DNA-Programmed Tuning of the Growth and Enzyme-Like Activity of a Bimetallic Nanozyme and Its Biosensing Applications

On-site tracking of trace Aflatoxin B1 in food waste composting via a portable colorimetric sensing platform with nanozymes

Rapid, on-site accurate tracking of harmful mycotoxin in food waste composting is essential to provide instant content information for efficient supervision. However, on-site analytical tools especially colorimetric sensors currently suffer from low sensitivity/selectivity and poor environment robustness, posing hurdles for their applications. In this work, we have proposed a portable paper-based colorimetric sensor to detect the representative mycotoxin (aflatoxin B1, AFB1) in the composting process, where the superior catalytic velocity (6-fold higher than the natural enzyme) and well-regulated catalytic activity of nanozyme by the aptamers ensure the high sensitivity (a wide linear range: 0.1-1000 ng/mL; an ultra-low limit of detection: 0.082 ng/mL) and good selectivity of the colorimetric sensing, respectively. The smartphone-based platform exhibits high accuracy with the relative standard deviation within 3.67 % compared commercial enzyme-linked immunosorbent assay. Finally, on-site tracking of the AFB1 content in food waste during the composting process with or without the oxidant (potassium persulfate) has been carried out using the developed colorimetric sensor. It is concluded that reducing the AFB1 generation in the food waste is more meaningful than the compost treatment. This study offers a promising method for in situ analysis of trace AFB1 in food waste compost to ensure environmental and human health safety.

Synergistic effect between bacteriophages and nanozymes for hybrid dual recognition of pathogenic bacteria from water, food, and agricultural samples: promising new tools for sensitive and specific biosensing

Worldwide, pathogenic bacteria are among the most significant causes of infections. Indeed, delays in diagnosis and detection of these bacteria result in high morbidity and mortality rates and detection platforms must be developed to overcome these challenges. Biosensors, as high-potential analytical tools, can play an important role in the detection of pathogenic bacteria. The application of nanozymes as nanomaterial-based artificial enzymes in the structure of biosensors can overcome the limitations of common biological elements. Furthermore, the integration of bacteriophages, as novel bioreceptors, with nanozymes enabled a clear distinction between viable and dead bacteria. The application of bacteriophage-nanozyme as hybrid probes in biosensors can boost pathogenic bacteria detection. In this review, the effects of different nanozymes, including metal-based, metal oxide-based, and metal-organic framework (MOF)-based nanozymes, after integration with bacteriophages are discussed. Perspectives and challenges of a combination of these novel bioreceptors and nanomaterial-based artificial enzymes are presented for detecting various pathogenic bacteria.

Applications of DNA functionalized gold nanozymes in biosensing

In recent years, nanozymes have emerged as highly potential substitutes, surpassing the performance of natural enzymes. Among them, gold nanoparticles (AuNPs) and their metal hybrids have become a hot topic in nanozyme research due to their facile synthesis, easy surface modification, high stability, and excellent enzymatic activity. The integration of DNA with AuNPs, by precisely controlling the assembly, arrangement, and functionalization of nanoparticles, greatly facilitates the development of highly sensitive and selective biosensors. This review comprehensively elaborates on three core strategies for the combination of DNA with AuNPs, and deeply analyzes two widely applied enzyme activities in the field of sensing technology and the catalytic principles behind them. On this basis, we systematically summarize various methods for regulating the activity of gold nanozymes by DNA. Following that, we comprehensively review the latest research trends of DNA-Au nanozymes in the field of biosensing, with a particular focus on several crucial application areas such as food safety, environmental monitoring, and disease diagnosis. In the conclusion of the article, we not only discuss the main challenges faced in current research but also look forward to potential future research directions.

Exploring Nucleic Acid Nanozymes: A New Frontier in Biosensor Development

With the growing interest in nucleic acids and nanozymes, nucleic acid nanozymes (NANs) have emerged as a promising alternative to traditional enzyme catalysts, combining the advantages of nucleic acids and nanomaterials, and are widely applied in the field of biosensing. This review provides a comprehensive overview of recent studies on NAN-based biosensors. It classifies NANs based on six distinct enzymatic activities: peroxidase-like, oxidase-like, catalase-like, superoxide dismutase-like, laccase-like, and glucose oxidase-like. This review emphasizes how the catalytic activity of nanozymes is significantly influenced by the properties of nucleic acids and explores the regulatory mechanisms governing the catalytic activity of NANs. Additionally, it systematically reviews important research progress on NANs in colorimetric, fluorescent, electrochemical, SERS, and chemiluminescent sensors, offering insights into the development of the NAN field and biosensor applications.

Construction of electrochemical immunosensors based on Au@MXene and Au@CuS nanocomposites for sensitive detection of carcinoembryonic antigen

Cancer is currently one of the major causes of human mortality and has received widespread attention. In this paper, Au@CuS composite nanomaterial as a sandwich immunosensor tag for carcinoembryonic antigen (CEA) detection strategy was studied. Herein, Au@CuS composite nanomaterials were obtained by Au nanoparticles modified with CuS, which were combined with secondary antibody (Ab2) to construct an immunosensor that interacted with H2O2 to produce a current response. The anti-CEA primary antibody (Ab1) was fixed on the glassy carbon electrode (GCE) modified by Au@MXene. The completed electrochemical immunosensor was constructed with rapid detection and high sensitivity for CEA. Under optimal conditions, the linearity ranged from 0.01 pg/mL to 0.5 ng/mL, and the detection limit was 3.8 fg/mL. This tactic possesses good reproducibility, constancy and selectivity. At the same time, this strategy has latent practical value for the test of other tumor markers.

Construction of a novel Au@Os mediated TMB-H2O2 platform with dual-signal output for rapid and accurate detection of ziram in food

The 3,3',5,5'-tetramethylbenzidine-H2O2 (TMB-H2O2) platform has gained widespread use for rapid detection of various analytes in foods. However, the existing TMB-H2O2 platforms suffer from limited accuracy, as their signal output is confined to the visible region, which is prone to interference from various food colorants in real samples. To address this challenge, a novel Au@Os-mediated TMB-H2O2 platform is developed for both rapid and accurate detection of analytes in foods. The prepared Au@Os NPs exhibit remarkable peroxidase-like activity, making the platform display dual absorption peaks in visible and near-infrared (NIR) regions, respectively. This Au@Os-mediated TMB-H2O2 platform exhibited three linear ranges across different concentrations of ziram from 1-100, 150-600, and 800-2000 nM with limit of detection (LOD) 7.9 nM and limit of quantification (LOQ) 24.15 nM respectively. Further, the Au@Os-mediated TMB-H2O2 platform was also used for rapid and accurate detection of ziram in real food samples like apple, tomato, and black tea.

Investigation for Regulation of a DNA-Programmed Bimetallic Nanozyme and Its Biosensing Applications

The DNA-mediated growth strategy of bimetallic nanozymes is considered as an effective approach to regulate their peroxidase activity via tuning the morphology and nanostructure. Albeit important, its biosensing application in rational methods' design and performance improvement is limited due to the deficiency of a systematic understanding of the interactions between DNA and nanomaterials used. Herein, four homo-oligonucleotides as capping ligands were employed to functionalize the bimetallic nanozymes, where Pt nanoparticles (PtNPs) were in situ synthesized onto DNA-bound Au nanorods (AuNRs), and the effects of DNA with different lengths on the state of bimetallic nanozymes were investigated in detail. It was found that the aggregation of AuNRs obviously depended on the variety and number of DNA oligonucleotides with the absorbance ratio at 810 and 525 nm (A810/A525), ranking as follows: AuNRs/A10/PtNPs > AuNRs/G10/PtNPs > AuNRs/C10/PtNPs ≫ AuNRs/T10/PtNPs, which is consistent with the value of Km for TMB, indicating that the dispersal/aggregation of the AuNRs is closely related to the deposition and growth of PtNPs, thereby significantly influencing their peroxidase activity. According to our discoveries, a novel colorimetric array platform was fabricated using the above four types of DNA-encoded Pt-Au bimetallic nanozymes as sensing elements for sensitively discriminating the five biological thiols (l-cys, GSH, Hcy, DTT, and Cys-Gly) and identifying the normal cells/tumor cells, respectively. Our work provides a new insight into DNA-programmed bimetallic nanozyme regulation and broadens its sensing applications.

An intelligent ratiometric fluorescent assay based on MOF nanozyme-mediated tandem catalysis that guided by contrary logic circuit for highly sensitive sarcosine detection and smartphone-based portable sensing application

As the well-known test-indicator for early prostate cancer (PCa), sarcosine (SA) is closely related to the differential pathological process, which makes its accurate determination increasingly significant. Herein, we for the first time expanded the peroxidase (POD)-like property of facile-synthesized Zn-TCPP(Fe) MOF to fluorescent substrates and exploited it to ratiometric fluorescent (RF) sensing. By harnessing the effective catalytic oxidation of MOF nanozyme toward two fluorescent substrates (Scopoletin, SC; Amplex Red, AR) with contrary changes, and target-responsive (SA + SOx)/MOF/(SC + AR) tandem catalytic reaction, we constructed the first MOF nanozyme-based RF sensor for the quantitative determination of SA. Superior to previous works, the operation of this RF sensor is under the guidance of AND-(AND^NAND) contrary logic circuit. The dual-channel binary output changes (from 1/0 to 0/1) not only enable the intelligent logical recognition of SA, bringing strengthened reliability and accuracy, but also manifest the proof-of-concept discrimination of PCa individuals and healthy ones. Through recording the fluorescence alterations of SC (F465) and AR (F585), two segments of linear relationships between ratiometric values (F585/F465) and varied contents of SA are realized successfully. The LOD for SA could reach to as low as 39.98 nM, which outperforms all nanozyme-originated SA sensors reported till now. Moreover, this sensor also demonstrates high selectivity and satisfactory performance in human serum samples. Furthermore, the portable sensing of SA is realized under the assistance of smartphone-based RGB analysis, demonstrating the potential of point-of-care diagnostics of PCa in the future.

Bimetallic nanozyme-bioenzyme hybrid material-mediated ultrasensitive and automatic immunoassay for the detection of aflatoxin B1 in food

Aflatoxin B1 (AFB1) is one of the most prevalent and dangerous biotoxin in crops and feedstuff, which poses a great threat to human health and also cause significant financial losses. Therefore, there is an urgent need to develop an effective method for AFB1 detection. In this work, we developed an automatic reaction equipment and nanozyme-enhanced immunosorbent assay (Auto-NEISA) for sensitive and accurate detection of AFB1 by combining the highly effective signal probes with a self-designed automated immunoreactive equipment. Wherein, polystyrene (PS) nanoparticles were used as signal carriers for loading a massive in situ-synthesized platinum and palladium bimetallic nanozyme, which could enrich horseradish peroxidase-labeled goat anti-mouse antibody (HRP-Ab2) on the nanozyme surface to form a bimetallic nanozyme-bioenzyme hybrid material for multiple signal amplification. The entire reaction could be automatically completed by the self-developed immunoreactive equipment. The Auto-NEISA method realized the sensitive detection of AFB1 with a wide linear detection range of 10-104 pg/mL, at a low limit of detection (LOD) of 5.52 pg/mL. The LOD was 65-fold lower than that of the enzyme-linked immunosorbent assay (ELISA). Additionally, Auto-NEISA was successfully applied to detect AFB1 in real food samples, demonstrating that it has considerable potential for detecting food contaminants with high accuracy and efficiency.

A comprehensive exploration of the latest innovations for advancements in enhancing selectivity of nanozymes for theranostic nanoplatforms

Nanozymes have captured significant attention as a versatile and promising alternative to natural enzymes in catalytic applications, with wide-ranging implications for both diagnosis and therapy. However, the limited selectivity exhibited by many nanozymes presents challenges to their efficacy in diagnosis and raises concerns regarding their impact on the progression of disease treatments. In this article, we explore the latest innovations aimed at enhancing the selectivity of nanozymes, thereby expanding their applications in theranostic nanoplatforms. We place paramount importance on the critical development of highly selective nanozymes and present innovative strategies that have yielded remarkable outcomes in augmenting selectivities. The strategies encompass enhancements in analyte selectivity by incorporating recognition units, refining activity selectivity through the meticulous control of structural and elemental composition, integrating synergistic materials, fabricating selective nanomaterials, and comprehensively fine-tuning selectivity via approaches such as surface modification, cascade nanozyme systems, and manipulation of external stimuli. Additionally, we propose optimized approaches to propel the further advancement of these tailored nanozymes while considering the limitations associated with existing techniques. Our ultimate objective is to present a comprehensive solution that effectively addresses the limitations attributed to non-selective nanozymes, thus unlocking the full potential of these catalytic systems in the realm of theranostics.

Bacteria-derived topologies of Cu2O nanozymes exert a variable antibacterial effect

The ability of bacteria to facilitate fabrication of nanomaterials has been adapted towards bacterial sensing applications. In this work, we fabricate spherical, cubic and truncated octahedron topologies of Cu2O nanoparticles via E. coli-facilitated redox reaction in an electrochemical setup. The Cu2O nanoparticles exhibit cytochrome c oxidase-like activity with the spherical topology displaying higher catalytic rate compared to the other geometries. The topology-dependent catalytic behavior of Cu2O nanoparticles has not been reported previously. The Cu2O nanozymes also display E. coli killing activity in a topology-correlated manner. The E. coli mediated redox reaction in an electrochemical setup is being reported for the first time for synthesis of different topologies of Cu2O which also exert a variable antibacterial effect.