CuS nanoparticles as a mimic peroxidase for colorimetric estimation of human blood glucose level

A highly effective peroxidase-mimic nanozyme of S, N-carbon dot-decorated cerium organic framework-based colorimetric detection of Hg2+ ion and thiophanate methyl

In this study, we proposed a colorimetric probe as S, N-carbon dot-decorated Ce-MOF (S, N-CD@Ce-MOF) for the dual detection of mercury and thiophanate methyl (TM), which are simultaneously present pollutants in the environment and foodstuffs. These pollutants cause serious threats to human health, such as carcinogenicity and neurovirulence. Herein, we synthesized S, N-CD@Ce-MOF using the hydrothermal method and applied it to a "turn-off-on" probe to detect mercury and TM using the colorimetric method in water and food samples. S, N-CD@Ce-MOF shows excellent peroxidase activity by catalyzing the chromogenic substrate of 3,3',5,5'-tetramethylbenzidine (TMB), resulting in deep blue-colored oxidized TMB product (ox TMB) in the presence of H2O2 with a UV absorption wavelength at 654 nm. However, the addition of Hg(II) ions prohibits the oxidation of TMB by an electron transfer effect and easily binds with -S, -N-containing sites on the surface of carbon dots, obstructing the catalytic active sites and decreasing catalytic efficiency with weak UV absorption at 654 nm as a "turn-off". Subsequently, the addition of TM to the above sensing solution as a "turn-on" was triggered by the TM-Hg complex formation and permitted TMB oxidation with a strong absorption peak at 654 nm. Furthermore, this proposed sensor demonstrates a superior linear response to mercury ions and TM in the ranges from 0 to 15 μM and 0 to 14 μM, respectively. The developed colorimetric assay exhibits good sensitivity and selectivity against various possible interferences. Furthermore, we found that the limits of detection for Hg2+ and TM were as low as 0.01 μM and 0.03 μM, respectively. The developed sensor provides various benefits, such as cost-effectiveness, simplicity without a complex detection process, and naked-eye detection. Consequently, our proposed colorimetric technique worked well for the detection of Hg2+ in real water samples and TM in real apple and tomato juice.

MOF-derived nanozyme CuOx@C and its application for cascade colorimetric detection of phytosterols

Phytosterols (PSs), a class of naturally occurring bioactive lipid compounds, have been found to possess a significant cholesterol-lowering effect. In developing countries, the consumption of rapeseed oil is the primary pathway of PS intake for the general population. However, developing low-cost, real-time, and high-throughput screening techniques for PSs remains a challenge. Here, a Cu-based nanocomposite CuOx@C was synthesized via a simple method of the calcination of HKUST-1 and systematically characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The CuOx@C demonstrated excellent peroxidase-like (POD-like) activity, functioning as a peroxidase mimic to facilitate the catalysis of 3,3',5,5'-tetramethylbenzidine (TMB) into its oxidized form (oxTMB), thereby initiating a discernible color response. On the basis of this discovery, a CuOx@C-based colorimetric method for detecting total sterols in rapeseed was successfully constructed via cascade reactions. After optimizing the conditions, the high-throughput screening of total sterols in rapeseed could be completed in only 21 min, which significantly facilitated the sensing of PSs. A linear range of 0.6-6 mg/g was achieved for the detection of total sterols in rapeseed samples, thereby satisfying the requirements for detection. In addition, due to the high stability of CuOx@C and the specificity of cholesterol oxidase, the developed method had excellent stability and selectivity toward PSs, indicating that this work has huge prospects for commercial application. This innovative work overcomes the limitation of the instrumental method and provides a portable and reliable tool for total sterols detection. It can also facilitate the development of oilseeds with a high content of PSs.

Microwave-assisted synthesis of Limonia acidissima Groff gum stabilized palladium nanoparticles for colorimetric glucose sensing

Herein, we present a novel microwave-assisted method for the synthesis of palladium nanoparticles (PdNPs) supported by Limonia acidissima Groff tree extract gum. The synthesized PdNPs were characterized using various analytical techniques, including FTIR, SEM, TEM, UV-visible, and powder XRD analyses. TEM and XRD analysis confirmed that the synthesized LAG-PdNPs are highly crystalline nature spherical shapes with an average size diameter of 7-9 nm. We employed these gum-capped PdNPs to investigate their peroxidase-like activity for colorimetric detection of hydrogen peroxide (H2O2) and glucose. The oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2, catalyzed by PdNPs, produces oxidation products quantified at 652 nm using spectrophotometry. The catalytic activity of PdNPs was optimized with respect to temperature and pH. The developed method exhibited a linear range of detection from 1 to 50 µm, with detection limits of 0.35 µm for H2O2 and 0.60 µm for glucose.

Colorimetric sensing of hydrogen peroxide using capped Morus nigra-sawdust deposited zinc oxide nanoparticles via Trigonella foenum extract

Hydrogen peroxide (H2O2) is one of the main byproducts of most enzymatic reactions, and its detection is very important in disease conditions. Due to its essential role in healthcare, the food industry, and environmental research, accurate H2O2 determination is a prerequisite. In the present work, Morus nigra sawdust deposited zinc oxide (ZnO) nanoparticles (NPs) were synthesized by the use of Trigonella foenum extract via a hydrothermal process. The synthesized platform was characterized by various techniques, including UV-Vis, FTIR, XRD, SEM, EDX, etc. FTIR confirmed the presence of a Zn‒O characteristic peak, and XRD showed the hexagonal phase of ZnO NPs with a 35 nm particle size. The EDX analysis confirmed the presence of Zn and O. SEM images showed that the as-prepared nanoparticles are distributed uniformly on the surface of sawdust. The proposed platform (acetic acid-capped ZnO NPs deposited sawdust) functions as a mimic enzyme for the detection of H2O2 in the presence of 3,3',5,5'-tetramethylbenzidine (TMB) colorimetrically. To get the best results, many key parameters, such as the amount of sawdust-deposited nanoparticles, TMB concentration, pH, and incubation time were optimized. With a linear range of 0.001-0.360 μM and an R2 value of 0.999, the proposed biosensor's 0.81 nM limit of quantification (LOQ) and 0.24 nM limit of detection (LOD) were predicted, respectively. The best response for the proposed biosensor was observed at pH 7, room temperature, and 5 min of incubation time. The acetic acid-capped sawdust deposited ZnO NPs biosensor was also used to detect H2O2 in blood serum samples of diabetic patients and suggest a suitable candidate for in vitro diagnostics and commercial purposes.

Inorganic Fe-O and Fe-S oxidoreductases: paradigms for prebiotic chemistry and the evolution of enzymatic activity in biology

Oxidoreductases play crucial roles in electron transfer during biological redox reactions. These reactions are not exclusive to protein-based biocatalysts; nano-size (<100 nm), fine-grained inorganic colloids, such as iron oxides and sulfides, also participate. These nanocolloids exhibit intrinsic redox activity and possess direct electron transfer capacities comparable to their biological counterparts. The unique metal ion architecture of these nanocolloids, including electron configurations, coordination environment, electron conductivity, and the ability to promote spontaneous electron hopping, contributes to their transfer capabilities. Nano-size inorganic colloids are believed to be among the earliest 'oxidoreductases' to have 'evolved' on early Earth, playing critical roles in biological systems. Representing a distinct type of biocatalysts alongside metalloproteins, these nanoparticles offer an early alternative to protein-based oxidoreductase activity. While the roles of inorganic nano-sized catalysts in current Earth ecosystems are intuitively significant, they remain poorly understood and underestimated. Their contribution to chemical reactions and biogeochemical cycles likely helped shape and maintain the balance of our planet's ecosystems. However, their potential applications in biomedical, agricultural, and environmental protection sectors have not been fully explored or exploited. This review examines the structure, properties, and mechanisms of such catalysts from a material's evolutionary standpoint, aiming to raise awareness of their potential to provide innovative solutions to some of Earth's sustainability challenges.

Facile Fabrication of Wood-Derived Porous Fe3C/Nitrogen-Doped Carbon Membrane for Colorimetric Sensing of Ascorbic Acid

Fe3C nanoparticles hold promise as catalysts and nanozymes, but their low activity and complex preparation have hindered their use. Herein, this study presents a synthetic alternative toward efficient, durable, and recyclable, Fe3C-nanoparticle-encapsulated nitrogen-doped hierarchically porous carbon membranes (Fe3C/N-C). By employing a simple one-step synthetic method, we utilized wood as a renewable and environmentally friendly carbon precursor, coupled with poly(ionic liquids) as a nitrogen and iron source. This innovative strategy offers sustainable, high-performance catalysts with improved stability and reusability. The Fe3C/N-C exhibits an outstanding peroxidase-like catalytic activity toward the oxidation of 3,3',5,5'-tetramethylbenzidine in the presence of hydrogen peroxide, which stems from well-dispersed, small Fe3C nanoparticles jointly with the structurally unique micro-/macroporous N-C membrane. Owing to the remarkable catalytic activity for mimicking peroxidase, an efficient and sensitive colorimetric method for detecting ascorbic acid over a broad concentration range with a low limit of detection (~2.64 µM), as well as superior selectivity, and anti-interference capability has been developed. This study offers a widely adaptable and sustainable way to synthesize an Fe3C/N-C membrane as an easy-to-handle, convenient, and recoverable biomimetic enzyme with excellent catalytic performance, providing a convenient and sensitive colorimetric technique for potential applications in medicine, biosensing, and environmental fields.

Sensitive and Label-Free Colorimetric Detection of Glyphosate Based on the Suppression Peroxidase-Mimicking Activity of Cu(II) Ions

The sensitive and accurate determination of glyphosate (Glyp) is urgently demanded because it is closely correlated with human health and environmental safety. In this work, we proposed a sensitive and convenient colorimetric assay by employing copper ion peroxidases for the detection of Glyp in the environment. Free Cu(II) ions displayed high peroxidase activity and can catalytically oxidize the colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxTMB, resulting in an obviously visible discoloration reaction. Once the Glyp is added, the ability of copper ions to mimic peroxidase can be largely suppressed because of the generation of Glyp-Cu²⁺ chelate. The favorable selectivity and sensitivity were demonstrated in the colorimetric analysis of Glyp. Furthermore, this rapid and sensitive method was successfully applied in the accurate and reliable determination of glyphosate in the real sample, holding promising applications in pesticide determination in the environment.

Quantitative and qualitative analyses of metal ions in food and water by using a multicolor sensor array and chemometrics

Rapid and accurate detection of toxic metal ions is the key to combating food contamination and environmental pollution. In sensor arrays, gold nanoparticles play a crucial role in monitoring metal ions based on surface plasmon resonance. However, identifying metal ions with unknown concentrations in a complex system through this assay is difficult because of its monotonous color change and weak anti-interference ability. To overcome these limitations, a sensitive, flexible, low-cost, and multicolor sensor array was designed herein. The applicability of the sensor array for the qualitative and quantitative analyses of metal ions in food and water was also verified. The developed sensor array could classify 14 metal ions (Cu²⁺, Fe²⁺, Fe³⁺, Mn²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Cr³⁺, Co²⁺, Ba²⁺, K⁺, Tl⁺, Pb²⁺, and Hg²⁺) of unknown concentration with an accuracy of 100%. In addition, partial least squares models were established to quantify Tl⁺, Pb²⁺, and Hg²⁺ in water and rice samples, with square correlation coefficients (R²) of 0.9991, 0.9742, and 0.9731, respectively. This method can be used for accurate quantitative and qualitative analyses of heavy metal ions in water and food.

Enhanced Peroxidase-like Activity of CuS Hollow Nanocages by Plasmon-Induced Hot Carriers and Photothermal Effect for the Dual-Mode Detection of Tannic Acid

High catalytic activity is one of the necessary parameters for nanozymes to substitute for natural enzymes. It remains a great challenge to improve the specific enzyme-like activity of nanozymes as much as possible using the characteristics of nanomaterials for avoiding complexity and introducing additional uncertainties. Here, by combining the peroxidase (POD)-like activity and plasmon properties of CuS hollow nanocages (CuS HNCs), we demonstrate the feasibility of modulating the catalytic activity of nanozymes by the localized surface plasmon resonance (LSPR) effect. Rough surfaces and hollow-cage structures endow CuS HNCs with abundant hot spots to produce strong LSPR in the near-infrared (NIR) region, which makes the CuS HNCs simultaneously generate plentiful high-energy hot carriers and thermal effect to mediate H₂O₂ cleavage to yield the reactive oxide species (ROS) as well as speed up the reaction, leading to a dramatically enhanced POD-like activity. Based on the light-enhanced catalytic activity and high photothermal efficiency of the reaction system, a dual-mode strategy for detecting tannic acid (TA) is developed and successfully applied to determine the content of TA in different kinds of teas. This work not only provides a novel path for tuning the specific enzyme-like activity of nanomaterials but also shows a perspective for dual-mode sensing based on a photoinduced plasmon-enhanced effect.

The valine-based N-doped carbon dots with high peroxidase-like activity

Developing artificial nanoparticles with peroxidase-like activity are being attracted great interests because their catalytic activity are not easy to lose under harsh conditions compared with natural enzymes. In this work, the N-doped carbon dots (CDs) were prepared, and it was found that the N-doped CDs showed high peroxidase-like catalytic activity towards the reaction system of hydrogen peroxide - 3, 3', 5, 5'-tetramethylbenzidine (TMB). The catalytic mechanism of the N-doped CDs was explored by usingelectron spin resonance (ESR) spectra, cyclic voltammetry (CV) method and simulation of density functional theory calculation. This work can offer a new feasible method for synthesizing N-doped CQDs used as artificial peroxidases in biological and environment applications.

Utilization of the peroxidase-like activity of silver nanoparticles nanozyme on O-phenylenediamine/H2O2 system for fluorescence detection of mercury (II) ions

Polyvinylpyrrolidone stabilized silver nanoparticles (PV-AgNPs) were synthesized from AgNO₃/trisodium citrate and with the assistance of microwave energy. The synthesized PV-AgNPs were found to own an actual peroxidase mimicking activity. This catalytic activity can oxidize the non-fluorescence reagent (o-phenylenediamine) to a high fluorescence reaction product (2,3-diaminophenazine). The reaction product exhibited a fluorescence emission at 563 nm upon the excitation at 420. Among many metals, only mercury (II) ions can inhibit the catalytic activity of PV-AgNPs nanozyme. Accordingly, the fluorescence intensity of the reaction product has been successfully quenched. This quenching effect in the fluorescence intensity was directly proportional to the concentration of mercury (II). Depending on this finding, a simple, cost-effective, and selective spectrofluorimetric approach has been designed for mercury (II) detection in water samples. The linear relationship between the inhibition in fluorescence intensity and mercury (II) concentration was found in 20–2000 nM with a detection limit of 8.9 nM.

What are the inorganic nanozymes? Artificial or inorganic enzymes!

The research on inorganic nanozymes remains very active since the first paper on the “intrinsic peroxidase-like properties of ferromagnetic nanoparticles” was published in Nature Nanotechnology in 2007. However, there is...

Construction of robust bienzyme-mimicking nanocatalysts for dye degradation by self-assembly of hematin, metal ions, and nucleotides

The growing proportion of the textile industry has led to an increase in the concentration of colored dyes in aquatic systems.

CuS nanoparticles-enhanced luminol-O2 chemiluminescence reaction used for determination of paracetamol and vancomycin

A new chemiluminescence (CL) method was proposed to measure two widely used drugs, including paracetamol (PCM) and vancomycin (VAN). The CL reaction used was the CuS nanoparticles (CuS NPs)-luminol-O₂ system. In this system, CuS NPs played the role of catalyst and increased the CL intensity. CuS NPs were easily synthesized by quick-precipitation. CuS NPs were characterized by spectroscopic techniques, and the mean size of NPs was estimated to be about 9 nm. In the developed CL methods, PCM and VAN decreased the CL intensity. In the proposed method, the linear concentration ranges were 4.0 × 10^-5-4.0 × 10^-4 mol L^-1 of PCM and 2.0 × 10^-5-6.0 × 10^-4 mol L^-1 of VAN. The limit of detections were 2.9 × 10^-5 mol L^-1 and 8.9 × 10^-6 mol L^-1 for PCM and VAN, respectively. The relative standard deviations (RSD) of the CL method were 2.99 and 4.31 (n = 6) for the determination of 3.0 × 10^-4 mol L^-1 PCM and VAN, respectively. It was also shown that the CL methods can measure PCM and VAN concentrations in various real samples.

Nanozymes Regulate Redox Homeostasis in ROS-Related Inflammation

Reactive oxygen species (ROS), in moderate amounts, play an essential role in regulating different physiological functions in organisms. However, increased amounts of ROS may cause oxidative stress and damage to biomolecules, leading to a variety of diseases including inflammation and even cancer. Therefore, ROS scavenging reagents are needed to maintain healthy levels of ROS. With considerable advances in nanotechnology, nanozymes possess SOD or CAT-like activities with outstanding free radical scavenging activity, facile synthesis conditions, and excellent biocompatibility. Based on these extraordinary properties, nanozymes has been used to modulate the redox homeostasis and relieve the ROS-related injury. This has led to the emergence of nanozyme-based therapies. In the current review, we presented recently developed applications of nanozymes to treat ROS-dependent disorders with an emphasis on inflammatory and brain diseases.

Nanozymes in Tumor Theranostics

Nanozymes, a new generation of enzyme mimics, have recently attracted great attention. Nanozymes could catalyze chemical reactions as biological enzymes under physiologically mild conditions with higher-efficiency catalytic activities. Moreover, nanozymes could overcome the shortcomings of natural enzymes, such as easy inactivation, high cost, and low yield. With the development of more and more smart and multi-functional nanosystems, nanozymes display great achievement in tumor biology. In this review, we outline the recent advances of nanozymes in tumor and tumor microenvironment diagnosis, therapy, and theranostics.

Understanding intricacies of bioinspired organic-inorganic hybrid nanoflowers: A quest to achieve enhanced biomolecules immobilization for biocatalytic, biosensing and bioremediation applications

The immobilization of biomolecules has been a subject of interest for scientists for a long time. The organic-inorganic hybrid nanoflowers are a new class of nanostructures that act as a host platform for the immobilization of such biomolecules. It provides better practical applicability to these functional biomolecules while also providing superior activity and reusability when catalysis is involved. These nanostructures have a versatile and straightforward synthesis process and also exhibit enzyme mimicking activity in many cases. However, this facile synthesis involves many intricacies that require in-depth analysis to fully attain its potential as an immobilization technique. A complete account of all the factors involving the synthesis process optimisation is essential to be studied to make it commercially viable. This paper explores all the different aspects of hybrid nanoflowers which sets them apart from the conventional immobilization techniques while also giving an overview of its wide range of applications in industries.

Calculation of Mass Transfer and Cell-Specific Consumption Rates to Improve Cell Viability in Bioink Tissue Constructs

Biofabrication methods such as extrusion-based bioprinting allow the manufacture of cell-laden structures for cell therapy, but it is important to provide a sufficient number of embedded cells for the replacement of lost functional tissues. To address this issue, we investigated mass transfer rates across a bioink hydrogel for the essential nutrients glucose and glutamine, their metabolites lactate and ammonia, the electron acceptor oxygen, and the model protein bovine serum albumin. Diffusion coefficients were calculated for these substances at two temperatures. We could confirm that diffusion depends on the molecular volume of the substances if the bioink has a high content of polymers. The analysis of pancreatic 1.1B4 β-cells revealed that the nitrogen source glutamine is a limiting nutrient for homeostasis during cultivation. Taking the consumption rates of 1.1B4 β-cells into account during cultivation, we were able to calculate the cell numbers that can be adequately supplied by the cell culture medium and nutrients in the blood using a model tissue construct. For blood-like conditions, a maximum of ~10⁶ cells·mL⁻¹ was suitable for the cell-laden construct, as a function of the diffused substrate and cell consumption rate for a given geometry. We found that oxygen and glutamine were the limiting nutrients in our model.

Biomimetic catalysts of iron-based metal-organic frameworks with high peroxidase-mimicking activity for colorimetric biosensing

The field of metal-organic framework (MOF)-based biomimetic catalysts has achieved great progress but is still in its infancy. The systematic investigation of the tailored construction of MOF-based biomimetic catalysts is required for further development. Herein, two iron-based MOFs, namely, [(Fe₃O)₂(H₂O)₄(HCOO)(L)₂]_n (HUST-5: H₆L = hexakis(4-formylphenoxy) cyclotriphosphazene; HUST = Huazhong University of Science and Technology) and [(Fe₃O)(H₂O)₃(L)]_n (HUST-7) have been fabricated through the assembly of different iron clusters and hexa-carboxylate ligand under the control of the added acid species. The two MOFs exhibit distinct secondary building units (SBUs) and topological structures, which could be used as biomimetic catalysts for the systematic comparisons of structural characteristics and the catalytic activity. Both MOFs possess catalytic activity similar to that of natural peroxidases towards the catalysis of the oxidation of a variety of substrates. Significantly, HUST-5 and HUST-7 can effectively catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H₂O₂ accompanied by significant colorimetric biosensing. With same compositions, different catalytic performances were obtained due to differences in the porous structures and characteristics of SBUs in two Fe-MOFs, which was also validated by theoretical calculation results. Furthermore, the phenomenon of colorimetric biosensing could be significantly suppressed by the addition of ascorbic acid (AA) during the oxidation process of TMB. It was observed from these findings that a facile colorimetric biosensing platform for detecting H₂O₂ and ascorbic acid has been successfully explored. Therefore, this work provides another unique perspective for the tailor-made preparation of stable MOF-based peroxidase mimics with excellent catalytic performance and colorimetric biosensing.

Magnetic nanomaterials with unique nanozymes-like characteristics for colorimetric sensors: A review

Colorimetric sensors for the rapid detection of numerous analytes have been widely applied in many fields such as biomedicine, food industry and environmental science due to their highly sensitive and selective response, easy operation and visual identification by naked eyes. In this review, the recent progress of the colorimetric sensors based on the magnetic nanomaterials with unique nanozymes-like catalytic activity (magnetic nanozyme) and their colorimetric sensing applications are presented. Emerging magnetic nanozyme-based colorimetric sensors, such as metal oxide/sulfides-based, metal-based, carbon-based, and aptamer-conjugated magnetic nanomaterials, offer many desirable features for target analytes detection. And due to the unique nanoscale physical-chemical properties, magnetic nanozymes have been used to mimic the catalytic activity of natural enzymes such as peroxidases, oxidases and catalases. This review also highlights the catalytic mechanisms of enzyme-like reactions, and promising colorimetric sensing system for the detection of chemical compounds like H₂O₂, pesticide, ascorbic acid, dopamine, tetracyclines, perfluorooctane sulfonate, phenolic compounds, heavy metal ion and sulfite have been deeply discussed. In addition, the remaining challenges and future directions in utilizing magnetic nanozyme for colorimetric sensors are addressed.

Molybdenum disulfide-based materials with enzyme-like characteristics for biological applications

Nanozyme, a kind of nanomaterials with enzymatic activity, has been developing vigorously over the past years owing to its advantages such as low-cost, easy storage, ease of use in harsh environments and so on, compared with natural enzymes. At present, as a typical two-dimensional nanomaterial, molybdenum disulfide (MoS₂) and their hybrids with unexpected enzyme-like activities have caused wide attention. In this review, we mainly investigated the enzyme-like activities of MoS₂ based nanomaterials, including peroxidase-like activity, catalase-like activity and superoxide dismutase-like activity. Furthermore, we systematically introduce recent research progress of MoS₂ based nanomaterials in the fields of biological applications such as radiation protection, cancer therapy, antibacterial, and wound healing. Finally, the current challenges and perspectives of MoS₂ based nanomaterials in the future are also discussed and proposed. We expect this review may be significant to understand the properties of MoS₂ based nanomaterials and the development of two-dimensional nanomaterials with enzyme mimicking activities.

The excellent peroxidase-like activity of uniform CuCo2O4 microspheres with oxygen vacancy for fast sensing of hydrogen peroxide and ascorbic acid

The uniform CuCo₂O₄ microspheres with oxygen vacancy were firstly found to possess excellent peroxidase-like activity which is essential for constructing a rapid and facile colorimetric sensor to determine H₂O₂ and interrelated biomolecules.

Detection of Glucose in Human Serum Based on Silicon Dot Probe

Background:

Diabetes Mellitus (DM) is a major public metabolic disease that influences 366 million people in the world in 2011, and this number is predicted to rise to 552 million in 2030. DM is clinically diagnosed by a fasting blood glucose that is equal or greater than 7 mM. Therefore, the development of effective glucose biosensor has attracted extensive attention worldwide. Fluorescence- based strategies have sparked tremendous interest due to their rapid response, facile operation, and excellent sensitivity. Many fluorescent compounds have been employed for precise analysis of glucose, including quantum dots, noble metal nanoclusters, up-converting nanoparticles, organic dyes, and composite fluorescent microspheres. Silicon dot as promising quantum dots materials have received extensive attention, owing to their distinct advantages such as biocompatibility, low toxicity and high photostability.

Methods:

MnO2 nanosheets on the Si nanoparticles (NPs) surface serve as a quencher. Si NPs fluorescence can make a recovery by the addition of H2O2, which can reduce MnO2 to Mn2+, and the glucose can thus be monitored based on the enzymatic conversion of glucose by glucose oxidase to generate H2O2. Therefore, the glucose concentration can be derived by recording the fluorescence recovery spectra of the Si NPs.

Results:

This probe enabled selective detection of glucose with a linear range of 1-100 μg/mL and a limit of detection of 0.98 μg/mL. Compared with the commercial glucometer, this method showed favorable results and convincing reliability.

Conclusion:

We have developed a novel method based on MnO2 -nanosheet-modified Si NPs for rapid monitoring of blood glucose levels. By combining the highly sensitive H2O2/MnO2 reaction with the excellent photostability of Si NPs, a highly sensitive, selective, and cost-efficient sensing approach for glucose detection has been designed and applied to monitor glucose levels in human serum with satisfactory results.

A novel selective and sensitive multinanozyme colorimetric method for glutathione detection by using an indamine polymer

A sensitive and selective novel multinanozyme colorimetric method for glutathione (GSH) detection was developed. MnO₂-nanozymes can catalyze the oxidation reaction of 3, 3՛-diaminobenzidine (DAB) and produce a brown indamine polymer. In the presence of GSH, this reaction slowly proceeds. When Au-nanozymes was used as peroxidase mimic along with MnO₂-nanozymes, the analytical signal and selectivity (particularly, over Cys and AA) were significantly improved for GSH detection. Therefore, this novel multinanozyme system was further developed through optimization for the colorimetric detection of GSH. The calibration curve presented two wide linear range from 0.05 to 0.19 and 0.19-11.35 mg L^{̶ 1} with a very low detection limit of 0.02 mg L^{̶ 1} (5 nM) for GSH. The developed method was employed for human serum analysis without any dilution and any deproteinization.

Blood-based FTIR-ATR spectroscopy coupled with extreme gradient boosting for the diagnosis of type 2 diabetes: A STARD compliant diagnosis research

Timely diagnosis of type 2 diabetes and early intervention and treatment of it are important for controlling metabolic disorders, delaying and reducing complications, reducing mortality, and improving quality of life. Type 2 diabetes was diagnosed by Fourier transform mid-infrared (FTIR) attenuated total reflection (ATR) spectroscopy in combination with extreme gradient boosting (XGBoost). Whole blood FTIR-ATR spectra of 51 clinically diagnosed type 2 diabetes and 55 healthy volunteers were collected. For the complex composition of whole blood and much spectral noise, Savitzky-Golay smoothing was first applied to the FTIR-ATR spectrum. Then PCA was used to eliminate redundant data and got the best number of principle components. Finally, the XGBoost algorithm was used to discriminate the type 2 diabetes from healthy volunteers and the grid search algorithm was used to optimize the relevant parameters of the XGBoost model to improve the robustness and generalization ability of the model. The sensitivity of the optimal XGBoost model was 95.23% (20/21), the specificity was 96.00% (24/25), and the accuracy was 95.65% (44/46). The experimental results show that FTIR-ATR spectroscopy combined with XGBoost algorithm can diagnose type 2 diabetes quickly and accurately without reagents.

A gold nanoparticle-intercalated mesoporous silica-based nanozyme for the selective colorimetric detection of dopamine

Highly dispersed aggregation-free gold nanoparticles intercalated into the walls of mesoporous silica (AuMS) were synthesized using thioether-functionalized silica as a nanozyme, which exhibited an excellent peroxidase mimic activity. The AuMS material was characterized via XRD, N₂ adsorption-desorption, FESEM, SEM-EDS particle mapping, TEM, and XPS. The peroxidase-like activity of the AuMS material was studied thoroughly, and the effect of pH and temperature was evaluated. The reproducibility of the peroxidase mimic activity and long-term stability of the AuMS catalyst were also studied. Furthermore, the AuMS catalyst was successfully utilized for the detection and quantification of dopamine, an important neurotransmitter, colorimetrically with a linear range of 10-80 μM and a limit of detection (LOD) value of 1.28 nM. The determination of dopamine concentration in commercially available dopamine hydrochloride injection showed high accuracy, good reproducibility, and high selectivity in the presence of uric acid, ascorbic acid, glucose, tryptophan, phenylalanine, and tyrosine.

AuCu bimetal nanoclusters as high-performance mimics for ultrasensitive recognition of biomolecules

Introducing novel mimic materials as alternatives for natural enzymes challenges the analysts. Study on the peroxidase-like materials is an active field in analytical research areas. Herein, Au/Cu bimetal nanoclusters (Au/Cu NCs) are introduced as highly efficient peroxidase mimics, which were investigated using fluorometric and colorimetric techniques. A comprehensive comparison between the catalytic activity of Au, Cu, and their bimetal NCs, with different ratios of Au/Cu was performed using some different peroxidase substrates (including 3,3′,5,5′-tetramethylbenzidine (TMB), o-phenylenediamine dihydrochloride (OPD), and terephthalic acid (TA)). Additionally, different capping agents were applied for the synthesis of NCs, and it was found that penicillamine-capped NCs with 50% Cu have higher activity than other synthesized NCs. Analytical application of the novel mimic for H2O2 detection caused a linear calibration in a wide linear range of 0.001–3 μmol/L, and a great detection limit (3S) of 0.18 nmol/L, using a sensitive fluorescence system. The developed system was also sensitive for recognizing glucose and cholesterol in blood samples, after their enzymatic oxidation and production of H2O2. Detection limits of 55 and 15 nmol/L were obtained for glucose and cholesterol, respectively. The presented method also showed good reliability, which was validated by certified reference materials.

De Novo Iron Oxide Hydroxide, Ferrihydrite Produced by Comamonas testosteroni Exhibiting Intrinsic Peroxidase-Like Activity and Their Analytical Applications

Natural enzyme mimics have attracted considerable attention due to leakage of enzymes and their easy denaturation during their storage and immobilization procedure. Here in this study, for the first time, a new iron oxide hydroxide, ferrihydrite - Fe_1.44O_0.32 (OH) _3.68 magnetic nanoparticles were synthesized by bacterial strain named Comamonas testosteroni. The characterization of the produced magnetic nanoparticles was confirmed by transmission electron microscopy (TEM), Fourier-transform spectroscopy (FTIR), X-ray diffraction (XRD), and magnetization hysteresis loops. Further, these extracted nanoparticles were proven to have biogenic magnetic behavior and to exhibit enhanced peroxidase-like activity. It is capable of catalyzing the oxidation of 3, 3', 5, 5'-Tetramethylbenzidine (TMB) by H₂O₂ to produce blue color (typical color reactions). Catalysis was examined to follow Michaelis-Menton kinetics and the good affinity to both H₂O₂ and TMB. The K _m value of the Fe_1.44O_0.32 (OH) _3.68 with H₂O₂ and TMB as the substrate was 0.0775 and 0.0155 mM, respectively, which were lower than that of the natural enzyme (HRP). Experiments of electron spin resonance (ESR) spectroscopy proved that the BMNPs could catalyze H₂O₂ to produce hydroxyl radicals. As a new peroxidase mimetic, the BMNPs were exhibited to offer a simple, sensitive, and selective colorimetric method for determination of H₂O₂ and glucose and efficiently catalyze the detection of glucose in real blood samples.

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.

A facile preparation of FePt-loaded few-layer MoS2 nanosheets nanocomposites (F-MoS2-FePt NCs) and their application for colorimetric detection of H2O2 in living cells

BACKGROUND

Rapid and sensitive detection of H2O2 especially endogenous H2O2 is of great importance for series of industries including disease diagnosis and therapy. In this work, uniform FePt nanoparticles are successfully anchored onto Few-layer molybdenum disulfide nanosheets (F-MoS2 NSs). The powder X-ray diffraction, transmission electron microscopy, UV-Vis spectra and atomic force microscopy were employed to confirm the structure of the obtained nanocomposites (F-MoS2-FePt NCs). The prepared nanocomposites show efficient peroxidase-like catalytic activities verified by catalyzing the peroxidation substrate 4,4'-diamino-3,3',5,5'-tetramethylbiphenyl (TMB) with the existence of H2O2.

RESULTS

The optimal conditions of the constructed colorimetric sensing platform is proved as 35 °C and pH 4.2. Under optimal catalytic conditions, the detection limit for H2O2 detection reaches 2.24 μM and the linear ranger is 8 μM to 300 μM. Furthermore, the proposed colorimetric sensing platform was successfully utilized to detect the intracellular H2O2 of cancer cells (MCF-7).

CONCLUSIONS

These findings indicated that the F-MoS2-FePt-TMB-H2O2 system provides a potential sensing platform for hydrogen peroxide monitoring in living cells.

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.

Functional nanomaterials with unique enzyme-like characteristics for sensing applications

We highlight the recent developments in functional nanomaterials with unique enzyme-like characteristics for sensing applications.

Ultra-small biocompatible jujube polysaccharide stabilized platinum nanoclusters for glucose detection

Jujube polysaccharide-stabilized platinum nanoclusters were used for the sensitive detection of glucose concentrations in serum and saliva.

Emerging Strategies of Nanomaterial-Mediated Tumor Radiosensitization

Nano-radiosensitization has been a hot concept for the past ten years, and the nanomaterial-mediated tumor radiosensitization method is mainly focused on increasing intracellular radiation deposition by high atomic number (high Z) nanomaterials, particularly gold (Au)-mediated radiation enhancement. Recently, various new nanomaterial-mediated radiosensitive approaches have been successively reported, such as catalyzing reactive oxygen species (ROS) generation, consuming intracellular reduced glutathione (GSH), overcoming tumor hypoxia, and various synergistic radiotherapy ways. These strategies may open a new avenue for enhancing the radiotherapeutic effect and avoiding its side effects. Nevertheless, reviews systematically summarizing these newly emerging methods and their radiosensitive mechanisms are still rare. Therefore, the general strategies of nanomaterial-mediated tumor radiosensitization are comprehensively summarized, particularly aiming at introducing the emerging radiosensitive methods. The strategies are divided into three general parts. First, methods on account of the intrinsic radiosensitive properties of nanoradiosensitizers for radiosensitization are highlighted. Then, newly developed synergistic strategies based on multifunctional nanomaterials for enhancing radiotherapy efficacy are emphasized. Third, nanomaterial-mediated radioprotection approaches for increasing the radiotherapeutic ratio are discussed. Importantly, the clinical translation of nanomaterial-mediated tumor radiosensitization is also covered. Finally, further challenges and outlooks in this field are discussed.