Elucidating the catalytic mechanism of Prussian blue nanozymes with self-increasing catalytic activity.

Although Prussian blue nanozymes (PBNZ) are widely applied in various fields, their catalytic mechanisms remain elusive. Here, we investigate the long-term catalytic performance of PBNZ as peroxidase (POD) and catalase (CAT) mimetics to elucidate their lifespan and underlying mechanisms. Unlike our previously reported Fe3O4 nanozymes, which exhibit depletable POD-like activity, the POD and CAT-like activities of PBNZ not only persist but slightly enhance over prolonged catalysis. We demonstrate that the irreversible oxidation of PBNZ significantly promotes catalysis, leading to self-increasing catalytic activities. The catalytic process of the pre-oxidized PBNZ can be initiated through either the conduction band pathway or the valence band pathway. In summary, we reveal that PBNZ follows a dual-path electron transfer mechanism during the POD and CAT-like catalysis, offering the advantage of a long service life.

Enhancing radiation-resistance and peroxidase-like activity of single-atom copper nanozyme via local coordination manipulation.

The inactivation of natural enzymes by radiation poses a great challenge to their applications for radiotherapy. Single-atom nanozymes (SAzymes) with high structural stability under such extreme conditions become a promising candidate for replacing natural enzymes to shrink tumors. Here, we report a CuN3-centered SAzyme (CuN3-SAzyme) that exhibits higher peroxidase-like catalytic activity than a CuN4-centered counterpart, by locally regulating the coordination environment of single copper sites. Density functional theory calculations reveal that the CuN3 active moiety confers optimal H2O2 adsorption and dissociation properties, thus contributing to high enzymatic activity of CuN3-SAzyme. The introduction of X-ray can improve the kinetics of the decomposition of H2O2 by CuN3-SAzyme. Moreover, CuN3-SAzyme is very stable after a total radiation dose of 500 Gy, without significant changes in its geometrical structure or coordination environment, and simultaneously still retains comparable peroxidase-like activity relative to natural enzymes. Finally, this developed CuN3-SAzyme with remarkable radioresistance can be used as an external field-improved therapeutics for enhancing radio-enzymatic therapy in vitro and in vivo. Overall, this study provides a paradigm for developing SAzymes with improved enzymatic activity through local coordination manipulation and high radioresistance over natural enzymes, for example, as sensitizers for cancer therapy.

Biomimetic synergistic effect of redox site and Lewis acid for construction of efficient artificial enzyme.

In enzymatic catalysis, the redox site and Lewis acid are the two main roles played by metal to assist amino acids. However, the reported enzyme mimics only focus on the redox-active metal as redox site, while the redox-inert metal as Lewis acid has, to the best of our knowledge, not been studied, presenting a bottleneck of enzyme mimics construction. Based on this, a series of highly efficient MxV2O5·nH2O peroxidase mimics with vanadium as redox site and alkaline-earth metal ion (M2+) as Lewis acid are reported. Experimental results and theoretical calculations indicate the peroxidase-mimicking activity of MxV2O5·nH2O show a periodic change with the Lewis acidity (ion potential) of M2+, revealing the mechanism of redox-inert M2+ regulating electron transfer of V-O through non-covalent polarization and thus promoting H2O2 adsorbate dissociation. The biomimetic synergetic effect of redox site and Lewis acid is expected to provide an inspiration for design of enzyme mimics.

Laminarin-modulated osmium nanozymes with high substrate-affinity and selective peroxidase-like behavior engineered colorimetric assay for hydroxyl radical scavenging capacity estimation.

Hydroxyl radical (·OH) scavenging capacity (HOSC) estimation is essential for evaluating antioxidants, natural extracts, or drugs against clinical diseases. While nanozymes offer advantages in related applications, they still face limitations in activity and selectivity. In response, this work showcases the fabrication of laminarin-modulated osmium (laminarin-Os) nanoclusters (1.45 ± 0.05 nm), functioning as peroxidase-like nanozymes within a colorimetric assay tailored for rational HOSC estimation. This study validates both the characterization and remarkable stability of laminarin-Os. By leveraging the abundant surface negative charges of laminarin-Os and the surface hydroxyls of laminarin, oxidation reactions are facilitated, augmenting laminarin-Os's affinity for 3,3',5,5'-tetramethylbenzidine (TMB) (KM = 0.04 mM). This enables the laminarin-Os-based colorimetric assay to respond to ·OH more effectively than citrate-, albumin-, or other polysaccharides-based Os. In addition, experimental results also validate the selective peroxidase-like behavior of laminarin-Os under acidic conditions. Antioxidants like ascorbic acid, glutathione, tannic acid, and cysteine inhibit absorbance at 652 nm in the colorimetric platform using laminarin-Os's peroxidase-like activity. Compared with commercial kits, this assay demonstrates superior sensitivity (e.g., responds to ascorbic acid 0.01-0.075 mM, glutathione 1-15 µg/mL, tannic acid 0.5-5 µM, and monoammonium glycyrrhizinate cysteine 1.06-10.63 µM) and HOSC testing for glutathione, tannic acid, and monoammonium glycyrrhizinate cysteine. Overall, this study introduces a novel Os nanozyme with exceptional TMB affinity and ·OH selectivity, paving the way for HOSC estimation in biomedical research, pharmaceutical analysis, drug quality control, and beyond.

Deciphering the Catalytic Mechanism of Peroxidase-like Activity of Iron Sulfide Nanozymes.

Iron sulfide nanomaterials represented by FeS2 and Fe3S4 nanozymes have attracted increasing attention due to their biocompatibility and peroxidase-like (POD-like) catalytic activity in disease diagnosis and treatments. However, the mechanism responsible for their POD-like activities remains unclear. Herein, taking the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) by H2O2 on FeS2(100) and Fe3S4(001) surfaces, the catalytic mechanism was investigated in detail using density functional theory (DFT) calculations and experimental characterizations. Our experimental results showed that the catalytic activity of FeS2 nanozymes was significantly higher than that of Fe3S4 nanozymes. Our DFT calculations indicated that the surface iron ions of iron sulfide nanozymes could effectively catalyze the production of HO• radicals via the interactions between Fe 3d electrons and the frontier orbitals of H2O2 in the range of -10 to 5 eV. However, FeS2 nanozymes exhibited higher POD-like activity due to the surface Fe(II) binding to H2O2, forming inner-orbital complexes, which results in a larger binding energy and a smaller energy barrier for the base-like decomposition of H2O2. In contrast, the surface iron ions of Fe3S4 nanozymes bind to H2O2, forming outer-orbital complexes, which results in a smaller binding energy and a larger energy barrier for the base-like decomposition of H2O2. The charge transfer analysis showed that FeS2 nanozymes transferred 0.12 e and Fe3S4 nanozymes transferred 0.05 e from their surface iron ions to H2O2, respectively. The simulations were consistent with the experimental observations that the FeS2 nanozymes had a greater affinity for H2O2 compared to that of Fe3S4 nanozymes. This work provides a theoretical foundation for the rational design and accurate preparation of iron sulfide functional nanozymes.

Synthesis and Characterization of Cross-Linked Aggregates of Peroxidase from Megathyrsus maximus (Guinea Grass) and Their Application for Indigo Carmine Decolorization.

We present the synthesis of a cross-linking enzyme aggregate (CLEAS) of a peroxidase from Megathyrsus maximus (Guinea Grass) (GGP). The biocatalyst was produced using 50%v/v ethanol and 0.88%w/v glutaraldehyde for 1 h under stirring. The immobilization yield was 93.74% and the specific activity was 36.75 U mg-1. The biocatalyst surpassed by 61% the free enzyme activity at the optimal pH value (pH 6 for both preparations), becoming this increase in activity almost 10-fold at pH 9. GGP-CLEAS exhibited a higher thermal stability (2-4 folds) and was more stable towards hydrogen peroxide than the free enzyme (2-3 folds). GGP-CLEAS removes over 80% of 0.05 mM indigo carmine at pH 5, in the presence of 0.55 mM H2O2 after 60 min of reaction, a much higher value than when using the free enzyme. The operational stability showed a decrease of enzyme activity (over 60% in 4 cycles), very likely related to suicide inhibition.

Multifunctional Fe/Cu Dual-Single Atom Nanozymes with Enhanced Peroxidase Activity for Isoniazid Detection and Levofloxacin Degradation.

The design of single-atom nanozymes with dual active sites to increase their activity and for the detection and degradation of contaminants is rare and challenging. In this work, a single-atom nanozyme (FeCu-NC) based on a three-dimensional porous Fe/Cu dual active site was developed as a colorimetric sensor for both the quantitative analysis of isoniazid (INH) and the efficient degradation of levofloxacin (LEV). FeCu-NC was synthesized using a salt template and freeze-drying method with a three-dimensional hollow porous structure and dual active sites (Fe-Nx and Cu-Nx). In terms of morphology and structure, FeCu-NC exhibits excellent peroxidase-like activity and catalytic properties. Therefore, a colorimetric sensor was constructed around FeCu-NC for sensitive and rapid quantitative analysis of INH with a linear range of 0.9-10 µM and a detection limit as low as 0.3 µM, and the sensor was successfully applied to the analysis of INH in human urine. In addition, FeCu-NC promoted the efficient degradation of LEV by peroxymonosulfate activation, with a degradation rate of 90.4% for LEV at 30 min. This work sheds new light on the application of single-atom nanozymes to antibiotics for colorimetric sensing and degradation.

Staphylococcal peroxidase inhibitor (SPIN): Investigation of the inhibitory N-terminal domain via a stabilizing disulfide insertion.

Staphylococcus aureus secretes an array of small proteins that inhibit key enzyme-catalyzed reactions necessary for proper function of the human innate immune system. Among these, the Staphylococcal Peroxidase Inhibitor, SPIN, blocks the activity of myeloperoxidase (MPO) and thereby disrupts the HOCl-generating system of neutrophils. Previous studies on S. aureus SPIN have shown that it relies on a C-terminal α-helical bundle domain to mediate initial binding to MPO, but requires a disordered N-terminal region to fold into a ß-hairpin conformation to inhibit MPO activity. To further investigate the structure/function relationship of SPIN, we introduced two cysteine residues into its N-terminal region to trap SPIN in its MPO-bound conformation and characterized the modified protein, which we refer to here as SPIN-CYS. Although control experiments confirmed the presence of the disulfide bond in SPIN-CYS, solution structure determination revealed that the N-terminal region of SPIN-CYS adopted a physically constrained series of lariat-like structures rather than a well-defined ß-hairpin. Nevertheless, SPIN-CYS exhibited a gain in inhibitory potency against human MPO when compared to wild-type SPIN. This gain of function persisted even in the presence of deleterious mutations within the C-terminal α-helical bundle domain. Surface plasmon resonance studies showed that the gain in potency arose through an increase in apparent affinity of SPIN-CYS for MPO, which was driven primarily by an increased association rate with MPO when compared to wild-type SPIN. Together, this work provides new information on the coupled binding and folding events required to manifest biological activity of this unusual MPO inhibitor.

Palladium/Platinum/Ruthenium Trimetallic Dendritic Nanozymes Exhibiting Enhanced Peroxidase-like Activity for Signal Amplification of Lateral Flow Immunoassays.

Developing ultrasensitive lateral flow immunoassays (LFIAs) has garnered significant attention in the field of point-of-care testing. In this study, a trimetallic dendritic nanozyme (Pd@Pt-Ru) was synthesized through Ru deposition on a Pd@Pt core and utilized to enhancing the sensitivity of LFIAs. Pd@Pt-Ru exhibited a Km value of 5.23 mM for detecting H2O2, which indicates an H2O2 affinity comparable with that of horseradish peroxidase. The Ru surface layer reduces the activation energy barrier, which increases the maximum reaction rate. As a proof of concept, the proposed Pd@Pt-Ru nanozyme was incorporated into LFIAs (A-Pd@Pt-Ru-LFIAs) for detecting human chorionic gonadotropin (hCG). Compared with conventional gold nanoparticle (AuNP)-LFIAs, A-Pd@Pt-Ru-LFIAs demonstrated 250-fold increased sensitivity, thereby enabling a visible detection limit as low as 0.1 IU/L. True positive and negative rates both reached 100%, which renders the proposed Pd@Pt-Ru nanozyme suitable for detecting hCG in clinical samples.

Construct a Magnetic Pt/Ru Alloy Peroxidase Mimic As a Reusable and Cost-Effective "Signal-Off" Sensing Platform for Sensitive and Wide-Linear-Range Assay.

"Signal-off" nanozyme sensing platforms are usually employed to detect analytes (e.g., ascorbic acid (AA) and alkaline phosphatase (ALP)), which are mostly based on oxidase (OXD) nanozymes. However, their drawbacks, like dissolved oxygen-dependent catalysis capability, relatively low enzyme activity, limited amount, and kind, may not favor sensing platforms' optimization. Meanwhile, with the need for sustainable development, a reusable "signal-off" sensing platform is essential for cutting down the cost of the assay, but it is rarely developed in previous studies. Magnetic peroxidase (POD) nanozymes potentially make up the deficiencies and become reusable and better "signal-off" sensing platforms. As a proof of concept, we first construct Fe3O4@polydopamine-supported Pt/Ru alloy nanoparticles (IOP@Pt/Ru) without stabilizers. IOP@Pt/Ru shows high POD activity with Vmax of 83.24 × 10-8 M·s-1 for 3,3',5,5'-Tetramethylbenzidine (TMB) oxidation. Meanwhile, its oxidation rate for TMB is slower than the reduction of oxidized TMB by reducers, favorable for a more significant detection signal. On the other hand, IOP@Pt/Ru possesses great magnet-responsive capability, making itself be recycled and reused for at least 15-round catalysis. When applying IOP@Pt/Ru for AA (ALP) detection, it performs better detectable adaptability, with a linear range of 0.01-0.2 mM (0.1-100 U/L) and a limit of detection of 0.01 mM (0.05 U/L), superior to most of OXD nanozyme-based ALP sensing platform. Finally, IOP@Pt/Ru's reusable assay was demonstrated in real blood samples for ALP assay, which has never been explored in previous studies. Overall, this study develops a reusable "signal-off" nanozyme sensing platform with superior assay capabilities than traditional OXD nanozymes, paves a new way to optimize nanozyme-based "signal-off" sensing platforms, and provides an idea for constructing inexpensive and sustainable sensing platforms.

Visual and photoelectrochemical analysis of antibiotic resistance genes enabled by surface-engineered ZIF-8@Au cascade nanozymes.

The aggravation of antibiotic resistance genes (ARGs) in the environment has posed a significant global health crisis. Accurate evaluation of ARGs levels in a facile manner is a pressing issue for environmental surveillance. Here, we demonstrate a unique dumbbell-shaped cascade nanozyme for visual/photoelectrochemical (PEC) dual-mode detection of ARGs. Gold nanoparticles (AuNPs) with tunable exposed facets are controllably anchored onto ZIF-8 dodecahedrons, exhibiting glucose oxidase (GOx)-like (ZIF-8@Au/G) and peroxidase (POD)-like (ZIF-8@Au/P) activities. Upon the occurrence of ARGs, an asymmetric cascade-amplified "dumbbell" configuration is spontaneously generated via target-induced DNA hybridization, comprising GOx-like ZIF-8@Au/G with capture DNA on one side and POD-like ZIF-8@Au/P with signal DNA on the opposite side. Such a cascade nano-system can efficiently oxidize colorless 2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) into its green oxidation state and synergistically decompose H2O2, realizing colorimetric/PEC dual-mode ARGs detection with a detection limit of 0.112 nM. The applicability of the present bioassay is validated through measuring ARGs in real sludge samples. This work suggests the possibility to rationally design task-specific nanozymes and develop target-responsive nano-cascade assays for environmental monitoring.

Inhibition effect of p-d orbital hybridized PtSn nanozymes for colorimetric sensor array of antioxidants.

Rational design of peroxidase (POD)-like nanozymes with high activity and specificity still faces a great challenge. Besides, the investigations of nanozymes inhibitors commonly focus on inhibition efficiency, the interaction between nanozymes-involved catalytic reactions and inhibitors is rarely reported. In this work, we design a p-block metal Sn-doped Pt (p-d/PtSn) nanozymes with the selective enhancement of POD-like activity. The p-d orbital hybridization interaction between Pt and Sn can effectively optimize the electronic structure of PtSn nanozymes and thus selectively enhance POD-like activity. In addition, the antioxidants as nanozymes inhibitors can effectively inhibit the POD-like activity of p-d/PtSn nanozymes, which results in the fact that antioxidants absorbed on the p-d/PtSn surface can hinder the adsorption of hydrogen peroxide. The inhibition type (glutathione as a model molecule) is reversible mixed-inhibition with inhibition constants (Ki' and Ki) of 0.21 mM and 0.03 mM. Finally, based on the varying inhibition levels of antioxidant molecules, a colorimetric sensor array is constructed to distinguish and simultaneously detect five antioxidants. This work is expected to design highly active and specific nanozymes through p-d orbital hybrid engineering, and also provides insights into the interaction between nanozymes and inhibitors.

Multifunctional N, Fe-doped carbon dots with peroxidase-like activity for the determination of H2O2 and ascorbic acid and cell protection against oxidation.

Multifunctional N, Fe-doped carbon dots (N, Fe-CDs) were synthesized by the one-step hydrothermal method using ferric ammonium citrate and dicyandiamide as raw materials. The N, Fe-CDs exhibited peroxidase-like (POD) activity by catalyzing the oxidization of 3,3',5,5'-tetramethylbenzidine (TMB) to the green oxidation state ox-TMB in the presence of hydrogen peroxide (H2O2). Subsequently, based on the POD activity of N, Fe-CDs, an efficient and sensitive colorimetric method for the detection of H2O2 and ascorbic acid (AA) was established with a limit of detection of 0.40 µM and 2.05 µM. The proposed detection method has been successfully applied to detect AA in fruit juice, vitamin C tablets, and human serum samples and has exhibited excellent application prospects in biotechnology and food fields. Furthermore, N, Fe-CDs also showed a protective effect on the cell damage caused by H2O2 and could be used as an antioxidant agent.

Integration of Myrica rubra-based N-doped carbon dots with Fe3S4 as excellent peroxidase mimics for colorimetric assay and smartphone-based intelligent sensing of p-aminophenol in waters.

To realize the reutilization of waste Myrica rubra in the analytical field, we synthesized Myrica rubra-based N-doped carbon dots (MN-CDs) and further anchored them onto the surface of Fe3S4 to fabricate Fe3S4@MN-CD nanocomposites. The as-fabricated nanocomposites possessed higher peroxidase-mimetic activity than its two precursors, resulting from the synergistic effect between them, and could catalyze colorless 3,3',5,5'-tetramethylbenzidine (TMB) into deep blue oxTMB with a strong 652-nm absorption. Under optimized conditions (initial solution pH, 3.5; incubation temperature, 35 ℃; Fe3S4@MN-CD concentration, 50 µg mL-1, and 652-nm absorption), Fe3S4@MN-CDs were employed for colorimetric assay of p-aminophenol (p-AP) with wide linear range (LR, 2.9-100 µM), low detection limit (LOD, 0.87 µM), and satisfactory recoveries (86.3-105%) in environmental waters. Encouragingly, this colorimetric assay provided the relative accuracy of 97.0-99.4% as compared with  conventional HPLC-UV detection. A portable smartphone-based colorimetric application was developed by combining the Fe3S4@MN-CD-based visually chromogenic reaction with a "Thing Identify" APP software. Besides, we engineered an image-capturing device feasible for field use, in which the internal-compact sealing prevented external light source from entering photography chamber, thereby reducing light interference, and also the bottom light source enhanced the intensity of blue imaging. This colorimetric platform exhibited satisfactory LR (1-500 µM), low LOD (0.3 µM), and fortification recoveries (86.6-99.6%). In the chromogenic reaction catalyzed by Fe3S4@MN-CDs, ·O2- played a key role in concomitant with the participation of •OH and h+. Both the colorimetric assay and smartphone-based intelligent sensing show great promising in on-site monitoring of p-AP under field conditions.

Structural engineering of Pt-on-Rh hollow nanorods with high-performance peroxidase-like specific activity for colorimetric detection.

The preparation of nanozymes with high specific activity is highly important for various applications. However, only a few nanozymes have specific activities comparable to natural enzymes. Herein, novel Pt-on-Rh hollow nanorods (PtRh HNRs) were developed, in which surface Pt exhibited adjustable dispersity and interior Rh served as the support. The optimized PtRh HNRs demonstrated high-performance peroxidase (POD)-like activity, with a specific activity as high as 1352 U mg-1, which was 3.86 times that of their monometallic Pt counterparts. Density functional theory (DFT) calculations illustrated that the presence of Rh decreased the energy barrier of the rate-determining step. When PtRh HNRs were used as nanozymes in the colorimetric detection of hydrogen peroxide (H2O2) and ascorbic acid (AA), the limits of detection (LODs) were as low as 9.97 µM and 0.039 µM, respectively. The current work highlights a facile and powerful strategy for manufacturing nanozymes with high specific activity and demonstrates that the prepared PtRh HNRs have the potential for analysis and determination.

Raspberry-shaped ZIF-8/Au nanozymes with excellent peroxidase-like activity for simple and visual detection of glutathione.

Artificial enzymes with high stability, adjustable catalytic activity, controllable preparation, and good reproducibility have been widely studied. Noble metal nanozymes, particularly gold nanoparticles (Au NPs), exhibit good catalytic activity, but their stability is poor. In this study, zeolitic imidazolate framework-8 (ZIF-8) was used as a carrier for Au NPs, thus improving the utilization efficiency and conservation stability of the nanozymes. A ZIF-8/Au nanocomposite with peroxidase activity and a raspberry-shaped structure was synthesized. In the assay, ZIF-8/Au catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product oxidized TMB (oxTMB). Glutathione (GSH) selectively inhibited this reaction, with a detection limit of 0.28 µM and linear range of 0.5-60 µM. Using the photo and chromaticity analysis functions, we developed a portable analysis method using a smartphone equipped with a camera module as a detection terminal for a wide range of rapid screening techniques for GSH. Preparation of raspberry-shaped ZIF-8/Au improved the catalytic activity of Au NPs and good results were demonstrated in serum, which suggests their promising application under physiological conditions.

A metal-phenolic coordination framework nanozyme exhibits dual enzyme mimicking activity and its application is effective for colorimetric detection of biomolecules.

Biomolecules play vital roles in many biological processes and diseases, making their identification crucial. Herein, we present a colorimetric sensing method for detecting biomolecules like cysteine (Cys), homocysteine (Hcy), and glutathione (GSH). This approach is based on a reaction system whereby colorless 3,3',5,5'-tetramethylbenzidine (TMB) undergoes catalytic oxidation to form blue-colored oxidized TMB (ox-TMB) in the presence of hydrogen peroxide (H2O2), utilizing the peroxidase and catalase-mimicking activities of metal-phenolic coordination frameworks (MPNs) of Cu-TA, Co-TA, and Fe-TA nanospheres. The Fe-TA nanospheres demonstrated superior activity, more active sites and enhanced electron transport. Under optimal conditions, the Fe-TA nanospheres were used for the detection of biomolecules. When present, biomolecules inhibit the reaction between TMB and H2O2, causing various colorimetric responses at low detection limits of 0.382, 0.776 and 0.750 µM for Cys, Hcy and GSH. Furthermore, it was successfully applied to real water samples with good recovery results. The developed sensor not only offers a rapid, portable, and user-friendly technique for multi-target analysis of biomolecules at low concentrations but also expands the potential uses of MPNs for other targets in the environmental field.

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.

AI-Powered Knowledge Base Enables Transparent Prediction of Nanozyme Multiple Catalytic Activity.

Nanozymes are unique materials with many valuable properties for applications in biomedicine, biosensing, environmental monitoring, and beyond. In this work, we developed a machine learning (ML) approach to search for new nanozymes and deployed a web platform, DiZyme, featuring a state-of-the-art database of nanozymes containing 1210 experimental samples, catalytic activity prediction, and DiZyme Assistant interface powered by a large language model (LLM). For the first time, we enable the prediction of multiple catalytic activities of nanozymes by training an ensemble learning algorithm achieving R2 = 0.75 for the Michaelis-Menten constant and R2 = 0.77 for the maximum velocity on unseen test data. We envision an accurate prediction of multiple catalytic activities (peroxidase, oxidase, and catalase) promoting novel applications for a wide range of surface-modified inorganic nanozymes. The DiZyme Assistant based on the ChatGPT model provides users with supporting information on experimental samples, such as synthesis procedures, measurement protocols, etc. DiZyme (dizyme.aicidlab.itmo.ru) is now openly available worldwide.

Sensitive colorimetric detection of Vibrio vulnificus based on target-induced shielding against the peroxidase-mimicking activity of CeO2@PtRu nanozyme.

Vibrio vulnificus infection caused by contaminated aquatic products and seawater can lead to severe disease and high mortality. The development of a rapid and sensitive detection method for Vibrio vulnificus is vital to effectively prevent infection in advance. In this study, CeO2@PtRu with high peroxidase activity was used to construct a colorimetric immunoassay for Vibrio vulnificus detection by conjugating polyclonal antibodies via the biotin-streptavidin system. The developed colorimetric biosensor for Vibrio vulnificus demonstrated rapid operability and good sensitivity with a detection range from 104 CFU/mL to 109 CFU/mL, and the limit of detection (LOD) is 193 CFU/mL. Moreover, the colorimetric biosensor showed excellent specificity and good recoveries from 98.70% to 102.10% with RSD < 7.45% for spiked real samples. This novel CeO2@PtRu-based colorimetric biosensor has great application potential for the sensitive detection of Vibrio vulnificus in seafood.