Electron coupling effect-triggered monatomic copper laccase-mimicking nanozyme for the degradation and detection of guaiacol produced by Alicyclobacillus acidoterrestris

Screening broad-spectrum aptamers for cephalosporin antibiotics using real samples and development of a DNA walker-driven dual-mode aptasensor

Cephalosporin antibiotics are commonly used to treat mastitis in dairy cattle, but their overuse often results in excessive residues in milk, posing a significant food safety concern. Aptasensors provide a promising solution for the simultaneous detection of these residues. However, differences between screening conditions and real-world detection environments can affect aptamer performance. In this study, a broad-spectrum aptamer (Apt-93) with high affinity and specificity for cephalosporin antibiotics was successfully screened using a milk dilution-assisted graphene oxide (GO)-SELEX technique, achieving binding dissociation constants (Kd) of 27.21-43.45 nM. Leveraging Apt-93, we developed a DNA walker-based dual-mode aptasensor for detecting cephalosporin residues in milk. The sensor utilized streptavidin magnetic beads (SA-MBs) functionalized with hairpin chain-1 (H1) and a walking strand (aptamer hybridized with complementary DNA). Upon selective binding of cephalosporin antibiotics, the walking strand was released, triggering the opening of the H1 hairpin structure and exposing an enzymatic cleavage site. The enzymatic process cleaved carboxyfluorescein (FAM)-labeled H1, generating a fluorescent signal. Subsequently, the remaining H1 sequence bound to hairpin chain-2 (H2), releasing a G-rich sequence, which formed a G-quadruplex structure in the presence of hemin and K+, catalyzing a colorimetric reaction with 3,3',5,5'-tetramethylbenzidine (TMB). The dual-mode aptasensor achieved detection limits of 8.10 nM (fluorescence) and 20.3 nM (colorimetric). High recoveries in both pretreated and untreated milk samples demonstrated the robustness of the aptamer in terms of specificity and interference resistance. The dual-mode aptasensor offers a rapid and effective platform for detecting antibiotic residues, demonstrating a potential to enhance food safety monitoring.

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.

Biomimetically Engineering Valency in Copper Aerogel Toward Efficient Laccase-Mimicking Nanozyme

Developing nanozymes with high intrinsic activity to bridge the gap with natural enzymes has received unremitting attention. In this study, inspired by the copper active center for natural laccase and the multivalent characteristic of Cu, the valence state of Cu-based aerogel is modulated via adjusting the reductant usage for mimicking laccase. The laccase-mimicking activity is well-tailored via valence state manipulation, and theoretical calculations unveil the mechanism that the Cu0 and CuI species enhance the substrate adsorption capability and the CuII species are paramount to lowering the activation barrier synergistically. Heterogeneous metals are further incorporated to promote the valency-conversion of Cu and biomimetic electron transfer, conferring the constructed CuPt7.5% aerogel nanozyme with an ultralow detectable limit of 1 nm for phenolic pollutants. This work highlights the multivalence of Cu on laccase-mimicking activity and provides insights into the underlying catalytic mechanism, shedding light on the rational design of high-performance nanozymes for practical application.

Recent Progress on the Rational Design of Laccase Mimics

Laccase, a type of copper-containing natural oxidase, is known as a green catalyst because only water was produced as the reduction product. It has shown great potential for applications in wastewater treatment, dye degradation, food and pharmaceutical industries, biosensors, and other fields. Despite the above advantages of natural laccase, challenges arise from its inherent instability, recovery difficulties, and the associated high costs exist. To address such issues, a plethora of nanomaterials that possess laccase-mimicking activity, ranging from monometallic ions-containing nanomaterials to multimetal-based composites, was discovered in the past decade. In general, these materials demonstrate considerable performance variability. A comprehensive understanding of the design principles to achieve high laccase-like activity, particularly those on the Cu2+-involved structures and the related electron transfer, is thus demanded. Therefore, in this review, the structure-activity relationship of native laccase was first summarized, followed by the categorization of the recent design strategies of laccase-like nanozymes. After distilling the insights from the currently reported laccase-mimicking nanomaterials, a further prospect on the rational design of laccase mimics with high efficiency in the future was also proposed.

Tuning Atomically Dispersed Metal Sites in Nanozymes for Sensing Applications

Nanozymes with atomically dispersed metal sites (ADzymes), especially single-atom nanozymes, have attracted widespread attention in recent years due to their unique advantages in mimicking the active sites of natural enzymes. These nanozymes not only maximize exposure of catalytic sites but also possess superior catalytic activity performance, achieving challenging catalytic reactions. These advantages position ADzymes as highly promising candidates in the field of sensing and biosensing. This review summarizes the classification and properties of ADzymes, systematically highlighting some typical regulation strategies involving central metal, coordination environment, etc., to achieve their catalytical activity, specificity, and multifunctionality. Then, we present the recent advances of ADzymes in different sensing fields, including colorimetry, fluorescence, electrochemistry, chemiluminescence, photoelectrochemistry, and electrochemiluminescence. Taking advantage of their unique catalytic performance, the resultant ADzymes show great potential in achieving the goal of sensitivity, selectivity and accuracy for the detection of various targets. Specifically, the underlying mechanisms in terms of signal amplification were discussed in detail. Finally, the current challenges and perspectives on the development of advanced ADzymes are discussed.

A rapid and sensitive sandwich assay for the detection of Alicyclobacillus acidoterrestris in apple juice based on magnetosome immunomagnetic separation combined with quantum dots immunoassay technology

The contamination of apple juice by Alicyclobacillus acidoterrestris (A. acidoterrestris) can cause significant economic losses. Therefore, developing a rapid and sensitive method for detecting A. acidoterrestris is necessary. To address this issue, this study prepared magnetosome-monoclonal antibodies immunomagnetic microspheres (IMMs) as capture probes to enrich A. acidoterrestris (IMMs-Aa) and monoclonal antibodies-quantum dots (mAb-CdTeQDs) as detection probes for detecting A. acidoterrestris. The obtained IMMs-Aa-mAb-CdTeQDs "sandwich" structure was used to detect A. acidoterrestris based on the fluorescence intensity. The strategy presented a good linear correlation (y = 1048× + 1891, R2 = 0.995) between the fluorescence intensity and the concentration of A. acidoterrestris (101-105 CFU/mL) with a low detection limit of 25.4 CFU/mL within 50 min. The recovery rate of this strategy in spiked apple juice ranged from 88.16 % to 107.03 %. Thus, this study established an efficient and highly sensitive magnetic capture-enrichment-separation-detection method for A. acidoterrestris.

High-power "nesting-doll" biofuel cell enabled by free-standing electrodes with inherent enzymatic function

Biofuel cell (BFC) is a type of green energy device based on the biocatalyst-mediated redox reaction. However, their relatively low performance has limited their wider application. Here, we proposed a novel all-in-one strategy to design the free-standing electrodes with the inherent enzyme-like activity and high conductivity, in which, the dynamic limitations of the enzyme-electrode interface were eliminated. This approach facilitated rapid electron transfer by removing the need to coat enzymes on the electrode. Furthermore, the enzyme-mimic characteristic enhanced the stability of BFC. Notably, the step-by-step "ionic corrosion-electrografting coordination" of Cu foam yielded the free-standing cathode, which exhibited excellent laccase-like activity. Concurrently, the in-situ loading of gold particles on the Ni foam can serve as an exemplary mimic of the glucose oxidase. Furthermore, a "nesting doll" nanozyme BFC device was developed, in which, the anode was placed inside the cathode to create a multi-shell coaxial configuration. The four-tier devices demonstrated an elevated open-circuit voltage of 1.7 V, and the output power density was 3639.0 μW cm⁻2 measured by resistance method, which was superior to that of the reported literatures. This study presents a pioneering approach to improving output performance and stability, thereby broadening the potential scope of BFC application.

Ultrasensitive and label-free electrochemical immunosensor using gold nanoparticles deposited on a carbon electrode for the quantification of osteopontin: A serum-based oncomarker

Early detection of cancer biomarkers is crucial for effective diagnosis and treatment, prompting the development of an ultrasensitive label-free electrochemical immunosensor. In this study, we fabricated an ultrasensitive label-free electrochemical immunosensor using a glassy carbon electrode/gold nanoparticles (GCE/AuNPs) modification for quantification of osteopontin (OPN), an oncomarker. The surface features of the modified electrodes were confirmed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. The electrochemical behavior of the bare and modified electrode was characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The quantification of the OPN antigen was achieved through the differential pulse voltammetry (DPV) method. The fabricated immunosensor demonstrated excellent detection capabilities in both commercial serum samples and phosphate-buffered saline (PBS). It showed sensitive quantification of OPN in the range of 0.001 to 1000 ng/mL with a limit of detection (LOD) of 0.005 ng/mL in PBS. Furthermore, the immunosensor retained approximately 89.3 % of its initial signal after storage for up to 8 weeks. The results were validated by detecting OPN-spiked commercial serum samples with a satisfactory recovery rate. The potential of this immunosensor makes it suitable for assaying OPN in real cancer patient's serum samples with minimal interference from complex sample matrices.

Unlocking dual-mode enzyme activities on bacterial surface: Directional recognition and swift capture of Alicyclobacillus acidoterrestris from fruit juices

The acidophilic and heat-resistant characteristics of Alicyclobacillus acidoterrestris (A. acidoterrestris) pose significant challenges to fruit juice production. Traditional thermal removal methods are often ineffective against this resilient bacterium. To address this issue, we developed a novel adsorbent, magnetic carbonation carbon-lysozyme nanohybrid (MCL), composed of magnetic nanoparticles with a thin carbon shell and covalently grafted lysozyme. The outer lysozyme facilitates binding to the bacterial surface through two modes: electrostatic attraction and chemical interaction, acting as a vital engine for bacterial adhesion. The ultrathin carbon coating enhances dispersion, reduces magnetic loss, provides more adsorption sites for lysozyme grafting, and ensures stable function in acidic environments. Benefiting from the large surface area of MCL and the specific peptidoglycan recognition structure of lysozyme, MCL exhibits rapid adsorption kinetics and can completely remove 104 CFU/mL of A. acidoterrestris from juice within 20 min. The MCL demonstrates excellent capture performance, negligible cytotoxicity, and no significant impact on juice quality, offering a promising non-thermal strategy to improve juice safety.

Copper formate-lysine nanoparticles with polyphenol oxidase-like activity for the detection of epinephrine

Laccase is an enzyme known for its eco-friendly uses in environmental cleanup and biotechnology. However, it has limitations such as low stability, high cost, and complex recycling. So, there is a need for laccase mimics that can effectively imitate its properties. Herein, we created copper formate-lysine nanoparticles (Cuf-Lys) that mimic laccase's activity. The developed Cuf-Lys demonstrated remarkable polyphenol oxidase-like activity, stability, and recyclability, making them suitable for the fabrication of efficient colorimetric sensors for the detection of epinephrine. These sensors had a specific response and could accurately measure epinephrine concentrations ranging from 2.5 to 50 μM, with a detection limit as low as 1 μM. Furthermore, the biosensor demonstrated high sensitivity and selectivity when applied to the detection of rutin. The limit of detection for rutin was determined to be 0.16 μM while in the linear concentration range of 0.25 to 150.0 μM. We believe that Cuf-Lys provide a new route for the design of laccase mimics, showing potential applications for biomedical diagnosis and environmental monitoring.

A Bioinspired Single-Atom Fe Nanozyme with Excellent Laccase-Like Activity for Efficient Aflatoxin B1 Removal

The applications of natural laccases are greatly restricted because of their drawbacks like poor biostability, high costs, and low recovery efficiency. M/NC single atom nanozymes (M/NC SAzymes) are presenting as great substitutes due to their superior enzyme-like activity, excellent selectivity and high stability. In this work, inspired by the catalytic active center of natural enzyme, a biomimetic Fe/NC SAzyme (Fe-SAzyme) with O2-Fe-N4 coordination is successfully developed, exhibiting excellent laccase-like activity. Compared with their natural counterpart, Fe-SAzyme has shown superior catalytic efficiency and excellent stability under a wide range of pH (3.0-9.0), temperature (4-80 °C) and NaCl strength (0-300 mm). Interestingly, density functional theory (DFT) calculations reveal that the high catalytic performance is attributed to the activation of O2 by O2-Fe-N4 sites, which weakened the O─O bonds in the oxygen-to-water oxidation pathway. Furthermore, Fe-SAzyme is successfully applied for efficient aflatoxin B1 removal based on its robust laccase-like catalytic activity. This work provides a strategy for the rational design of laccase-like SAzymes, and the proposed catalytic mechanism will help to understand the coordination environment effect of SAzymes on laccase-like catalytic processes.

Pt/Zn-TCPP Nanozyme-Based Flexible Immunoassay for Dual-Mode Pressure-Temperature Monitoring of Low-Abundance Proteins

Pressure and temperature, as common physical parameters, are important for monitoring human health. In contrast, single-mode monitoring is prone to causing experimental errors. Herein, we innovatively designed a dual-mode flexible sensing platform based on a platinum/zinc-meso-tetrakis(4-carboxyphenyl)porphyrin (Pt/Zn-TCPP) nanozyme for the quantitative monitoring of carcinoembryonic antigen (CEA) in biological fluids with pressure and temperature readouts. The Pt/Zn-TCPP nanozyme with catalytic and photothermal efficiencies was synthesized by means of integrating photosensitizers into porous materials. The flexible sensing system after the antigen-antibody reaction recognized the pressure using a flexible skin-like pressure sensor with a digital multimeter readout, whereas the temperature was acquired via the photoheat conversion system of the Pt/Zn-TCPP nanozyme under 808 nm near-infrared (NIR) irradiation using a portable NIR imaging camera on a smartphone. Meanwhile, the dual-mode flexible sensing system was carried out on a homemade three-dimensional (3D)-printed device. Results revealed that the developed dual-mode immunosensing platform could exhibit good pressure and temperature responses within the dynamic range of 0.5-100 ng mL-1 CEA with the detection limits of 0.24 and 0.13 ng mL-1, respectively. In addition, the pressure and temperature were sensed simultaneously without crosstalk interference. Importantly, the dual-mode flexible immunosensing system can effectively avoid false alarms during the measurement, thus providing great potential for simple and low-cost development for point-of-care testing.

A novel colorimetric and fluorometric dual-signal identification of organics and Baijiu based on nanozymes with peroxidase-like activity

Nanozymes were nanomaterials with enzymatic properties. They had diverse functions, adjustable catalytic activity, high stability, and easy large-scale production, attracting interest in biosensing. However, nanozymes were scarcely applied in Baijiu identification. Herein, a colorimetric and fluorometric dual-signal determination mediated by a nanozyme-H2O2-TMB system was developed for the first time to identify organics and Baijiu. Since the diverse peroxidase-like activity of nanozymes, resulted in different degrees of oxidized TMB. Based on this, 21 organics were identified qualitatively and quantitatively by colorimetric method with a rapid response (<12 min), broad linearity (0.0005-35 mM), and low detection limits (a minimum of 30 nM for glutaric acids). Furthermore, the fluorometric method exhibited excellent potential for accurate determination of organics, with detection ranges of 2-200 µmol/L (LOD: 0.22 µmol/L) for l-ascorbic acid and 2-300 µmol/L (LOD: 0.59 µmol/L) for guaiacol. Finally, the sensor was successfully applied to identify fake Baijiu and Baijiu from 16 different brands.

Dual-mode colorimetric and fluorescence biosensors for the detection of foodborne bacteria

Due to the growing demand for detection technologies, there has been significant interest in the development of integrated dual-modal sensing technologies, which involve combining two signal transduction channels into a single technique, particularly in the context of food safety. The integration of two detection signals not only improves diagnostic performance by reducing assumptions, but also enhances diagnostic functions with increased application flexibility, improved accuracy, and a wider detection linear range. The top two output signals for emerging dual-modal probes are fluorescent and colorimetric, due to their exceptional advantages for real-time sensitive sensing and point-of-care applications. With the rapid progress of nanotechnology and material chemistry, the integrated colorimetric/fluorimetric dual-mode systems show immense potential in sensing foodborne pathogenic bacteria. In this comprehensive review, we present a detailed summary of various colorimetric and fluorimetric dual-modal sensing methods, with a focus on their application in detecting foodborne bacteria. We thoroughly examine the sensing methodologies and the underlying principles of the signal transduction systems, and also discuss the challenges and future prospects for advancing research in this field.