Artificial enzyme with magnetic properties and peroxidase activity on indoleamine metabolite tumor marker

Enhancing the substrate selectivity of enzyme mimetics in biosensing and bioassay: Novel approaches

A substantial development in nanoscale materials possessing catalytic activities comparable with natural enzymes has been accomplished. Their advantages were owing to the excellent sturdiness in an extreme environment, possibilities of their large-scale production resulting in higher profitability, and easy manipulation for modification. Despite these advantages, the main challenge for artificial enzyme mimetics is the lack of substrate selectivity where natural enzymes flourish. This review addresses this vital problem by introducing substrate selectivity strategies to three classes of artificial enzymes: molecularly imprinted polymers, nanozymes (NZs), and DNAzymes. These rationally designed strategies enhance the substrate selectivity and are discussed and exemplified throughout the review. Various functional mechanisms associated with applying enzyme mimetics in biosensing and bioassays are also given. Eventually, future directives toward enhancing the substrate selectivity of biomimetics and related challenges are discussed and evaluated based on their efficiency and convenience in biosensing and bioassays.

Synthesis of Finely Controllable Sizes of Au Nanoparticles on a Silica Template and Their Nanozyme Properties

The precise synthesis of fine-sized nanoparticles is critical for realizing the advantages of nanoparticles for various applications. We developed a technique for preparing finely controllable sizes of gold nanoparticles (Au NPs) on a silica template, using the seed-mediated growth and interval dropping methods. These Au NPs, embedded on silica nanospheres (SiO₂@Au NPs), possess peroxidase-like activity as nanozymes and have several advantages over other nanoparticle-based nanozymes. We confirmed their peroxidase activity; in addition, factors affecting the activity were investigated by varying the reaction conditions, such as concentrations of tetramethyl benzidine and H₂O₂, pH, particle amount, reaction time, and termination time. We found that SiO₂@Au NPs are highly stable under long-term storage and reusable for five cycles. Our study, therefore, provides a novel method for controlling the properties of nanoparticles and for developing nanoparticle-based nanozymes.

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.

How Reliable Is the Electrochemical Readout of MIP Sensors?

Electrochemical methods offer the simple characterization of the synthesis of molecularly imprinted polymers (MIPs) and the readouts of target binding. The binding of electroinactive analytes can be detected indirectly by their modulating effect on the diffusional permeability of a redox marker through thin MIP films. However, this process generates an overall signal, which may include nonspecific interactions with the nonimprinted surface and adsorption at the electrode surface in addition to (specific) binding to the cavities. Redox-active low-molecular-weight targets and metalloproteins enable a more specific direct quantification of their binding to MIPs by measuring the faradaic current. The in situ characterization of enzymes, MIP-based mimics of redox enzymes or enzyme-labeled targets, is based on the indication of an electroactive product. This approach allows the determination of both the activity of the bio(mimetic) catalyst and of the substrate concentration.

Evaluation of the QuEChERS and magnetic micro dispersive solid-phase extraction of brominated flame retardants in red fruits with determination by GC/MS

A sample preparation method, QuEChERS extraction combined with a magnetic micro dispersive solid phase extraction (MµdSPE), was optimized and evaluated for the trace analysis of 9 brominated flame retardants in red fruit samples (strawberries, blueberries, and raspberries) using gas chromatography-mass spectrometry. Magnetic nanomaterials were used as sorbents providing an extraction of the target compounds. Linearity was established for all the analytes (from 10 to 200 µg kg^-1). Seven concentration levels were analyzed with three measurements at each concentration. Linear responses (R² > 0.99) were obtained, recoveries of all target analytes were within the range of 65-141%, relative standard deviations were <20% at all three spiking levels, while intraday and interday precisions were below 20%. This study demonstrated that the new sample preparation with magnetic nanoparticles could potentially be expanded to extract and pre-concentrate the BFRs in different red fruit samples. The method has been successfully applied to study BFRs in 12 samples from conventional and organic farming.

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.

Magnetic dispersive micro solid-phase extraction and gas chromatography determination of organophosphorus pesticides in strawberries

Magnetic nanoparticles (MNPs) with different sizes and characteristics were synthesized to be used as a QuEChERS sorbents for the determination of seven organophosphorus pesticides (OPPs) in strawberries by gas chromatography analysis with flame photometric and mass spectrometry detection. To achieve the optimum conditions of modified QuEChERS procedure several parameters affecting the cleanup efficiency including the amount of the sorbents and cleanup time were investigated. The results were compared with classical QuEChERS methodologies and the modified QuEChERS procedure using MNPs showed the better performance. Under the optimum conditions of the new methodology, three spiking levels (25, 50 and 100 μg kg^-1) were evaluated in a strawberry sample. The results showed that the average recovery was 93% and the relative standard deviation was less than 12%. The enrichment factor ranged from 111 to 145%. The good linearity with coefficients of determination of 0.9904-0.9991 was obtained over the range of 25-250 μg kg^-1 for 7 OPPs. It was determined that the MNPs have an excellent function as sorbent when purified even using less amount of sorbents and the magnetic properties allowed non-use of the centrifugation in cleanup step. The new methodology was applied in strawberry samples from conventional and organic farming. The new sorbents were successfully applied for extraction and determination of OPPs in strawberries.

MIPs and Aptamers for Recognition of Proteins in Biomimetic Sensing

Biomimetic binders and catalysts have been generated in order to substitute the biological pendants in separation techniques and bioanalysis. The two major approaches use either "evolution in the test tube" of nucleotides for the preparation of aptamers or total chemical synthesis for molecularly imprinted polymers (MIPs). The reproducible production of aptamers is a clear advantage, whilst the preparation of MIPs typically leads to a population of polymers with different binding sites. The realization of binding sites in the total bulk of the MIPs results in a higher binding capacity, however, on the expense of the accessibility and exchange rate. Furthermore, the readout of the bound analyte is easier for aptamers since the integration of signal generating labels is well established. On the other hand, the overall negative charge of the nucleotides makes aptamers prone to non-specific adsorption of positively charged constituents of the sample and the "biological" degradation of non-modified aptamers and ionic strength-dependent changes of conformation may be challenging in some application.

Nanozymes in bionanotechnology: from sensing to therapeutics and beyond

Nanozymes are nanomaterials with enzyme-like characteristics, which have found broad applications in various areas including bionanotechnology and beyond.

Preparation and application of molecularly imprinted polymer for isolation of chicoric acid from Chicorium intybus L. medicinal plant

Molecularly imprinted polymer (MIP) was synthesized and applied for the extraction of chicoric acid from Chicory herb (Chicorium intybus L.). A computational study was developed to find a suitable template to functional monomer molar ratio for MIP preparations. The molar ratio was chosen based on the comparison of the binding energy of the complexes between the template and functional monomers. Based on the computational results, eight different polymers were prepared using chicoric acid as the template. The MIPs were synthesized in a non-covalent approach via thermal free-radical polymerization, using two different polymerization methods, bulk and suspension. Batch rebinding experiments were performed to evaluate the binding properties of the imprinted polymers. The best results were obtained with a MIP prepared using bulk polymerization with 4-vinylpyridine (4-VP) as the functional monomer and ethylene glycol dimethacrylate (EGDMA) as the crosslinker with a molar ratio of 1:4:20. The best MIP showed selective binding ability toward chicoric acid in the presence of the template's structural analogues, caffeic acid, caftaric acid and chlorogenic acid.