Ultrathin graphitic carbon nitride nanosheets: a novel peroxidase mimetic, Fe doping-mediated catalytic performance enhancement and application to rapid, highly sensitive optical detection of glucose

Rosette-shaped graphitic carbon nitride acts as a peroxidase mimic in a wide pH range for fluorescence-based determination of glucose with glucose oxidase

Rosette-shaped graphitic carbon nitride (rosette-GCN) is described as a promising alternative to natural peroxidase for its application to fluorescence-based glucose assays. Rosette-GCN was synthesized via a rapid reaction between melamine and cyanuric acid for 10 min at 35 °C, followed by thermal calcination for 4 h. Importantly, rosette-GCN possesses a peroxidase-like activity, producing intense fluorescence from the oxidation of Amplex UltraRed in the presence of H₂O₂ over a broad pH-range of, including neutral pH; the peroxidase activity of rosette-GCN was ~ 10-fold higher than that of conventional bulk-GCN. This enhancement of peroxidase activity is presumed to occur because rosette-GCN has a significantly larger surface area and higher porosity while preserving its unique graphitic structure. Based on the high peroxidase activity of rosette-GCN along with the catalytic action of glucose oxidase (GOx), glucose was reliably determined down to 1.2 μM with a dynamic linear concentration range of 5.0 to 275.0 μM under neutral pH conditions. Practical utility of this strategy was also successfully demonstrated by determining the glucose levels in serum samples. This work highlights the advantages of GCNs synthesized via rapid methods but with unique structures for the preparation of enzyme-mimicking catalysts, thus extending their applications to the diagnostics field and other biotechnological fields. Graphical abstract.

Preparation of Few-Layered Wide Bandgap MoS2 with Nanometer Lateral Dimensions by Applying Laser Irradiation

In this study, we report a new method for the quick, green, and one-step preparation of few-layered molybdenum disulfide (MoS2) nanosheets with wide bandgap. MoS2 nanosheets with small lateral dimension and uniform size distribution were synthesized for various applications. MoS2 powder was synthesized using the hydrothermal method; then, thinned by applying laser irradiation with different energies from 40 to 80 mJ. Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV-Vis absorption spectra, and photoluminescence (PL) spectra were applied for the characterization of the MoS2 nanosheets in terms of morphology, crystal structures, and optical properties. The widest calculated bandgap 4.7 eV was for the sample under 80 mJ laser energy. The results confirmed the successful preparation of highly pure, uniform, and few-layered MoS2 nanosheets. Furthermore, it was possible to enhance the production rate of MoS2 nanosheets (including nanosheets and nanoparticles) through laser irradiation. Thus, the present paper introduces a simple and green alternative approach for preparing few-layered MoS2 nanosheets of transition metal dichalcogenides or other layered materials.

Colorimetric Assay Using Mesoporous Fe-Doped Graphitic Carbon Nitride as a Peroxidase Mimetic for the Determination of Hydrogen Peroxide and Glucose

Iron can enter the electron-rich cavities of graphitic carbon nitride (g-C₃N₄). On account of this phenomenon, Fe-doped g-C₃N₄ (Fe-g-C₃N₄) was prepared as a peroxidase mimetic by using one-step pyrolysis of urea and FeCl₃·6H₂O. Compared to g-C₃N₄, Fe-g-C₃N₄ has a large specific surface area due to the presence of mesopores and cracks, a smaller band gap, and a high loading of Fe in its structure. Thus, Fe-g-C₃N₄ exhibits greater peroxidase activity with a more obvious color change when using 3,3',5,5'-tetramethylbenzidine (TMB) as a substrate in the presence of hydrogen peroxide (H₂O₂). The color of a mixture of TMB and Fe-g-C₃N₄ gradually deepens with increasing concentrations of H₂O₂. Accordingly, a rapid, sensitive, and low-cost colorimetric assay for the detection of H₂O₂ was developed. After optimization, this method boasts a wide linear dynamic range for H₂O₂ detection from 0.005 to 400 μM (r² = 0.9971) with a detection limit of 0.005 μM. Because H₂O₂ is a main product of glucose oxidation by glucose oxidase (GOx), a colorimetric assay for glucose detection was also realized, with a linear dynamic range of 1-1000 μM (r² = 0.9996) and a detection limit of 0.5 μM. These assays were applied to the quantitative detection of H₂O₂ in milk and glucose in human serum, respectively.

Fluorescent Se-modified carbon nitride nanosheets as biomimetic catalases for free-radical scavenging

Se-modified carbon nitride nanosheets with fluorescent properties and high biocompatibility show efficient free radical cleaning activity, and can be used as biomimetic catalases for resisting oxidative stress.

One-step cascade detection of glucose at neutral pH based on oxidase-integrated copper(ii) metal–organic framework composites

An integrated system was fabricated from a copper(ii) metal–organic framework (Cu-MOF) and glucose oxidase (GOx) for one-step cascade determination of glucose at neutral pH (pH = 7.0).

Two-dimensional iron MOF nanosheet as a highly efficient nanozyme for glucose biosensing

A 2D Fe-BTC nanosheet was preparedviaa cation exchange route. Its peroxidase-like activity is 2.2 times that of 3D MIL-100(Fe) due to highly accessible surface active sites. This is helpful for substrate contact with the catalyst during the catalytic reaction.

Facile one-pot synthesis of mesoporous g-C3N4 nanosheets with simultaneous iodine doping and N-vacancies for efficient visible-light-driven H2 evolution performance

Direct and efficient visible-light water splitting by photocatalysis is essential for the sustainable conversion of solar energy into H₂ fuel.

In situ polymerization and covalent functionalisation of trithiocyanuric acid by MoS2 nanosheets resulting in a novel nanozyme with enhanced peroxidase activity

MoS₂ catalysed the polymerisation of trithiocyanuric acid, resulting in a network exhibiting peroxidase activity via a ping-pong mechanism.

Therapeutic applications of multifunctional nanozymes

Nanozymes, which are functional nanomaterials with enzyme-like characteristics, have emerged as a highly-stable and low-cost alternative to natural enzymes. Apart from overcoming the limitations of natural enzymes (e.g., high cost, low stability or complex production), nanozymes are also equipped with the unique intrinsic properties of nanomaterials such as magnetism, luminescence or near infrared absorbance. Therefore, the development of nanozymes exhibiting additional functions to their catalytic activity has opened up new opportunities and applications within the biomedical field. To highlight the progress in the field, this review summarizes the novel applications of multifunctional nanozymes in various biomedical-related fields ranging from cancer diagnosis, cancer and antibacterial therapy to regenerative medicine. Future challenges and perspectives that may advance nanozyme research are also discussed at the end of the review.

Ce-Doped Graphitic Carbon Nitride Derived from Metal Organic Frameworks as a Visible Light-Responsive Photocatalyst for H2 Production

Novel fibrous graphitic carbon nitride (g-C₃N₄) derivatives prepared from metal organic frameworks (MOFs) were doped with Ce³⁺ (Ce-C₃N₄) as photocatalytic materials. Ce-C₃N₄ was characterized using various techniques, revealing its high specific surface area, excellent photocatalytic activity, and stability for H₂ evolution under visible light irradiation. The fluorine modified samples show superior photocatalytic activity under visible light irradiation, which is due to the presence of more active sites and enhanced absorption of solar energy. This work provides a new synthetic route for MOF-derived g-C₃N₄ that can be doped with different metal ions. The fluorine modified Ce-C₃N₄ is an efficient photocatalyst with potential for many applications related to energy and the environment.

A bromine-catalysis-synthesized poly(3,4-ethylenedioxythiophene)/graphitic carbon nitride electrochemical sensor for heavy metal ion determination

In this paper, poly(3,4-ethylenedioxythiophene)/graphitic carbon nitride (PEDOT/g-C3N4) composites were prepared by the bromine catalysed polymerization (BCP) method with varying weight ratios of monomer to g-C3N4. For comparison, solid-state polymerization (SSP) and metal oxidative polymerization (MOP) methods were also used for the synthesis of PEDOT/g-C3N4 composites. Electrochemical determination of heavy metal ions (Cd2+ and Pb2+) was carried out by differential pulse voltammetry (DPV) on composite-modified glass carbon electrodes (GCEs), which were prepared by different methods. The obtained composites were analysed by Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible absorption spectroscopy (UV-vis), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results showed that the bromine catalysed polymerization (BCP) method is an effective way to prepare the PEDOT/g-C3N4 composite, and the combination of PEDOT with g-C3N4 can improve the electrochemical activity of electrode materials. And, the composite from the BCP method modified electrode (PEDOT/10 wt% g-C3N4/GCE) exhibited the widest linear responses for Cd2+ and Pb2+, ranging from 0.06-12 μM and 0.04-11.6 μM with detection limits (S/N = 3) of 0.0014 μM and 0.00421 μM, respectively.

Enhanced peroxidase-like activity of AuNPs loaded graphitic carbon nitride nanosheets for colorimetric biosensing

Nanozymes have emerged as promising alternatives to overcome the high cost and low stability issues of natural enzymes. Particularly, those with peroxidase-like activities have been extensively studied to construct versatile biosensors. In this article, we demonstrate that the modification of the graphitic carbon nitride nanosheets (g-C₃N₄ nanosheets) by plasmonic gold nanoparticles (AuNPs) greatly enhances its catalytic performance as peroxidase mimetic. In the presence of H₂O₂, the AuNPs@g-C₃N₄ nanosheets can catalyze the redox reaction of 3,3',5,5'- tetramethylbenzidine (TMB) to produce a blue color. Based on the observation, a colorimetric sensing method for glucose is further developed with the assistance of glucose oxidase (GOx). The linear range for glucose is from 5 to 100 μmol L^-1 (R² = 0.9967) and the limit of detection (LOD) is 1.2 μmol L^-1. The LOD can be further lowered down to 0.75 μmol L^-1 by using H₂SO₄ as termination agent and measuring the absorbance of the yellow product at λ = 451 nm. Moreover, the practical usefulness of AuNPs@g-C₃N₄ nanosheets as a peroxidase nanozyme for glucose determination in human serum and urine is also demonstrated.

A DNA electrochemical biosensor based on triplex DNA-templated Ag/Pt nanoclusters for the detection of single-nucleotide variant

A label-free electrochemical biosensor based on the triplex DNA-templated Ag/Pt bimetallic nanoclusters (triplex-Ag/PtNCs) and locked nucleic acid (LNA) modified X-shaped DNA probe was developed for the detection of single-nucleotide variant (SNV) related to β-thalassemia. Firstly, using triplex DNA as template, a site-specific and homogeneous Ag/PtNCs was prepared, which can effectively catalyze the 3,3,5,5-tetramethylbenzidine-H₂O₂ system and thus be employed as a signal reporter in the field of electrochemical biosensor. Secondly, the LNA modified X-shaped probes were assembled on gold electrode surface, which can only be dissociated in the presence of target, leading to the hybridization with triplex-Ag/PtNCs and significant increase of current signal. In this way, the detection limit for SNV of β-thalassemia was 0.8 fM with variant allele frequency (VAF) as low as 0.0001%.

A Unique Interactive Nanostructure Knitting based Passive Sampler Adsorbent for Monitoring of Hg2+ in Water

This work reports the development of ultralight interwoven ultrathin graphitic carbon nitride (g-CN) nanosheets for use as a potential adsorbent in a passive sampler (PAS) designed to bind Hg²⁺ ions. The g-CN nanosheets were prepared from bulk g-CN synthesised via a modified high-temperature short-time (HTST) polycondensation process. The crystal structure, surface functional groups, and morphology of the g-CN nanosheets were characterised using a battery of instruments. The results confirmed that the as-synthesized product is composed of few-layered nanosheets. The adsorption efficiency of g-CN for binding Hg²⁺ (100 ng mL⁻¹) in sea, river, rain, and Milli-Q quality water was 89%, 93%, 97%, and 100%, respectively, at natural pH. Interference studies found that the cations tested (Co²⁺, Ca²⁺, Zn²⁺, Fe²⁺, Mn²⁺, Ni²⁺, Bi³⁺, Na⁺, and K⁺) had no significant effect on the adsorption efficiency of Hg²⁺. Different parameters were optimised to improve the performance of g-CN such as pH, contact time, and amount of adsorbent. Optimum conditions were pH 7, 120 min incubation time and 10 mg of nanosheets. The yield of nanosheets was 72.5%, which is higher compared to other polycondensation processes using different monomers. The g-CN sheets could also be regenerated up to eight times with only a 20% loss in binding efficiency. Overall, nano-knitted g-CN is a promising low-cost green adsorbent for use in passive samplers or as a transducing material in sensor applications.

Direct glucose detection in whole blood by colorimetric assay based on glucose oxidase-conjugated graphene oxide/MnO2 nanozymes

We herein report a facile approach for the preparation of horseradish peroxidase (HRP)-mimic glucose oxidase-conjugated graphene oxide/MnO2 (GOD-GO/MnO2) as new nanozyme to detect the glucose concentration in whole blood. The nano-sized of MnO2 nanoparticles embedded in bovine serum albumin (BSA)-coated GO by in situ growth were evaluated focusing on the principle of HRP-mimic activity catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide. Furthermore, we constructed dual sensing platforms based on the combination of a plasma separation pad and GOD-GO/MnO2 for direct detection of glucose concentration in whole blood by colorimetric assay without blood sample pretreatment. As a proof-of-concept, a limit of detection of 3.1 mg dL-1 for glucose was obtained with a wide linear quantification range from 25 mg dL-1 to 300 mg dL-1 through visual observation and quantitative analysis, suggesting potential clinical applications in blood glucose monitoring for diabetic patients.

Advanced drug delivery systems and artificial skin grafts for skin wound healing

Cutaneous injuries, especially chronic wounds, burns, and skin wound infection, require painstakingly long-term treatment with an immense financial burden to healthcare systems worldwide. However, clinical management of chronic wounds remains unsatisfactory in many cases. Various strategies including growth factor and gene delivery as well as cell therapy have been used to enhance the healing of non-healing wounds. Drug delivery systems across the nano, micro, and macroscales can extend half-life, improve bioavailability, optimize pharmacokinetics, and decrease dosing frequency of drugs and genes. Replacement of the damaged skin tissue with substitutes comprising cell-laden scaffold can also restore the barrier and regulatory functions of skin at the wound site. This review covers comprehensively the advanced treatment strategies to improve the quality of wound healing.

Three-Dimensional Branched Crystal Carbon Nitride with Enhanced Intrinsic Peroxidase-Like Activity: A Hypersensitive Platform for Colorimetric Detection

Graphitic carbon nitride (g-C₃N₄) as a metal-free nanozyme has attracted huge attention for catalytic applications. However, the catalytic activity of pure g-C₃N₄ causes very moderate H₂O₂ activation. Herein, a novel three-dimensional (3D) branched carbon nitride nanoneedle (3DBC-C₃N₄) nanozyme has been proposed to overcome such shortcoming. This unique 3D branched structure of 3DBC-C₃N₄ facilitated effective mass transfer during catalytic reaction and induced a lightning rodlike effect to accelerate electron collection at the tip area for H₂O₂ activation. With improved H₂O₂ activation for hydroxyl radical (^•OH) generation, 3DBC-C₃N₄ showed excellent peroxidase-like activity toward 3,3',5,5'-tetramethylbenzidine oxidation in the presence of H₂O₂. As for H₂O₂, the V_max value of 3DBC-C₃N₄ was found to be 20 times higher than that of natural horseradish peroxidase. Moreover, the 3D branched structure of 3DBC-C₃N₄ offered large interface for the reversible conjugation of single-stranded DNA, which enhanced the colorimetric sensitivity. Moreover, 3DBC-C₃N₄ exhibited high sensitivity toward oxytetracycline detection, with the detection limit and quantitative limit of 1 and 50 μg/L, respectively.

Peroxidase-Like Activity of Smart Nanomaterials and Their Advanced Application in Colorimetric Glucose Biosensors

Diabetes is a dominating health issue with 425 million people suffering from the disease worldwide and 4 million deaths each year. To avoid further complications, the diabetic patient blood glucose level should be strictly monitored despite there being no cure for diabetes. Colorimetric biosensing has attracted significant attention because of its low cost, simplicity, and practicality. Recently, some nanomaterials have been found that possess unexpected peroxidase-like activity, and great advances have been made in fabricating colorimetric glucose biosensors based on the peroxidase-like activity of these nanomaterials using glucose oxidase. Compared with natural horseradish peroxidase, the nanomaterials exhibit flexibility in structure design and composition, and have easy separation and storage, high stability, simple preparation, and tunable catalytic activity. To highlight the significant progress in the field of nanomaterial-based peroxidase-like activity, this work discusses the various smart nanomaterials that mimic horseradish peroxidase and its mechanism and development history, and the applications in colorimetric glucose biosensors. Different approaches for tunable peroxidase-like activity of nanomaterials are summarized, such as size, morphology, and shape; surface modification and coating; and metal doping and alloy. Finally, the conclusion and challenges facing peroxidase-like activity of nanomaterials and future directions are discussed.

Modified carbon nitride nanozyme as bifunctional glucose oxidase-peroxidase for metal-free bioinspired cascade photocatalysis

Nanomaterials-based biomimetic catalysts with multiple functions are necessary to address challenges in artificial enzymes mimicking physiological processes. Here we report a metal-free nanozyme of modified graphitic carbon nitride and demonstrate its bifunctional enzyme-mimicking roles. With oxidase mimicking, hydrogen peroxide is generated from the coupled photocatalysis of glucose oxidation and dioxygen reduction under visible-light irradiation with a near 100% apparent quantum efficiency. Then, the in situ generated hydrogen peroxide serves for the subsequent peroxidase-mimicking reaction that oxidises a chromogenic substrate on the same catalysts in dark to complete the bifunctional oxidase-peroxidase for biomimetic detection of glucose. The bifunctional cascade catalysis is successfully demonstrated in microfluidics for the real-time colorimetric detection of glucose with a low detection limit of 0.8 μM within 30 s. The artificial nanozymes with physiological functions provide the feasible strategies for mimicking the natural enzymes and realizing the biomedical diagnostics with a smart and miniature device.

High-Performance Photoelectrochemical Water Oxidation with Phosphorus-Doped and Metal Phosphide Cocatalyst-Modified g-C3 N4 Formation Through Gas Treatment

Graphitic carbon nitride (g-C₃ N₄ ) has been widely explored as a photocatalyst for water splitting. The anodic water oxidation reaction (WOR) remains a major obstacle for such processes, with issues such as low surface area of g-C₃ N₄ , poor light absorption, and low charge-transfer efficiency. In this work, such longtime concerns have been partially addressed with band gap and surface engineering of nanostructured graphitic carbon nitride (g-C₃ N₄ ). Specifically, surface area and charge-transfer efficiency are significantly enhanced through architecting g-C₃ N₄ on nanorod TiO₂ to avoid aggregation of layered g-C₃ N₄ . Moreover, a simple phosphide gas treatment of TiO₂ /g-C₃ N₄ configuration not only narrows the band gap of g-C₃ N₄ by 0.57 eV shifting it into visible range but also generates in situ a metal phosphide (M=Fe, Cu) water oxidation cocatalyst. This TiO₂ /g-C₃ N₄ /FeP configuration significantly improves charge separation and transfer capability. As a result, our non-noble-metal photoelectrochemical system yields outstanding visible light (>420 nm) photocurrent: approximately 0.3 mA cm^-2 at 1.23 V and 1.1 mA cm^-2 at 2.0 V versus RHE, which is the highest for a g-C₃ N₄ -based photoanode. It is expected that the TiO₂ /g-C₃ N₄ /FeP configuration synthesized by a simple phosphide gas treatment will provide new insight for producing robust g-C₃ N₄ for water oxidation.

Immobilized Ferrous Ion and Glucose Oxidase on Graphdiyne and Its Application on One-Step Glucose Detection

Graphdiyne (GDY) is a novel two-dimensional (2D) carbon allotrope with sp-hybridized carbon atoms and hexagonal rings. Because of its unique structure and electronic property, GDY was reported as a promising candidate applied in energy storage, catalysis, biosensing and so on. However, using GDY as a platform to immobilize metal ion or enzyme was still not reported. Here, we presented a GDY-based composite with dual-enzyme activity by immobilizing ferrous ion and glucose oxidase onto GDY sheet. GDY showed great adsorption capacity and maintained the high catalytic activity of ferrous ion. The ferrous ion preferred to adsorb in between the neighboring two C-C triple bonds of GDY with lower adsorption energy (-5.64 eV) if compared to graphene (-1.69 eV). Meanwhile, GDY exhibited the ability of adsorbing glucose oxidase while did not obviously influence the structure and catalytic activity of the enzyme. The as-prepared composite was successfully used in one-step blood glucose detection. This work provides a new insight on ion and enzyme immobilization by 2D material.

Single-stranded DNA modified protonated graphitic carbon nitride nanosheets: A versatile ratiometric fluorescence platform for multiplex detection of various targets

Facile and cost-effective detection of multiple targets is essential for a variety of applications ranging from life sciences to environmental monitoring. Here, we report a versatile ratiometric fluorescence platform for multiple detection of various targets based on the conjugation of single-stranded DNA (ssDNA) with protonated graphitic carbon nitride nanosheets (Pg-C₃N₄ NSs). We demonstrate that intrinsic peroxidase-like activity of Pg-C₃N₄ NSs is enhanced by conjugating with ssDNA, and thus the oxidation of substrate o-phenylenediamine (OPD) is promoted in the presence of H₂O₂. The oxidation product 2,3-diaminophenazine (DAP) can deliver a new fluorescence signal at 564 nm, and concurrently quench the intrinsic fluorescence of conjugates ssDNA/Pg-C₃N₄ NSs at 443 nm upon excitation at 370 nm. The transformation of fluorescence provides us a novel strategy for ratiometric fluorescence-based analytical sensing. Taking ssDNA as the target-recognition element of the conjugates ssDNA/Pg-C₃N₄ NSs, we favorably present ratiometric fluorescence detection of various targets including heavy metal ions (Hg²⁺) and biomolecules (Aflatoxin B1 (AFB1) and adenosine triphosphate (ATP)) in real samples by varying the ssDNA sequences. The present work provides a new strategy to develop facile methods for quantitative determination of various analytes and uncovers an innovative horizon for Pg-C₃N₄ NSs-based sensing platform fabrication.

2D metal chalcogenides with surfaces fully covered with an organic “promoter” for high-performance biomimetic catalysis

2D catalytic materials whose inorganic surfaces are fully covered with pre-designed “promoter” groups showed excellent biomimetic catalytic activity.

In situ sulfur-doped graphitic carbon nitride nanosheets with enhanced electrogenerated chemiluminescence used for sensitive and selective sensing of l-cysteine

In this study, in situ sulfur-doped carbon nitride nanosheets (S-g-C₃N₄ NSs) are used for the sensitive and selective sensing of l-cysteine (l-Cys) based on the competitive coordination chemistry of Cu²⁺ between l-Cys and S-g-C₃N₄ NSs.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Enhanced Peroxidase-Like Activity of MoS₂ Quantum Dots Functionalized g-C₃N₄ Nanosheets towards Colorimetric Detection of H₂O₂

MoS₂ quantum dots (QDs) functionalized g-C₃N₄ nanosheets (MoS₂@CNNS) were prepared through a protonation-assisted ion exchange method, which were developed as a highly efficient biomimetic catalyst. Structural analysis revealed that uniformly-dispersed MoS₂ QDs with controllable size and different loading amount grew in-situ on the surface of CNNS, forming close-contact MoS₂@CNNS nanostructures and exhibiting distinct surface properties. Compared to MoS₂ QDs and CNNS, the MoS₂@CNNS nanocomposites exhibited a more than four times stronger peroxidase-like catalytic activity, which could catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂ to generate a blue oxide. Among the MoS₂@CNNS nanocomposites, MoS₂@CNNS(30) was verified to present the best intrinsic peroxidase-like performance, which could be attributed to the more negative potential and larger specific surface area. A simple, rapid and ultrasensitive system for colorimetric detection of H₂O₂ was thus successfully established based on MoS₂@CNNS, displaying nice selectivity, reusability, and stability. The detection limit of H₂O₂ could reach as low as 0.02 μM. Furthermore, the kinetic and active species trapping experiments indicated the peroxidase-like catalytic mechanism of MoS₂@CNNS. This work develops a novel, rapid, and ultrasensitive approach for visual assay of H₂O₂, which has a potential application prospect on clinical diagnosis and biomedical analysis.

Graphitic C3N4 nanosheet and hemin/G-quadruplex DNAzyme-based label-free chemiluminescence aptasensing for biomarkers

Here we first reported that graphitic carbon nitride nanosheet (g-C₃N₄ NS) could effectively quench the chemiluminescence (CL) of luminol-hydrogen peroxide (H₂O₂) system. According to the new discovery, a label-free and homogeneous CL aptasensing platform was designed for sensitive detecting of biomarkers. In the absence of target, DNA probe containing hemin/G-quadruplex DNAzyme structure was adsorbed on the surface of g-C₃N₄ NS, causing the CL quenching of luminol through an electron transfer process. However, in the presence of the target, a DNA-DNA duplex was formed due to DNA hybridization reaction and target recognition effect, which could not be adsorbed onto the g-C₃N₄ NS surface because of its weak affinity. Thus, the electron transfer was blocked and the CL emission of luminol could be enhanced. The proposed CL aptasensor could detect carcinoembryonic antigen (CEA) with a detection limit of 63.0 pg/mL and it can also be used as a general detecting strategy for adenosinetriphosphate (ATP) detection. This aptasensing platform exhibited high sensitivity toward biomarkers and the probe need not be labeled, showing great promise for disease diagnosis.

Preparation and Characterization of Chiral Transition-Metal Dichalcogenide Quantum Dots and Their Enantioselective Catalysis

Two-dimensional transition-metal dichalcogenides (TMDs) had attracted enormous interests owing to their extraordinary optical, physical, and chemical properties. Herein, we prepared for the first time a series of chiral TMD quantum dots (QDs) from MoS₂ and WS₂ bulk crystals by covalent modification with chiral ligands cysteine and penicillamine. The chiral TMD QDs were carefully investigated by spectroscopic and microscopic techniques. Their chiral optical activity was confirmed by distinct circular dichroism signals different to those of the chiral ligands. Interestingly, with the assistance of copper ions, the chiral QDs displayed strong and chiral selective peroxidase-like activity. Up to now, inorganic nanomaterials with peroxidase-like activity were tremendous but seldom examples with enantioselectivity. The enantioselectivity of our chiral TMD QDs toward chiral substrates d- and l-tyrosinol was highly up to 6.77, which was almost the best performance ever reported. The mechanisms of enantioselectivity was further investigated by quartz crystal microbalance assays. We believed that because of the extraordinary electronic and optical properties, the chiral TMD QDs should be useful for nonlinear optical materials, asymmetric catalysis, chiral and biological sensors, and so on.

Strong electrochemiluminescent interactions between carbon nitride nanosheet-reduced graphene oxide nanohybrids and folic acid, and ultrasensitive sensing for folic acid

Graphite-like carbon nitride nanosheets (g-C3N4 NSs) have recently emerged as electrochemiluminescent (ECL) nanomaterials and have attracted more and more attention due to their excellent ECL properties and promising applications in ECL sensing. However, the ECL study of g-C3N4 NSs is still in the early stages. Many studies are required to reveal the exact ECL mechanisms of g-C3N4 NSs and thus boost their sensing applications. In this paper, we have investigated ECL interactions between folic acid (FA) and a g-C3N4 NS/S2O8(2-) ECL system at a g-C3N4 NS-reduced graphene oxide (rGO) nanohybrid/glassy carbon electrode in aqueous solutions. Compared with bare g-C3N4 NSs, the nanohybrids of g-C3N4 NS-rGO give a much stable ECL emission due to the prevention of over electrochemical reduction of g-C3N4 by rGO. The stable ECL emission from the g-C3N4 NS-rGO/S2O8(2-) ECL system can be strongly quenched by FA, even in a very low concentration (pM levels). The ECL quenching mechanisms are investigated and discussed in detail. Based on the strong interactions between FA and g-C3N4 NSs, a novel, sensitive, stable and selective ECL sensor has been constructed for the detection of FA, with a wide linear response range from 0.1 to 90 nM, and an excellent detection limit (62 pM). This work not only further clarifies ECL mechanisms of g-C3N4 NSs, but also suggests a promising application of the newly emerging ECL nanomaterial.

Ultrasensitive colorimetric determination of silver(I) based on the peroxidase mimicking activity of a hybrid material composed of graphitic carbon nitride and platinum nanoparticles

A hybrid material composed of graphitic carbon nitride (g-C₃N₄) and platinum nanoparticles (PtNPs) with peroxidase mimicking activity was used to design a rapid, sensitive and low-cost colorimetric method for the determination of Ag(I). The g-C₃N₄-PtNPs hybrid was synthesized by reduction of chloroplatinic acid using sodium borohydride under ultrasonication and in the presence of g-C₃N₄. The hybrid can catalyze the oxidation 3,3',5,5'-tetramethylbenzidine (TMB) to produce a blue-colored product with an absorption maximum at 652 nm. On addition of Ag(I) and in the presence of citric acid, it will be reduced to form Ag(0) under the catalytic action of PtNPs. Ag(0) is then adsorbed on the surface of the g-C₃N₄-PtNPs. This results in the inhibition of the enzyme mimetic activity of the hybrid. Hence, less blue product will be formed from TMB. Under optimum conditions, Ag(I) can be quantified in the 0.05-5.0 nM concentration range with a 22 pM detection limit. This assay is rapid and reliable and was applied to the determination of Ag(I) in spiked real water samples. Graphical abstract A hybrid nanomaterial consisting of graphitic carbon nitride and platinum nanoparticles (g-C₃N₄-PtNPs) can catalyze the oxidation of tetramethylbenzidine (TMB) to produce a blue-colored product (TMBox). The enzyme mimetic activity of the hybrid is inhibited by Ag⁺, thereby decreasing the generation of blue product from TMB.