Nano-in-Nano Approach for Enzyme Immobilization Based on Block Copolymers

Self-Assembled Block Copolymers as a Facile Pathway to Create Functional Nanobiosensor and Nanobiomaterial Surfaces

Block copolymer (BCP) surfaces permit an exquisite level of nanoscale control in biomolecular assemblies solely based on self-assembly. Owing to this, BCP-based biomolecular assembly represents a much-needed, new paradigm for creating nanobiosensors and nanobiomaterials without the need for costly and time-consuming fabrication steps. Research endeavors in the BCP nanobiotechnology field have led to stimulating results that can promote our current understanding of biomolecular interactions at a solid interface to the never-explored size regimes comparable to individual biomolecules. Encouraging research outcomes have also been reported for the stability and activity of biomolecules bound on BCP thin film surfaces. A wide range of single and multicomponent biomolecules and BCP systems has been assessed to substantiate the potential utility in practical applications as next-generation nanobiosensors, nanobiodevices, and biomaterials. To this end, this Review highlights pioneering research efforts made in the BCP nanobiotechnology area. The discussions will be focused on those works particularly pertaining to nanoscale surface assembly of functional biomolecules, biomolecular interaction properties unique to nanoscale polymer interfaces, functionality of nanoscale surface-bound biomolecules, and specific examples in biosensing. Systems involving the incorporation of biomolecules as one of the blocks in BCPs, i.e., DNA-BCP hybrids, protein-BCP conjugates, and isolated BCP micelles of bioligand carriers used in drug delivery, are outside of the scope of this Review. Looking ahead, there awaits plenty of exciting research opportunities to advance the research field of BCP nanobiotechnology by capitalizing on the fundamental groundwork laid so far for the biomolecular interactions on BCP surfaces. In order to better guide the path forward, key fundamental questions yet to be addressed by the field are identified. In addition, future research directions of BCP nanobiotechnology are contemplated in the concluding section of this Review.

An Artificial Miniaturized Peroxidase for Signal Amplification in Lateral Flow Immunoassays

Signal amplification strategies are widely used for improving the sensitivity of lateral flow immunoassays (LFiAs). Herein, the artificial miniaturized peroxidase Fe(III)-MimochromeVI*a (FeMC6*a), immobilized on gold nanoparticles (AuNPs), is used as a strategy to obtain catalytic signal amplification in sandwich immunoassays on lateral flow strips. The assay scheme uses AuNPs decorated with the mini-peroxidase FeMC6*a and anti-human-IgG as a detection antibody (dAb), for the detection of human-IgG, as a model analyte. Recognition of the analyte by the capture and detection antibodies is first evidenced by the appearance of a red color in the test line (TL), due to the accumulation of AuNPs. Subsequent addition of 3,3',5,5'-tetramethylbenzidine (TMB) induces an increase of the test line color, due to the TMB being converted into an insoluble colored product, catalyzed by FeMC6*a. This work shows that FeMC6*a acts as an efficient catalyst in paper, increasing the sensitivity of an LFiA up to four times with respect to a conventional LFiA. Furthermore, FeMC6*a achieves lower limits of detection that are found in control experiments where it is replaced with horseradish peroxidase (HRP), its natural counterpart. This study represents a significant proof-of-concept for the development of more sensitive LFiAs, for different analytes, based on properly designed artificial metalloenzymes.

A lipase/poly (ionic liquid)-styrene microspheres/PVA composite hydrogel for esterification application

Enzymes are particularly attractive as biocatalysts for the green synthesis of chemicals and pharmaceuticals. However, the traditional enzyme purification and separation process is complex and inefficient, which limits the wide application of enzyme catalysis. In this paper, an efficient strategy for enzyme purification and immobilization in one step is proposed. A novel poly (ionic liquid)-styrene microsphere is prepared by molecular design and synthesis for adsorbing and purifying high activity lipase from fermentation broth directly. By optimizing the surface morphologies and charge of the microspheres, the enzyme loading is significantly improved. In order to further stabilize the catalytic environment of lipase, the resulting lipase/poly (ionic liquid)-styrene microspheres are immobilized in physical crosslinking hydrogel to obtain a complex lipase catalytic system, which can be prepared into various shapes according to the requirements of catalytic environment. In the actual catalytic reaction process, this complex lipase catalytic system exhibits excellent catalytic activity (6314.69 ± 21.27 U mg^-1) and good harsh environment tolerance compared with the lipase fermentation broth (1672.87 ± 36.68 U mg^-1). Under the condition of cyclic catalysis, the complex lipase catalytic system shows the outstanding reusability (After 8 cycles the enzymatic activity is still higher than that of the lipase fermentation broth) and is easily separated from the products.

Robust nanocarriers to engineer nanobiocatalysts for bioprocessing applications

The synergistic integration of bio-catalysis engineering with nanostructured materials, as unique multifunctional carrier matrices, has emerged as a new interface of nanobiocatalysis (NBC). NBC is an emerging innovation that offers significant considerations to expand the designing and fabrication of robust catalysts at the nanoscale with improved catalytic characteristics for multipurpose bioprocessing applications. In addition, nanostructured materials with unique structural, physical, chemical, and functional entities have manifested significant contributions in mimicking the enzyme microenvironment. A fine-tuned enzyme microenvironment with an added-value of NBC offers chemo- regio- and stereo- selectivities and specificities. Furthermore, NBC is growing rapidly and will become a powerful norm in bio-catalysis with much controlled features, such as selectivity, specificity, stability, resistivity, induce activity, reaction efficacy, multi-usability, improved mass transfer efficiency, high catalytic turnover, optimal yield, ease in recovery, and cost-effectiveness. Considering the above critics and unique structural, physicochemical, and functional attributes, herein, we present and discuss advances in NBC and its bioprocessing applications in different fields. Briefly, this review is focused on four parts, i.e., (1) NBC as a drive towards applied nanobiocatalysts (as an introduction with opportunities), (2) promising nanocarriers to develop nanobiocatalysts, (3) applications in the fields of biotransformation, biofuel production, carbohydrate hydrolysis, bio-/nanosensing, detergent formulations, and extraction and purification of value-added compounds, and (4) current challenges, concluding remarks, and future trends.

Design of Switchable Enzyme Carriers Based on Stimuli-Responsive Porous Polymer Membranes for Bioapplications

Design of efficient enzyme carriers, where enzymes are conjugated to supports, has become an attractive research avenue. Immobilized enzymes are advantageous for practical applications because of their convenience in handling, ease of separation, and good reusability. However, the main challenge is that these traditional enzyme carriers are unable to regulate the enzymolysis efficiency or to protect the enzymes from proteolytic degradation, which restricts their effectiveness of enzymes in bioapplications. Enlightened by the stimuli-responsive channels in the natural cell membranes, conjugation of the enzymes within flat-sheet stimuli-responsive porous polymer membranes (SR-PPMs) as artificial cell membranes is an efficient strategy for circumventing this challenge. Controlled by the external stimuli, the multifunctional polymer chains, which are incorporated within the membranes and attached to the enzyme, change their structures to defend the enzyme from the external environmental disturbances and degradation by proteinases. Specifically, smart SR-PPM enzyme carriers (SR-PPMECs) not only permit convective substrate transfer through the accessible porous network, dramatically improving enzymolysis efficiency due to the adjustable pore sizes and the confinement effect, but they also act as molecular switches for regulating its permeability and selectivity. In this review, the concept of SR-PPMECs is presented. It covers the latest developments in design strategies of flat-sheet SR-PPFMs, fabrication protocols of SR-PPFMECs, strategies for the regulation of enzymolysis efficiency, and their cutting-edge bioapplications.

Understanding Design Rules for Optimizing the Interface between Immobilized Enzymes and Random Copolymer Brushes

A long-standing goal in the field of biotechnology is to develop and understand design rules for the stabilization of enzymes upon immobilization to materials. While immobilization has sometimes been successful as a strategy to stabilize enzymes, the design of synthetic materials that stabilize enzymes remains largely empirical. We sought to overcome this challenge by investigating the mechanistic basis for the stabilization of immobilized lipases on random copolymer brush surfaces comprised of poly(ethylene glycol) methacrylate (PEGMA) and sulfobetaine methacrylate (SBMA), which represent novel heterogeneous supports for immobilized enzymes. Using several related but structurally diverse lipases, including Bacillus subtilis lipase A (LipA), Rhizomucor miehei lipase, Candida rugosa lipase, and Candida antarctica lipase B (CALB), we showed that the stability of each lipase at elevated temperatures was strongly dependent on the fraction of PEGMA in the brush layer. This dependence was explained by developing and applying a new algorithm to quantify protein surface hydrophobicity, which involved using unsupervised cluster analysis to identify clusters of hydrophobic atoms. Characterization of the lipases showed that the optimal brush composition correlated with the free energy of solvation per enzyme surface area, which ranged from -17.1 kJ/mol·nm² for LipA to -11.8 kJ/mol·nm² for CALB. Additionally, using this algorithm, we found that hydrophobic patches consisting of aliphatic residues had a higher free energy than patches consisting of aromatic residues. By providing the basis for rationally tuning the interface between enzymes and materials, this understanding will transform the use of materials to reliably ruggedize enzymes under extreme conditions.

Clickable artificial heme-peroxidases for the development of functional nanomaterials

Artificial metalloenzymes as catalysts are promising candidates for their use in different technologies, such as bioremediation, biomass transformation, or biosensing. Despite this, their practical exploitation is still at an early stage. Immobilized natural enzymes have been proposed to enhance their applicability. Immobilization may offer several advantages: (i) catalyst reuse; (ii) easy separation of the enzyme from the reaction medium; (iii) better tolerance to harsh temperature and pH conditions. Here, we report an easy immobilization procedure of an artificial peroxidase on different surfaces, by means of click chemistry. FeMC6*a, a recently developed peroxidase mimic, has been functionalized with a pegylated aza-dibenzocyclooctyne to afford a "clickable" biocatalyst, namely FeMC6*a-PEG₄@DBCO, which easily reacts with azide-functionalized molecules and/or nanomaterials to afford functional bioconjugates. The clicked biocatalyst retains its structural and, to some extent, its functional behaviors, thus housing high potential for biotechnological applications.

Lipase immobilized on functionalized superparamagnetic few-layer graphene oxide as an efficient nanobiocatalyst for biodiesel production from Chlorella vulgaris bio-oil

BACKGROUND

Microalgae, due to its well-recognized advantages have gained renewed interest as potentially good feedstock for biodiesel. Production of fatty acid methyl esters (FAMEs) as a type of biodiesel was carried out from Chlorella vulgaris bio-oil. Biodiesel was produced in the presence of nano-biocatalysts composed of immobilized lipase on functionalized superparamagnetic few-layer graphene oxide via a transesterification reaction. A hybrid of few-layer graphene oxide and Fe3O4 (MGO) was prepared and characterized. The MGO was functionalized with 3-aminopropyl triethoxysilane (MGO-AP) as well as with a couple of AP and glutaraldehyde (MGO-AP-GA). The Rhizopus oryzae lipase (ROL) was immobilized on MGO and MGO-AP using electrostatic interactions as well as on MGO-AP-GA using covalent bonding. The supports, MGO, MGO-AP, and MGO-AP-GA, as well as nano-biocatalyst, ROL/MGO, ROL/MGO-AP, and ROL/MGO-AP-GA, were characterized using FESEM, VSM, FTIR, and XRD. The few-layer graphene oxide was characterized using AFM and the surface charge of supports was evaluated with the zeta potential technique. The nano-biocatalysts assay was performed with an evaluation of kinetic parameters, loading capacity, relative activity, time-course thermal stability, and storage stability. Biodiesel production was carried out in the presence of nano-biocatalysts and their reusability was evaluated in 5 cycles of transesterification reaction.

RESULTS

The AFM analysis confirmed the few-layer structure of graphene oxide and VSM also confirmed that all supports were superparamagnetic. The maximum loading of ROL (70.2%) was related to MGO-AP-GA. The highest biodiesel conversion of 71.19% achieved in the presence of ROL/MGO-AP-GA. Furthermore, this nano-biocatalyst could maintain 58.77% of its catalytic performance after 5 cycles of the transesterification reaction and was the best catalyst in the case of reusability.

CONCLUSIONS

In this study, the synthesized nano-biocatalyst based on bare and functionalized magnetic graphene oxide was applied and optimized in the process of converting microalgae bio-oil to biodiesel for the first time and compared with bare lipase immobilized on magnetic nanoparticles. Results showed that the loading capacity, kinetic parameters, thermal stability, and storage stability improved by the functionalization of MGO. The biocatalysts, which were prepared via covalent bonding immobilization of enzyme generally, showed better characteristics.

Real-time regulation of catalysis by remote-controlled enzyme-conjugated gold nanorod composites for aldol reaction-based applications

Remote-controlled nanomaterials, used to regulate rapid conversion of light energy into internal energy, are an emerging technology for achieving real-time control of enzymatic and catalytic industrial processes.

Artificial Heme Enzymes for the Construction of Gold-Based Biomaterials

Many efforts are continuously devoted to the construction of hybrid biomaterials for specific applications, by immobilizing enzymes on different types of surfaces and/or nanomaterials. In addition, advances in computational, molecular and structural biology have led to a variety of strategies for designing and engineering artificial enzymes with defined catalytic properties. Here, we report the conjugation of an artificial heme enzyme (MIMO) with lipoic acid (LA) as a building block for the development of gold-based biomaterials. We show that the artificial MIMO@LA can be successfully conjugated to gold nanoparticles or immobilized onto gold electrode surfaces, displaying quasi-reversible redox properties and peroxidase activity. The results of this work open interesting perspectives toward the development of new totally-synthetic catalytic biomaterials for application in biotechnology and biomedicine, expanding the range of the biomolecular component aside from traditional native enzymes.