Dual-amplification system based on CRISPR-Cas12a and horseradish peroxidase-tethered magnetic microspheres for colorimetric detection of microcystin-LR.

A novel dual-amplification system based on CRISPR-Cas12a and horseradish peroxidase (HRP) was developed for colorimetric determination of MC-LR. This dual-amplification was accomplished by combining the nuclease activity of CRISPR-Cas12a with the redox activity of HRP. HRP linked to magnetic beads through an ssDNA (MB-ssDNA-HRP) was used to induce a color change of the 3,3',5,5'-tetramethylbenzidine (TMB)-H2O2 chromogenic substrate solution. Specific binding of MC-LR with its aptamer initiated the release of a complementary DNA (cDNA), which was designed to activate the trans-cleavage activity of CRISPR-Cas12a. Upon activation, Cas12a cut the ssDNA linker in MB-ssDNA-HRP, causing a reduction of HRP on the magnetic beads. Consequently, the UV-Vis absorbance of the HRP-catalyzed reaction was decreased. The dual-signal amplification facilitated by CRISPR-Cas12a and HRP enabled the colorimetric detection of MC-LR in the range 0.01 to 50 ng·mL-1 with a limit of detection (LOD) of 4.53 pg·mL-1. The practicability of the developed colorimetric method was demonstrated by detecting different levels of MC-LR in spiked real water samples. The recoveries ranged from 86.2 to 118.5% and the relative standard deviation (RSD) was 8.4 to 17.6%. This work provides new inspiration for the construction of effective signal amplification platforms and demonstrates a simple and user-friendly colorimetric method for determination of trace MC-LR.

Multimetallic nanoparticles decorated metal-organic framework for boosting peroxidase-like catalytic activity and its application in point-of-care testing.

Metal-organic frameworks (MOFs) are a sort of promising peroxidase-like nanozyme but face the challenge that the inorganic nodes in most of the MOF structures are generally blocked by the organic linkers. Further enhancement or activation of their peroxidase-like activity plays an important role in developing MOF-based nanozymes. Herein, a multimetallic nanoparticle (NP) decorated-MOF, Cu/Au/Pt NP decorated-Cu-TCPP(Fe) nanozyme (CuAuPt/Cu-TCPP(Fe)) was synthesized in situ and served as a peroxidase-like nanozyme. The peroxidase-like activity of this stable CuAuPt/Cu-TCPP(Fe) nanozyme was enhanced due to the decreased potential barriers for *OH generation in the catalytic process. Owing to the remarkable peroxidase-like activity, a CuAuPt/Cu-TCPP(Fe)-based colorimetric assay was established for the sensitive determination of H2O2 and glucose with the limit of detection (LOD) of 9.3 µM and 4.0 µM, respectively. In addition, a visual point-of-care testing (POCT) device was developed by integrating the CuAuPt/Cu-TCPP(Fe)-based test strips with a smartphone and was employed for a portable test of 20 clinical serum glucose samples. The results determined by this method agree well with the values deduced by clinical automatic biochemical analysis. This work not only represents an inspiration for the usage of MNP/MOF composite as a novel nanozyme for POCT diagnosis, but also provides a deeper insight and understanding into the enhanced enzyme-mimic effect of MNP-hybrid MOF composites, which in turn will guide the engineering of MOF-based functional nanomaterials. Graphical Abstract.

Aptamer-AuNP-conjugated carboxymethyl chitosan-functionalized graphene oxide for colorimetric identification of Salmonella typhimurium.

A novel aptamer-AuNP-conjugated carboxymethyl chitosan-functionalized graphene oxide (CMC/GO@Apt-Au NP) probe was for the first time developed for the determination of Salmonella typhimurium (S. typhimurium). Owing to the conformational change of the aptamers in the presence of S. typhimurium, the Au NPs, which were pre-adsorbed on the aptamers through van der Waals forces, were released into the solution phase and induced the color change of the solution. As a result, S. typhimurium ranging from 102 to 107 CFU/mL was successfully identified using the designed assay with a limit of detection (LOD) of 10 CFU/mL. This low detection level allowed the sensitive recognition of S. typhimurium in milk samples within 40 min without sample pretreatment, a conclusion that agreed well with the traditional plate counting method. The developed method not only provides a rapid way for the determination of S. typhimurium with simplicity and sensitivity but also shows potential universality in the quantification of other pathogenic microorganisms.

A novel CRISPR/Cas14a system integrated with 2D porphyrin metal-organic framework for microcystin-LR determination through a homogeneous competitive reaction.

Selective and sensitive detection of microcystin-LR (MC-LR) is of vital importance because of its high toxicity and broad distribution. Herein, a novel and versatile fluorescence sensor (Cas14-pMOFs fluorescence sensor) was developed by combining the CRISPR/Cas14a system with a 2D porphyrin metal-organic framework nanosheets (2D-pMOFs) for MC-LR determination. The designed CRISPR/Cas14a system was activated by the unbound complementary DNA (cDNA), which was positively correlated with MC-LR concentration. Furthermore, the activated Cas14a protein was utilized to indiscriminately cleave the FAM-labeled single-stranded DNA (ssDNA-FAM), which was pre-absorbed on Cu-TCPP(Fe) nanosheets. Because of the desorption of the cleaved ssDNA-FAM, the pre-quenched fluorescence signal was recovered. Owing to the excellent performance in quantifying cDNA using this Cas14-pMOFs fluorescence sensor with a limit of detection (LOD) of 0.12 nM, this Cas14-pMOFs fluorescence sensor was able to detect MC-LR in a range from 50 pg/mL to 1 µg/mL with the LOD of 19 pg/mL. This work not only provided a new insight for the exploration of fluorescence sensors based on 2D-pMOFs coupled with CRISPR/Cas14a, but also, demonstrated its universality in both nucleic acid and non-nucleic acid targets determination.

Recent advances in performance improvement of Metal-organic Frameworks to remove antibiotics: Mechanism and evaluation.

Antibiotic pollution is a serious global problem, which may threaten the health of human and ecosystem. Thereinto, water pollution is the most common way. Thus, it is necessary to develop effective methods to remove antibiotics from the natural aqueous environments. Metal-organic Frameworks (MOFs) - based adsorption and photocatalysis strategies have been demonstrated to be efficient, environmental and promising methods to solve antibiotic pollution and repair the environment. In this review, several strategies to improve the properties of MOFs for removal were summarized and discussed. And the removal mechanisms were also discussed. Besides, new and more reliable evaluation methods of MOFs to remove antibiotics were presented, including preferential adsorption (qp), quantum yields (QY), space time yields (SY) and figure of merit (FOM). This paper provides alternative perspectives for researchers to improve the properties of MOFs and raise analytic efficiency of antibiotic removal.

Recent advances in immunoassay technologies for the detection of human coronavirus infections.

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the seventh coronavirus (CoV) that has spread in humans and has become a global pandemic since late 2019. Efficient and accurate laboratory diagnostic methods are one of the crucial means to control the development of the current pandemic and to prevent potential future outbreaks. Although real-time reverse transcription-polymerase chain reaction (rRT-PCR) is the preferred laboratory method recommended by the World Health Organization (WHO) for diagnosing and screening SARS-CoV-2 infection, the versatile immunoassays still play an important role for pandemic control. They can be used not only as supplemental tools to identify cases missed by rRT-PCR, but also for first-line screening tests in areas with limited medical resources. Moreover, they are also indispensable tools for retrospective epidemiological surveys and the evaluation of the effectiveness of vaccination. In this review, we summarize the mainstream immunoassay methods for human coronaviruses (HCoVs) and address their benefits, limitations, and applications. Then, technical strategies based on bioinformatics and advanced biosensors were proposed to improve the performance of these methods. Finally, future suggestions and possibilities that can lead to higher sensitivity and specificity are provided for further research.

Cell density-dependent regulation of microcystin synthetase genes (mcy) expression and microcystin-LR production in Microcystis aeruginosa that mimics quorum sensing.

As the secondary metabolites of cyanobacterial harmful algal blooms (Cyano-HABs), microcystins (MCs) were generated under various environmental and cellular conditions. The understanding of the causes of MCs generation is of great interest in the field of water treatment and environmental science. In this work, we studied how Microcystis aeruginosa (FACHB-905) cell densities affect the MCs synthetase genes (mcy) expression, microcystin-LR (MC-LR) and quorum sensing molecules (Acyl-homoserine lactones (AHLs)) production. An electrochemical sensor was developed here for sensitive and quantitative detection of MC-LR that cultured at different cell densities. The results showed that mcy expression and MC-LR concentration started to increase when the cell density reached ca. 22 × 106 cells/mL, and was significantly increased with increasing cell densities. Moreover, the up-regulation of AHLs with increasing cell densities revealed that MC-LR is quorum sensing-mediated. Our results undoubtedly confirmed that MC-LR was produced in a cell density-dependent way that mimics quorum sensing, and the minimum cell density (ca. 22 × 106 cells/mL) that was required to produce MC-LR was provided and offered a reference standard for the prevention and control of MCs pollution in the actual water environment.

A regenerable ion-imprinted magnetic biocomposite for selective adsorption and detection of Pb2+ in aqueous solution.

A regenerable ion-imprinted magnetic biocomposite (IIMB) was successfully synthesized for simultaneous removal of Pb2+ using Serratia marcescens and carboxymethyl chitosan (CMC) as functional carriers, Pb2+ was utilized as the imprinted ion, while Fe3O4 served as the magnetic component. The structure and properties of IIMB were characterized by various techniques. The adsorption kinetics, isotherms and thermodynamics were applied to interpret the Pb2+ adsorption process on IIMB. The results showed the IIMB possessed prominent uptake ability toward Pb2+. The pseudo-second-order kinetic (R2 = 0.9989) and Langmuir models (R2 = 0.9555) fitted the data well. Adsorption thermodynamics revealed that the adsorption was a spontaneous endothermic reaction. The possible adsorption mechanisms involved physical adsorption, electrostatic attraction and complexing. Moreover, because Pb2+ can be specifically and strongly adsorbed on IIMB, a simple method for detection of Pb2+ was established by coupling IIMB with flame atomic absorption spectrometry (IIMB-FAAS). The developed IIMB-FAAS assay can sensitively detect Pb2+ with a linear range from 5.0 to 500.0 µg/L. The detection limit (LOD) of 0.95 µg/L as well as a quantification limit (LOQ) of 3.20 µg/L were obtained. This work proved that the IIMB could selective and efficient adsorb Pb2+, which provided some insights into wastewater treatment, water quality inspection and environmental remediation.

A Mini-Review on Detection Methods of Microcystins.

Cyanobacterial harmful algal blooms (CyanoHABs) produce microcystins (MCs) which are associated with animal and human hepatotoxicity. Over 270 variants of MC exist. MCs have been continually studied due of their toxic consequences. Monitoring water quality to assess the presence of MCs is of utmost importance although it is often difficult because CyanoHABs may generate multiple MC variants, and their low concentration in water. To effectively manage and control these toxins and prevent their health risks, sensitive, fast, and reliable methods capable of detecting MCs are required. This paper aims to review the three main analytical methods used to detect MCs ranging from biological (mouse bioassay), biochemical (protein phosphatase inhibition assay and enzyme linked immunosorbent assay), and chemical (high performance liquid chromatography, liquid chromatography-mass spectrometry, high performance capillary electrophoresis, and gas chromatography), as well as the newly emerging biosensor methods. In addition, the current state of these methods regarding their novel development and usage, as well as merits and limitations are presented. Finally, this paper also provides recommendations and future research directions towards method application and improvement.

Cu/Au/Pt trimetallic nanoparticles coated with DNA hydrogel as target-responsive and signal-amplification material for sensitive detection of microcystin-LR.

Sensitive and reliable analytical methods for monitoring of microcystin-LR (MC-LR) are urgently necessary due to its great harm to human health and aquatic organisms. In this work, a novel Cu/Au/Pt trimetallic nanoparticles (Cu/Au/Pt TNs)-encapsulated DNA hydrogel was prepared for colorimetric detection of MC-LR. The Cu/Au/Pt TNs were captured and released with precise control by the target-responsive 3D DNA hydrogels, which combined dual advantages of the target responsive DNA hydrogel and Cu/Au/Pt TNs of enhanced peroxidase-like activity. The DNA hydrogel network was constructed by hybridizing MC-LR aptamer with two complementary DNA strands on linear polyacrylamide chains. As long as MC-LR presented, the aptamer competitively binds with the MC-LR, causing the hydrogel to dissolve and release the preloaded Cu/Au/Pt TNs which could catalyze the reaction between H2O2 and TMB to produce color changes. In view of this sensitive strategy, this Cu/Au/Pt TNs-encapsulated DNA hydrogel-based colorimetric biosensor can achieve quantitative determination of MC-LR. The results showed that as-proposed colorimetric biosensor could sensitively detect MC-LR with a linear range of 4.0-10000 ng L-1 and a detection limit of 3.0 ng L-1. This work proved that the sensor had great potential to be applied in MC-LR detection and also provided the opportunity to develop colorimetric biosensor for other targets using this target-responsive and signal-amplification strategy.

The research of aptamer biosensor technologies for detection of microorganism.

The activities and transmissions of microorganisms are closely related to human, and all kinds of diseases caused by pathogenic microorganisms have attracted attention in the world and brought many challenges to human health and public health. The traditional microbial detection technologies have characteristics of longer detection cycle and complicated processes, therefore, which can no longer meet the detection requirements in the field of public health. At present, it is the focus to develop and design a novel, rapid, and simple microbial detection method in the field of public health. Herein, this article summarized the development of aptamer biosensor technologies for detection of microorganism in the aspect of bacteria, viruses, and toxins in detail, including optical aptamer sensors such as fluorometry and colorimetry, electrochemical aptamer sensors, and other technologies combined with aptamer. KEY POINTS: • Aptamer biosensor is a good platform for microbial detection. • Aptamer biosensors include optical sensors and electrochemical sensors. • Aptamer sensors have been widely used in the detection of bacteria, viruses, and other microorganisms.

Photocatalytic degradation of microcystin-LR by modified TiO2 photocatalysis: A review.

Microcystin-LR (MC-LR), the most toxic and commonly encountered cyanotoxin, is produced by harmful cyanobacterial blooms and potentially threatens human and ecosystems health. Titanium dioxide (TiO2) photocatalysis is attracting growing attention and has been considered as an efficient, environmentally friendly and promising solution to eliminate MC-LR in the aquatic ecosystems. Over recent decades, scientific efforts have been directed towards the understanding of fundamentals, modification strategies, and application potentials of TiO2 photocatalysis in degrading MC-LR. In this article, recent reports have been reviewed and progress has been summarized in the development of heterogeneous TiO2-based photocatalysts for MC-LR photodegradation under visible, UV, or solar light. The proposed photocatalytic principles of TiO2 and destruction of MC-LR have been thoroughly discussed. Specifically, some main modification methods for improving the drawbacks and performance of TiO2 nanoparticle were highlighted, including element doping, semiconductor coupling, immobilization, floatability amelioration and magnetic separation. Moreover, the performance evaluation metrics quantum yield (QY) and figure of merit (FOM) were used to compare different photocatalysts in MC-LR degradation. The best performance was seen in N-TiO2 with QY and FOM values of 2.20E-07 molecules/photon and 1.00E-11 mol·L/(g·J·h). N-TiO2 or N-TiO2-based materials may be excellent options for photocatalyst design in terms of MC-LR degradation. Finally, a summary of the remaining challenges and perspectives on new tendencies in this exciting frontier and still an emerging area of research were addressed accordingly. Overall, the present review will offer a deep insight for understanding the photodegradation of MC-LR with modified TiO2 to further inspire researchers that work in associated fields.

Development of a highly sensitive detection method for TTX based on a magnetic bead-aptamer competition system under triple cycle amplification.

We have established an assay that relies on aptamer and isothermal amplification for the tetrodotoxin (TTX)detection. The method uses triple cycle amplification (strand displacement amplification combined with catalytic hairpin assembly) and fluorescent reporter as an output signal. Free TTX and cDNA compete for binding to aptamer-modified magnetic beads. The cDNA collected by magnetic separation then used as a primer to trigger triple cycle amplification to obtain more ssDNA. The ssDNA combined with the reporter probe, and the original quenched fluorescence can be recovered. In addition, a linear relationship between fluorescence spectrum and different target concentrations is revealed. This method allows TTX to be detected by fluorometry with a detection limit as low as 0.265 pg mL-1. It was applied to clams and shellfish, achieving recoveries ranging from 100% to 107.33% and 99.67%-116.67%, respectively. The results were consistent with the commercial TTX ELISA kit. This assay is highly sensitive, reliable and has a good specificity. Therefore, it provides a better alternative to the standard method for quantitative detection of TTX.

Biodegradation of microcystin-RR and nutrient pollutants using Sphingopyxis sp. YF1 immobilized activated carbon fibers-sodium alginate.

A novel biological material named activated carbon fibers-sodium alginate@Sphingopyxis sp. YF1 (ACF-SA@YF1) was synthesized for microcystin-RR (MC-RR) and nutrient pollutant degradation in eutrophic water. The synthesized biomaterial was characterized by scanning electron microscopy (SEM). Box-Behnken design and response surface methodology (RSM) were utilized for the optimization of conditions during the MC-RR degradation. The degradation of MC-RR and nutrient pollutants was dynamically detected. The results revealed that the optimal conditions were temperature 32.51 °C, pH 6.860, and inoculum 14.97%. The removal efficiency of MC-RR, nitrogen, phosphorus, and chemical oxygen demand were 0.76 µg/mL/h, 32.45%, 94.57%, and 64.07%, respectively. In addition, ACF-SA@YF1 also performed satisfactory cyclic stability, while the MC-RR removal efficiency was 70.38% after seven cycles and 78.54% of initial activity after 20 days of storage. Therefore, it is reasonable to believe that ACF-SA@YF1 is an effective material which has a great prospect in removing MC-RR and nutrients from freshwater ecosystems.

Optimization on preparation of Fe3O4/chitosan as potential matrix material for the removal of microcystin-LR and its evaluation of adsorption properties.

Adsorbent Fe3O4/chitosan was successfully synthesized for the removal of microcystin-LR and characterized by Scanning electron microscope, Fourier transform infra-red, thermogravimetric analysis and vibrating sample magnetometer. The effects of reaction conditions, including pH, temperature and ratio of Fe3O4 to chitosan on microcystin-LR adsorption capacity were investigated by the Box-Behnken response surface methodology design, and the optimal adsorption conditions were determined. The adsorption properties of microcystin-LR were examined by adsorption kinetics, isothermal and thermodynamics experiments. The results demonstrated that Fe3O4/chitosan was successfully prepared and the maximum adsorption capacity of microcystin-LR was under optimum conditions in which pH value was 5.53, temperature was 40 °C and the ratio of Fe3O4 to chitosan was 1:1.39. The data revealed that kinetics was fitted well with the pseudo-second-order model, Langmuir isotherm model was more appropriate for describing than the Freundlich isotherm model and the adsorption of microcystin-LR was a spontaneous process. The material maintained good adsorption capacity after five cycles. The results suggested that Fe3O4/chitosan was an efficient and low-cost adsorbent for removing microcystin-LR from polluted water.

High-efficient and sustainable biodegradation of microcystin-LR using Sphingopyxis sp. YF1 immobilized Fe3O4@chitosan.

The microcystin-LR (MC-LR) produced due to harmful cyanobacterial blooms have brought great harm to human and aquatic organisms, attracting a wide public health attention. To deal with MC-LR contamination, we synthesized a novel bio-functionalized composite for the high-efficient and sustainable biodegradation of microcystin-LR by covalent immobilizing Sphingopyxis sp. YF1 onto chitosan-grafted Fe3O4 magnetic particles (Fe3O4@CTS). The Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM) were utilized to characterize the structural properties of Fe3O4@CTS/Sphingopyxis sp. YF1. The immobilization conditions were optimized. And the MC-LR-degrading capabilities of Fe3O4@CTS/Sphingopyxis sp. YF1 were assessed under various conditions. The results showed that the optimal immobilization conditions containing 1.0 % (v/v) glutaraldehyde, immobilization for 4 h at 30 ℃. The Fe3O4@CTS/Sphingopyxis sp. YF1 showed an attractive degradation performance which possesed a wide torlerance to pH (6.0-9.0) and temperature (25-35 ℃). More interesting is that the Fe3O4@CTS/Sphingopyxis sp. YF1 exhibited significantly increased MC-LR-degrading capabilities after recycling and reusing which degradation rate reached 1.50 µg/mL/h in the sixth cycle, and it was easily recycled by using a magnet (Ms 21.5 emug-1). Two intermediates (tetrapeptide and Adda) and three degradation related genes (mlrA, mlrB and mlrC) were obtained in this study and the pathway for the degradation was proposed. These results revealed that Fe3O4@CTS/Sphingopyxis sp. YF1 can be potentially used for treatment of MC-LR contaminated environment.

A composite prepared from carboxymethyl chitosan and aptamer-modified gold nanoparticles for the colorimetric determination of Salmonella typhimurium.

An aptamer-based assay is described for the determination of Salmonella typhimurium (S. typh). Carboxymethyl chitosan was loaded with amino-modified aptamer against S. typh, and then adsorbed on gold nanoparticles by electrostatic interaction to form a composite that acts as the molecular recognition element. In the presence of S. typh, it will be bound by the aptamer, and this changes the structure of the recognition element. On addition of salt solution, the gold nanoparticles agglomerate so that the color of the solution changes from red to blue. S. typh can be detected via measurement of the absorbance at 550 nm. Absorbance increases linearly with the logarithm of the S. typh concentration in the range from 100 to 109 cfu·mL-1. The limit of detection is 16 cfu·mL-1. The specificity and practicability of the assay were evaluated. The recoveries of S. typh from spiked milk samples are between 92.4 and 97.2%. The analytical results are basically consistent with those of a plate counting method. Graphical abstract Schematic representation of the colorimetric assay for Salmonella typhimuium (S. typh) using carboxymethyl chitosan (CMCS)-aptamer (Apt)-gold nanoparticles (AuNPs) composites.

Efficient removal of Pb(II) from aqueous solution by a novel ion imprinted magnetic biosorbent: Adsorption kinetics and mechanisms.

It is vital to understand the adsorption mechanisms and identify the adsorption kinetics when applying an adsorbent to remove heavy metals from aqueous solution. A Pb(II) imprinted magnetic biosorbent (Pb(II)-IMB) was developed for the removal of Pb2+ via lead ion imprinting technology and crosslinking reactions among chitosan (CTS), Serratia marcescens and Fe3O4. The effect of different parameters such as solution pH, adsorbent dosage, selectivity sorption and desorption were investigated on the absorption of lead ion by Pb(II)-IMB. The adsorbent was characterized by a Brunauer-Emmett Teller (BET) analysis, X-ray diffraction (XRD), vibrating sample magnetometry (VSM), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The adsorption kinetics, equilibrium and thermodynamics of Pb(II)-IMB for Pb(II) were studied. The results of the abovementioned analyses showed that the adsorption kinetic process fit well with the second-order equation. The adsorption isotherm process of Pb(II) on the Pb(II)-IMB was closely related to the Langmuir model. Thermodynamic studies suggested the spontaneous and endothermic nature of adsorption of Pb(II) by Pb(II)-IMB. The adsorption mechanism of Pb(II)-IMB was studied by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results indicated that the nitrogen in the amino group and the oxygen in the hydroxyl group of Pb(II)-IMB were coordination atoms.

One-pot synthesized Cu/Au/Pt trimetallic nanoparticles as a novel enzyme mimic for biosensing applications.

Multimetallic nanomaterials have aroused special attention owing to the unique characteristics of chemical, optical and enhanced enzyme mimetic capabilities resulting from the synergistic effect of different metal elements. In this work, we present a facile, gentle, fast and one-pot method for preparing Cu/Au/Pt trimetallic nanoparticles (TNPs), which possess intrinsic and enhanced peroxidase-like activity as well as excellent stability, sustainable catalytic activity, and robustness to harsh environments. Kinetic analysis indicated that Cu/Au/Pt TNPs exhibited strong affinities with H2O2 and 3,3,5,5-tetramethylbenzidine (TMB) as the substrates. To investigate the feasibility of Cu/Au/Pt TNPs-based strategy in biological analysis, H2O2 was chosen as a model analyte and a sensitive and specific detection for H2O2 was acquired with a detection limit of 17 nM. By coupling with glucose oxidase (GOD), this assay could also achieve a sensitive and selective detection of glucose with a detection limit of 33 µM, indicating the versatility of the method. In view of the potential combination with diverse enzyme-related reactions, the Cu/Au/Pt TNPs-based strategy is promising as a universal platform for biosensors.