Synthesis, characterization of copper oxide-gold nanoalloys and their peroxidase-like activity towards colorimetric detection of hydrogen peroxide and glucose

The novel nanozyme-based electrochemical-driven electrochromic visual biosensor based on PEDOT:PSS/RGO conductive film for rapid detection of nitrite in food samples

An efficient and facile nitrite (NO2-) detection system was developed using Fe3O4@Au-Cu/MOF, which was manufactured through self-assembly as the nanozyme, and a PEDOT:PSS/RGO thin film produced by chemical synthesis as the counter electrode, in conjunction with smartphone-based colorimetry. The Fe3O4@Au-Cu/MOF nanozyme exhibits remarkable catalytic efficiency and can significantly enhance the conversion of NO2-. PEDOT:PSS/RGO films exhibit outstanding electron transport and electrochromic properties. The color of PEDOT:PSS/RGO films can be modified by applying voltage and the electronic current generated by NO2- within the reaction system. The colorimetric assessment of film color alteration using a smartphone, supplemented by electrochemical validation. Under ideal conditions, the sensor detected NO2- within a linear range of 0.01 to 100 mmol/L and exhibited a detection limit of 3.37 μmol/L. This method demonstrated no significant difference compared to the results obtained using the electrochemical method and was effectively employed for the detection of NO2- in real samples.

Reactive oxygen species augmented polydopamine-chlorin e6 nanosystem for enhanced chemo/photothermal/photodynamic therapy: A synergistic trimodal combination approach in vitro & in vivo

Amalgamation of near-infrared laser phototherapies with chemotherapy in multi-modal synergistic therapy holds great promise for future precision cancer nanomedicine due to its minimal invasiveness, reduced adverse reactions, and high anticancer efficacy. Herein, CuO nanoparticles were functionalized with photosensitizer molecule, chlorin e6 (Ce6) and coated with polydopamine (PDA) to achieve a drug delivery system (CuO@Ce6-PDA) with photothermal/photodynamic therapy (PTT/PDT). Subsequently, chemical drug PTX was loaded for chemotherapy, and folic acid (FA) serving as cancer-targeting exterior material. Prepared FA@CuO@Ce6-PDA/PTX nanoparticles were nano-sized with favorable biocompatibility, colloidal stability, optimal surface charge, effective PTX loading, and controllable PTX release. In vitro studies on 4T1 cells showed that FA@CuO@Ce6-PDA/PTX had noteworthy synergistic therapeutic antitumour effects featuring chemo/PTT/PDT with IC50 of 50 μg/mL lower than that FA@CuO@Ce6-PDA/PTX without NIR laser irradiation (225 μg/mL). Additionally, FA@CuO@Ce6-PDA/PTX produced intracellular high reactive oxygen species (ROS) in presence of 660 nm laser, altering mitochondrial membrane potential and promoting tumour cell death. In vivo results indicate nanoplatform could accumulate in tumour spots enabling thermal imaging capabilities and exhibit synergistic therapeutic effect if irradiated with NIR laser (808 and 660 nm), evident from in vitro antitumour assay. Therefore, in vitro finding postulates FA@CuO@Ce6-PDA/PTX could be an intriguing nanoplatform for Chemo/PTT/PDT-based combination therapy.

The Mn-doped CeO2 nanoparticles with enhanced peroxidase-like activity for one-pot analysis of glucose at neutral pH based on bio-inorganic cascade reactions

Enzyme catalytic cascade reactions based on peroxidase nanozymes and natural enzymes have aroused extensive attention in analytical fields. However, a majority of peroxidase nanozymes perform well only in acidic environments, resulting in their optimal pH mismatch with a neutral pH of natural enzymes, further restricting their application in biochemical sensing. Herein, Mn-doped CeO2 (Mn/CeO2) performing enhanced peroxidase-like activity at neutral conditions was prepared via a facile and feasible strategy. An effective enzyme cascade catalysis system via integrating glucose oxidase (GOx) with Mn/CeO2 was developed for one-pot detection of glucose in serum at neutral conditions. Using one-pot multistep catalytic reactions, this work provided a detection platform that allows for faster detection and easier operations than traditional methods. Under optimized conditions, our assay performed a sensitive detection of glucose ranging from 2.0 μΜ to 300 μΜ and a low detection limit of 0.279 μΜ. Notably, favorable analytical outcomes for glucose detection in serum samples were obtained, exhibiting potential applications in clinical diagnosis.

Propelling gold nanozymes: catalytic activity and biosensing applications

Recently, gold nanomaterials have been rapidly developed owing to their high stability, good biocompatibility, and multifunctionality. The unique catalytic activity of gold nanomaterials has driven the emergence of the concept for a "gold nanozyme." Understanding the characteristics of gold nanozymes is crucial for improving their catalytic performance as well as expanding their applications. In this review, we provide an overview of the intrinsic enzyme-like activities of gold nanozymes, including peroxidase-, catalase-, superoxide dismutase-, and glucose oxidase-like activities, and the catalytic mechanisms involved. In addition, strategies for modulating the catalytic activity of gold nanozymes and their applications in biosensing were discussed in detail. Moreover, we highlight the current challenges of gold nanozymes and look forward to attracting more attention for propelling the developments in this field.

High-loading ficin@AuNPs on polymer-UiO-66 surface with enhanced peroxidase-mimetic catalytic activity for colourimetric detection of dopamine

Recently, MOFs@AuNPs composites-based catalysts via anchoring of AuNPs onto metal-organic-frameworks (MOFs) have attracted great attention. However, the influence of the AuNPs loading amounts on the catalytic activity of MOFs@AuNPs composites remains largely unexplored. Here, ficin (Fic) protected AuNPs (Fic@AuNPs) anchored onto the surface of UiO-66-NH2 (UiO) modified with poly(2-vinyl-4,4-dimethyl-2-oxazolidine) (PV) were designed and constructed. The UiOPVFic@AuNPs composites with longer PV chains leading to high-loading Fic@AuNPs exhibited intense peroxidase (POD)-mimetic activity in 3,3'5,5'-tetramethylbenzidine (TMB) oxidation. Further, following the colour-fading, dopamine (DA) was sensitively and selectively monitored in the composites-TMB-H2O2 system. The portable smartphone sensing platform-based colourimetric method had good linearity ranging from 3.34 to 36.7 μM (R2 = 0.995), with a limit of detection of 0.3 μM. This protocol explores high-loading AuNPs on polymer-MOFs composites, providing deep insights into understanding catalytic activity improvements of polymer-MOFs@AuNPs catalysts and revealing their application potential in real biological samples analysis.

Sensitive colorimetric detection of glutathione in human serum based on peroxidase-like activity of chitosan-stabilized gold nanoparticles

A colorimetric sensor for the rapid and sensitive detection of GSH was developed. The hydrothermal method was utilized to synthesize chitosan-stabilized gold nanoparticles (CS-AuNPs). The synthesized CS-AuNPs were characterized by UV-vis absorption spectroscopy, transmission electron microscopy (TEM), X-ray diffractograms (XRD), and Fourier transform infrared spectroscopy (FTIR). The CS-AuNPs are well-dispersed and possess a spherical shape with an average particle size of 10.05 ± 2.26 nm in aqueous solution. They show an intrinsic peroxidase-like activity, which could efficiently catalyze the decomposition of H2O2 to produce •OH radicals. These radicals then oxidized 3, 3´, 5, 5´-tetramethylbenzidine (TMB), resulting in the formation of the blue oxidized product oxTMB, observed a visible color change (from colorless to blue), and oxTMB had an obvious absorption peak at 652 nm. The presence of GSH could inhibit the peroxidase-like activity of CS-AuNPs, thereby reducing the formation of oxTMB. The solution's blue hue underwent a reduction in absorption intensity. Based on this fact, a novel and sensitive colorimetric sensor for detection of GSH was constructed. Under optimal conditions, the results of detection had an excellent linear relationship between the concentration of GSH and ∆A within the range 0.5 ~ 50.0 × 10-6 mol/L. The limit of detection (LOD) for GSH was 2.10 × 10-7 mol/L, which was much lower than those in most previous works. Furthermore, for detection in real human serum samples, the recoveries of GSH and the relative standard deviations (RSD) in the serum were in the range 98.40 ~ 103.32% and 1.85 ~ 3.54%, respectively. Thus, this visual colorimetric method has good precision and can be used for GSH detection in practical applications, promising in the fields of bioanalysis and illness diagnostics.

A fluorimetric and colorimetric dual-mode sensor based on N, S co-doped carbon dots functionalized silver nanoparticles for glucose detection

A fluorescent-colorimetric dual-signal platform, N, S co-doped carbon dots functionalized silver nanoparticles (NS-CDs-AgNPs), was designed in situ by reducing AgNO3 in the presence of N, S co-doped carbon dots (NS-CDs) under the assistance of microwave irradiation for glucose determination. With the formation of silver nanoparticles (AgNPs), the intrinsic fluorescence of NS-CDs was quenched, showing the fluorescence state was off. Whereas the fluorescence of NS-CDs can be switched on when a trace amount of H2O2 was added. Based on this novel phenomenon, the peroxidase-like activity of NS-CDs-AgNPs by using 3,3',5,5'-tetramethylbenzidine (TMB) chromogen and H2O2 as substrates was evaluated. The Km values of the prepared probe for H2O2 and TMB were 0.84 mM and 0.01 mM with the Vm of 6.65 × 10-8 M S-1 and 3.01 × 10-8 M S-1, respectively. The results showed that NS-CDs-AgNPs had good peroxidase-like activity and strong affinity to TMB and H2O2. It confirmed that there is a redox interaction between AgNPs and H2O2, and H2O2 can oxidize Ag to produce Ag+, which is the main reason that the fluorescence of NS-CDs-AgNPs can be activated by H2O2. The hydroxyl radical (·OH) was formed in the process of reaction, which can further oxidize TMB for color reaction. Meanwhile, glucose can be oxidized to produce H2O2 in the presence of glucose oxidase (GOx). Based on the phenomenon, a fluorimetric and colorimetric dual-mode sensor for glucose detection was established. Satisfactory results were obtained with the linear range of 0.1-80 μM for fluorimetric mode and 0.5-5 μM for colorimetric mode, respectively. Additionally, the LOD was below 0.32 μM and 0.21 μM, respectively. The method was successfully applied to determine the glucose in human serum with satisfactory recovery and RSD.

Ultra-trace Ag doped carbon quantum dots with peroxidase-like activity for the colorimetric detection of glucose

Carbon quantum dots (CQDs) have significant applications in nanozymes. However, previous studies have not elucidated the structure-activity relationship and enzyme mechanism. In this study, we employed a one-step microwave method to synthesize ultra-trace Ag-doped carbon quantum dots (Ag-CQDs). In the presence of hydrogen peroxide (H2O2), we used the oxidative coupling reaction of 3,3',5,5'-tetramethylbenzidine (TMB) to evaluate the intrinsic peroxidase-like activity, kinetics, and mechanism of Ag-CQDs. The trace amount of doped Ag (1.64 %) facilitated electron transfer from the CQDs interior to the surface. The electron transfer triggered the peroxide activity of CQDs, producing hydroxyl radical (·OH), which oxidized the colorless TMB to blue-colored TMB (oxTMB). By coupling with glucose oxidase (GOx), the Ag-CQDs/H2O2/TMB system has been used for colorimetric glucose determination. The system demonstrated a low detection limit (0.17 µM), wide linear range (0.5-5.5 µM), and satisfactory results when fruit juice was analyzed. This study reports a feasible method for the colorimetric detection of glucose by synthesizing ultra-trace Ag-doped carbon quantum dots with peroxidase-mimicking activity.

Designing Nanocomposite-Based Electrochemical Biosensors for Diabetes Mellitus Detection: A Review

This review will unveil the development of a new generation of electrochemical sensors utilizing a transition-metal-oxide-based nanocomposite with varying morphology. There has been considerable discussion on the role of transition metal oxide-based nanocomposite, including iron, nickel, copper, cobalt, zinc, platinum, manganese, conducting polymers, and their composites, in electrochemical and biosensing applications. Utilizing these materials to detect glucose and hydrogen peroxide selectively and sensitively with the correct chemical functionalization is possible. These transition metals and their oxide nanoparticles offer a potential method for electrode modification in sensors. Nanotechnology has made it feasible to develop nanostructured materials for glucose and H2O2 biosensor applications. Highly sensitive and selective biosensors with a low detection limit can detect biomolecules at nanomolar to picomolar (10-9 to 10-12 molar) concentrations to assess physiological and metabolic parameters. By mixing carbon-based materials (graphene oxide) with inorganic nanoparticles, nanocomposite biosensor devices with increased sensitivity can be made using semiconducting nanoparticles, quantum dots, organic polymers, and biomolecules.

Dual-mode colorimetric and photothermal aptasensor for detection of kanamycin using flocculent platinum nanoparticles

Chitosan (CS)-stabilized platinum nanoparticles (CS/PtNPs) were employed to develop a novel aptamer-based dual-mode colorimetric and photothermal biosensor for selective detection of kanamycin (KAN). As a peroxidase-like catalyst, the CS/PtNPs showed outstanding catalytic activity for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2). As a stabilizing agent, CS excelled at fixing the KAN binding aptamer on the surface of the CS/PtNPs, amplifying their catalytic activity and enhancing colloidal dispersion and stability. The oxidized TMB (TMBox) functioned as a signal for the colorimetric, photothermal aptasensor because of its observable absorbance of light in the visible and near-infrared (NIR) regions. When light from a NIR laser was absorbed by the TMBox in the reaction solution, heat was generated in inverse proportion to the KAN concentration. The developed colorimetric and photothermal modes of the aptasensor showed a linear detection range of 0.1-50 and 0.5-50 μM, with a limit of detection (LOD) of 0.04 and 0.41 μM, respectively. Moreover, the aptasensor successfully determined KAN concentrations in spiked milk samples, verifying the reliability and reproducibility in practical applications. The dual-mode aptasensor based on CS/PtNPs for KAN detection, utilizing both color change and heat generation signals through a single probe (TMBox), demonstrates rapid response, simplicity in operation, cost-effectiveness, and high sensitivity. In addition, unlike typical immunoassays, this aptamer-based peroxidase-like nanozyme activation and inhibition strategy required no washing process, which was very effective in terms of reducing the time required for an assay and sustaining a high sensitivity.

Oxidase-like manganese oxide nanoparticles: a mechanism of organic acids/aldehydes as electron acceptors and potential application in cancer therapy

Identifying the underlying catalytic mechanisms of synthetic nanocatalysts or nanozymes is important in directing their design and applications. Herein, we revisited the oxidation process of 4,4'-diamino-3,3',5,5'-tetramethylbiphenyl (TMB) by Mn3O4 nanoparticles and revealed that it adopted an organic acid/aldehyde-triggered catalytic mechanism at a weakly acidic or neutral pH, which is O2-independent and inhibited by the pre-addition of H2O2. Importantly, similar organic acid/aldehyde-mediated oxidation was applied to other substrates of peroxidase in the presence of nanoparticulate or commercially available MnO2 and Mn2O3 but not MnO. The selective oxidation of TMB by Mn3O4 over MnO was further supported by density functional theory calculations. Moreover, Mn3O4 nanoparticles enabled the oxidation of indole 3-acetic acid, a substrate that can generate cytotoxic singlet oxygen upon single-electron transfer oxidation, displaying potential in nanocatalytic tumor therapy. Overall, we revealed a general catalytic mechanism of manganese oxides towards the oxidation of peroxidase substrates, which could boost the design and various applications of these manganese-based nanoparticles.

Synergistic antibacterial mechanism of silver-copper bimetallic nanoparticles

The excessive use of antibiotics in clinical settings has resulted in the rapid expansion, evolution, and development of bacterial and microorganism resistance. It causes a significant challenge to the medical community. Therefore, it is important to develop new antibacterial materials that could replace traditional antibiotics. With the advancements in nanotechnology, it has become evident that metallic and metal oxide nanoparticles (MeO NPs) exhibit stronger antibacterial properties than their bulk and micron-sized counterparts. The antibacterial properties of silver nanoparticles (Ag NPs) and copper nanoparticles (Cu NPs) have been extensively studied, including the release of metal ions, oxidative stress responses, damages to cell integrity, and immunostimulatory effects. However, it is crucial to consider the potential cytotoxicity and genotoxicity of Ag NPs and Cu NPs. Numerous experimental studies have demonstrated that bimetallic nanoparticles (BNPs) composed of Ag NPs and Cu NPs exhibit strong antibacterial effects while maintaining low cytotoxicity. Bimetallic nanoparticles offer an effective means to mitigate the genotoxicity associated with individual nanoparticles while considerably enhancing their antibacterial efficacy. In this paper, we presented on various synthesis methods for Ag-Cu NPs, emphasizing their synergistic effects, processes of reactive oxygen species (ROS) generation, photocatalytic properties, antibacterial mechanisms, and the factors influencing their performance. These materials have the potential to enhance efficacy, reduce toxicity, and find broader applications in combating antibiotic resistance while promoting public health.

Novel colorimetric detection of oxytetracycline in foods by copper nanozyme

In this study, copper nanozyme (CuNZs) possess good laccase-like activity were synthesized by grinding method with cupric chloride dihydrate as copper source, sodium borohydride as reducing agent and β-cyclodextrin as protective agent. The CuNZs can oxidize colorless 2,4-dinitrophenol (2,4-DP) to red product. When oxytetracycline (OTC) was added to the above three solutions, the color changed from red to orange and the absorbance increased again, indicating that OTC was also an affinity substrate for CuNZs. When CuNZs was mixed with OTC alone, the color changed from colorless to yellow, and the absorption intensity was related to OTC concentration. It has good selectivity and sensitivity, and had a good linear response to the concentration of OTC in the range of 50-500 μM, and the limit of detection was 0.148 μM. Thus, a fast and simple colorimetric assay for the determination of OTC was established by using the laccase-like activity of CuNZs, and it was applied successfully to detect OTC in food samples.

Near-infrared light responsive intensified multiphoton ultraviolet upconversion in nanostructures towards efficient reactive oxygen species generation

Near-infrared-to-ultraviolet (NIR-to-UV) multiphoton upconversion has recently received increasing attention owing to its promising frontier applications in the fields of biomedicine and nanophotonics. However, the realization of high-efficiency NIR-to-UV upconversion remains a dispiriting challenge due to weak excitation light harvesting and photo-conversion efficiency. Herein, we propose a mechanistic strategy to achieve intensified UV upconversion by manipulating the injected excitation energy flux. A simple LiYbF4:Tm@LiYF4 host-sensitized sublattice core-shell nanostructure was initially proposed to compete with the concentration quenching effect and increase energy transfer efficiency. Then, the organic dye ICG was further coated to introduce the antenna sensitization effect to highly increase the absorption ability of nanocrystals. After optimizing the ICG number loaded on the surface and separation distance, up to 167-fold UV upconversion emission enhancement was achieved under low-power excitation of 808 nm. More importantly, the efficient UV upconversion exhibits enhanced reactive oxygen species (ROS) generation activity by fabricating a TiO2-modified upconversion nanocomposite, revealing great application potential in frontier fields such as in vivo photodynamic therapy and bioimaging-guided therapeutics. Our results can provide versatile designs to achieve efficient UV upconversion, overcome conventional limitations, and offer exciting opportunities for potential applications in biomedical fields.

Pd nanocatalysts adsorbed onto silica nanoparticle coated indium tin oxide: a reusable nanozyme for glucose detection

Nanozymes are nanomaterials that exhibit enzyme-like activity upon exposure to a substrate solution. The use of noble and platinum group metals enhances enzyme-like catalytic activity. However, noble metals are obtained at a high cost; therefore, their recovery after use is of high importance. Herein, we report the fabrication of indium tin oxide-silica nanoparticles decorated with palladium nanoparticles (ITO-SiO2-prS-PdNPs). The ITO-SiO2-prS-PdNPs were evaluated for peroxidase-like activity toward the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. A colour change from clear or colourless TMB to blue colour (oxidized TMB products) was observed confirming the peroxidase-like activity. A typical Michaelis-Menten enzyme-like behaviour is observed with Km values of 0.68 mM for H2O2 and 0.47 mM for TMB, which are better than the reported values for horse-radish peroxidase (HRP) for the same substrate. The peroxidase-like activity of ITO-SiO2-prS-PdNPs was found to proceed via the electron-transfer mechanism. The ITO-SiO2-prS-PdNPs were cleaned successfully after each use by rinsing with water and ethanol solution thus making the surface simple and easy to recover and reuse. A reusable and highly selective colorimetric assay for glucose detection based on the peroxidase-like activity of ITO-SiO2-prS-PdNPs gave excellent results. ITO-SiO2-prS-PdNPs exhibited a good linear range of 5.0-30 μM, a low limit of detection (LOD) of 1.84 μM and a limit of quantification (LOQ) of 6.14 μM. Finally, the nanozyme (ITO-SiO2-prS-PdNPs) was successfully used to detect glucose in a complex newborn calf serum (NCS), representing a real sample.

Apta-sensor for selective determination of dopamine using chitosan-stabilized Prussian blue nanoparticles

Chitosan-stabilized Prussian blue nanoparticles (CS/PBNPs) were fabricated by a simple synthetic method and used to develop a novel aptamer-based colorimetric assay for selective determination of dopamine (DA). Scanning electron microscopy (SEM) images exhibited a uniform shape of the CS/PBNPs with an average diameter of 37.0 ± 3.2 nm. The CS/PBNPs exhibited strong peroxidase-like activity that catalyzed the reaction between 3,3',5,5'-tetramethylbenzidine (TMB) and hydrogen peroxide (H₂O₂). Chitosan was used for stabilization of the PBNPs and fixation of the DA aptamer on the surface of the CS/PBNPs. The catalytic mechanism of the CS/PBNPs was confirmed to involve first the decomposition of H₂O₂ into a hydroxyl radical (˙OH) and then oxidation of TMB by the ˙OH to produce a blue color. An aptamer-based colorimetric assay was made with the CS/PBNPs to detect DA at concentrations of 0.25-100 μM with a limit of detection (LOD) of 0.16 μM. For comparison, a gold nanoparticle (AuNP)-based apta-sensor detected DA in concentrations of 1-25 μM with a LOD of 0.55 μM. The recovery results of DA concentrations (0.25, 0.5, and 1 μM) from spiked human serum were 92.6%, 102.1%, and 103.9%, verifying the reliability and reproducibility of the CS/PBNP-based apta-sensor for determination of DA level in clinical applications. Moreover, compared to traditional immunoassay, this aptamer-based nanozyme activation/inhibition system needs no washing step, which is very useful to shorten the assay time and maintain high sensitivity.

Mesoporous Mixed-Metal-Organic Framework Incorporating a [Ru(Phen)3]2+ Photosensitizer for Highly Efficient Aerobic Photocatalytic Oxidative Coupling of Amines

[Ru(Phen)₃]²⁺ (phen = phenanthroline) as a very classical photosensitizer possesses strong absorption in the visible range and facilitates photoinduced electron transfer, which plays a vital role in regulating photochemical reactions. However, it remains a significant challenge to utilize more adequately and exploit more efficiently the ruthenium-based materials due to the uniqueness, scarcity, and nonrenewal of the noble metal. Here, we integrate the intrinsic advantages of the ruthenium-based photosensitizer and mesoporous metal-organic frameworks (meso-MOFs) into a [Ru(Phen)₃]²⁺ photosensitizer-embedded heterometallic Ni(II)/Ru(II) meso-MOF (LTG-NiRu) via the metalloligand approach. LTG-NiRu, with an extremely robust framework and a large one-dimensional (1D) channel, not only makes ruthenium photosensitizer units anchored in the inner wall of meso-MOF tubes to circumvent the problem of product/catalyst separation and recycling of catalysts in heterogeneous systems but also exhibits exceptional activities for the aerobic photocatalytic oxidative coupling of amine derivatives as a general photocatalyst. The conversion of the light-induced oxidative coupling reaction for various benzylamines is ∼100% in 1 h, and more than 20 chemical products generated by photocatalytic oxidative cycloaddition of N-substituted maleimides and N,N-dimethylaniline can be synthesized easily in the presence of LTG-NiRu upon visible light irradiation. Moreover, recycling experiments demonstrate that LTG-NiRu is an excellent heterogeneous photocatalyst with high stability and excellent reusability. LTG-NiRu represents a great potential photosensitizer-based meso-MOF platform with an efficient aerobic photocatalytic oxidation function that is convenient for gram-scale synthesis.

Detection of Glucose Based on Noble Metal Nanozymes: Mechanism, Activity Regulation, and Enantioselective Recognition

Glucose monitoring is essential to evaluate the degree of glucose metabolism disorders. The enzymatic determination has been the most widely used method in glucose detection because of its high efficiency, accuracy, and sensitivity. Noble metal nanomaterials (NMs, i.e., Au, Ag, Pt, and Pd), inheriting their excellent electronic, optical, and enzyme-like properties, are classified as noble metal nanozymes (NMNZs). As the NMNZs are often involved in two series of reactions, the oxidation of glucose and the chromogenic reaction of peroxide, here the chemical mechanism by employing NMNZs with glucose oxidase (GOx) and peroxidase (POD) mimicking activities is briefly summarized first. Subsequently, the regulation strategies of the GOx-like, POD-like and tandem enzyme-like activities of NMNZs are presented in detail, including the materials, size, morphology, composition, and the reaction condition of the representative NMs. In addition, in order to further mimic the enantioselectivity of enzyme, the design of NMNZs with enantioselective recognition of d-glucose and l-glucose by using different chiral compounds (DNA, amino acids, and cyclodextrins) and molecular imprinting is further described in this review. Finally, the feasible solutions to the existing challenges and a vision for future development possibilities are discussed.

Light-enhanced transparent hydrogel for uric acid and glucose detection by four different analytical platforms

The lack of solid-phase media limits the portability of colorimetric sensing platforms. In this study, a series of transparent polyvinyl alcohol (PVA) hydrogels encapsulated antimony tin oxide nanoparticles (ATO NPs) and 3,3',5,5'-tetramethylbenzidine (TMB) were developed as the solid-phase sensing media for glucose and uric acid. Under the conditions of H₂O₂ and UV light, the hydrogel presented a multicatalytic ability (photo Fenton-like and peroxidase-like activities), which accelerated the oxidation of TMB, turning the hydrogel from colorless to blue and finally enhancing the detection signal. The plasticity of the hydrogel allowed it to be designed into various shapes (membrane, microsphere etc.) to adapt multiple detection platforms (a liquid/solid-phase UV spectrophotometer, a NanoPhotometer, and smartphone spectroscopy). The hydrogel sensing media exhibited excellent tunability and enhanced the photocatalytic ability. The proposed material was successfully applied to detect glucose and uric acids in real samples by four detection platforms to evaluate its practicability.

A Multifunctional Dental Resin Composite with Sr-N-Doped TiO2 and n-HA Fillers for Antibacterial and Mineralization Effects

Dental caries, particularly secondary caries, which is the main contributor to dental repair failure, has been the subject of extensive research due to its biofilm-mediated, sugar-driven, multifactorial, and dynamic characteristics. The clinical utility of restorations is improved by cleaning bacteria nearby and remineralizing marginal crevices. In this study, a novel multifunctional dental resin composite (DRC) composed of Sr-N-co-doped titanium dioxide (Sr-N-TiO2) nanoparticles and nano-hydroxyapatite (n-HA) reinforcing fillers with improved antibacterial and mineralization properties is proposed. The experimental results showed that the anatase-phase Sr-N-TiO2 nanoparticles were synthesized successfully. After this, the curing depth (CD) of the DRC was measured from 4.36 ± 0.18 mm to 5.10 ± 0.19 mm, which met the clinical treatment needs. The maximum antibacterial rate against Streptococcus mutans (S. mutans) was 98.96%, showing significant inhibition effects (p < 0.0001), which was experimentally verified to be derived from reactive oxygen species (ROS). Meanwhile, the resin exhibited excellent self-remineralization behavior in an SBF solution, and the molar ratio of Ca/P was close to that of HA. Moreover, the relative growth rate (RGR) of mouse fibroblast L929 indicated a high biocompatibility, with the cytotoxicity level being 0 or I. Therefore, our research provides a suitable approach for improving the antibacterial and mineralization properties of DRCs.

Specific colorimetric detection of methylmercury based on peroxidase-like activity regulation of carbon dots/Au NPs nanozyme

Methylmercury (MeHg⁺) is one of the common organic species of mercury, and has much higher toxicity than inorganic mercury. Based on the selective enhancement of the activity of nanozyme (NA-CDs/AuNPs) by MeHg⁺, a novel colorimetric nanoprobe for MeHg⁺ assay is proposed. The noradrenaline-based carbon dots (NA-CDs) as the reducing agent was applied to prepare the NA-CDs/AuNPs. The formation of gold amalgamation (Au@HgNPs) between nanozyme and MeHg⁺ allows to simultaneously accelerate the electron transfer from Au and Hg to NA-CDs and the generation of radicals (i.e. ∙OH, ∙O₂^- and ∙CH₃). The NA-CDs/AuNPs has an outstanding anti-interference performance even in the presence of different mercury. Further density functionality theory (DFT) calculations revealed that the formation of Au@HgNPs via MeHg⁺ contributes to the significantly lowered activation energy, resulting in the peroxidase-like activity generation and acceleration. This leads to rapid (10 min) and specific colorimetric detection of MeHg⁺ with the detection limit of 0.06 μg L^-1. This introduces a novel method for simple and sensitive detection of MeHg⁺, giving a new horizon for the assay of organometallic compounds.

The initiation of oxidative stress and therapeutic strategies in wound healing

When the production of reactive oxygen species (ROS) is overloaded surpassing the capacity of the reductive rheostat, mammalian cells undergo a series of oxidative damage termed oxidative stress (OS). This phenomenon is ubiquitously detected in many human pathological conditions. Wound healing program implicates continuous neovascularization, cell proliferation, and wound remodeling. Increasing evidence indicates that reactive oxygen species (ROS) have profound impacts on the wound healing process through regulating a series of the physiological and pathological program including inflammatory response, cell proliferation, angiogenesis, granulation as well as extracellular matrix formation. In most pathological wound healing processes, excessive ROS exerts a negative role on the wound healing process. Interestingly, the moderate increase of ROS levels is beneficial in killing bacteria at the wound site, which creates a sterile niche for revascularization. In this review, we discussed the physiological rhythms of wound healing and the role of ROS in this progress, aim to explore the potential manipulation of OS as a promising therapeutic avenue.

MnO2 nanosheet-mediated generalist probe: Cancer-targeted dual-microRNAs detection and enhanced CDT/PDT synergistic therapy

While integrated nanoplatform for diagnosis and therapy has received much recent interest, its widespread application has been hampered by the complicated preparation process, high-cost and low-efficacy. Herein, we designed a MnO₂ nanosheet-mediated generalist probe (MNSGP), for intracellular dual-microRNAs (miRNAs) imaging and enhanced synergistic therapy of chemodynamic therapy (CDT) and photodynamic therapy (PDT). Because MNSGP can specifically target nucleolin receptor overexpressed on the cancer cell surface, it can be internalized via a receptor-mediated endocytosis pathway. After entering the cells, MnO₂ NS was degraded to Mn²⁺ by the excessive glutathione (GSH), releasing the DNA probes for cyclic amplification detection of miR-155 and miR-21 based on toehold-mediated strand displacement amplification (TSDA). Meanwhile, the produced O₂ by MnO₂ NS catalysis can promote the photosensitizer TMPyP4 to produce singlet oxygen (¹O₂) for PDT. The degraded Mn²⁺, as Fenton reagent, can convert endogenous H₂O₂ to cytotoxic hydroxyl radical (·OH) for CDT. In addition, the depletion of GSH impairs the antioxidant defense system (ADS), enhancing the CDT/PDT synergistic effect. The prepared generalist probe was fully characterized. Accuracy of dual-miRNAs detection and the high curative effect of enhanced CDT/PDT synergistic therapy were attested via in vitro and in vivo experiments. Unarguably, MNSGP broadens new horizons in the design of nucleic acid nanoplatform, cancer-targeted detection and theranostic application.

Integrated Platform of Oxygen Self-enriched Nanovesicles: SP94 Peptide-directed Chemo/sonodynamic Therapy for Liver Cancer

Hepatocellular carcinoma (HCC) is a most common primary liver cancer among the most deadly malignancies. Selectively killing the cancer cells within the liver urgently requires the novel treatment strategies. The combination of sonodynamic therapy (SDT) and chemotherapy based on the nanotechnology have achieved some achievements in the HCC treatments. However, off-targeting drug delivery to healthy cells and the hypoxic microenvironment in the solid tumors frustrate the efforts to the combined strategy. The hypoxic microenvironment restrains the generation of ROS, leading to the decreased effects of SDT. To improve the clinical outcomes of chemo/SDT strategy, we created a novel oxygen self-enriched active targeted nanovesicle (ICG-DOX NPs/PFH@SP94-Lip). SP94 peptide could enhance the selectivity of the nanovesicles to liver tumor cells rather than normal liver cells. Besides, an oxygen carrier, perfluorohexanes (PFH), was co-loaded into liposomes to increase the oxygen level in tumor tissue, thus improving the effects of SDT. The in vivo studies showed that the ICG-DOX NPs/PFH@SP94-Lip combined with the external US stimulation significantly inhibited effects on tumor growth. Therefore, this novel oxygen self-enriched chemo/SDT nanocomposites represents a proof-of-concept liver tumor treatment strategy.

New Insight into Assembled Fe3O4@PEI@Ag Structure as Acceptable Agent with Enzymatic and Photothermal Properties

Metal-based enzyme mimics are considered to be acceptable agents in terms of their biomedical and biological properties; among them, iron oxides (Fe₃O₄) are treated as basement in fabricating heterogeneous composites through variable valency integrations. In this work, we have established a facile approach for constructing Fe₃O₄@Ag composite through assembling Fe₃O₄ and Ag together via polyethyleneimine ethylenediamine (PEI) linkages. The obtained Fe₃O₄@PEI@Ag structure conveys several hundred nanometers (~150 nm). The absorption peak at 652 nm is utilized for confirming the peroxidase-like activity of Fe₃O₄@PEI@Ag structure by catalyzing 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H₂O₂. The Michaelis–Menten parameters (K_m) of 1.192 mM and 0.302 mM show the higher catalytic activity and strong affinity toward H₂O₂ and TMB, respectively. The maximum velocity (V_max) value of 1.299 × 10⁻⁷ M∙s⁻¹ and 1.163 × 10⁻⁷ M∙s⁻¹ confirm the efficiency of Fe₃O₄@PEI@Ag structure. The biocompatibility illustrates almost 100% cell viability. Being treated as one simple colorimetric sensor, it shows relative selectivity and sensitivity toward the detection of glucose based on glucose oxidase. By using indocyanine green (ICG) molecule as an additional factor, a remarkable temperature elevation is observed in Fe₃O₄@PEI@Ag@ICG with increments of 21.6 °C, and the absorption peak is nearby 870 nm. This implies that the multifunctional Fe₃O₄@PEI@Ag structure could be an alternative substrate for formatting acceptable agents in biomedicine and biotechnology with enzymatic and photothermal properties.

CuCo2S4 nanozyme-based stimulus-responsive hydrogel kit for rapid point-of-care testing of uric acid

An efficient analysis platform composed of nanozyme-based hydrogel kit and smartphone was constructed for on-site detection of uric acid (UA) in a rapid and realiable manner. CuCo₂S₄ nanoparticles (CuCo₂S₄ NPs) as a peroxidase mimic were successfully prepared and the peroxidase-like activity and catalytic mechanism were studied in detail. The hydrogen peroxide (H₂O₂) stimulus-responsive nanozyme-based hydrogel kit was manufactured by integrating agarose, CuCo₂S₄ NPs, and 3,3',5,5'-tetramethylbenzidine (TMB) into the cap of centrifuge tube. H₂O₂ generated via UA oxidation acts as stimulus signal, which triggers the oxidation of TMB to form blue product (oxTMB) under the catalysis of CuCo₂S₄ NPs, resulting in the color response of the constructed kit. The color image of the kit was captured by a smartphone built-in camera and converted into color intensity using ImageJ software, thus achieving the quantitative determination of UA. The portable kit possesses high selectivity and was used to monitor UA in human serum with satisfactory results (recovery was in the range 95.8-107.3% and RSD was not greater than 4.6%). The established sensing platform is convenient and reliable, which provides a new strategy for point-of-care testing of UA and has a broad prospect in the fields of chemical sensing and biomedical.

Fabrication of stable electrospun blended chitosan-poly(vinyl alcohol) nanofibers for designing naked-eye colorimetric glucose biosensor based on GOx/HRP

In this study, designing of a stable electrospun blended chitosan (CS)-poly(vinyl alcohol) (PVA) nanofibers for colorimetric glucose biosensing in an aqueous medium was investigated. CS and PVA solutions were blended to acquire an optimum content (CS/PVA:1/4) and electrospunned to obtain uniform and bead-free CS/PVA nanofiber structures following the optimization of the electrospinning parameters (33 kV, 20 cm, and 1.2 ml.h^-1). Crosslinking process applied subsequently provided mechanically and chemically stable nanofibers with an average diameter of 378 nm. The morphological homogeneity, high fluid absorption ability (>%50), thermal (<230 °C) and morphological stability, surface hydrophilicity and degrability properties of cross-linked CS/PVA nanofiber demonstrated their great potential to be developed as an eye-readable strip for biosensing applications. The glucose oxidase (GOx) and horseradish peroxidase (HRP) was immobilized by physical adsorption on the cross-linked CS/PVA nanofiber. The glucose assay analysis by ultraviolet-visible (UV-Vis) spectrophotometry using the same enzymatic system of the proposed glucose strips in form of absorbance versus concentration plot was found to be linear over a glucose concentration range of 2.7 to 13.8 mM. The prepared naked eye colorimetric glucose detection strips, with lower detection limit of 2.7 mM, demonstrated dramatic color change from white (0 mM) to brownish-orange (13.8 mM). The developed cross-linked CS/PVA nanofiber strips, prepared by electrospinnig procedure, could be easily adapted to a color map, as an alternative material for glucose sensing. Design of a practical, low-cost, and environmental-friendly bio-based CS/PVA testing strips for eye readable detection were presented and suggested as an applicable medium for a wide range of glucose concentrations.

Application of Au or Ag nanomaterials for colorimetric detection of glucose

In recent years, Au and Ag nanomaterials have been widely used in the determination of glucose owing to their specific properties such as large specific surface area, high extinction coefficient, strong localized surface plasmon resonance effect and enzyme-mimicking activity. Compared with other methods, colorimetric determination of glucose with Au or Ag nanomaterials features the advantages of simple operation, low cost and easy observation. In this review, several typical synthesis methods of Au and Ag nanomaterials are introduced. Strategies for the colorimetric determination of glucose by Au or Ag nanomaterials are elaborated. The challenges and prospects of the application of Au or Ag nanomaterials for colorimetric detection of glucose are also discussed.

Oxidation triggered formation of polydopamine-modified carboxymethyl cellulose hydrogel for anti-recurrence of tumor

In this research, a hydrogel that combined the tumor photodynamic therapy (PDT) and photothermal therapy (PTT) ability was designed, using dopamine-modified sodium carboxymethyl cellulose (CMC-DA) as the matrix and Chlorin e6 (Ce6) as the photosensitizer. The gel formation was initiated by adding the oxidizing agent sodium periodate (NaIO4) to the CMC-DA solution, during which the dopamine was simultaneously oxidized to polydopamine (PDA) and NaIO4 was reduced to sodium iodide (NaI). The formed NaI was encapsulated in the hydrogel and endowed the hydrogel with computerized tomography (CT) imaging ability to monitor the hydrogel degradation and the tumor therapy process. Moreover, the photosensitizer Ce6 can be loaded by the gel system via directly soaking the hydrogel in the Ce6 solution. Under the near-infrared light irradiation, Ce6 can produce cytotoxic reactive oxygen species and the PDA can produce heat to trigger the tumor PDT and PTT respectively to eradicate the tumor recurrence. In general, the designed hydrogel is biocompatible and biodegradable, has a good photothermal conversion, drug loading and CT imaging ability, which laid the foundation for the rational design of biodegradable hydrogels for multifunctional applications.

Bimetallic gold and palladium nanoparticles supported on copper oxide nanorods for enhanced H2O2 catalytic reduction and sensing

The emergence of nanoscience and nanotechnology has revitalised research interest in using copper and its derived nanostructures to find exciting and novel applications. In this work, mono- and bimetallic gold and palladium nanoparticles supported on copper oxide nanorods (CuONRs) were prepared and their catalytic performance towards the reduction of H2O2 to form reactive oxygen radical species (ROS) was evaluated. The characterisation using microscopy and spectroscopic techniques confirms the successful synthesis of CuONRs, CuONRs@Au6NPs, CuONRs@Pd6NPs and CuONRs@Au3Pd3NPs. The efficient generation of ROS was confirmed using UV-vis spectroscopy and 1,3-diphenylisobenzofuran (DPBF) as a radical scavenger. The CuONRs possess excellent catalytic reduction activity for H2O2 by generating ROS. However, CuONRs also have lattice oxygens which do not participate in the catalytic reduction step. The lattice oxygens however allowed for the adsorption of gold and palladium nanoparticles (Au6NPs, Pd6NPs and Au3Pd3NPs) and thus enhanced catalytic reduction of H2O2 to produce ROS. The produced ROS was subsequently involved in the catalytic oxidation of a chromogenic substrate (TMB), resulting in blue coloured diimine (TMBDI) complex which was monitored using UV-vis and could also be observed using the naked eye. The catalyst dependence on pH, temperature, and H2O2 concentration towards efficient ROS generation was investigated. The gold and palladium-supported CuONRs nanocatalysts were evaluated for their potential applications in the fabrication of colorimetric biosensors to detect glucose oxidation by glucose oxidase (GOx). Glucose was used as a model analyte. The enzymatic reaction between GOx and β-d-glucose produces H2O2 as a by-product, which is then catalytically converted to ROS by the nanoparticles.

Genetically modified bacteria for targeted phototherapy of tumor

Live attenuated bacteria have been used as target vehicles for genetic therapy of malignant carcinoma because they can be reprogrammed by following simple genetic rules and have the ability to target tumor hypoxic region. In this research, noninvasive Escherichia coli (E. Coli) is genetically modified through the plasmid transfection to afford E. Coli(p) with overexpressed human catalase for catalyzing H₂O₂ into O₂ in the tumor site. The produced O₂ is consequently converted to cytotoxic ¹O₂ under near-infrared (NIR) light irradiation for photodynamic therapy. Chlorin e6 (Ce6) is chosen as the photosensitizer for its excellent photodynamic ability, and polydopamine (pDA) is employed to encapsulate Ce6 for its good biosafety, photothermal ability, and adhesion capacity with bacteria. Dopamine polymerizes in the presence of Ce6 to form pDA/Ce6, and then E. Coli(p) is coated with pDA/Ce6 to afford the final E. Coli(p)/pDA/Ce6. The obtained system is intravenously administrated for selective accumulation and replication in the hypoxic tumor. NIR light irradiation is introduced to enable photothermal and O₂-enhanced photodynamic therapy. On account of complementary combination, the system exhibits efficient antitumor effect in vitro and in vivo. Thus, the integration of genetically modified bacteria with pDA/Ce6 presents a promising application potential for precise tumor inhibition.

AuNPs@PMo12 nanozyme: highly oxidase mimetic activity for sensitive and specific colorimetric detection of acetaminophen

The design of a highly specific and sensitive approach for the quantitative and qualitative determination of acetaminophen (AP) is crucial from a human health point of view. In this study, AuNPs@PMo12, as a nanozyme, has been developed for the highly sensitive and selective detection of AP with 3,3',5,5'-tetramethylbenzidine (TMB) within a few seconds without adding oxidizing reagents (e.g. H2O2). Synthesized nanosensors are able to oxidize TMB to yellow-brown oxidized TMB (oxTMB). The maximum peak wavelength of oxTMB was observed at 450 nm. The addition of AP and then increasing its concentration led to the production of different products in blue color. In experimental measurements, the limit of detection was obtained as 14.52 mg L-1. The quantitative determination of AP concentrations can be carried out using UV-vis spectroscopy. The design of nanosensors is cost-effective and application of them in H2O2-free and enzyme-free conditions provides a rapid sensing approach for practical use in disease monitoring and diagnosis.

Nanomagnet-Silica Nanoparticles Decorated with Au@Pd for Enhanced Peroxidase-Like Activity and Colorimetric Glucose Sensing

Nanomagnet-silica shell (Fe₃O₄@SiO₂) decorated with Au@Pd nanoparticles (NPs) were synthesized successfully. The characterization of Fe₃O₄@SiO₂-NH₂-Au@PdNPs was achieved using several spectroscopic and microscopic techniques. The quantitative surface analysis was confirmed using X-ray photoelectron spectroscopy. The Fe₃O₄@SiO₂-NH₂-Au@Pd_0.30NPs exhibited excellent peroxidase-like activity by effectively catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂. The absorption peaks at 370 and 652 nm confirmed the peroxidase-like activity of the Fe₃O₄@SiO₂-NH₂-Au@Pd_0.30NPs. The Michaelis-Menten constant (K_m) of 0.350 and 0.090 mM showed strong affinity toward H₂O₂ and TMB at Fe₃O₄@SiO₂-NH₂-Au@Pd_0.30NPs. The mechanism of the peroxidase-like activity was found to proceed via an electron transfer process. A simple colorimetric sensor based on glucose oxidase and Fe₃O₄@SiO₂-NH₂-Au@Pd_0.30NPs showed excellent selectivity and sensitivity towards the detection of glucose. The fabricated glucose biosensor exhibited a wide linear response toward glucose from 0.010 to 60.0 μM with an limit of detection of 60.0 nM and limit of quantification of 200 nM. The colorimetric biosensor based on Fe₃O₄@SiO₂-NH₂-Au@Pd_0.30NPs as a peroxidase mimic was also successfully applied for the determination of glucose concentrations in serum samples. The synthesized Fe₃O₄@SiO₂-NH₂-Au@Pd_0.30NPs nanozymes exhibited excellent potential as an alternative to horseradish peroxidase for low-cost glucose monitoring.

An Au@NH2-MIL-125(Ti)-based multifunctional platform for colorimetric detections of biomolecules and Hg2+

Au@NH₂-MIL-125(Ti) was fabricated and explored as a multifunctional platform for sensitive colorimetric detections of biomolecules and Hg²⁺.

The design and characterization of a hypersensitive glucose sensor: two enzymes co-fixed on a copper phosphate skeleton

A new glucose sensor GOx&DhHP-6–Cu₃(PO₄)₂ showed the best catalytic ability at a neutral temperature and pH.

Au–Hg/rGO with enhanced peroxidase-like activity for sensitive colorimetric determination of H2O2

Au–Hg/rGO is applied as a novel nanozyme to construct a sensitive sensing platform for the colorimetric determination of H₂O₂.

Colorimetric sensing for ascorbic acid based on peroxidase-like of GoldMag nanocomposites

A new scheme for sensitive and rapid colorimetric detection of ascorbic acid (AA) has been developed by the GoldMag-ABTS free radical scavenging system. The well-dispersed Gold and magnetic particles (GoldMag) was successfully prepared by self-assembly method and characterized by Fourier transform infrared (FTIR), X-Ray Photoelectron Spectroscopic (XPS) techniques. Nanocomposites combine the advantages of superparamagnetic, biocompatibility and high catalytic activity of Fe₃O₄ and gold nanoparticles (AuNPs) and exhibit enhanced the intrinsic peroxidase-like activity, which can be used to catalyze the oxidation of the peroxidase substrates 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) produce a green-colored product in presence of hydrogen peroxide. Ascorbic acid as an effective antioxidant have scavenging effects on ABTS radicals and induce the reduction of green ABTS.⁺ to colorless ABTS^2-, resulting in a significant green color fading. On this basis, a rapid, sensitive and selective colorimetric assay for ascorbic acid has been developed. Under optimal conditions, ascorbic acid has a linear response range from 0.01 mmol/L to 1 mmol/L with a detection limit of 0.12 μmol/L and a short assay time of the 30 s. Furthermore, the colorimetric system showed good sensitivity, stability, selectivity, and repeatability. It also successfully applied to the determination of ascorbic acid in real samples.