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The nanomaterials with enzyme-like catalytic activity, named as nanozymes, have aroused wide research interest owing to their striking merits. Metal-organic frameworks (MOFs) have showed great prospect in the construction of novel nanozymes. In this review, firstly, we summarize the most recent contributions in the design construction of the MOFs-based nanozymes. Then, we concentrate our attention on their applications in the fields of sensing and cancer therapies. According to the design strategies, we categorized MOFs-based nanozymes into four classes for review (i.e. pristine MOFs, MOFs with modification, MOFs-based nanocomposites, and MOF derivatives). Meanwhile, the emerging and fascinating 2D MOFs-based nanozymes were also reviewed. A variety of novel applications are also discussed, including nanozymes catalytic mediated signal amplification in sensing applications (e.g. colorimetric sensing, fluorescent sensing, chemiluminescent sensing, electrochemical sensing, and surface-enhanced Raman scattering (SERS)), and nanozymes catalytic mediated cancer therapy (i.e. cancer-starvation therapy, enhancing photodynamic therapy, and cancer-starvation and PDT synergistic therapy). At the end of the article, future opportunities and challenges in this promising research area are tentatively proposed. The design construction of MOFs-based nanozymes and the applications of the MOFs-based nanozymes to sensing and cancer therapy. Image 1 • Progress in the design construction of MOFs-based nanozymes was reviewed. • The applications of MOFs-based nanozymes to sensing were summarized. • The applications of MOFs-based nanozymes in cancer therapy were summarized. • The challenges and opportunities of MOFs-based nanozymes are put forward. [ABSTRACT FROM AUTHOR]

Early detection and diagnosis have great practical significances for the effective prevention and treatment of cancer. In this study, we developed a novel, facile and ultra-sensitive fluorescence assay for the determination of tumor invasive biomarker β-glucuronidase (GLU) based on the inner-filter effect (IFE). The nitrogen-doped carbon quantum dots (N-CQDs) with green photoluminescence were employed as the fluorophore in IFE, and 4-nitrophenyl-β-D-glucuronide (PNPG) was used to act as GLU substrate, and GLU catalytic product (p-nitrophenol (PNP)) was capable of acting as the robust absorber in IFE to turn off the fluorescence of N-CQDs due to the complementary overlap between the absorption of PNP and the excitation of N-CQDs. Thus, signal of GLU activity could be recorded by the fluorescence intensity of N-CQDs. Unlike other fluorescence sensing mechanism such as fluorescence resonance energy transfer (FRET) or photoinduced electron transfer (PET), IFE has no requirement for electron or energy transfer process or any chemical modification of fluorophore, which makes our assay more flexible and simple. The proposed method exhibited a good linear relationship from 1 U L −1 to 60 U L −1 (R 2 =0.9967) with a low detection limit of 0.3 U L −1 . This method was also successfully applied to the analysis of serum samples and the inhibitor screening from natural product. The developed sensor platform was proven to be reliable, facile, sensitive, and selective, making it promising as a candidate for GLU activity detection in clinic tumor diagnose and anti-tumor drug screening. [ABSTRACT FROM AUTHOR]

The medicines targeted at α-glucosidase played an important role in anti-diabetes and anti-HIV therapy. Unfortunately, the method based on fluorescent assay strategy for α-glucosidase inhibitor screening remains poorly investigated. In this study, a novel “Turn On” fluorescence sensor platform has been developed for trace α-glucosidase inhibitor screening from natural medicines. Firstly, carbon dots were prepared by one-pot synthesis and used as the signal output. Combining with the carbon dots, cobalt oxyhydroxide (CoOOH) nanoflakes were employed to build the fluorescence resonance energy transfer (FRET) based sensor platform. Secondly, L-ascorbic acid-2-O-α-D-glucopyranosyl (AAG) was innovatively introduced as α-glucosidase substrate. With hydrolysis of AAG by α-glucosidase, ascorbic acids (AA) were released that can rapidly reduce CoOOH nanoflakes to Co 2+ , and then FRET was stopped accompanying with the fluorescence recovery of CDs. The sensor platform was ultrasensitive to AA with a detection limit of 5 nM, ensuring the sensitive monitoring of enzyme activity. Acarbose was used as the inhibitor model and its inhibition rate is proportional to the logarithm of concentration in range of 10 −9 –10 −3 M with the correlation coefficient of R 2 =0.996, and an ultralow limit of detection of ~1×10 −9 M was obtained. The inhibiting ability of seven compounds isolated from natural medicines was also evaluated. The constructed sensor platform was proven to be sensitive and selective as well as cost-effective, facile and reliable, making it promising as a candidate for trace α-glucosidase inhibitor screening. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs), as an emerging class of porous crystalline polymers, are built by the combination of the light elements through the strong covalent bonds. In the past decade, COFs have been reported to show plenty of unique properties (such as ordered channels, large specific surface area, highly tunable porosity, optional building blocks, predictable and stable structure, and abundant functional groups), and have been widely applied in multiple fields. Recently, to further improve the potential performances of COFs and extend their applicability, a number of COFs with various functionalities have been successfully developed through the functionalization modification. In this review, we summarized the advanced design and construction of functionalized COFs, including COFs with post-synthetic modification, COFs-based composites (e.g. COFs-metal nanoparticles composites, COFs-metal oxide nanoparticles composites, COFs-MOFs composites, and COFs-enzyme composites), and molecularly imprinted COFs. Impressively, the applications of functionalized COFs to sensing also have been comprehensively summarized, including colorimetric sensing, fluorescent sensing, electrochemical sensing, and other sensing (such as quartz crystal microbalance (QCM) sensing, photoelectrochemical sensing, and humidity sensing). In the end, future opportunities and challenges in this promising field are tentatively proposed. The construction of functionalized covalent organic frameworks and their applications to sensing. Image 1 • Progress in the design construction of functionalized COFs was reviewed. • The applications of functionalized COFs to sensing were summarized. • The challenges and opportunities of functionalized COFs are put forward. [ABSTRACT FROM AUTHOR]

Enzyme inhibition based drug screening strategy has been widely employed for new drug discovery. But this strategy faces some challenges in practical application especially for the trace active compound screening from natural products such as the stability of enzyme and the sensitivity of screening approach. Inspired by the above, we for the first time demonstrate the self-assembly of α-glucosidase (GAA) and glucose oxidase (GOx) into one multi-enzymes-inorganic nanoreactor with hierarchical structure (flower shape). The hybrid enzyme nanoreactor enjoys the merits including the character of assembly line, the enhanced enzymatic activity and robust stability. The flower shape of enzyme nanoreactor possessed a bigger specific surface area, facilitating the trace GAA inhibitor detection. Based on the above, we proposed an enzyme nanoreactor mediated plasmonic sensing strategy for anti-diabetic drug screening. First, maltose was chosen as the substrate for GAA and the generated glucose were immediately utilized by GOx to generate H 2 O 2 , and finally, H 2 O 2 etched the Ag nanoprism to round nanodiscs, resulting in the blue shift of surface plasmon resonance (SPR) absorption band. With the aid of hybrid enzyme nanoreactor guided SPR, the ultrasensitive screening of GAA inhibitor (i.e. anti-diabetic drug) can be realized with the detection limit of 5 nM for acarbose. The proposed approach was successfully utilized for GAA inhibitor screening from natural products. We anticipate that the proposed sensing method may provide new insights and inspirations in the enzyme inhibition based drug discovery and clinical diagnosis. [ABSTRACT FROM AUTHOR]

We developed an aptamer recognition-trigged enzyme-free catalyzed hairpin assembly (CHA) assisted signal amplification homogeneous naked-eyes and surface-enhanced Raman scattering (SERS) dual-mode sensor for highly sensitive and portable detection of Aflatoxin B 1 (AFB 1) in food samples. The recognition of AFB 1 by aptamer induced the generation of HP1-AFB 1 complexes, which hybridized with Ag+-labeled hairpin DNA (HP2) and released Ag+, subsequently initiating the enzyme-free CHA reaction by a designed helper DNA (HP3) to form double-stranded DNA (HP2-HP3) and accompanied by the release of HP1-AFB 1 complexes. The released HP1-AFB 1 complexes were recognized by HP2 and HP3 again to trigger cascade recycling amplification and resulted in the generation of a larger number of free Ag+ and dsDNA. Then, methylene blue as Raman tag to intercalate into dsDNA and generating strong SERS signal with the assistance of Fe 3 O 4 @Au. Meanwhile, the free Ag+ induced the AuNPs aggregation and resulted in naked-eye distinguishable color transitions from red to black blue. Benefitting from the efficiently enzyme-free CHA assisted signal amplification and portably dual-mode detection system, this work successfully proposed a novel homogeneous biosensing strategy for highly sensitive and portable detection of AFB 1. The SERS intensity and visualization signals were linearly correlated with the concentration of AFB 1 ranging from 0.0156 to 31.2 ng mL−1 and 0.61–39 ng mL−1, and the limit of detections were 1.6 pg mL−1 and 152 pg mL−1, respectively. This strategy was successfully applied to real samples and provided an alternative approach for the highly sensitive detection of mycotoxins. [ABSTRACT FROM AUTHOR]

Inspired by the structure of the catalytically active center of natural laccase, a novel laccase mimics (named LM nanozymes) with a superior catalytic activity was successfully prepared by using glutathione (GSH) and copper (II) chloride as precursors via a facile hydrothermal method. The catalytically active center structure of LM nanozymes was revealed, which was constructed based on the numerous copper (Ⅰ) and copper (II) coordinating with thiol/amino group. The possible catalytic mechanism of LM nanozymes was also proposed. Similar to natural laccase, the prepared LM nanozymes can catalyze the oxidative coupling reaction between 2,4-dichlorophenol (2,4-DP) and 4-aminoantipyrine (4-AP) to produce an obvious red product. Compared with natural laccase, the LM nanozymes showed many outstanding advantages such as robust stability, lower cost, stronger catalytic activity and substrate affinity. Based on its excellent performances, LM nanozymes were employed as a powerful alternative to the natural enzyme in a traditional enzyme-linked immunosorbent assay (ELISA) to establish a nanozyme-based ELISA towards alpha-lactalbumin (allergenic protein). Impressively, a high-throughput and portable detection method was established by the integration of the nanozyme-based ELISA with a smartphone. The portable detection strategy achieved a limit of detection as low as 0.056 ng/mL with high specificity, and also showed excellent applicability in food sample analysis. This work not only enriches the diversities of nanozymes, but also broadens the promising applications of nanozymes in the biosensing area. • Bioinspired nanozymes with laccase-like catalytic activity were prepared. • The catalytic mechanism of laccase-mimicking nanozymes was proposed. • Nanozyme-based enzyme-linked immunosorbent assay was constructed. • A portable smartphone-based allergenic protein detection system was established. [ABSTRACT FROM AUTHOR]

Magnetic covalent organic frameworks (COFs) are useful mesoporous materials for the enrichment and separation of analytes, and are utilized in the pretreatment of samples. However, the use of magnetic COFs in electrochemical immunosensors has rarely reported. Herein, a novel electrochemical assay for the determination of prostate specific antigen (PSA) was developed using black phosphorene (BPene) as a platform and magnetic COFs for signal amplification. BPene was prepared via water-phase exfoliation. BPene nanocomposite (Au@BPene) was prepared by depositing Au nanoparticles (Au NPs) onto BPene. This nanocomposite was utilized as an immunsensing platform to bind primary antibodies and improve electron transfer. Subsequently, an Au NP-loaded magnetic COF was used to immobilize the secondary antibodies and abundant electronic signals of methylene blue (MB). The fabricated sensor exhibited linearity ranging from 0.0001 ng mL-1 to 10 ng mL−1 with the detection limit of 30 fg mL−1. The sensor could determine the PSA in a real sample with excellent specificity, good stability, and desirable reproducibility. The effective signal amplification of the proposed sensor is attributed to the good electron transfer of Au@BPene, excellent enrichment capacity of signal molecules (MB) of the COF, and efficient catalytic activity of Fe 3 O 4. This work not only provides an effective electrochemical assay to detect PSA in real sample, but also broadens the utilization scope of magnetic COFs in immunosensing. • An ultrasensitive electrochemical immunosensor for prostate specific antigen was developed. • The sensor was based on phosphorene and magnetic covalent organic framework. • The detection limit of the sensor was 30 fg mL-1. • The sensor was successfully adopted to determine PSA in real sample. • The sensor showed excellent specificity, good stability, and desirable reproducibility. [ABSTRACT FROM AUTHOR]