Thermoresponsive Porous Polymer Membrane as a Switchable Enzyme Reactor for d-Amino Acid Oxidase Kinetics Study

Atomic Engineering of Single-Atom Nanozymes for Biomedical Applications

Single-atom nanozymes (SAzymes) showcase not only uniformly dispersed active sites but also meticulously engineered coordination structures. These intricate architectures bestow upon them an exceptional catalytic prowess, thereby captivating numerous minds and heralding a new era of possibilities in the biomedical landscape. Tuning the microstructure of SAzymes on the atomic scale is a key factor in designing targeted SAzymes with desirable functions. This review first discusses and summarizes three strategies for designing SAzymes and their impact on reactivity in biocatalysis. The effects of choices of carrier, different synthesis methods, coordination modulation of first/second shell, and the type and number of metal active centers on the enzyme-like catalytic activity are unraveled. Next, a first attempt is made to summarize the biological applications of SAzymes in tumor therapy, biosensing, antimicrobial, anti-inflammatory, and other biological applications from different mechanisms. Finally, how SAzymes are designed and regulated for further realization of diverse biological applications is reviewed and prospected. It is envisaged that the comprehensive review presented within this exegesis will furnish novel perspectives and profound revelations regarding the biomedical applications of SAzymes.

Design of enzyme@metal organic framework composites with thermo-responsivity for colourimetric detection of glucose

Enzyme immobilization on metal-organic frameworks (MOFs) has interested researchers in recent decades due to the outstanding characteristics of MOFs. However, despite some enzyme@MOF composites exhibiting better tolerance, stability and catalysis than free enzymes, boosting the catalytic performance of stimuli-responsive polymer-grafted MOFs composites remains a challenging task. Herein, a glucose oxidase (GOx)-horseradish peroxidase (HRP)@MOF (UiO-66-NH2, U)@polymer composite with tunable catalytic ability was constructed by modification with thermo-responsive poly(N-isopropylacrylamide) (PN) via a surface-selective post-synthetic protocol. Temperature increases changed the PN-based soft armour from a "stretch" to a "coil" conformation on the MOF surface, resulting in the confinement effect and boosting the catalytic performance of the GOx-HRP@U@PN composites. Compared with its maximum catalytic reaction rate at 25 °C, the proposed composites showed 18-fold improvement in catalytic performance at 37 °C. Additionally, a colourimetric method for serum glucose analysis was developed using a GOx-HRP-based catalytic cascade reaction with a linear range from 0.1 to 2.0 mM and a low detection limit of 0.03 mM. Remarkably, the surface PN-shell-based soft armour proved to be the key factor for enhancing the catalytic performance of the as-designed composites. The co-immobilization of GOx-HRP onto the thermo-responsive U@PN surface provides a new approach for the development of highly sensitive colourimetric glucose sensing protocols.

Fabrication of Polymer Membrane Enzyme Reactors with a Dual-Responsive Feature for Cascade Enzyme Reaction Regulation

Enzymes are known to drive biological processes efficiently and uniquely. However, the integration of multienzymes and immobilization technology to improve the stability of enzymes and boost the catalytic efficiency in cascade reactions by controlling the biocatalysis process in complex conditions via an external stimulus is still facing a significant challenge. Herein, we demonstrate a concept for cascade enzyme reaction regulation by controlling the catalytic efficiency step by step based on a dual-stimuli-responsive porous polymer membrane enzyme reactor (DPMER). Poly(styrene-maleicanhydride-acrylic acid-4-[(4-methacryloyloxy)phenylazo] benzoic acid) was designed for the fabrication of the DPMER with glutaminase and alanine aminotransferase as the model modified enzymes. Under UV light irradiation and by regulating the solution pH, the cascade enzyme reaction was carried out step by step. The polymer membrane surface demonstrated a configuration change while improving the enzymolysis efficiency of the DPMER. The enzymatic kinetics of the DPMER was investigated by a chiral capillary electrophoresis technique, and the cascade enzyme reaction regulation capability was evaluated. Under pH of 4.9 and 365 nm UV irradiation, the poly(4-[(4-methacryloyloxy)phenylazo] benzoic acid) and poly(acrylic acid) moieties changed from a "stretched state" to a "curled state" to form surface nanopores, which embedded the enzymes into the surface nanopores while causing the spatial confinement effect and enhancing the enzymolysis efficiency of the DPMER by 9.9-fold in comparison with the free enzymes. This concept provided a potential platform for cascade enzyme reaction regulation and highlighted the perspective of stimuli-responsive polymers.

Magnetic Nanoparticle-Containing Supports as Carriers of Immobilized Enzymes: Key Factors Influencing the Biocatalyst Performance

In this short review (Perspective), we identify key features of the performance of biocatalysts developed by the immobilization of enzymes on the supports containing magnetic nanoparticles (NPs), analyzing the scientific literature for the last five years. A clear advantage of magnetic supports is their easy separation due to the magnetic attraction between magnetic NPs and an external magnetic field, facilitating the biocatalyst reuse. This allows for savings of materials and energy in the biocatalytic process. Commonly, magnetic NPs are isolated from enzymes either by polymers, silica, or some other protective layer. However, in those cases when iron oxide NPs are in close proximity to the enzyme, the biocatalyst may display a fascinating behavior, allowing for synergy of the performance due to the enzyme-like properties shown in iron oxides. Another important parameter which is discussed in this review is the magnetic support porosity, especially in hierarchical porous supports. In the case of comparatively large pores, which can freely accommodate enzyme molecules without jeopardizing their conformation, the enzyme surface ordering may create an optimal crowding on the support, enhancing the biocatalytic performance. Other factors such as surface-modifying agents or special enzyme reactor designs can be also influential in the performance of magnetic NP based immobilized enzymes.

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.