Multicopper Laccase Mimicking Nanozymes with Nucleotides as Ligands

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.

Carbon Dot Nanozymes: How to Be Close to Natural Enzymes

The design, catalytic process, and property study of nanozymes are of importance for both fundamental research and application demand. Here, the peroxidase-mimicking properties of a series of carbon dots (C-dots) was systematically investigated and they were found to be probably closer to their natural counterparts, as compared to the known corresponding nanozymes. Firstly, four kinds of metal-free and surface-modulated C-dots were bottom-up fabricated using glucose, α-cyclodextrin (CD), β-CD, and γ-CD as precursors, respectively, and their formation processes, structures, as well as surface chemistry were investigated. Secondly, in the peroxidase-mimicking catalytic system, no hydroxyl radicals were produced, which indicates a different and special catalytic mode. By employing a joint experimental-theoretical study, a probable catalytic mechanism is proposed. Thirdly, the present C-dots maintained well their catalytic activity even in complicated serum matrices because their catalytic performances are completely irrelevant of any cation-related binding sites. Finally, the catalytic performances of the as-prepared C-dots were modulated by either pre-engineering NP surface structures or subsequently introducing photo-regulated host-guest reactions.

Continuously Tunable Nucleotide/Lanthanide Coordination Nanoparticles for DNA Adsorption and Sensing

Metal-organic coordination polymers (CPs) have attracted great research interest because they are easy to prepare, porous, flexible in composition, and designable in structure. Their applications in biosensor development, drug delivery, and catalysis have been explored. Lanthanides and nucleotides can form interesting CPs, although most previous works have focused on a single type of metal ligand. In this work, we explored mixed nucleotides and studied their DNA adsorption properties using fluorescently labeled oligonucleotides. Adenosine monophosphate (AMP) and guanosine monophosphate (GMP) formed negatively charged CP nanoparticles with most lanthanides, and thus a salt was required to adsorb negatively charged DNA. DNA adsorption was faster and reached a higher capacity with lighter lanthanides. Desorption of pre-adsorbed DNA by inorganic phosphates, urea, proteins, surfactants, and competing DNA was successively carried out. The results suggested the importance of the DNA phosphate backbone, although hydrogen bonding and DNA bases also contributed to adsorption. The AMP CPs adsorbed DNA more strongly than the GMP ones, and using mixtures of AMP and GMP, continuous tuning of DNA adsorption affinity was achieved. Such CPs were also used as a sensor for DNA detection based on the different affinities of single- and double-stranded DNA, and a detection limit of 0.9 nM target DNA was achieved. Instead of tuning DNA adsorption by varying the length and sequence of DNA, the composition of CPs can also be controlled to achieve this goal.

Cu2+-Directed Liposome Membrane Fusion, Positive-Stain Electron Microscopy, and Oxidation

Natural lipid headgroups contain a few types of metal ligands, such as phosphate, amine, and serine, which interact with metal ions differently. Herein, we studied the binding between Cu²⁺ and liposomes with four types of headgroups: phosphocholine (PC), phosphoglycerol (PG), phosphoserine (PS), and cholinephosphate (CP). Using fluorescently headgroup-labeled liposomes, Cu²⁺ strongly quenched the CP and PS liposomes, whereas quenching of PC and PG was weaker. Dynamic light scattering indicated that all of the four liposomes aggregated at high Cu²⁺ concentrations, and ethylenediaminetetraacetic acid (EDTA) only restored the original size of the PC liposome, implying fusion of the other three types of liposomes. The leakage tests revealed that the integrity of PC liposomes was not affected by Cu²⁺, but the other three liposomes leaked. Under TEM, all of the liposomes show a positive-stain feature in the presence of Cu²⁺ and Cu²⁺-stained individual liposomes with a short incubation time (<1 min). The oxidative catalytic property of Cu²⁺ was also tested, and a tight binding by the PS liposome inhibited the activity of Cu²⁺. Finally, a model of interaction for each liposome was proposed, and each one has a different metal-binding and interaction mechanism.

Proximity aptasensor for protein detection based on an enzyme-free amplification strategy

A novel electrochemical aptasensor for the detection of trace protein is proposed based on proximity binding-induced strand displacement and hybridization chain reaction. This method is proven to be highly selective and has potential practical utility, and offers new opportunities for the convenient detection of proteins with an enzyme-free amplification process.

Constructing Redox-Responsive Metal-Organic Framework Nanocarriers for Anticancer Drug Delivery

Metal-organic frameworks (MOFs), which are a unique class of hybrid porous materials built from metal ions and organic ligands, have attracted significant interest in recent years as a promising platform for controlled drug delivery. Current approaches for creating MOFs-based responsive drug carriers involve encapsulation of stimuli-responsive compositions into MOFs or postsynthetic surface modification with sensitive molecules. In this study, we developed a novel intrinsic redox-responsive MOFs carrier, MOF-M(DTBA) (M = Fe, Al or Zr) by using iron, aluminum, or zirconium as metal nodes and 4,4'-dithiobisbenzoic acid (4,4'-DTBA) as the organic ligand. The disulfide bond in 4,4'-DTBA is cleavable by glutathione (GSH), which is often overexpressed in tumor cells. It was found that MOF-Zr(DTBA) synthesized at 40 °C displayed the appropriate size and properties as a drug carrier. By incorporating curcumin (CCM) into MOF-Zr(DTBA), CCM@MOF-Zr(DTBA) nanoparticles were obtained that displayed a faster releasing behavior in vitro and enhanced the cell death compared with free CCM. The in vivo anticancer experiments indicate that CCM@ MOF-Zr(DTBA) exhibits much higher antitumor efficacy than free CCM. This strategy for constructing responsive MOFs-based nanocarriers might open new possibilities for the application of MOFs in drug delivery, molecular imaging, or theranostics.

Robust Hydrogels from Lanthanide Nucleotide Coordination with Evolving Nanostructures for a Highly Stable Protein Encapsulation

Metal coordination with organic ligands often produce crystalline metal-organic frameworks and sometimes amorphous nanoparticles. In this work, we explore a different type of material from the same chemistry: hydrogels. Lanthanides are chosen as the metal component because of their important technological applications and continuously tunable properties. Adenosine monophosphate (AMP) and lanthanides form two types of coordination materials: the lighter lanthanides from La³⁺ to Tb³⁺ form nanoparticles, whereas the rest heavier ones initially form nanoparticles but later spontaneously transform to hydrogels. This slow sol-to-gel transition is accompanied by heat release, as indicated by isothermal titration calorimetry. The transition is also accompanied by a morphology change from nanoparticles to nanofibers, as indicated by transmission electron microscopy. These gels are insensitive to ionic strength or temperature with excellent stability. Gelation is unique to AMP because other nucleotides or other adenine derivatives only yield nanoparticles or soluble products. Entrapment of guest molecules such as glucose oxidase is also explored, where the hydrogels allow a better enzyme activity and stability compared to nanoparticles. Further applications of lanthanide coordinated hydrogels might include biosensors, imaging agents, and drug delivery.

Rational Design of Au@Pt Multibranched Nanostructures as Bifunctional Nanozymes

One of the current challenges in nanozyme-based nanotechnology is the utilization of multifunctionalities in one material. In this regard, Au@Pt nanoparticles (NPs) with excellent enzyme-mimicking activities due to the Pt shell and unique surface plasmon resonance features from the Au core have attracted enormous research interest. However, the unique surface plasmon resonance features from the Au core have not been widely utilized. The practical problem of the optical-damping nature of Pt hinders the research into the combination of Au@Pt NPs' enzyme-mimicking properties with their surface-enhanced Raman scattering (SERS) activities. Herein, we rationally tuned the Pt amount to achieve Au@Pt NPs with simultaneous plasmonic and enzyme-mimicking activities. The results showed that Au@Pt NPs with 2.5% Pt produced the highest Raman signal in 2 min, which benefited from the remarkably accelerated catalytic oxidation of 3,3',5,5'-tetramethylbenzidine with the decorated Pt and strong electric field retained from the Au core for SERS. This study not only demonstrates the great promise of combining bimetallic nanomaterials' multiple functionalities but also provides rational guidelines to design high-performance nanozymes for potential biomedical applications.

Contemporary enzyme based technologies for bioremediation: A review

The persistent disposal of xenobiotic compounds like insecticides, pesticides, fertilizers, plastics and other hydrocarbon containing substances is the major source of environmental pollution which needs to be eliminated. Many contemporary remediation methods such as physical, chemical and biological are currently being used, but they are not sufficient to clean the environment. The enzyme based bioremediation is an easy, quick, eco-friendly and socially acceptable approach used for the bioremediation of these recalcitrant xenobiotic compounds from the natural environment. Several microbial enzymes with bioremediation capability have been isolated and characterized from different natural sources, but less production of such enzymes is a limiting their further exploitation. The genetic engineering approach has the potential to get large amount of recombinant enzymes. Along with this, enzyme immobilization techniques can boost the half-life, stability and activity of enzymes at a significant level. Recently, nanozymes may offer the potential bioremediation ability towards a broad range of pollutants. In the present review, we have described a brief overview of the microbial enzymes, different enzymes techniques (genetic engineering and immobilization of enzymes) and nanozymes involved in bioremediation of toxic, carcinogenic and hazardous environmental pollutants.

Cu2+ -Modified Metal-Organic Framework Nanoparticles: A Peroxidase-Mimicking Nanoenzyme

The synthesis and characterization of UiO-type metal-organic framework nanoparticles (NMOFs) composed of Zr⁴⁺ ions bridged by 2,2'-bipyridine-5,5'-dicarboxylic acid ligands and the postmodification of the NMOFs with Cu²⁺ ions are described. The resulting Cu²⁺ -modified NMOFs, Cu²⁺ -NMOFs, exhibit peroxidase-like catalytic activities reflected by the catalyzed oxidation of Amplex-Red to the fluorescent Resorufin by H₂ O₂ , the catalyzed oxidation of dopamine to aminochrome by H₂ O₂ , and the catalyzed generation of chemiluminescence in the presence of luminol/H₂ O₂ . Also, the Cu²⁺ -NMOFs mimic NADH peroxidase functions and catalyze the oxidation of dihydronicotinamide adenine dinucleotide, NADH, to nicotinamide adenine dinucleotide, NAD⁺ , in the presence of H₂ O₂ . The Cu²⁺ -NMOFs-catalyzed generation of chemiluminescence in the presence of luminol/H₂ O₂ is used to develop a glucose sensor by monitoring the H₂ O₂ formed by the aerobic oxidation of glucose to gluconic acid in the presence of glucose oxidase. Furthermore, loading the Cu²⁺ -NMOFs with fluorescein and activating the catalyzed generation of chemiluminescence in the presence of luminol/H₂ O₂ yield an efficient chemiluminescence resonance energy transfer (CRET) process to the fluorescein reflected by the activation of the fluorescence of the dye (λ = 520 nm, CRET efficiency 35%).

Highly active fluorogenic oxidase-mimicking NiO nanozymes

NiO nanoparticles can quickly catalyze oxidation of Amplex red to produce fluorescent products for intracellular imaging, much more efficiently than other types of tested nanozymes.

Nucleobases, nucleosides, and nucleotides: versatile biomolecules for generating functional nanomaterials

The incorporation of biomolecules into nanomaterials generates functional nanosystems with novel and advanced properties, presenting great potential for applications in various fields. Nucleobases, nucleosides and nucleotides, as building blocks of nucleic acids and biological coenzymes, constitute necessary components of the foundation of life. In recent years, as versatile biomolecules for the construction or regulation of functional nanomaterials, they have stimulated interest in researchers, due to their unique properties such as structural diversity, multiplex binding sites, self-assembly ability, stability, biocompatibility, and chirality. In this review, strategies for the synthesis of nanomaterials and the regulation of their morphologies and functions using nucleobases, nucleosides, and nucleotides as building blocks, templates or modulators are summarized alongside selected applications. The diverse applications range from sensing, bioimaging, and drug delivery to mimicking light-harvesting antenna, the construction of logic gates, and beyond. Furthermore, some perspectives and challenges in this emerging field are proposed. This review is directed toward the broader scientific community interested in biomolecule-based functional nanomaterials.