in this work are a promising nano-mouthwash for eliminating oral pathogenic biofilms, prompting wound healing as well as tooth whitening, highlighting their significance in oral health management.

Double-signal quantification of amoxicillin based on interaction with 4-aminoantipyrine at copper and nitrogen co-doped carbon quantum dots as an artificial nanozyme

An one-pot hydrothermal method was developed for synthesis of carbon quantum dots co-doped with copper and nitrogen (Cu, N@CQDs). The synthesized Cu, N@CQDs has unique advantages such as high fluorescence quantum yield (39.1%) and high catalytic activity. Oxidative coupling of amoxicillin (AMX) with 4-aminoantipyrine (4-NH₂-APE) in the presence of H₂O₂ as an oxidant to produce pink quinoneimine chromogen was carried out with the aid of Cu, N@CQDs as a peroxidase-like catalyst. This system was used for the colorimetric and fluorometric assays of AMX with reliable results. Colorimetric method is based on the measurement of a pink-colored product at λ_max = 505 nm while the fluorometric assay is based on the quenching of the fluorescence emission of Cu, N@CQDs at 440 nm after excitation at 370 nm. For the colorimetric method, the absorption intensity linearly increased over the concentration range 4.3-110.0 µM with LOD (S/N = 3) of 1.3 µM. For the fluorometric method, the emission intensity of Cu, N@CQDs linearly decreased upon addition of AMX in the concentration range 0.2-120.0 µM with a limit of detection (LOD, S/N = 3) of 0.06 µM. The proposed system was applied to the determination of AMX in different real samples such as pharmaceutical capsules, human serum, milk, and conduit water samples with recoveries in the range 95.8-104.1% and relative standard deviation (RSD %) less than 4.1%.

Copper(II)-Doped Carbon Dots as Catalyst for Ozone Degradation of Textile Dyes

A catalytic ozonation advanced oxidation process (AOP) with a copper(II)-doped carbon dot as catalyst, Cu-CD (using L-cysteine and polyethylene glycol (PEG) as precursors and passivation agents), was developed for textile wastewater treatment (T = 25 °C and pH = 7). Four dyes were analyzed—Methyl Orange (MO), Orange II sodium salt (O-II), Reactive Black 5 (RB-5) and Remazol Brilliant Blue R (RBB-R), as well as a real effluent from the dying and printing industry. The Cu-CD, with marked catalytic ozonation properties, was successfully synthesized by one-pot hydrothermal procedure with a size of 4.0 nm, a charge of −3.7 mV and a fluorescent quantum yield of 31%. The discoloration of the aqueous dye solutions followed an apparent first-order kinetics with the following rate constants (kap in min−1): MO, 0.210; O-II, 0.133; RB-5, 0.177; RBB-R, 0.086. In the presence of Cu-CD, the following apparent first-order rate constants were obtained (kapc in min−1) with the corresponding increase in the rate constant without catalyst (%Inc): MO, 1.184 (464%); O-II, 1.002 (653%); RB-5, 0.709 (301%); RBB-R, 0.230 (167%). The presence of sodium chloride (at a concentration of 50 g/L) resulted in a marked increase of the discoloration rate of the dye solution due to generation of other radicals, such as chlorine and chlorine oxide, resulting from the reaction of ozone and chloride. Taking into consideration that the real textile effluent under research has a high carbonate concentration (>356 mg/L), which inhibits ozone decomposition, the discoloration first-order rate constants without and with Cu-CD (kap = 0.0097 min−1 and kapc = 0.012 min−1 (%Inc = 24%), respectively) were relatively small. Apparently, the Cu-CD, the surface of which is covered by a soft and highly hydrated caramelized PEG coating, accelerates the ozone decomposition and dye adsorption, increasing its degradation.

Synthesis of Doped/Hybrid Carbon Dots and Their Biomedical Application

Carbon dots (CDs) are a novel type of carbon-based nanomaterial that has gained considerable attention for their unique optical properties, including tunable fluorescence, stability against photobleaching and photoblinking, and strong fluorescence, which is attributed to a large number of organic functional groups (amino groups, hydroxyl, ketonic, ester, and carboxyl groups, etc.). In addition, they also demonstrate high stability and electron mobility. This article reviews the topic of doped CDs with organic and inorganic atoms and molecules. Such doping leads to their functionalization to obtain desired physical and chemical properties for biomedical applications. We have mainly highlighted modification techniques, including doping, polymer capping, surface functionalization, nanocomposite and core-shell structures, which are aimed at their applications to the biomedical field, such as bioimaging, bio-sensor applications, neuron tissue engineering, drug delivery and cancer therapy. Finally, we discuss the key challenges to be addressed, the future directions of research, and the possibilities of a complete hybrid format of CD-based materials.

Dual-mode sensing of biomarkers based on nano 3D Cu-Flo.@AuNPs-electrocatalyzed oxidation of glucose inducing in-situ H2O2-generation system

A bimodal 3D-electrochemiluminescence (ECL) analysis method was developed, which integrated simpleness, label-free, high-throughput and real time detection together. Firstly, a novel 3D copper-based nanosheet micro-material (Cu-Flo. NMs) coupled with gold nanoparticles/Cysteine (Cu-Flo.@AuNPs-Cys) was prepared to use as the versatile label for both colorimetric and ECL techniques. The 3D-Cu-Flo.@AuNPs-Cys having glucose oxidase-like activity could catalyze glucose to produce H₂O₂ in situ, which was further found to be capable of exhibiting a 30.95-fold higher ECL-intensity for luminol than bare glassy carbon electrodes (GCE). Taking advantages of the 3D-Cu-Flo.@AuNPs-Cys above, a colorimetric and ECL-channel sensor (GCE/3D-Cu-Flo.@AuNPs-Cys) were constructed simultaneously for glucose detection. The fabricated sensor displayed a wide linear range (Glucose: 0.001-50 mmol L^-1, AFP: 2.25 × 10^-7-225 ng mL^-1), impressive low limit of detection (Glucose: 1.27 × 10^-7 mol L^-1, AFP: 1.92 × 10^-8 ng mL^-1, S/N = 3) and acceptable recovery (Glucose: 94% ∼ 104%, AFP: 96.04% ∼ 102.29%) in practical sample. Furthermore, the biosensor showed ultrafast (0.5 min) analysis efficiency, high stability for 6 cyclic potential scans and satisfactory reproducibility for 7 repeated tests. These results demonstrated the proposed 3D dual-modal ECL-biosensor for biomarkers detection had a great potential in clinical diagnostics, promoting the application in biomedical researching and POCT.

Enzyme-mimicking capacities of carbon-dots nanozymes: Properties, catalytic mechanism, and applications - A review

Nanozymes, novel engineered nanomaterial-based artificial enzymes, have been developed to overcome intrinsic drawbacks exist in natural enzymes including high-cost storage, structural instability, and chemical sensitivity. More recently, carbon dots (CDs) have received significant attention due to their biocompatibility, high catalytic activity, and simple surface functionalization, thus emerging as possible alternatives for biomedical and environmental applications. In this review, we analyze methods and precursors used to synthesize CDs with enzyme-mimicking behaviors. In addition, approaches such as doping or constructing hybrid nanozymes are included as possible strategies to enhance the catalytic performance of CDs. Recent studies have reported CDs that mimic different oxidoreductases, exhibiting peroxidase-, catalase-, oxidase/laccase-, and superoxide dismutase-like activities. Therefore, this review presents a detailed discussion of the mechanism, recent advances, and application for each oxidoreductase-like activity reported on nanozymes based on CDs nanomaterials. Finally, current challenges faced in the successful translation of CDs to potential applications are addressed to suggest research directions.

Electrospinning One-dimensional Surface-phosphorized CuCo/C nanofibers for Enzyme-free Glucose Sensing

Developing novel electrocatalysts is of great importance for the practical application of non-enzymatic glucose sensors. One-dimensional (1D) carbon fiber-supported copper-cobalt bimetallic electrocatalysts (CuCo-P350) are successfully prepared via electrospinning technology and...

Probing the emission dynamics in nitrogen doped carbon dots by reversible capping with mercury (II) through surface chemistry

In this study, the mechanistic insight and emission dynamics have been explored of size dependent nitrogen doped carbon quantum dots (namely 3A,3B & 3C) with toxic metal Hg2+ ions via...

Green and facile synthesis of iron-doped biomass carbon dots as a dual-signal colorimetric and fluorometric probe for the detection of ascorbic acid

A new method based on biomass Fe-CDs with fluorescence properties and simulated oxidase activity colorimetric and fluorometric dual-readout assay for highly effective detection of AA was established.

Natural catalyst for Luminol chemiluminesence - Application to validate peroxide levels in commercial hair dyes

Herein, we report hydrothermally treated green leaves (Moringa Oleifera) extract exploited as an efficient and highly-sensitive catalyst to catalyse the Chemiluminescence (CL) reaction of luminol. In the absence of enhancer, this green and hydrothermally treated catalyst (GHT) was found to significantly enhance the CL intensity about 3.5 fold as compared to the traditionally used K₃ Fe(CN)₆ catalyst. The structure and surface morphology of the catalyst was elucidated by XPS, SEM, XRD and Raman spectroscopy. The synergistic effect of the catalyst in the CL reaction was systematically investigated in the presence of hydrogen peroxide using UV Visible and chemiluminesence spectroscopy. Studies show that the sensitivity of the catalyst could be amplified by adjusting several parameters such as pH of the medium, concentrations of the base and luminol. The sensitivity of the novel-type catalyst was examined through the validation of hydrogen peroxide levels in the commercial hair dye samples. Remarkably, the catalyst displayed ultra-sensitivity to hydrogen peroxide as the limit of detection (LOD) of H₂ O₂ using this catalyst is determined to be 0.02 μM under optimized conditions. In general, the proposed inexpensive, eco-friendly, and non-toxic catalyst could enable the determination of the hydrogen peroxide for diverse analytical applications.

A multifunctional nanozyme-based enhanced system for tert-butyl hydroquinone assay by surface-enhanced Raman scattering

An Au-based nanozyme composite (AuNPs/Cu,I) was constructed by using Cu,I-doped carbon dots (Cu,I-CDs) as the reducing agent as well as the nanozyme. Notably, AuNPs/Cu,I nanozyme not only possessed the intrinsic activity of mimicking enzymes of superoxide dismutase, peroxidase, and catalase at different conditions but was also employed as surface-enhanced Raman spectroscopy (SERS) enhancer. The combination of Cu,I-CDs and AuNPs promoted the electron transferability, leading to increased peroxidase-like activity and superoxide-like activity. Compared to the individual Cu,I-CDs and AuNPs nanozyme, the AuNPs/Cu,I composite demonstrated promising peroxidase-like activity by transferring electrons instead of generating OH. Interestingly, the multienzyme-like activity of AuNPs/Cu,I nanozyme could be finely tuned by changing the composition of Cu⁰/Cu⁺ and Au. The tert-butyl hydroquinone (TBHQ) as the substrate could be catalyzed with AuNPs/Cu,I nanozyme to produce red substances, resulting in a significant Raman enhancement effect at the same time, showing good linear range from 0.11 to 10 mg L^-1. Overall, the current investigation provides a flexible and controllable way to design multifunctional nanozymes along with the Raman enhancement strategy based on the catalysis of nanozyme.

Development of Ag nanoparticle-carbon quantum dot nanocomplex as fluorescence sensor for determination of gemcitabine

Gemcitabine hydrochloride is an established chemotherapeutic agent in several solid tumors. In spite of outstanding therapeutic efficacy, there are some serious fetal side effects with gemcitabine in higher concentrations which necessitate developing a sensitive sensor for its quantification. Herein, a fluorescent metal-nanoparticles conjugated carbon quantum dot (MN-CQD) was prepared by a mixture of citric acid/ammonia sulfate and different metals using hydrothermal method. Based on the primary experiments, the efficiency of Ag nanoparticle-CQDs for gemcitabine determination was found to be much better than others. The AgNp-CQDs fluorescence was quenched by gemcitabine anticancer drug via photo-induced charge transfer which renders the system into fluorescence "OFF" status. Under the experimental conditions, the linear range of detection was 0.003-0.1 μM in an aqueous solution with a correlation coefficient of 0.96 and a limit of detection equal to 0.002 µM. The relative standard deviation (RSD) for gemcitabine determination was 3.4% (n = 3). Finally, after optimizing the conditions, the concentration of analyte was determined in real samples including human plasma and urine. These results confirm that the as prepared fluorescence based nanosensor can be used for sensitive quantification of gemcitabine in real samples.

Enzymeless copper microspheres@carbon sensor design for sensitive and selective acetylcholine screening in human serum

Follow up of neuronal disorders, such as Alzheimer's and Parkinson's diseases using simple, sensitive, and selective assays is urgently needed in clinical and research investigation. Here, we designed a sensitive and selective enzymeless electrochemical acetylcholine sensor that can be used in human fluid samples. The designed electrode consisted of a micro spherical construction of Cu-metal decorated by a thin layer of carbon (CuMS@C). A simple and one-pot synthesis approach was used for Cu-metal controller formation with a spherical like structures. The spherical like structure was formed with rough outer surface texture, circular build up, homogeneous formation, micrometric spheres size (0.5 -1 µm), and internal hollow structure. The formation of a thin layer of carbon materials on the surface of CuMS sustained the catalytic activity of Cu atoms and enriched negatively charge of the surface. CuMS@C acted as a highly active mediator surface that consisted of Cu metal as a highly active catalyst and carbons as protecting, charge transport, and attractive surface. Therefore, the CuMS@C surface morphology and composition played a key role in various aspects such as facilitated ACh diffusion/loading, increased the interface surface area, and enhanced the catalytic activity. The CuMS@C acted as an electroactive catalyst for ACh electrooxidation and current production, due to the losing of two electrons. The fabricated CuMS@C could be a highly sensitive and selective enzymeless sensor for detecting ACh with a detection limit of 0.1 µM and a wide linear range of 0.01 - 0.8 mM. The designed ACh sensor assay based on CuMS@C exhibited fast sensing property as well as sensitivity, selectivity, stability, and reusability for detecting ACh in human serum samples. This work presents the design of a highly active electrode surface for direct detection of ACh and further clinical investigation of ACh levels.

A fluorimetric and colorimetric dual-signal sensor for hydrogen peroxide and glucose based on the intrinsic peroxidase-like activity of cobalt and nitrogen co-doped carbon dots and inner filter effect

Herein, cobalt and nitrogen co-doped carbon dots (Co-N-CDs) were fabricated via a one-pot hydrothermal approach. The obtained Co-N-CDs displayed peroxidase-like activity and fluorescence properties. It could catalyze the oxidization of guaiacol (GA) in the presence of hydrogen peroxide (H₂O₂), and thus, resulted in color change, accompanied by a new absorption peak in 470 nm. Owing to the inner filter effect, the oxidized product of GA (known as 2-PQ) largely absorbed the Co-N-CD fluorescence which was excited at 380 nm. Such changes in absorbance and fluorescence intensity were H₂O₂ concentration-dependent. Specifically, H₂O₂ could be generated by glucose oxidase to catalyze the oxidation of glucose, and thus, a colorimetric and fluorimetric sensor for glucose was established with high selectivity and excellent sensitivity. After the optimization of experimental conditions, this colorimetric sensor has a good linear range from 2 to 100 μM for glucose and the detection limit was 1.16 μM. Besides, the linear relationship between the fluorescence quenching value (ΔF) and the glucose concentration (0.4-40 μM) was obtained with a detection limit of 0.18 μM. Meanwhile, the proposed sensor has also been successfully applied for glucose detection in human serum samples, and the results were consistent with those of the standard method.

Nitrogen and copper-doped carbon quantum dots with intrinsic peroxidase-like activity for double-signal detection of phenol

Herein, a simple and facile one-step hydrothermal carbonization synthesis procedure for the fabrication of N, Cu-doped carbon quantum dots (N, Cu-CQDs) as a peroxidase-mimicking enzyme was reported. The peroxidase-like performance of N, Cu-CQDs was assessed based on the oxidative coupling reaction of phenol with 4-aminoantipyrine (4-AAP) in the presence of hydrogen peroxide (H2O2). The N, Cu-CQDs/4-AAP/H2O2 system was applied to sensing phenol based on double signals of absorption spectra (or colorimetric visualization) as well as fluorescence spectra. The obtained limits of detection (LODs) were as low as 0.12 μM and 0.02 μM, respectively. Moreover, the proposed method was successfully applied to the determination of phenol in sewage with satisfactory recovery. Our results demonstrate that the N, Cu-CQDs/4-AAP/H2O2/phenol sensing system has a great potential prospect for applications in environmental chemistry and biotechnology.

Carbon Dots: An Emerging Smart Material for Analytical Applications

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

An ultrasensitive chemiluminescence assay for 4-nitrophenol by using luminol-NaIO4 reaction catalyzed by copper, nitrogen co-doped carbon dots

A chemiluminescence (CL) assay on the basis of the tremendous enhancing effect of copper and nitrogen co-doped carbon dots (Cu,N-CDs) on the luminol-NaIO₄ reaction was introduced for the determination of nanomolar levels of 4-nitrophenol (4-NP). Cu,N-CDs were synthesized by a hydrothermal approach and characterized by TEM, XRD, EDX, and FTIR analysis. The potential CL mechanism was elucidated by recording the CL spectrum and by evaluating the influence of reactive oxygen species. It was found that 4-NP remarkably inhibited the luminol-NaIO₄-Cu,N-CDs reaction and reduced the CL signal of the reaction. This fact was applied for developing a CL assay for 4-NP. Under the optimized conditions, 4-NP could be determined in the concentration range of 0.25 to 150 nM, with a detection limit as low as 0.06 nM. This assay was successfully exploited for the analysis of 4-NP in real environmental samples.

Green mitigation of microbial corrosion by copper nanoparticles doped carbon quantum dots nanohybrid

Recently, nanomaterials have been introduced as a new generation of inhibitors to control the microbiologically influenced corrosion (MIC). In this study, copper nanoparticles doped carbon quantum dots (Cu/CQDs) nanohybrid was used as an inhibitor to reduce the MIC. FESEM, EDS, FTIR, and XRD were used to characterize the nanohybrid. The dose-response test was performed to evaluate the inhibitory effect of Cu/CQDs against SRB. Design-Expert software was used to design the matrix of experiment and analyze the result. Cu/CQDs showed significant inhibitory effect against SRB compared to the copper nanoparticles (CuNPs) and carbon quantum dots (CQDs), at 50 ppm. Moreover, corrosion behavior of X60 steel was evaluated via electrochemical impedance spectroscopy (EIS) and Tafel polarization techniques in the presence of SRB and Cu/CQDs. The fitted result of EIS showed that the charge transfer resistance (R_ct) value increased in the presence of Cu/CQDs owing to the enhancement in the thickness of the electrical double layer, indicating that Cu/CQDs is able to provide significant corrosion protection to X60 steel in the presence of SRB. In addition, FESEM, EDS, and XRD were used to study the formed corrosion products and biofilm on the surface of X60 steel. Corrosion test results indicated that the addition of the Cu/CQDs reduced the surface damage of X60 steel in the presence of SRB. It is attributed to the carbon dots adsorption film formation, which possessed a significant protective ability to inhibit the corrosion of steel in the presence of SRB.

Boric-acid-modified Fe3O4@PDA@UiO-66 for enrichment and detection of glucose by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Herein, boric-acid-modified multifunctional Zr-based metal-organic frameworks (denoted as Fe₃O₄@PDA@B-UiO-66) were synthesized by hydrothermal reaction and surface modification. Compared to traditional matrix, Fe₃O₄@PDA@B-UiO-66 has the advantages of high ionization efficiency, high surface area, low matrix background, porous structure, and numerous boric-acid-active sites. By combining matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), Fe₃O₄@PDA@B-UiO-66 was used as an adsorbent and matrix for enrichment and detection of glucose, based on a specific reaction between boric acid and glucose. The limit of detection was 58.5 nM. The proposed method provides a simple and efficient approach for the sensitive and quantitative detection of glucose in complex samples based on MALDI-TOF MS. Design and synthesis of boric-acid-modified multifunctional magnetic metal-organic frameworks (designated as Fe₃O₄@PDA@B-UiO-66) applied as adsorbent and matrix for the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis of glucose in complex biosamples.