Metal-pyrimidine nanocubes immobilized enzymes with pH-switchable multienzyme-like activity for broad-pH-responsive sensing assay for organophosphorus pesticides

Iron/manganese-zeolitic imidazolate framework (Fe/Mn-ZIF) nanozyme combined with acetylcholinesterase for colorimetric rapid detection of organophosphorus pesticides

Organophosphorus pesticides (OPs) are extensively utilized in agricultural production, but they pose significant threats to environment and organisms. This study aims to develop a novel method for the rapid and efficient detection of OPs. Initially, an iron/manganese zeolitic imidazolate framework (Fe/Mn-ZIF) with excellent oxidase-like activity was synthesised. The catalytic performance was evaluated, and the main factors influencing catalytic activity were investigated. Subsequently, a combined acetylcholinesterase assay was employed to detect three OPs. The specificity and recyclability of Fe/Mn-ZIF were also studied. The proposed colorimetric strategy demonstrated strong linear relationships: 0.1-2 mg/L for trichlorfon, 0.2-14 mg/L for glyphosate, and 0.4-10 mg/L for glufosinate, with the low detection limits of 0.024, 0.080, and 0.121 mg/L (3 S/N) respectively. Good recoveries were observed in real sample detection. This work lays a foundation for enhancing the catalytic performance of Fe/Mn-ZIF, which holds promise for biosensing applications.

Colorimetric sensor array constructed based on bimetallic porphyrin-based metal organic framework nanozyme for the detection and recognition of tannic acid

Colorimetric sensor arrays based on nanozymes hold promise for the simultaneous detection of multiple target analytes, but the rational design of nanozymes with high catalytic activity remains a major challenge. Herein, a porphyrin-based metal organic framework (Zr-MOFFe/CuPh) with bimetallic reaction centers (M - N4) were prepared by solvothermal method. Zr-MOFFe/CuPh nanozyme formed a redox cycle between different valence states, which significantly improved the peroxidase-like activity of the nanozyme, and further revealed its catalytic mechanism. In view of tannic acid (TA) can effectively inhibit nanozyme activity, an enzyme-driven colorimetry method was designed to detect TA, the method showed a good linear relationship in the range of 0.5-6.0 μM and the detection limit was as low as 0.143 μM. Interestingly, due to the varying inhibition levels of antioxidant molecules, resulting in different colorimetric response and forming a unique "fingerprint". A three-channel colorimetric sensor array to accurately identify and detect TA and other antioxidants was developed based on Zr-MOFFe/CuPh as a single sensing receptor. The proposed colorimetric sensor array achieved 100 % accuracy in identifying TA and other antioxidants, and was capable of measuring TA in real samples. This work not only designed an effective method for the TA detection, but also carried out a promising way for the application of bimetallic nanozymes in food monitoring.

Dual-mode colorimetric and chemiluminescence aptasensor for organophosphorus pesticides detection using aptamer-regulated peroxidase-like activity of TA-Cu

The residues of organophosphorus pesticides (OPs) in food pose a huge threat to human health. Therefore, the development of detection methods with simple design and high sensitivity is urgently needed. Here, a colorimetric/chemiluminescence (CL) dual-mode aptasensor strategy with high selectivity and sensitivity for detecting Parathion-methyl (PM) was designed based on aptamer-regulated nanozyme activity. The Parathion-methyl specific aptamer was anchored onto the surface of trimesic acid-Cu (TA-Cu) nanozyme, which can regulate the catalytic ability of TA-Cu nanozyme towards substrates and also serve as a specific recognition unit for PM. In the presence of PM, the aptamers bind to PM and detach from the surface of TA-Cu nanozyme, which effects the catalytic ability of TA-Cu nanozyme towards substrates. Based on the above experimental phenomena, a colorimetric/CL dual-mode aptasensor method for PM was developed, with the linear ranges of 0.01-20 and 1-100 ng/mL, the limit of detections of 0.004 and 0.45 ng/mL, respectively. More importantly, compared with most single mode analysis methods, this dual-mode sensing system can conduct self-inspection by comparing the detection results of each mode, thus improving the reliability of the detection results.

A DNA tweezer-actuated nanozyme-enzyme hybrid nanoreactor for pesticide detection

The construction of a nanozyme-enzyme hybrid cascade system is an effective protocol to optimize the performance of biosensors. Yet, the integration has limitations due to the lack of harmonious collaboration between nanozyme and enzyme. Herein, we have constructed an efficient enzymatic cascade system by utilizing the base complementary pairing and the targeting capability of DNA tweezers to combine DNA-regulated copper nanoflowers (CuNFs) with acetylcholinesterase (AChE). The DNA tweezers were immobilized onto the CuNFs undergo regular base complementary pairing, and subsequently employed as aptamer to capture AChE gently, forming CuNFs-Apt-AChE cascade system. This system not only enhanced the spatial proximity of CuNFs and AChE to increase cascade catalytic activity, but also demonstrated excellent stability under harsh conditions. Harnessing the nanoarchitecture and characteristics, the CuNFs-Apt-AChE composites were embedded into the hydrogel to fabricate a sensitive biosensor for on-site detecting carbamate pesticides with a detection limit of 0.19 ng mL-1. The hydrogel sensor exhibited high specificity for carbamate pesticides and had been successfully applied in water and juice samples for pesticide detection with strong anti-interference ability. This method holds great potential for the on-site detection of pesticides, offering a new strategy for constructing nanozyme-enzyme cascade hybrid systems with accuracy and sensitivity.

Immobilized Multi-Enzyme/Nanozyme Biomimetic Cascade Catalysis for Biosensing Applications

Multiple enzyme-induced cascade catalysis has an indispensable role in the process of complex life activities, and is widely used to construct robust biosensors for analyzing various targets. The immobilized multi-enzyme cascade catalysis system is a novel biomimetic catalysis strategy that immobilizes various enzymes with different functions in stable carriers to simulate the synergistic catalysis of multiple enzymes in biological systems, which enables high stability of enzymes and efficiency enzymatic cascade catalysis. Nanozymes, a type of nanomaterial with intrinsic enzyme-like characteristics and excellent stabilities, are also widely applied instead of enzymes to construct immobilized cascade systems, achieving better catalytic performance and reaction stability. Due to good stability, reusability, and remarkably high efficiency, the immobilized multi-enzyme/nanozyme biomimetic cascade catalysis systems show distinct advantages in promoting signal transduction and amplification, thereby attracting vast research interest in biosensing applications. This review focuses on the research progress of the immobilized multi-enzyme/nanozyme biomimetic cascade catalysis systems in recent years. The construction approaches, factors affecting the efficiency, and applications for sensitive biosensing are discussed in detail. Further, their challenges and outlooks for future study are also provided.

Bimetallic coreshell nanorods with thioglycolic acid monolayer for highly sensitive and rapid SERS detection of thiabendazole and ziram residues in Prunus Persica peaches

Simultaneous assessment of agrochemical residues in agricultural entities is crucial for ensuring food safety and protecting consumer health. A highly sensitive and stable thioglycolic acid (TGA) based surface modified coreshell nanorod (Au@Ag@TGANR) arrays were developed for simultaneous fungicide detection in peach samples. The developed Au@Ag@TGANRs exhibited superior surface enhance Raman scattering (SERS) performance, enabling the simultaneous examination of ziram (ZIR) and thiabendazole (TBZ) residues in peach samples with detection limits as low as 0.003 and 0.028 ppm and high R2 values of 0.996 and 0.995, for ZIR and TBZ, respectively. Good recoveries of 86.2 to 108.6 % and 80.2 to 105.7 % were also achieved for peach samples, highlighting the effectiveness of the established protocol for accurate and reliable detection of pesticides in fruits. These results suggest that the proposed method could be a valuable addition to current food safety protocols, with potential application in investigating toxic residues in agricultural entities.

Fabrication of Compartmentalized Multienzyme Reactor for Colorimetric Biosensing of Glucose and Phenol with High Sensitivity

Enzymatic cascade reactions are widely utilized in food security, environmental monitoring, and disease diagnostics, whereas their practical application was hindered due to their limited catalytic efficiency and intrinsic fragility to environmental influences. Herein, a compartmentalized dual-enzyme cascade nanoreactor was constructed in metal-organic frameworks (ZIF-8) by a shell-by-shell growth method. ZIF-8 provided a good microenvironment to maintain the activity of enzymes and protected them against harsh conditions. Importantly, experimental results revealed that the encapsulation order and enzyme ratio affected the cascade catalytic activity. When the cascade enzyme ratio was 1:1 and horseradish peroxidase (HRP) was encapsulated in the inner layer with glucose oxidase (GOx) in the outer layer (H@ZIF-8@G@ZIF-8), the nanoreactor facilitated the mass transfer process of substrates and showed the highest cascade catalytic efficiency. The maximum reaction rate (Vmax) of H@ZIF-8@G@ZIF-8 was 294.96 nM s-1, which was 1.6 times greater than G@ZIF-8@H@ZIF-8 (182.84 nM s-1). Therefore, H@ZIF-8@G@ZIF-8 was effectively applied in glucose monitoring and phenol sensing. The glucose biosensor showed a low detection limit of 0.76 μM and a broad linear range of 5-300 μM. The phenol biosensor demonstrated a wide linear range (20-300 μM) with a detection limit of 0.60 μM. In addition, the spiked recovery experiments for glucose and phenol were carried out in serum (recovery: 95.26-100.04%) and tap water (recovery: 97.05-106.50%), respectively. The high accuracy demonstrated potential applications of the cascade system in biosensing and environmental detection.

Recent advances and applications of stimuli-responsive nanomaterials for water treatment: A comprehensive review

The development of stimuli-responsive nanomaterials holds immense promise for enhancing the efficiency and effectiveness of water treatment processes. These smart materials exhibit a remarkable ability to respond to specific external stimuli, such as light, pH, or magnetic fields, and trigger the controlled release of encapsulated pollutants. By precisely regulating the release kinetics, these nanomaterials can effectively target and eliminate contaminants without compromising the integrity of the water system. This review article provides a comprehensive overview of the advancements in light-activated and pH-sensitive nanomaterials for controlled pollutant release in water treatment. It delves into the fundamental principles underlying these materials' stimuli-responsive behaviour, exploring the design strategies and applications in various water treatment scenarios. In particular, the article indicates how integrating stimuli-responsive nanomaterials into existing water treatment technologies can significantly enhance their performance, leading to more sustainable and cost-effective solutions. The synergy between these advanced materials and traditional treatment methods could pave the way for innovative approaches to water purification, offering enhanced selectivity and efficiency. Furthermore, the review highlights the critical challenges and future directions in this rapidly evolving field, emphasizing the need for further research and development to fully realize the potential of these materials in addressing the pressing challenges of water purification.

Perspectives for the Role of Single-Atom Nanozymes in Assisting Food Safety Inspection and Food Nutrition Evaluation

Single-atom nanozymes (SAzymes) have been greatly developed for rapid detection, owing to their rich active sites and excellent catalytic activity. Although several excellent reviews concentrating on SAzymes have been reported, they mainly focused on advanced synthesis, sensing mechanisms, and biomedical applications. To date, few reviews elaborate on the promising applications of SAzymes in food safety inspection and food nutrition evaluation. In this paper, we systematically reviewed the enzyme-like activity of SAzymes and the catalytic mechanism, in addition to recent research advances of SAzymes in the domain of food safety inspection and food nutrition evaluation in the past few years. Furthermore, current challenges hampering practical applications of SAzymes in food assay are summarized and analyzed, and possible research areas focusing on SAzyme-based sensors in rapid food testing are also proposed.