Hydrolysis enabled specific colorimetric assay of carbosulfan with sensitivity manipulation via metal-doped or metal-free carbon nanozyme

Sensitive and specific colorimetric detection of glyphosate utilizing laccase-mimicking activity of copper-based metal-organic framework

Glyphosate (Gly), a widely used potent herbicide worldwide, possess potential harm to human health and environment due to accumulation in water and soil. Hence, there is a pressing need to realize the simple and precise detection of Gly to ensure human health and environmental safety. Although various nanozyme-based detection methods have been developed for Gly, they frequently require additional enzymes and hydrogen peroxide (H2O2). H2O2 not only exhibits certain toxicity but is also prone to decomposition, resulting in poor accuracy and reproducibility. In this study, we report the synthesis of nanoscale copper-based metal-organic framework (Cu-MOF) through a facile ultrasound method, and the resulting Cu-MOF demonstrate excellent laccase-mimicking activity. Our Cu-MOF nanozyme can catalyze the conversion of substrates into chromogenic products without the need for H2O2, offering a simple and mild operational approach. The presence of Gly significantly inhibits the catalytic activity of the Cu-MOF, hindering the chromogenic reaction between 2,4-dichlorophenol (2,4-DP) and 4-aminoantipyrine (4-AP). We propose a detection method for Gly that is repeatable, reliable, highly selective, and cost-effective, eliminating the need for additional H2O2, or bioenzymes. This facile strategy paves a new path for the applications of laccase-mimicking nanozyme in environmental monitoring.

Unveiling a novel nanozyme cofactor: a highly activated Fe-CDs-derived colorimetric sensor array for comprehensive authentication of diverse tea products

Tea has antioxidant, anti-aging, hypotensive, and other functions. The tea polyphenol profile is of great significance for the identification and quality control of diverse tea products. Herein, an iron-doped carbon dots (Fe-CDs) with peroxidase-like activity was synthesized to construct a colorimetric sensor array for the tea polyphenols analysis in a complex matrix. Unexpectedly, it is found that the addition of tea polyphenols leads to an admirable increase in the activity of Fe-CDs, indicating the role of tea polyphenols as a cofactor of Fe-CDs nanozyme. The exploration based on multiple techniques reveals that the polyphenols can absorb on the Fe-CDs surface to form the new complex and effectively enhance the catalytic performance of Fe-CDs. This enhancement effect is closely related to the elemental doping, surface condition of nanozyme, and the polyphenol concentration. Taking TMB as the substrate, the colorimetric fingerprint generated in the presence of different tea polyphenols are extracted from the sensing array. The results of principal component analysis (PCA) and hierarchical clustering analysis (HCA) show that five tea polyphenols of different types, concentrations, and tea polyphenol mixtures of different proportions are successfully distinguished through pattern recognition methods. Moreover, the identification of tea leaves from different years and types, as well as various tea drinks, has been further realized. This study not only paves a new direction for enhancing the nanozyme activity, but provides an effective and convenient strategy for the quality control of tea products.

Breaking the conventional: Ligand-triggered Zn-MOF nanozyme with unusual oxidase activity for dual-channel sensing of benfuracarb

The activity of MOF-based nanozyme mainly relies on the metal sites, the development of organic ligands with intrinsic enzymatic-activity is of great significance for nanozyme-mediated sensors but it remains a huge challenge. Herein, the oxidase-like activity of an azo ligand, 4,4'-azodipyridine (AZPY), was first discovered by rational screening. A new Zn-MOF (JLU-MOF221) was successfully constructed based on the pillar-layered strategy to achieve well-isolated AZPY ligand and robust framework. JLU-MOF221 exhibited excellent affinity for 3,3',5,5'-tetramethylbenzidine (TMB) (Km: 0.180 mM; Kcat: 5.72 s-1), as well as a rapid response time (60 s) and high storage stability (87 % activity over 8 months). The study revealed the unique four-electron O2-to-H2O reaction pathway without relying on active oxygen species. Moreover, combining the hydrolysis behavior of benfuracarb and nanozyme inhibition strategy, a colorimetry and fluorescent dual-channel sensor was firstly developed towards benfuracarb, reaching a low limit of detection of 130 ng/mL and 76 ng/mL, respectively. The breakthrough in enzyme activity of organic ligands not only provides an efficient alternative for the traditional assay to detect benfuracarb, but also greatly promotes nanozyme-mediated sensors to a new stage.

Metal-organic framework-based nanozymes for water-soluble antioxidants and Total antioxidant capacity detection: Principles and applications

Nanozymes, engineered catalysts exhibiting catalytic properties, have emerged as key players at the interface of nanotechnology and biology, holding great promise in diverse food applications. Notably, nanoscale metal-organic frameworks (MOFs) have gained widespread recognition as flexible platforms for developing potent nanozymes. This review explores the design, development, and applications of MOF-based nanozymes, with a focus on their potential in detecting antioxidants and total antioxidant capacity (TAC), two critical parameters in the assessment of oxidative stress and related diseases. A comprehensive classification of these MOF-based nanozymes is presented, based on their catalytic activities, and recent advancements in their application to antioxidants and TAC detection are discussed. The review further delves into the challenges faced by MOF nanozymes in these areas, including issues related to stability, reproducibility, and selectivity. By addressing these challenges and proposing potential solutions, the review offers future perspectives on advancing the use of MOF nanozymes in sensing applications.

Cerium-based metal-organic framework nanozyme with high oxidase-like activity at neutral pH for discrimination and detection of antioxidants

Oxidase-mimicking nanozymes have witnessed extensive applications in biosensing, however, a huge shortcoming is their activity limited by acidic conditions. Herein, a Ce-MOF containing hexanuclear clusters was developed, which exhibited robust oxidase-like activity at neutral pH (0.97 U mg-1) with the extremely high affinity for 3,3',5,5'-tetramethylbenzidine (TMB) (Km: 0.012 mM) and wide temperature adaptability (0-50 °C). Experiment screening and theoretical calculations revealed that the high activity was derived from unsaturated CeIV active sites and the redox cycling of unique Ce4+/Ce3+ node. These factors endow Ce-MOF generating more O2•- species and significantly reducing the energy barrier of the rate-controlling step in the catalytic process. Given the exceptional activity for two chromogenic substrates, a two-channel colorimetric array is constructed to successfully distinguish four antioxidants. The detection was operated within 2 min in ultrapure water at room temperature, showing excellent convenience and efficiency. This study carries significant implications for developing oxidase-mimics with high activity under neutral pH and constructing simple and practical platforms to identify antioxidants in complex samples.

Acetylcholinesterase-free colorimetric sensing platform for carbosulfan detection based on hollow PDA/MnO2 nanozyme

Rapid and accurate detection of carbosulfan residues in vegetables is important for ensuring food safety. Herein, based on the unique hydrolysis behavior of carbosulfan, a nanozyme-based colorimetric sensing platform was proposed for detection of carbosulfan. Hollow polydopamine/MnO2 nanoparticles (H-PDA/MnO2 NPs) with excellent oxidase-like activity were synthesized, which can promote the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxidative product (oxTMB). Under acidic conditions, carbosulfan can be decomposed and produce reductive sulfide species (-SH), which are capable to disintegrate MnO2 NPs, resulting in decreased oxidase-like activity of H-PDA/MnO2 NPs. Based on the inhibitory effect on oxidase activity of H-PDA/MnO2 NPs, an acetylcholinesterase-free colorimetric assay was proposed for detection of carbosulfan with low limit of detection of 0.63 ng mL-1. Integrating test swabs with smartphone, a portable colorimetric sensor was constructed, showing great potential for on-site detection. To demonstrate the feasibility of this method, carbosulfan in real vegetable samples were determined.

A rapid and sensitive paper-based sensor for sulfide ion detection in Chinese liquors

The accurate monitoring of sulfide ion concentrations is vital for ensuring food safety, but current detection methods are often cumbersome and confined to laboratories. This study introduces an innovative paper-based colorimetric sensor that leverages the peroxidase-like activity of cobalt tetrasulfonate phthalocyanine (CoTsPc) for rapid, sensitive, and selective sulfide ion quantification. The underlying mechanism relies on the interaction between cobalt and sulfide ions, modulating the catalytic efficiency of CoTsPc and triggering a visible color change when 3,3',5,5'-tetramethylbenzidine (TMB) and hydrogen peroxide are present. By controlling solvent evaporation, the reaction kinetics are standardized, enabling reproducible and accurate colorimetric measurements. Experimental results show that adding sulfide ions to the TMB-H₂O₂ reaction system causes a gradual decrease in color intensity on the paper substrate. This change verifies effectiveness of the sensor, highlighting its potential for reliable sulfide ion detection in food safety applications, while providing a simple and portable alternative to conventional methods.

Medium entropy-derived flower-like FeCeCu nanozyme with excellent oxidase-like activity for on-site and visual detection of carbosulfan

BACKGROUND

Carbosulfan residues in environment is very harmful to human health. The rapid and high sensitive detection of carbosulfan residues is particularly important to guarantee human health and safety. The conventional chromatographic techniques and enzyme inhibition strategies cannot realize on-site and visual detection of carbosulfan. It is clear that a novel nanozyme-based method was need, which exhibited advantages in low-cost, rapidity, and portability with easy-to-use operation.

RESULTS

A medium entropy-derived flower-like FeCeCu nanozyme (FeCeCuzyme) were prepared via the metal-organic coordination method with "Ostwal ripening" growth process. FeCeCuzyme exhibited an excellent oxidase-like activity due to an abundant active sites in the flower-like structure. Carbosulfan can produce the sulfide compound by hydrolysis reaction under acidic condition, which could easily form sulfide-metal bonds with FeCeCuzyme, thereby significantly quenching their oxidase-like activity and hindering nanozyme-mediated chromogenic reaction. Given this phenomenon, the FeCeCuzyme were used as a colourimetric sensor for highly-specific carbosulfan detection without using acetylcholinesterase and H2O2. The FeCeCuzyme colourimetric sensor showed a wide linear range from 0.15 to 50.00 μM (R2 = 0.9970) with low detection limit of 0.13 μM. Meanwhile, FeCeCuzyme sensor was integrated with smartphone to design a portable detection platform, which realizes the on-site and rapid detection of carbosulfan with easy-to-operation. A low detection limit of 0.14 μM was obtained in the linear relation of 0.15-50.00 μM. The satisfactory recoveries (91.17%-108.00 %) from the spiking method were highly agreed with HPLC technique, and which further verified the feasibility of FeCeCuzyme-based strategies in real samples.

SIGNIFICANCE AND NOVELTY

This work provides a pioneer new avenue for design of novel nanozymes, and offers an efficient alternative to the conventional methods for specifical, fast, and on-sites detection of carbosulfan in environment.

Self-reduction of gold@platinum bimetallic nanoparticles on Ti3C2Tx MXene nanoribbons coupled with hydrogel and smartphone technology for colorimetric detection of silver ions

In recent years, numerous colorimetric methods have been developed for the detection of silver ions (Ag+), yet there remains a need for a simple, sensitive, real-time and quantitative sensing platform. Herein, Ti3C2Tx MXene nanoribbons (Ti3C2TxNRs) were utilized as the carrier material, and gold@platinum (Au@Pt) bimetallic nanoparticles were decorated onto the Ti3C2TxNR surface, for the first time, via a facile self-reduction method. The resulting Au@Pt-Ti3C2TxNR nanohybrid exhibited excellent catalytic activity, facilitating the oxidation of 3,3',5,5'-tetramethylbenzidine, a colorless substrate, to generate a blue product (oxTMB), displaying prominent peroxidase-like activity. In the presence of Ag+, a remarkable inhibiting effect was observed on the catalytic activity of the Au@Pt-Ti3C2TxNR nanohybrids, effectively halting the generation of oxTMB. Based on this, the as-obtained Au@Pt-Ti3C2TxNR nanozyme was then utilized to develop a novel colorimetric sensing platform for Ag+ detection, with a low detection limit of 1.57 nM and a wide linear detection range from 5.0 nM to 9.0 μM. In addition, by combining the unique advantages of hydrogel materials and smartphone technology, a simple, real-time and quantitative platform for Ag+ monitoring was constructed, highlighting its potential for practical applications in Ag+ detection.

Selective colorimetric detection of carbosulfan based on its hydrolysis behavior and Ti3C2/AuPt nanozyme

BACKGROUND

Carbosulfan (CBS) is a widely used carbamate pesticide in agricultural production, its easy decomposition into hypertoxic carbofuran poses serious threats to human health and food safety. Therefore, sensitive and accurate detection of CBS is of significant importance. Conventional chromatography-based techniques require expensive instruments and complicated sample pretreatment, limiting their application for fast detection. Current electrochemical and colorimetric methods for detection of pesticides based on the cascade catalytic reactions between acetylcholinesterase (AChE) and nanozymes, which exhibit inferior selectivity. Hence, selective, sensitive and fast detection of CBS is still challenging.

RESULTS

In this work, an AChE-free colorimetric method was proposed for selective detection of CBS based on its unique hydrolysis behavior and nanozyme. Ti3C2 nanosheets/AuPt nanoparticles (Ti3C2/AuPt NPs) with enhanced peroxidase-like activity were prepared via one-step self-reduction reaction. CBS can be hydrolyzed under acidic condition and produce -SH moieties, which could bond to Pt atoms of Ti3C2/AuPt NPs and shield the active sites of nanozyme, resulting in decreased catalytic activity. Based on the inhibitory effect on the peroxidase-like activity of Ti3C2/AuPt NPs, a colorimetric method was proposed for direct detection of CBS. Under optimal conditions, the method showed wide linear range (0.5 ng mL-1-5 μg mL-1), low limit of detection (0.342 nM), good selectivity and anti-interference ability. The feasibility of this method for practical use was confirmed by analysis of CBS in real lake water samples.

SIGNIFICANCE

This work proposed a simple colorimetric method for selective and fast detection of CBS, which avoided employing AChE and cascade catalytic reactions, significantly lowering the detection cost and improving detection efficiency. The method showed great potential for accurate detection of CBS in actual samples, and provided a new avenue for developing nanozyme-based colorimetric method for detection of other pesticide residues.

Palladium-platinum bimetallic modified MXene nanozyme for highly sensitive detection of active substances with acetylcholinesterase inhibitory effect

Alzheimer's disease (AD) is a chronic neurodegenerative disease that threatens to the health of global elderly population. Acetylcholinesterase (AChE) inhibitors are an effective therapeutic agent for AD, and screening of these substances is important for AD treatment. In this work, a Pd-Pt MXene nanoenzyme was successfully synthesized by using the in-situ reduction technique. A colorimetric method for sensitive AChE inhibitor detection was designed based on enzymatic cascade reaction between Pd-Pt MXene and AChE. Briefly, The Pd-Pt MXene material exhibited excellent peroxidase (POD)-like activity due to its bimetallic composition, effectively catalyzing the oxidation of colorless 3,3,5,5-tetramethylbenzidine (TMB) to generate blue oxidized TMB (oxTMB). Under the presence of AChE and acetylthiocholine chloride (ATCh), the POD-like activity of Pd-Pt MXene was significantly inhibited. The activity of this nanoenzyme could be restored after the addition of AChE inhibitors. Using donepezil as an example, colorimetric detection was conducted within a linear range of 0.1 nmol/L to 10 nmol/L and the lowest detection boundary was only 0.35 nmol/L (S/N = 3). Finally, a paper-based platform was designed and constructed, and it has been successfully employed for AChE inhibitor detection in real samples with the aid of a smartphone. In all, this work paves a new way for designing nanoenzyme-based devices towards medicine determination or screening like AChE inhibitor.

Ni2+ mediated oxidation and aggregation of o-phenylenediamine: an enhanced photothermal effect for direct, specific and background-free detection of thiophanate-methyl

A novel photothermal probe, o-phenylenediamine trimer (triOPD)-Ni2+ aggregates with a photothermal conversion efficiency of up to 74.4%, was prepared by CuNi-BTC catalytic oxidation and assembly of OPD. Based on the specific inhibition activity of thiophanate-methyl toward CuNi-BTC, a direct and background-free photothermal sensing platform was fabricated.

Carbon-based nanozymes: design, catalytic mechanisms, and environmental applications

Carbon-based nanozymes are synthetic nanomaterials that are predominantly constituted of carbon-based materials, which mimic the catalytic properties of natural enzymes, boasting features such as tunable catalytic activity, robust regenerative capacity, and exceptional stability. Due to the impressive enzymatic performance similar to various enzymes such as peroxidase, superoxide dismutase, and oxidase, they are widely used for detecting and degrading pollutants in the environment. This paper presents an exhaustive review of the fundamental design principles, catalytic mechanisms, and prospective applications of carbon-based nanozymes in the environmental field. These studies not only serve to augment the comprehension on the intricate operational mechanism inherent in these synthetic nanostructures, but also provide essential guidelines and illuminating perspectives for advancing their development and practical applications. Future studies that are imperative to delve into the untapped potential of carbon-based nanozymes within the environmental domain was needed to be explored to fully harness their ability to deliver broader and more impactful environmental preservation and management outcomes.

Ultrasensitive and Highly Selective Detection of Staphylococcus aureus at the Single-Cell Level Using Bacteria-Imprinted Polymer and Vancomycin-Conjugated MnO2 Nanozyme

Pathogenic bacterial infections, even at extremely low concentrations, pose significant threats to human health. However, the challenge persists in achieving high-sensitivity bacterial detection, particularly in complex samples. Herein, we present a novel sandwich-type electrochemical sensor utilizing bacteria-imprinted polymer (BIP) coupled with vancomycin-conjugated MnO2 nanozyme (Van@BSA-MnO2) for the ultrasensitive detection of pathogenic bacteria, exemplified by Staphylococcus aureus (S. aureus). The BIP, in situ prepared on the electrode surface, acts as a highly specific capture probe by replicating the surface features of S. aureus. Vancomycin (Van), known for its affinity to bacterial cell walls, is conjugated with a Bovine serum albumin (BSA)-templated MnO2 nanozyme through EDC/NHS chemistry. The resulting Van@BSA-MnO2 complex, serving as a detection probe, provides an efficient catalytic platform for signal amplification. Upon binding with the captured S. aureus, the Van@BSA-MnO2 complex catalyzes a substrate reaction, generating a current signal proportional to the target bacterial concentration. The sensor displays remarkable sensitivity, capable of detecting a single bacterial cell in a phosphate buffer solution. Even in complex milk matrices, it maintains outstanding performance, identifying S. aureus at concentrations as low as 10 CFU mL-1 without requiring intricate sample pretreatment. Moreover, the sensor demonstrates excellent selectivity, particularly in distinguishing target S. aureus from interfering bacteria of the same genus at concentrations 100-fold higher. This innovative method, employing entirely synthetic materials, provides a versatile and low-cost detection platform for Gram-positive bacteria. In comparison to existing nanozyme-based bacterial sensors with biological recognition materials, our assay offers distinct advantages, including enhanced sensitivity, ease of preparation, and cost-effectiveness, thereby holding significant promise for applications in food safety and environmental monitoring.

Nanomaterials with Enzyme-like Properties for Combatting Foodborne Pathogen Infections: Classifications, Mechanisms, and Applications in Food Preservation

During the transportation and storage of food, foodborne spoilage caused by bacterial and biofilm infection is prone to occur, leading to issues such as short shelf life, economic loss, and sensory quality instability. Therefore, the development of novel and efficient antibacterial agents capable of efficiently inhibiting bacteria throughout various stages of food processing, transportation, and storage is strongly recommended by researchers. The emergence of nanozymes is considered to be an effective candidate for inhibiting foodborne bacteria agents in the food industry. As potent antibacterial agents, nanozymes have the advantages of low cost, high stability, strong broad-spectrum antibacterial ability, and biocompatibility. Herein, we aim to summarize the classification status of various nanozymes. Furthermore, the general catalytic bacteriostatic mechanism of nanozymes against intracellular bacteria, planktonic bacteria, and biofilm activities are highlighted, mainly concerning the destruction of cell walls and/or membranes, reactive oxygen species regulation, HOBr/Cl generation, damage of intracellular components, and so forth. In particular, the review focuses on the pivotal role of nanozymes as antibacterial agents and delivery vehicles in the fields of food preservation applications. We look forward to the future prospects, especially in the field of food preservation, to promote broader applications based on antimicrobial nanozymes.

MOF-based Ag NPs/Co3O4 nanozyme for colorimetric detection of thiophanate-methyl based on analyte-enhanced sensing mechanism

Silver nanoparticles supported on metal-organic framework (ZIF-67)-derived Co3O4 nanostructures (Ag NPs/Co3O4) were synthesized via a facile in situ reduction strategy. The resulting materials exhibited pH-switchable peroxidase/catalase-like catalytic activity. Ag NP doping greatly enhanced the catalytic activity of Ag NPs/Co3O4 towards 3,3',5,5'-tetramethylbenzidine (TMB) oxidation and H2O2 decomposition which were 59 times (A652 of oxTMB) and 3 times (A240 of H2O2) higher than that of ZIF-67, respectively. Excitingly, thiophanate-methyl (TM) further enhanced the peroxidase-like activity of Ag NPs/Co3O4 nanozyme due to the formation of Ag(I) species in TM-Ag NPs/Co3O4 and generation of more radicals resulting from strong interaction between Ag NPs and TM. The TM-Ag NPs/Co3O4 nanozyme exhibited lower Km and higher Vmax values towards H2O2 when compared with Ag NPs/Co3O4 nanozyme. A simple, bioelement-free colorimetric TM detection method based on Ag NPs/Co3O4 nanozyme via analyte-enhanced sensing strategy was successfully established with high sensitivity and selectivity. Our study demonstrated that hybrid noble metal NPs/MOF-based nanozyme can be a class of promising artificial nanozyme in environmental and food safety applications.