A Cell-Mimicking Structure Converting Analog Volume Changes to Digital Colorimetric Output with Molecular Selectivity

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.

Tailoring molecular recognition in predesigned multifunctional enzyme mimicking porphyrin imprinted interface for high affinity and differential selectivity; sensing etoposide in lung cancer patients

Nanozymes are cost-effective and robust but they lack specificity and selectivity, limiting their potential practical applications. Herein, molecularly imprinted polymers (MIPs) were grown in combination with multifunctional 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphyrin (THPP) oxidase-like nanozyme to engineer THPP@MIP interface with high affinities and differential selectivity for structurally related target analytes. THPP nanozyme displayed a high level of predefined binding affinity for etoposide (ETO), and served as a predesigned functional monomer to rationally tailor the selectivity of THPP@MIP surface in the presence of different guest molecules. THPP nanozyme in combination with conventional monomers was imprinted on a portable and disposable cellulose paper matrix under UV light to create a UV-cured imprinted interface for optical detection of ETO. The THPP@MIP enzyme mimicking interface, having ETO specific and selective target recognition pockets, catalyzed the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to generate visible blue oxidized TMB (oxTMB) without exogenous hydrogen peroxide (H2O2). The ETO binding on the THPP@MIP surface blocked the channels for TMB access to THPP cavities. The THPP@MIP sensor permitted to detect ETO in the linear range of 0.005-10 μg mL-1, with a limit of detection (LoD) of 0.002 μg mL-1, and showed a remarkable specificity and selectivity against other drug molecules. Furthermore, the THPP@MIP sensor successfully differentiated the serum samples of lung cancer patients and healthy volunteers. The obtained results were validated with standard High performance liquid chromatography-mass spectrometry (HPLC/MS) analysis of the serum samples. Additionally, ETO injection/infusion solutions and ETO-free serum samples were used to perform the matrix effect and recovery studies. This work demonstrates that molecular imprinting with predesigned, enzyme mimicking, high-affinity functional monomer can serve as a highly selective and specific universal interface for broad spectrum sensing applications in various analytical domains.

Salt-Induced Adsorption and Rupture of Liposomes on Microplastics

Microplastics have attracted considerable attention because of concerns regarding their environmental risks to living systems. The interaction between the lipid bilayer and microplastics is important for examining the potential harm to biological membranes in the presence of microplastics. In addition, membrane coatings may change the surface and colloidal properties of microplastics. Herein, phosphatidylcholine (PC) lipids, whose headgroup is most common in cell membranes, were used as model lipids. The adsorption and rupture of PC liposomes on microplastics were systematically studied. We found that divalent metal ions, such as Mg2+ and Ca2+, facilitate liposome adsorption onto microplastics and induce 40-55% liposome leakage at 2.5 mM. In contrast, to achieve a similar effect, 300 mM Na+ was required. Adsorption and rupture followed the same metal concentration requirements, suggesting that liposome adsorption was the rate-limiting step. After adsorption with liposomes, microplastics became more hydrophilic and were better dispersed in water. A similar behavior was observed for all five types of tested microplastics, including PP, PE, PVC, PET, and PS. Leakage also occurred in ocean water. This study provides fundamental insights into the interactions between liposomes and microplastics and has implications for the colloidal and transport properties of microplastics.

Surface imprinted bio-nanocomposites for affinity separation of a cellular DNA repair protein

Apurinic/apyrimidinic endonuclease 1 (APE1) is a multifunctional DNA repair protein localized in different subcellular compartments. The mechanisms responsible for the highly regulated subcellular localization and "interactomes" of this protein are not fully understood but have been closely correlated to the posttranslational modifications in different biological context. In this work, we attempted to develop a bio-nanocomposite with antibody-like properties that could capture APE1 from cellular matrices to enable the comprehensive study of this protein. By fixing the template APE1 on the avidin-modified surface of silica-coated magnetic nanoparticles, we first added 3-aminophenylboronic acid to react with the glycosyl residues of avidin, followed by addition of 2-acrylamido-2-methylpropane sulfonic acid as the second functional monomer to perform the first step imprinting reaction. To further enhance the affinity and selectivity of the binding sites, we carried out the second step imprinting reaction with dopamine as the functional monomer. After the polymerization, we modified the nonimprinted sites with methoxypoly(ethylene glycol) amine (mPEG-NH₂ ). The resulting molecularly imprinted polymer-based bio-nanocomposite showed high affinity, specificity, and capacity for template APE1. It allowed for the extraction of APE1 from the cell lysates with high recovery and purity. Moreover, the bound protein could be effectively released from the bio-nanocomposite with high activity. The bio-nanocomposite offers a very useful tool for the separation of APE1 from various complex biological samples.

Synthesis of a magnetic micelle molecularly imprinted polymers to selective adsorption of rutin from Sophora japonica

Rutin is a naturally active compound with biological and medical value. The traditional extraction and separation method not only destroys the structure and activity of rutin, but results in a low extraction rate. In this work, the magnetic micellar molecularly imprinted polymer of rutin with a selective recognition function, i.e., RMMMIP was synthesized from 4 to Vinylphenylboron acid and 4-Vinylpyridine as functional monomer, derivatives of cholic acid as amphiphilic molecules. The internal hydrophobic and external hydrophilic characteristics of micelle was used to weaken the solvation of rutin and strengthen the non-covalent interaction between functional monomer and rutin. Fe₃O₄, as the core, endowed the composite materials with good magnetic responsiveness and was easy to separate solid from liquid. Then its structure and adsorption were studied, adsorbing capacity and recognition specific factor of RMMMIP are 11.9 mg·g^-1 and 3.55 respectively. RMMMIP was used for the separation of rutin from crude extracts of Sophora japonica Linn and showed a better selective adsorption capacity than quercetin, naringin and cyanidin-3-O-glucose. It indicated that RMMMIP as a specific adsorbent had the potential to be a practical way to purify rutin from rutin crude extracts in the future.

Organic–inorganic hybrid phosphite-participating S-shaped penta-CeIII incorporated tellurotungstate as electrochemical enzymatic hydrogen peroxide for β-D-glucose detection

Polyoxometalate chemistry has made rapid advances in innovative structural chemistry. The lower valence state and lone electron pair effect of subgroup-valence heteroatom Te(IV) can be introduced into the tungsten-oxygen system...

Recent development in the design of artificial enzymes through molecular imprinting technology

Enzymes, a class of proteins or RNA with high catalytic efficiency and specificity, have inspired generations of scientists to develop enzyme mimics with similar capabilities. Many enzyme mimics have been...

Construction of nano receptors for ubiquitin and ubiquitinated proteins based on the region-specific interactions between ubiquitin and polydopamine

Ubiquitination is a prevalent post-translational modification that controls a multitude of important biological processes. Due to the low abundance of ubiquitinated proteins, highly efficient separation and enrichment approaches are required...

A Titanium Nitride Nanozyme for pH-Responsive and Irradiation-Enhanced Cascade-Catalytic Tumor Therapy

Nanozyme-based catalytic tumor therapy is an emerging therapeutic method with high reactivity in response to tumor microenvironments (TMEs). To overcome the current limitations of deficient catalytic activity of nanozymes, we studied the contributing factors of enzymatic activity based on non-metallic-atom doping and irradiation. Nitrogen doping significantly enhanced the peroxidase activity of Ti-based nanozymes, which was shown experimentally and theoretically. Based on the excellent NIR-adsorption-induced surface plasmon resonance and photothermal effect, the enzymatic activity of TiN nanoparticles (NPs) was further improved under NIR laser irradiation. Hence, an acidic TME-responsive and irradiation-mediated cascade nanocatalyst (TLGp) is presented by using TiN-NP-encapsulated liposomes linked with pH-responsive PEG-modified glucose oxidase (GOx). The integration of pH-responsive GOx-mediated H₂ O₂ self-supply, nitrogen-doping, and irradiation-enhanced enzymatic activity of TiN NPs and mild-photothermal therapy enables an effective tumor inhibition by TLGp with minimal side effects in vivo.

Micro-Bio-Chemo-Mechanical-Systems: Micromotors, Microfluidics, and Nanozymes for Biomedical Applications

Wireless nano-/micromotors powered by chemical reactions and/or external fields generate motive forces, perform tasks, and significantly extend short-range dynamic responses of passive biomedical microcarriers. However, before micromotors can be translated into clinical use, several major problems, including the biocompatibility of materials, the toxicity of chemical fuels, and deep tissue imaging methods, must be solved. Nanomaterials with enzyme-like characteristics (e.g., catalase, oxidase, peroxidase, superoxide dismutase), that is, nanozymes, can significantly expand the scope of micromotors' chemical fuels. A convergence of nanozymes, micromotors, and microfluidics can lead to a paradigm shift in the fabrication of multifunctional micromotors in reasonable quantities, encapsulation of desired subsystems, and engineering of FDA-approved core-shell structures with tuneable biological, physical, chemical, and mechanical properties. Microfluidic methods are used to prepare stable bubbles/microbubbles and capsules integrating ultrasound, optoacoustic, fluorescent, and magnetic resonance imaging modalities. The aim here is to discuss an interdisciplinary approach of three independent emerging topics: micromotors, nanozymes, and microfluidics to creatively: 1) embrace new ideas, 2) think across boundaries, and 3) solve problems whose solutions are beyond the scope of a single discipline toward the development of micro-bio-chemo-mechanical-systems for diverse bioapplications.

Molecular Imprinting on Nanozymes for Sensing Applications

As part of the biomimetic enzyme field, nanomaterial-based artificial enzymes, or nanozymes, have been recognized as highly stable and low-cost alternatives to their natural counterparts. The discovery of enzyme-like activities in nanomaterials triggered a broad range of designs with various composition, size, and shape. An overview of the properties of nanozymes is given, including some examples of enzyme mimics for multiple biosensing approaches. The limitations of nanozymes regarding lack of selectivity and low catalytic efficiency may be surpassed by their easy surface modification, and it is possible to tune specific properties. From this perspective, molecularly imprinted polymers have been successfully combined with nanozymes as biomimetic receptors conferring selectivity and improving catalytic performance. Compelling works on constructing imprinted polymer layers on nanozymes to achieve enhanced catalytic efficiency and selective recognition, requisites for broad implementation in biosensing devices, are reviewed. Multimodal biomimetic enzyme-like biosensing platforms can offer additional advantages concerning responsiveness to different microenvironments and external stimuli. Ultimately, progress in biomimetic imprinted nanozymes may open new horizons in a wide range of biosensing applications.

Robust magnetic laccase-mimicking nanozyme for oxidizing o-phenylenediamine and removing phenolic pollutants

In this study, we report a novel magnetic biomimetic nanozyme (Fe₃O₄@Cu/GMP (guanosine 5'-monophosphate)) with high laccase-like activity, which could oxidize toxic o-phenylenediamine (OPD) and remove phenolic compounds. The magnetic laccase-like nanozyme was readily obtained via complexed Cu²⁺ and GMP that grew on the surface of magnetic Fe₃O₄ nanoparticles. The prepared Fe₃O₄@Cu/GMP catalyst could be magnetically recycled for at least five cycles while still retaining above 70% activity. As a laccase mimic, Fe₃O₄@Cu/GMP had more activity and robust stability than natural laccase for the oxidization of OPD. Fe₃O₄@Cu/GMP retained about 90% residual activity at 90°C and showed little change at pH 3-9, and the nanozyme kept its excellent activity after long-term storage. Meanwhile, Fe₃O₄@Cu/GMP had better activity for removing phenolic compounds, and the removal of naphthol was more than 95%. Consequently, the proposed Fe₃O₄@Cu/GMP nanozyme shows potential for use as a robust catalyst for applications in environmental remediation.

Growing a Nucleotide/Lanthanide Coordination Polymer Shell on Liposomes

Coating liposomes with a shell is a useful strategy to increase membrane stability and prevent leakage or fusion. Nucleotide/lanthanide coordination nanoparticles (NPs) are formed by a simple mixing at ambient conditions. Because some lipid headgroups contain lanthanide binding ligands, they may direct the growth of such coordination NPs. Herein, a gadolinium/adenosine monophosphate (Gd³⁺/AMP) shell was formed on liposomes (liposome@Gd³⁺/AMP) using lipids containing phosphoserine (PS) or cholinephosphate (CP) headgroups, while phosphocholine liposomes did not support the shell. Liposome binding Gd³⁺ is confirmed by transmission electron microscopy (TEM). The negatively charged CP and PS liposomes reversed to positive upon Gd³⁺ binding, while other metals such as Ca²⁺ and Zn²⁺ did not reverse the charge. Binding of Gd³⁺ did not leak the PS liposomes. Then, AMP was further added to cross-link Gd³⁺ on the liposome surface. A shell was formed as indicated by TEM, and the content inside the liposome remained for the PS liposomes. While adding Triton X-100 still induced leakage of the encapsulated liposomes, the shell protected the liposomes from leakage induced by ZnO NPs, suggesting a porous structure of the Gd³⁺/AMP shell which allowed penetration of Triton X-100 but not the larger ZnO NPs. This work provides a simple method to coat liposomes, and also offers a fundamental understanding of liposome adsorption of lanthanide ions.

One-step synthesis of cross-linked and hollow microporous organic-inorganic hybrid nanoreactors for selective redox reactions

Hollow microporous nanostructures (HMNs) are powerful platforms for multiple promising applications, including energy storage, drug/gene delivery, nanoreactors/catalysis, adsorption, and separation. Herein, we report a facile one-step method to synthesize highly cross-linked organic-inorganic hybrid poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) (PZS) HMNs via a salt-induced liquid-liquid separation process. The size of inner cavities can be properly tuned by modulating the concentration of the NaOH solution. The regulation mechanism of the PZS HMNs was further confirmed by encapsulating water-dispersed Pt nanoclusters into the cavities. Interestingly, the resulting yolk-shell Pt@PZS serves as nanoreactors and exhibits excellent substrate selectivity and recyclability for the catalytic oxidation of 1,3,5-trimethylbenzene.

Discovery of precise pH-controlled biomimetic catalysts: defective zirconium metal-organic frameworks as alkaline phosphatase mimics

The well-controlled structural motifs of zirconium metal-organic frameworks (Zr-MOFs) and their similarity to enzyme cofactors make them ideally suited for biomimetic catalysis. However, the activation methodologies for these motifs, the structural information about active conformations and the reaction mechanism during these biomimetic reactions, are largely unknown. Herein, we have explored the precise pH-controlled activation processes, active sites, and reaction mechanisms for a series of Zr-MOFs as alkaline phosphatase mimics. Activation of the Zr-MOFs with a broad range and precise changes of pH led to the discovery of the MOF-catalyzed volcano plot with activity versus pH changes. This unique response revealed the existence of the precisely pH-controlled active form of the material, which was confirmed with computational analysis using density functional theory and diffuse reflectance infrared Fourier transform spectroscopy. These results will open a window for state-of-the-art design of efficient MOF enzyme mimics in aqueous solution.

Emerging Biomimetic Applications of DNA Nanotechnology

Re-engineering cellular components and biological processes has received great interest and promised compelling advantages in applications ranging from basic cell biology to biomedicine. With the advent of DNA nanotechnology, the programmable self-assembly ability makes DNA an appealing candidate for rational design of artificial components with different structures and functions. This Forum Article summarizes recent developments of DNA nanotechnology in mimicking the structures and functions of existing cellular components. We highlight key successes in the achievements of DNA-based biomimetic membrane proteins and discuss the assembly behavior of these artificial proteins. Then, we focus on the construction of higher-order structures by DNA nanotechnology to recreate cell-like structures. Finally, we explore the current challenges and speculate on future directions of DNA nanotechnology in biomimetics.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Nanozymes in Nanofibrous Mats with Haloperoxidase-like Activity To Combat Biofouling

Electrospun polymer mats are widely used in tissue engineering, wearable electronics, and water purification. However, in many environments, the polymer nanofibers prepared by electrospinning suffer from biofouling during long-term usage, resulting in persistent infections and device damage. Herein, we describe the fabrication of polymer mats with CeO_{2- x} nanorods that can prevent biofouling in an aqueous environment. The embedded CeO_{2- x} nanorods are functional mimics of natural haloperoxidases that catalyze the oxidative bromination of Br^- and H₂O₂ to HOBr. The generated HOBr, a natural signaling molecule, disrupted the bacterial quorum sensing, a critical step in biofilm formation. The polymer fibers provide porous structures with high water wettability, and the embedded cerium oxide nanozymes act as a catalyst that can efficiently trigger oxidative bromination, as shown by a haloperoxidase assay. Additionally, the embedded nanozymes enhance the mechanical property of polymer mats, as shown by a single-fiber bending test using atomic force microscopy. We envision that the fabricated polymer mats with CeO_{2- x} nanorods may be used to provide mechanically robust coatings with antibiofouling properties.

DNA Oligonucleotide-Functionalized Liposomes: Bioconjugate Chemistry, Biointerfaces, and Applications

Interfacing DNA with liposomes has produced a diverse range of programmable soft materials, devices, and drug delivery vehicles. By simply controlling liposomal composition, bilayer fluidity, lipid domain formation, and surface charge can be systematically varied. Recent development in DNA research has produced not only sophisticated nanostructures but also new functions including ligand binding and catalysis. For noncationic liposomes, a DNA is typically covalently linked to a hydrophobic or lipid moiety that can be inserted into lipid membranes. In this article, we discuss fundamental biointerfaces formed between DNA and noncationic liposomes. The methods to prepare such conjugates and the interactions at the membrane interfaces are also discussed. The effect of DNA lateral diffusion on fluid bilayer membranes and the effect of membrane on DNA assembly are emphasized. DNA hybridization can be programmed to promote fusion of lipid membranes. Representative applications of this conjugate for drug delivery, biosensor development, and directed assembly of materials are briefly described toward the end. Some future research directions are also proposed to further understand this biointerface.

Ultrahigh Selective Colorimetric Quantification of Chromium(VI) Ions Based on Gold Amalgam Catalyst Oxidoreductase-like Activity in Water

Hexavalent chromium ion (Cr⁶⁺) is one of the most toxic substances for plants, for animals, and is a confirmed human respiratory carcinogen. However, so far, there are few independent and efficient colorimetric methods for detection of Cr⁶⁺. Here, we introduce a convenient, label-free, catalysis-based, and efficient strategy for quantification of Cr⁶⁺ by using a colorimetric sensing probe 3,3',5,5'-tetramethylbenzidine (TMB). In the presence of a trace amount of gold amalgam nanocomposites (Au@Hg) and Cr⁶⁺, TMB can be oxidized to oxTMB and the color changed to an intense blue that was observed by naked-eye and absorption spectroscopic method. In addition, the colorimetric method shows the high selectivity against 34 other interfering substances, and it can be performed at room temperature, in water, and requires only ∼5 min. Thus, the catalysis-based colorimetric assay for accurate and ultrahigh selective identification of Cr⁶⁺ will find widespread use in the world.

Nanozyme Sensor Arrays for Detecting Versatile Analytes from Small Molecules to Proteins and Cells

Nanozymes have emerged as promising alternatives to overcome the high cost and low stability of natural enzymes. Nanozymes with peroxidase-like activities have been studied to construct versatile biosensors by using specific biorecognition ligands (such as enzymes, antibodies, and aptamers) or molecularly imprinted polymers (MIPs). However, the use of bioligands compromises the high stability and low cost promise of nanozymes, while the MIPs may not be applicable to multiplex detection. To address these limitations, here we constructed the nanozyme sensor arrays based on peroxidase-like Pt, Ru, and Ir nanozymes. The cross-reactive nanozyme sensor arrays were successfully used for the detection of biothiols and proteins as well as the discrimination of cancer cells because of the differential nonspecific interactions between the components of the sensor arrays and the analytes. The usefulness of the nanozyme sensor arrays was further validated by the detection of blind unknown samples, where 28 of 30 biothiols and 42 of 45 proteins were correctly identified. Moreover, the practical application of the nanozyme sensor arrays was demonstrated by the successful discrimination of biothiols in serum and proteins in human urine.

Ag+ -Gated Surface Chemistry of Gold Nanoparticles and Colorimetric Detection of Acetylcholinesterase

Chemical regulation of enzyme-mimic activity of nanomaterials is challenging because it requires a precise understanding of the surface chemistry and mechanism, and rationally designed applications. Herein, Ag+ -gated peroxidase activity is demonstrated by successfully modulating surface chemistry of cetyltrimethylammonium bromide-capped gold nanoparticles (CTAB-AuNPs). A surface blocking effect of long-chain molecules on surfaces of AuNPs that inhibit peroxidase activity of AuNPs is found. Ag+ ions can selectively bind on the surfaces of AuNPs and competitively destroy CTAB membrane forming Ag+ @CTAB-AuNPs complexes to result in enhanced peroxidase activity. Ag+ @CTAB-AuNPs show the highest peroxidase activity compared to similar-sized citrate-capped and ascorbic acid-capped AuNPs. Ag+ @CTAB-AuNPs can potentially develop into analyte-responsive systems and exhibit advantages in the optical sensing field. For example, the Ag+ @CTAB-AuNPs system shows an enhanced sensitivity and selectivity for acetylcholinesterase activity sensing compared to other methods.

Molecularly Imprinted Porous Aromatic Frameworks Serving as Porous Artificial Enzymes

Artificially designed enzymes are in demand as ideal catalysts for industrial production but their dense structure conceals most of their functional fragments, thus detracting from performance. Here, molecularly imprinted porous aromatic frameworks (MIPAFs) which are exploited to incorporate full host-guest interactions of porous materials within the artificial enzymes are presented. By decorating a porous skeleton with molecularly imprinted complexes, it is demonstrated that MIPAFs are porous artificial enzymes possessing excellent kinetics for guest molecules. In addition, due to the abundance of accessible sites, MIPAFs can perform a wide range of sequential processes such as substrate hydrolysis and product transport. Through its two functional sites in tandem, the MIPAF subsequently manifests both hydrolysis and transport behaviors. Advantageously, the obtained catalytic rate is ≈58 times higher than that of all other conventional artificial enzymes and even surpasses by 14 times the rate for natural organophosphorus hydrolase (Flavobacterium sp. strain ATCC 27551).