Alkali-Etched Imprinted Mn-Based Prussian Blue Analogues with Superior Oxidase-Mimetic Activity and Precise Recognition for Tetracycline Colorimetric Sensing

Mixed-valence Ce-Fe bimetallic MOFs with multi-enzyme-like activities for colorimetric biosensing and catalytic degradation

Metal-organic frameworks (MOFs) have emerged as highly sought-after artificial nanozymes due to the distinct crystalline, tailored structure, tunable composition. In this work, a one-step solvothermal method was adopted to synthesize a series of bimetallic MOFs (CexFey-MOF) through the substitute of Fe into Ce-MIL-140A. Interestingly, with introducing Fe(III) ions, MOFs crystal structure gradually changed from Ce-MIL-140A to Fe-MIL-88B. The resulted bimetallic CexFey-MOF exhibited controllable multiple enzyme-like properties, including peroxidase-like (POD-like), oxidase-like (OXD-like) and phosphatase-like activities, which can be modulated by varying the Ce/Fe ratio. Specifically, Ce5Fe5-MOF displayed much more remarkable OXD-like and POD-like activities, while Ce9Fe1-MOF demonstrated high phosphatase-like activity. The reaction kinetics and potential influence factors of Ce5Fe5-MOF and Ce9Fe1-MOF were systematically investigated, demonstrating their high catalytic activity, outstanding durability and recyclability. Finally, Ce5Fe5-MOF were applied for detection of ascorbic acid (AA) and degradation of phenol with its OXD-like and POD-like activities, respectively. This work opens new insight into design of mixed mental MOFs as multiple nanozymes.

A simple post-processing approach induced Interface recombination to construct hollow cubic-shape Prussian blue analogs for biosensing and degradation of aflatoxins B1

Multifunctional Prussian blue analogs (PBAs) have received extensive attention in the detection and degradation of food hazards. However, the development of new structural adjustment strategies to further improve their performance remains a huge challenge. Herein, the "interface recombination" post-processing approach was established to regulate the structure of PBAs using a microwave-assisted solvothermal method combined with acid etching. Hollow cube-shaped M-NiMnFe-PBA with elevated peroxidase-mimetic activity, photothermal effect, and photo-Fenton performance was obtained. Based on M-NiMnFe-PBA, a dual-mode nanoenzyme-linked immunoassay sensing platform was constructed for aflatoxins B1 (AFB1) detection, achieving low detection limits of 4.96 fg/mL in the colorimetric mode and 1.5 pg/mL in the photothermal mode. Due to its admirable photo-Fenton performance, AFB1 was almost completely degraded within 3 h, resulting in a significant reduction in its cytotoxicity. This work provides a new solution for synthetic regulation and property enhancement of PBAs, which promotes their application in control of food hazards.

Sensitive chemiluminescence detection platform for H2O2 and glucose through facile inorganic salt etching of cobalt Prussian blue analogues

A facile method is reported for rapid etching of cobalt Prussian blue analogues (Co PBA) with inorganic salt NaClO at room temperature, resulting in Co PBANaClO, which has been successfully applied to sensitive chemiluminescence (CL) detection. Initially, Co PBA was synthesized using the classical coprecipitation method. Subsequently, without the need for additional steps, Co PBANaClO was obtained by simply mixing NaClO with Co PBA at room temperature. This fabrication process led to the formation of numerous Co nanoparticles on the surface of Co PBA, thereby exposing more active sites. Based on the exceptional peroxidase-mimicking activity exhibited by Co PBANaClO, we constructed the Co PBANaClO-luminol-H2O2 CL platform and successfully utilized it for the sensitive detection of both H2O2 and glucose, with detection ranges of 0.05-20 µM and 1-50 µM, respectively, and detection limits of 23 nM and 36 nM, respectively. Finally, the possible mechanism of the Co PBANaClO-luminol-H2O2 system was investigated. This work demonstrates the feasibility of etching PBAs with inorganic salts to enhance their peroxidase-like activity and expands the application of etched PBAs in the area of CL sensing.

Nanozyme-Enabled Biomedical Diagnosis: Advances, Trends, and Challenges

As nanoscale materials with the function of catalyzing substrates through enzymatic kinetics, nanozymes are regarded as potential alternatives to natural enzymes. Compared to protein-based enzymes, nanozymes exhibit attractive characteristics of low preparation cost, robust activity, flexible performance adjustment, and versatile functionalization. These advantages endow them with wide use from biochemical sensing and environmental remediation to medical theranostics. Especially in biomedical diagnosis, the feature of catalytic signal amplification provided by nanozymes makes them function as emerging labels for the detection of biomarkers and diseases, with rapid developments observed in recent years. To provide a comprehensive overview of recent progress made in this dynamic field, here an overview of biomedical diagnosis enabled by nanozymes is provided. This review first summarizes the synthesis of nanozyme materials and then discusses the main strategies applied to enhance their catalytic activity and specificity. Subsequently, representative utilization of nanozymes combined with biological elements in disease diagnosis is reviewed, including the detection of biomarkers related to metabolic, cardiovascular, nervous, and digestive diseases as well as cancers. Finally, some development trends in nanozyme-enabled biomedical diagnosis are highlighted, and corresponding challenges are also pointed out, aiming to inspire future efforts to further advance this promising field.

Highly specific colorimetric detection of sarcosine using surface molecular imprinted Zn/Ce-ZIF

Despite significant progress in nanozyme research and the advancement of analytical techniques, the inherent lack of specificity for target analytes often limits their utility in analysis. Integrating specific recognition capabilities into inorganic nanomaterials, independent of biological catalysts or adaptors, represents a crucial breakthrough in the field. Detecting Sarcosine (Sar) in human urine has recently emerged as a non-invasive biomarker for prostate cancer (PCa), presenting a valuable diagnostic tool. This study introduces a novel method for embedding molecular imprinting sites directly onto the surface of a Zn/Ce-based zeolitic imidazolate framework (Zn/Ce-ZIF) nanozyme, facilitating the development of a highly specific colorimetric assay for precise Sar measurement. By utilizing the lanthanide metal cerium as the catalytic element and ZIF-8 as the structural scaffold, we synthesized spherical Zn/Ce-ZIF nanozymes with exceptional oxidase-like catalytic efficiency. The efficiency of molecular imprinting experiments and the ability of molecularly imprinted polymers (MIPs) to identify target molecules were significantly enhanced by using theortical calculations to screen suitable functional monomers. The molecularly imprinted nanozyme (Zn/Ce-ZIF@MIP) initiates a colorimetric oxidation reaction of 3,3',5,5'-tetramethylbenzidine (TMB), wherein the presence of Sar facilitates selective recognition and capture by the MIP shell, modulating the colorimetric response by hindering TMB's access to the catalytic site. An intelligent color extraction detection device has been developed for the rapid perception of Sar. This colorimetric sensing platform has been validated through the detection of Sar in simulated urine samples. Overall, the application of surface molecular imprinting enhances the functionality of nanozymes in analytical fields.

Molecularly Imprinted Nanozymes with Substrate Specificity: Current Strategies and Future Direction

Molecular imprinting technology (MIT) stands out for its exceptional simplicity and customization capabilities and has been widely employed in creating artificial antibodies that can precisely recognize and efficiently capture target molecules. Concurrently, nanozymes have emerged as promising enzyme mimics in the biomedical field, characterized by their remarkable stability, ease of production scalability, robust catalytic activity, and high tunability. Drawing inspiration from natural enzymes, molecularly imprinted nanozymes combine the unique benefits of both MIT and nanozymes, thereby conferring biomimetic catalysts with substrate specificity and catalytic selectivity. In this review, the latest strategies for the fabrication of molecularly imprinted nanozymes, focusing on the use of organic polymers and inorganic nanomaterials are explored. Additionally, cutting-edge techniques for generating atom-layer-imprinted islands with ultra-thin atomic-scale thickness is summarized. Their applications are particularly noteworthy in the fields of catalyst optimization, detection techniques, and therapeutic strategies, where they boost reaction selectivity and efficiency, enable precise identification and quantification of target substances, and enhance therapeutic effectiveness while minimizing adverse effects. Lastly, the prevailing challenges in the field and delineate potential avenues for future progress is encapsulated. This review will foster advancements in artificial enzyme technology and expand its applications.

Introducing molecular imprinting onto nanozymes: toward selective catalytic analysis

The discovery of enzyme-like catalytic characteristics in nanomaterials triggers the generation of nanozymes and their multifarious applications. As a class of artificial mimetic enzymes, nanozymes are widely recognized to have better stability and lower cost than natural bio-enzymes, but the lack of catalytic specificity hinders their wider use. To solve the problem, several potential strategies are explored, among which molecular imprinting attracts much attention because of its powerful capacity for creating specific binding cavities as biomimetic receptors. Attractively, introducing molecularly imprinted polymers (MIPs) onto nanozyme surfaces can make an impact on the latter's catalytic activity. As a result, in recent years, MIPs featuring universal fabrication, low cost, and good stability have been intensively integrated with nanozymes for biochemical detection. In this critical review, we first summarize the general fabrication of nanozyme@MIPs, followed by clarifying the potential effects of molecular imprinting on the catalytic performance of nanozymes in terms of selectivity and activity. Typical examples are emphatically discussed to highlight the latest progress of nanozyme@MIPs applied in catalytic analysis. In the end, personal viewpoints on the future directions of nanozyme@MIPs are presented, to provide a reference for studying the interactions between MIPs and nanozymes and attract more efforts to advance this promising area.

Breaking the pH Limitation of Nanozymes: Mechanisms, Methods, and Applications

Although nanozymes have drawn great attention over the past decade, the activities of peroxidase-like, oxidase-like, and catalase-like nanozymes are often pH dependent with elusive mechanism, which largely restricts their application. Therefore, a systematical discussion on the pH-related catalytic mechanisms of nanozymes together with the methods to overcome this limitation is in need. In this review, various nanozymes exhibiting pH-dependent catalytic activities are collected and the root causes for their pH dependence are comprehensively analyzed. Subsequently, regulatory concepts including catalytic environment reconstruction and direct catalytic activity improvement to break this pH restriction are summarized. Moreover, applications of pH-independent nanozymes in sensing, disease therapy, and pollutant degradation are overviewed. Finally, current challenges and future opportunities on the development of pH-independent nanozymes are suggested. It is anticipated that this review will promote the further design of pH-independent nanozymes and broaden their application range with higher efficiency.

Preparation of highly adsorptive biochar by sequential iron impregnation under refluxing and pyrolysis at low temperature for removal of tetracycline

Iron-doping modification is a prevailing approach for improving adsorption capability of biochar with environmental friendliness, but usually requires high temperature and suffers from iron aggregation. Herein, a highly adsorptive biochar was manufactured via sequential disperse impregnation of iron by refluxing and pyrolysis at low temperature for eliminating tetracycline (TC) from aqueous solution. Iron oxides and hydroxides were impregnated and stably dispersed on the carbon matrix as pyrolyzed at 200 °C, meanwhile abundant oxygen and nitrogen functional groups were generated on surface. The iron-doped biochar exhibited up to 891.37 mg/g adsorption capacity at pH 5, and could be recycled with high adsorption capability. The adsorption of TC should be mostly contributed to the hydrogen bonding of N/O functional groups and the hydrogen bonding/coordination of iron oxides/hydroxides. This would provide a valuable guide for dispersedly doping iron and conserving functional groups on biochar, and a super iron-doped biochar was prepared with superior recyclability.

Fluorimetric determination of tetracycline antibiotics in animal derived foods using boron and nitrogen co-doped ceria-based nanoparticles

An innovative synthesis of boron and nitrogen co-doped ceria-based nanoparticles (B/N-CeFNPs) with bright blue fluorescence emission is reported using the hydrothermal method. Based on the aggregation-induced emission enhancement (AIEE) effect between B/N-CeFNPs and chlortetracycline (CTC), a rapid detection method for CTC through fluorescence enhancement was developed. In addition, through the electron transfer process (ET), fluorescence resonance energy transfer (FRET) effect and static quenching between B/N-CeFNPs and oxytetracycline (OTC), a ratio fluorescence strategy for detecting OTC was generated. The fluorescence of B/N-CeFNPs at 410 nm can be effectively quenched by OTC, and new fluorescence emission appears at a wavelength of 500 nm. B/N-CeFNPs showed good linear responses with CTC and OTC in the range 0.1-1 µM and 1-40 µM, respectively. This system was used to simultaneously detect the CTC and OTC in milk and honey, realizing multi-residues detection of TCs in actual samples by using the same ceria-based fluorescence nanomaterial.