Emerging Nanomaterials as Versatile Nanozymes: A New Dimension in Biomedical Research

The enzyme-mimicking nature of versatile nanomaterials proposes a new class of materials categorized as nano-enzymes, ornanozymes. They are artificial enzymes fabricated by functionalizing nanomaterials to generate active sites that can mimic enzyme-like functions. Materials extend from metals and oxides to inorganic nanoparticles possessing intrinsic enzyme-like properties. High cost, low stability, difficulty in separation, reusability, and storage issues of natural enzymes can be well addressed by nanozymes. Since 2007, more than 100 nanozymes have been reported that mimic enzymes like peroxidase, oxidase, catalase, protease, nuclease, hydrolase, superoxide dismutase, etc. In addition, several nanozymes can also exhibit multi-enzyme properties. Vast applications have been reported by exploiting the chemical, optical, and physiochemical properties offered by nanozymes. This review focuses on the reported nanozymes fabricated from a variety of materials along with their enzyme-mimicking activity involving tuning of materials such as metal nanoparticles (NPs), metal-oxide NPs, metal-organic framework (MOF), covalent organic framework (COF), and carbon-based NPs. Furthermore, diverse applications of nanozymes in biomedical research are discussed in detail.

Ratiometric fluorometric assay triggered by alkaline phosphatase: Proof-of-concept toward a split-type biosensing strategy for DNA detection

Herein, a sensitive ratiometric and split-type fluorescent sensing platform has been constructed for DNA detection based on one signal precursor and two fluorescent signal indicators. In this assay, o-phenylenediamine (OPD) was selected as the signal precursor. On one hand, Cu2+ can oxidize OPD to produce 2, 3-diaminophenazine (DAP), which with an emission peak at 555 nm. On the other hand, ascorbic acid (AA) could react with Cu2+ to generate dehydroascorbic acid (DHAA), which could further react with OPD to form 3-(1, 2-dihydroxy ethyl)furo[3, 4-b]quinoxalin-1 (3H)-on (DFQ) with a strong emission peak at 420 nm. As a result, the formation of DAP was inhibited, and leading to the decrease of fluorescence intensity at 555 nm. Alkaline phosphatase (ALP) could catalyze the substrate l-ascorbic acid-2-phosphate (AA2P) to produce AA in situ. Inspired by the successful use of ALP as a biocatalytic marker in bioassay, a split-type ratiometric fluorescent assay has been designed for DNA detection by using H1N1 DNA as the target model. It was realized for ratiometric fluorescent determination of H1N1 in a linear ranging from 50 pM to 1.5 nM with a limit of detection of 10 pM. The novel strategy could reduce the mutual interferences between the biomolecular recognition system and the fluorescence signal conversion system, which improving the accuracy of detection and effectively reducing the background signal. Furthermore, the strategy provided a promising platform for biomarkers detection in the fields of ratiometric fluorescent biosensors and bioanalysis.

Biomimetic and bioorthogonal nanozymes for biomedical applications

Nanozymes mimic the function of enzymes, which drive essential intracellular chemical reactions that govern biological processes. They efficiently generate or degrade specific biomolecules that can initiate or inhibit biological processes, regulating cellular behaviors. Two approaches for utilizing nanozymes in intracellular chemistry have been reported. Biomimetic catalysis replicates the identical reactions of natural enzymes, and bioorthogonal catalysis enables chemistries inaccessible in cells. Various nanozymes based on nanomaterials and catalytic metals are employed to attain intended specific catalysis in cells either to mimic the enzymatic mechanism and kinetics or expand inaccessible chemistries. Each nanozyme approach has its own intrinsic advantages and limitations, making them complementary for diverse and specific applications. This review summarizes the strategies for intracellular catalysis and applications of biomimetic and bioorthogonal nanozymes, including a discussion of their limitations and future research directions.

Post-Assay Chemical Enhancement for Highly Sensitive Lateral Flow Immunoassays: A Critical Review

Lateral flow immunoassay (LFIA) has found a broad application for testing in point-of-care (POC) settings. LFIA is performed using test strips-fully integrated multimembrane assemblies containing all reagents for assay performance. Migration of liquid sample along the test strip initiates the formation of labeled immunocomplexes, which are detected visually or instrumentally. The tradeoff of LFIA's rapidity and user-friendliness is its relatively low sensitivity (high limit of detection), which restricts its applicability for detecting low-abundant targets. An increase in LFIA's sensitivity has attracted many efforts and is often considered one of the primary directions in developing immunochemical POC assays. Post-assay enhancements based on chemical reactions facilitate high sensitivity. In this critical review, we explain the performance of post-assay chemical enhancements, discuss their advantages, limitations, compared limit of detection (LOD) improvements, and required time for the enhancement procedures. We raise concerns about the performance of enhanced LFIA and discuss the bottlenecks in the existing experiments. Finally, we suggest the experimental workflow for step-by-step development and validation of enhanced LFIA. This review summarizes the state-of-art of LFIA with chemical enhancement, offers ways to overcome existing limitations, and discusses future outlooks for highly sensitive testing in POC conditions.

Development of nanozyme based sensors as diagnostic tools in clinic applications: a review

Since 1970, many artificial enzymes that imitate the activity and structure of natural enzymes have been discovered. Nanozymes are a group of nanomaterials with enzyme-mimetic properties capable of catalyzing natural enzyme processes. Nanozymes have attracted great interest in biomedicine due to their excellent stability, rapid reactivity, and affordable cost. The enzyme-mimetic activities of nanozymes may be modulated by numerous parameters, including the oxidative state of metal ions, pH, hydrogen peroxide (H2O2) level, and glutathione (GSH) concentration, indicating the tremendous potential for biological applications. This article delivers a comprehensive overview of the advances in the knowledge of nanozymes and the creation of unique and multifunctional nanozymes, and their biological applications. In addition, a future perspective of employing the as-designed nanozymes in biomedical and diagnostic applications is provided, and we also discuss the barriers and constraints for their further therapeutic use.

Amalgamation of DNAzymes and Nanozymes in a Coronazyme

Artificial enzymes such as nanozymes and DNAzymes are economical and stable alternatives to natural enzymes. By coating Au nanoparticles (AuNPs) with a DNA corona (AuNP@DNA), we amalgamated nanozymes and DNAzymes into a new artificial enzyme with catalytic efficiency 5 times higher than AuNP nanozymes, 10 times higher than other nanozymes, and significantly greater than most of the DNAzymes on the same oxidation reaction. The AuNP@DNA demonstrates excellent specificity as its reactivity on a reduction reaction does not change with respect to pristine AuNP. Single-molecule fluorescence and force spectroscopies and density functional theory (DFT) simulations indicate a long-range oxidation reaction initiated by radical production on the AuNP surface, followed by radical transport to the DNA corona, where the binding and turnover of substrates take place. The AuNP@DNA is named coronazyme because of its natural enzyme mimicking capability through the well-orchestrated structures and synergetic functions. By incorporating different nanocores and corona materials beyond DNAs, we anticipate that the coronazymes represent generic enzyme mimics to carry out versatile reactions in harsh environments.

Cascaded Nanozyme System with High Reaction Selectivity by Substrate Screening and Channeling in a Microfluidic Device

Surpassing natural enzymes in cost, stability and mass production, nanozymes have attracted wide attention in fields from disease diagnosis to tumor therapy. However, nanozymes intrinsically have low reaction selectivity, which significantly restricts their applications. A general method is reported to address this challenge by following a biomimetic operation principle of substrates channeling and screening. Two oxidase- and peroxidase-like nanozymes (i.e., emerging N-doped carbon nanocages and Prussian blue nanoparticles), were cascaded as a proof of concept to improve the reaction selectivity in transforming the substrate into the targeted product by more than 2000 times. The cascaded nanozymes were also adopted to a spatially confined microfluidic device, leading to more than 100-fold enhancement of the reaction efficiency due to signal amplification.

Recent progress in the design of analytical methods based on nanozymes

Nanomaterials with intrinsic enzyme-like properties (nanozymes) have attracted growing interest owing to their striking merits over the traditional enzymes, such as low cost, easy surface modification, high stability and robustness, and tunable activity. These features enable them to be considered as a potent substitute for natural enzymes to construct novel analytical platforms to detect various analytes from small molecules to proteins and cells. In this review, we focus on recent advances in the design strategies using nanozyme catalytic mediated signal amplification for sensing applications. The progress of nanozyme-based analytical systems in the detection of different types of analytes, including ions, small biomolecules, biomacromolecules and others, is summarized. Furthermore, the future challenges and opportunities of nanozyme-based analytical methods are discussed.

Nanozymes in Point-of-Care Diagnosis: An Emerging Futuristic Approach for Biosensing

Nanomaterial-based artificial enzymes (or nanozymes) have attracted great attention in the past few years owing to their capability not only to mimic functionality but also to overcome the inherent drawbacks of the natural enzymes. Numerous advantages of nanozymes such as diverse enzyme-mimicking activities, low cost, high stability, robustness, unique surface chemistry, and ease of surface tunability and biocompatibility have allowed their integration in a wide range of biosensing applications. Several metal, metal oxide, metal-organic framework-based nanozymes have been exploited for the development of biosensing systems, which present the potential for point-of-care analysis. To highlight recent progress in the field, in this review, more than 260 research articles are discussed systematically with suitable recent examples, elucidating the role of nanozymes to reinforce, miniaturize, and improve the performance of point-of-care diagnostics addressing the ASSURED (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and deliverable to the end user) criteria formulated by World Health Organization. The review reveals that many biosensing strategies such as electrochemical, colorimetric, fluorescent, and immunological sensors required to achieve the ASSURED standards can be implemented by using enzyme-mimicking activities of nanomaterials as signal producing components. However, basic system functionality is still lacking. Since the enzyme-mimicking properties of the nanomaterials are dictated by their size, shape, composition, surface charge, surface chemistry as well as external parameters such as pH or temperature, these factors play a crucial role in the design and function of nanozyme-based point-of-care diagnostics. Therefore, it requires a deliberate exertion to integrate various parameters for truly ASSURED solutions to be realized. This review also discusses possible limitations and research gaps to provide readers a brief scenario of the emerging role of nanozymes in state-of-the-art POC diagnosis system development for futuristic biosensing applications.

A facile method for the fabrication of hierarchically structured Ni2CoS4 nanopetals on carbon nanofibers to enhance non-enzymatic glucose oxidation

Unique Ni₂CoS₄-carbon nanofiber (CNF) composite nanostructures were fabricated using a simple electrospinning-assisted hydrothermal route and used for the rapid and accurate electrochemical oxidation of glucose in real samples at the trace level. Electrochemical impedance spectroscopy and cyclic voltammetry of unmodified and modified electrodes revealed low charge-transfer resistance and the excellent electrocatalytic sensing of glucose when using the Ni₂CoS₄-CNF at a low potential due to the combined benefits of the highly conductive Ni₂Co₂S₄ anchored to the large surface area of the CNFs. Amperometric analysis of the fabricated sensor has shown an extremely low limit of detection (0.25 nM) and a large linear range (5-70 nM) for glucose at a working potential of 0.54 V (vs. Hg/HgO). The practicability of the Ni₂CoS₄-CNF for use in glucose determination was tested withl human saliva, blood plasma, and fruit juice samples. The Ni₂CoS₄-CNF/GCE showed acceptable recovery values for human saliva (99.1-100.8%), blood plasma (98.6-101.5%), and fruit juice (95.1-105.7%) samples. The proposed sensor also exhibited outstanding electroanalytical characteristics for glucose oxidation in these samples, including reusability, repeatability, and interference resistance, even in the presence of other biological substances and organic and inorganic metal ions.

Preparation, Functionalization, Modification, and Applications of Nanostructured Gold: A Critical Review

Gold nanoparticles (Au NPs) play a significant role in science and technology because of their unique size, shape, properties and broad range of potential applications. This review focuses on the various approaches employed for the synthesis, modification and functionalization of nanostructured Au. The potential catalytic applications and their enhancement upon modification of Au nanostructures have also been discussed in detail. The present analysis also offers brief summaries of the major Au nanomaterials synthetic procedures, such as hydrothermal, solvothermal, sol-gel, direct oxidation, chemical vapor deposition, sonochemical deposition, electrochemical deposition, microwave and laser pyrolysis. Among the various strategies used for improving the catalytic performance of nanostructured Au, the modification and functionalization of nanostructured Au produced better results. Therefore, various synthesis, modification and functionalization methods employed for better catalytic outcomes of nanostructured Au have been summarized in this review.

Biodegradable Multifunctional Nanotheranostic Based on Ag2S-Doped Hollow BSA-SiO2 for Enhancing ROS-Feedback Synergistic Antitumor Therapy

Stimuli-responsive silica nanoparticles are an attractive therapeutic agent for effective tumor ablation, but the responsiveness of silica nanoagents is limited by intrastimulation level and silica framework structure. Herein, a biodegradable hollow SiO₂-based nanosystem (Ag₂S-GOx@BHS NYs) is developed by a novel one-step dual-template (bovine serum albumin (BSA) and cetyltrimethylammonium bromide (CTAB)) synthetic strategy for image-guided therapy. The Ag₂S-GOx@BHS NYs can be specifically activated in the tumor microenvironment via a self-feedback mechanism to achieve reactive oxygen species (ROS)-induced multistep therapy. In response to the inherent acidity and H₂O₂ at the tumor sites, Ag₂S-GOx@BHS would accelerate the structural degradation while releasing glucose oxidase (GOx), which could efficiently deplete intratumoral glucose to copious amounts of gluconic acid and H₂O₂. More importantly, the sufficient H₂O₂ not only acts as a reactant to generate Ag⁺ from Ag₂S for metal-ion therapy and improves the oxidative stress but also combines with gluconic acid results in the self-accelerating degradation process. Moreover, the released Ag₂S nanoparticles can help the Ag₂S-GOx@BHS NYs realize the second near-infrared window fluorescence (NIR-II FL) and photoacoustic (PA) imaging-guided precise photothermal therapy (PTT). Taken together, the development of a self-feedback nanosystem may open up a new dimension for a highly effective multistep tumor therapy.

A Nanomedicine Fabricated from Gold Nanoparticles-Decorated Metal-Organic Framework for Cascade Chemo/Chemodynamic Cancer Therapy

The incorporation of new modalities into chemotherapy greatly enhances the anticancer efficacy combining the merits of each treatment, showing promising potentials in clinical translations. Herein, a hybrid nanomedicine (Au/FeMOF@CPT NPs) is fabricated using metal-organic framework (MOF) nanoparticles and gold nanoparticles (Au NPs) as building blocks for cancer chemo/chemodynamic therapy. MOF NPs are used as vehicles to encapsulate camptothecin (CPT), and the hybridization by Au NPs greatly improves the stability of the nanomedicine in a physiological environment. Triggered by the high concentration of phosphate inside the cancer cells, Au/FeMOF@CPT NPs effectively collapse after internalization, resulting in the complete drug release and activation of the cascade catalytic reactions. The intracellular glucose can be oxidized by Au NPs to produce hydrogen dioxide, which is further utilized as chemical fuel for the Fenton reaction, thus realizing the synergistic anticancer efficacy. Benefitting from the enhanced permeability and retention effect and sophisticated fabrications, the blood circulation time and tumor accumulation of Au/FeMOF@CPT NPs are significantly increased. In vivo results demonstrate that the combination of chemotherapy and chemodynamic therapy effectively suppresses the tumor growth, meantime the systemic toxicity of this nanomedicine is greatly avoided.

Biomimetic Platinum Nanozyme Immobilized on 2D Metal-Organic Frameworks for Mitochondrion-Targeting and Oxygen Self-Supply Photodynamic Therapy

Photodynamic therapy (PDT) as a noninvasive therapy mode has attracted considerable attention in the field of oncotherapy. However, the PDT efficacy is restricted either by the tumor hypoxia environment or the inherent properties of photosensitizers (PSs) including bad water solution, photobleaching, and easy aggregation. Herein, we designed and synthesized a new two-dimensional (2D) metal-organic framework, Sm-tetrakis(4-carboxyphenyl)porphyrin (TCPP) nanosheets, by assembling transition metal ions (Sm³⁺) and PSs (TCPP), on which the catalase (CAT)-mimicking platinum nanozymes were then in situ grown for sufficient oxygen supply during PDT. The prepared Sm-TCPP with nanoplate morphology (∼100 nm in diameter) and ultrathin thickness (<10 nm) showed significantly enhanced ¹O₂ generation capacity due to the improved physicochemical properties and the enhanced intersystem crossing from heavy Sm nodes. More importantly, the CAT-mimicking Pt nanozyme on the Sm-TCPP nanosheets could effectively convert over-expressed H₂O₂ in the tumor microenvironment into O₂ to relieve tumor hypoxia. Further, the triphenylphosphine (TPP) molecule was introduced to Sm-TCPP-Pt to develop a mitochondrion-targeting and O₂ self-supply PDT system. The in vitro and in vivo experimental results based on the MCF-7 breast cancer model revealed that Sm-TCPP-Pt/TPP could relieve tumor hypoxia and the generated reactive oxygen species nearby intracellular mitochondria significantly induced cell apoptosis. This study offers an engineering strategy to integrate 2D PS-based metal-organic frameworks and nanozymes into a nanoplatform to surmount the pitfalls of traditional PDT.

Sensitive CVG-AFS/ICP-MS label-free nucleic acid and protein assays based on a selective cation exchange reaction and simple filtration separation

Nowadays, label-free atomic spectrometric bioassays are attracting great research interest because of their advantages of low cost, simple design and operation, etc. Herein, a novel and simple chemical vapor generation-atomic fluorescence spectrometry (CVG-AFS)/inductively coupled plasma-mass spectrometry (ICP-MS) label-free detection method is presented for highly sensitive and selective assay of DNA and proteins. This work mainly combined a phenomenon that CdTe quantum dots (QDs) can be used to selectively differentiate free Hg2+ and the T-Hg2+-T complex, with the use of simple membrane filtration separation to improve the performance of the label-free bioassay methods. Upon hybridization with the DNA/protein (carcinoembryonic antigen, CEA) target, the T-Hg2+-T hairpin structure was opened and Hg2+ was released; this initiated the cation exchange reaction between Hg2+ and CdTe QDs which released Cd2+ simultaneously. Subsequently, the free Cd2+ was separated by the filtration membrane without separating the CdTe QDs, which could then be separated from the sample matrices for the CVG-AFS/ICP-MS assay. Under the optimal conditions, this method possessed high sensitivity for DNA and CEA determination with limits of detection (LODs) of 0.2 nM and 0.2 ng mL-1, and linear dynamic ranges of 1-160 nM and 0.5-20 ng mL-1, respectively, and exhibited excellent DNA sequence specificity and protein selectivity. This method preserves the advantages of the label-free atomic spectrometric bioassay, and combined with the selective cation exchange reaction and simple filtration separation to improve the performance.

Unveiling the Intrinsic Catalytic Activities of Single-Gold-Nanoparticle-Based Enzyme Mimetics

Gold nanoparticles (AuNPs) have been demonstrated to serve as effective nanomaterial-based enzyme mimetics (nanozymes) for a number of enzymatic reactions under mild conditions. The intrinsic glucose oxidase and peroxidase activities of single AuNPs and Ag-Au nanohybrids, respectively, were investigated by single NP collision electrochemical measurements. A significantly high turnover number of nanozymes was obtained from individual catalytic events compared with the results from the classical, ensemble-averaged measurements. The unusual enhancement of catalytic activity of single nanozymes is believed to originate from the high accessible surface area of monodispersed NPs and the high activities of carbon-supported NPs during single-particle collision at a carbon ultramicroelectrode. This work introduces a new method for the precise characterization of the intrinsic catalytic activities of nanozymes, giving further insights to the design of high-efficiency nanomaterial catalysts.

Nanostructure-based surface-enhanced Raman scattering biosensors for nucleic acids and proteins

Detection of nucleic acid and protein targets related to human health and safety has attracted widespread attention. Surface-enhanced Raman scattering (SERS) is a powerful tool for biomarker detection because of its ultrahigh detection sensitivity and unique fingerprinting spectra. In this review, we first introduce the development of nanostructure-based SERS-active substrates and SERS nanotags, which greatly influence the performance of SERS biosensors. We then focus on recent advances in SERS biosensors for DNA, microRNA and protein determination, including label-free, labeled and multiplex analyses as well as in vivo imaging. Finally, the prospects and challenges of such nanostructure-based SERS biosensors are discussed.

A V₂O₃-ordered mesoporous carbon composite with novel peroxidase-like activity towards the glucose colorimetric assay

It is of great scientific and practical significance to explore inorganic mimetic enzymes to replace natural enzymes due to their instability and high cost. Herein we present an interesting discovery that a V2O3-ordered mesoporous carbon composite (V2O3-OMC) has a novel peroxidase-like activity towards fast redox reaction of typical peroxidase substrates H2O2 and 2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) diammonium salt (ABTS). Due to the small size effect and large surface area of V2O3 nanoparticles supported by OMC, V2O3-OMC exhibited excellent catalytic performance with a k(cat) of 1.28 × 10(4) s(-1), K(M) (ABTS) of 0.067 mM and K(M) (H2O2) of 0.16 mM, and a significantly higher catalytic efficiency (k(cat)/K(M)) towards the oxidation of ABTS in comparison with the natural peroxidases. Furthermore, the Ping-pong BiBi mechanism was proposed to explain the catalytic reaction by V2O3-OMC. Based on this highly active biomimetic peroxidase and the colorimetric detection of H2O2, a facile analytical method was developed to detect glucose by using V2O3-OMC and glucose oxidase, which had a wide linear range (0.01-4 mM glucose), good selectivity and reliability for successful detection of various real samples. Thus, the novel V2O3-OMC peroxidase mimetic holds great promise for broad potential applications.

Quantitative investigation of the poly-adenine DNA dissociation from the surface of gold nanoparticles

In recent years, poly adenine (polyA) DNA functionalized gold nanoparticles (AuNPs) free of modifications was fabricated with high density of DNA attachment and high hybridization ability similar to those of its thiolated counterpart. This nanoconjugate utilized poly adenine as an anchoring block for binding with the AuNPs surface thereby facilitated the appended recognition block a better upright conformation for hybridization, demonstrating its great potential to be a tunable plasmonic biosensor. It's one of the key points for any of the practical applications to maintaining stable conjugation between DNA oligonucleotides and gold nanoparticles under various experimental treatments. Thus, in this research, we designed a simple but sensitive fluorescence turn-on strategy to systematically investigate and quantified the dissociation of polyA DNA on gold nanoparticles in diverse experimental conditions. DNA desorbed spontaneously as a function of elevated temperature, ion strength, buffer pH, organic solvents and keeping time. What's more, evaluating this conjugate stability as affected by the length of its polyA anchor was another crucial aspect in our study. With the improved understanding from these results, we were able to control some of our experimental conditions to maintain a good stability of this kind of polyA DNA-AuNPs nanoconjugates.

Nanoplasmonic imaging of latent fingerprints and identification of cocaine

Search for traces: Aptamer-bound Au nanoparticles (Au NPs) were used to provide high-resolution dark-field microscopy images of latent fingerprints (LFPs) with level 2 and level 3 details. Furthermore, the cocaine-induced aggregation of Au NPs results in a true green-to-red color change of the scattered light, providing a quasi-quantative method to identify cocaine loadings in LFPs.

Graphene oxide protected nucleic acid probes for bioanalysis and biomedicine

Recently, the binding ability of DNA on GO and resulting nuclease resistance have attracted increasing attention, leading to new applications both in vivo and in vitro. In vivo, nucleic acids absorbed on GO can be effectively protected from enzymatic degradation and biological interference in complicated samples, making it useful for targeted delivery, gene regulation, intracellular detection and imaging with high uptake efficiencies, high intracellular stability, and very low toxicity. In vitro, the adsorption of ssDNA on GO surface and desorption of dsDNA or well-folded ssDNA from GO surface result in the protection and deprotection of DNA from nucleic digestion, respectively, which has led to target-triggered cyclic enzymatic amplification methods (CEAM) for amplified detection of analytes with sensitivity 2-3 orders of magnitude higher than that of 1:1 binding strategies. This Concept article explores some of the latest developments in this field.

Tetra(p-tolyl)borate-functionalized solvent polymeric membrane: a facile and sensitive sensing platform for peroxidase and peroxidase mimetics

The determination of peroxidase activities is the basis for enzyme-labeled bioaffinity assays, peroxidase-mimicking DNAzymes- and nanoparticles-based assays, and characterization of the catalytic functions of peroxidase mimetics. Here, a facile, sensitive, and cost-effective solvent polymeric membrane-based peroxidase detection platform is described that utilizes reaction intermediates with different pKa values from those of substrates and final products. Several key but long-debated intermediates in the peroxidative oxidation of o-phenylenediamine (o-PD) have been identified and their charge states have been estimated. By using a solvent polymeric membrane functionalized by an appropriate substituted tetraphenylborate as a receptor, those cationic intermediates could be transferred into the membrane from the aqueous phase to induce a large cationic potential response. Thus, the potentiometric indication of the o-PD oxidation catalyzed by peroxidase or its mimetics can be fulfilled. Horseradish peroxidase has been detected with a detection limit at least two orders of magnitude lower than those obtained by spectrophotometric techniques and traditional membrane-based methods. As an example of peroxidase mimetics, G-quadruplex DNAzymes were probed by the intermediate-sensitive membrane and a label-free thrombin detection protocol was developed based on the catalytic activity of the thrombin-binding G-quadruplex aptamer.

Design and applications of gold nanoparticle conjugates by exploiting biomolecule-gold nanoparticle interactions

Gold nanoparticles (AuNPs) are a type of widely used nanomaterials with unique chemical and physical properties. AuNPs can be readily synthesized, and modified with various chemical or biological molecules, making them promising candidates for catalysis, drug delivery and biological imaging applications. In this review, we mainly focus on recent advances in the design and synthesis of conjugates of AuNPs by exploiting biomolecule-AuNP interactions. We will also discuss a variety of bioapplications of AuNP-based conjugates.