Improved adenylate cyclase activity via affinity immobilization onto co-modified GO with bio-inspired adhesive and PEI

Spacer arm of ionic liquids facilitated laccase immobilization on magnetic graphene enhancing its stability and catalytic performance

To fulfill the requirements of environmental protection, a magnetically recoverable immobilized laccase has been developed for water pollutant treatment. In order to accomplish this objective, we propose a polydopamine-coated magnetic graphene material that addresses the challenges associated with accumulation caused by electrostatic interactions between graphene and enzyme molecules, which can lead to protein denaturation and inactivation. To achieve this, we present a polydopamine-coated magnetic graphene material that binds to the enzyme molecule through flexible spacer arms formed by ionic liquids. The immobilized laccase exhibited a good protective effect on laccase and showed a high stability and recycling ability. Laccase-ILs-PDA-MGO has a wider pH and temperature range and retains about 80% of its initial activity even after incubation at 50 °C for 2 h, which is 2.2 times more active than free laccase. Furthermore, the laccase-ILs-PDA-MGO exhibited a remarkable removal efficiency of 97.0% and 83.9% toward 2,4-DCP and BPA within 12 h at room temperature. More importantly, laccase-ILs-PDA-MGO can be recovered from the effluent and used multiple times for organic pollutant removal, while maintaining a relative removal efficiency of 80.6% for 2,4-DCP and 81.4% for BPA after undergoing seven cycles. In this study, a strategy for laccase immobilization by utilizing ILs spacer arms to modify GO aims to provide valuable insights into the advancement of efficient enzyme immobilization techniques and the practical application of immobilized enzymes in wastewater treatment.

Enhanced stability and catalytic performance of laccase immobilized on magnetic graphene oxide modified with ionic liquids

Graphite oxide (GO) is an excellent laccase immobilization material. However, the electrostatic interaction between graphene leads to the accumulation of GO, as well as the interaction with the surface of enzyme molecules causing protein denaturation and deactivation, which limits its further industrial application. In this study, the ionic liquids (ILs) modification strategy was proposed to improve the stability and catalytic performance of immobilized laccase. The laccase-ILs-MGO exhibited remarkable enzymatic properties, with significant enhancements in organic solvent tolerance, thermal and operational stability. The laccase-ILs-MGO system exhibited a remarkable removal efficiency of 95.5% towards 2,4-dichlorophenol (2,4-DCP) within 12 h and maintained over 70.0% removal efficiency after seven reaction cycles. In addition, the efficient elimination of other phenolic compounds and recalcitrant polycyclic aromatic hydrocarbons could also be accomplished. Molecular dynamics simulation and molecular docking studies demonstrated that immobilized laccase exhibited superior structural rigidity and stronger hydrogen bond interactions with substrates compared to free laccase, which was beneficial for the stability of both the laccase and substrate degradation efficiency. Therefore, this study proposed a simple and practical strategy for modifying GO with ILs, providing novel insights into developing efficient enzyme immobilization techniques.

Electrochemiluminescence resonance energy transfer between Ru(bpy)32+@Cu3(HHTP)2 and GO-Au composites for C-reactive protein detection

Designing innovative electrochemiluminescence (ECL) immunosensors is critical for the detection of biomarkers with a low concentration and the precise evaluation of clinical diseases. Herein, a Cu₃(hexahydroxytriphenylene)₂ (Cu₃(HHTP)₂) nanoflake-based sandwich-type ECL immunosensor was constructed for C-Reactive Protein (CRP) detection. The Cu₃(HHTP)₂ nanoflake, an electronically conductive metal-organic framework (MOF), has a periodically arranged porous structure with a cavity size of 2 nm, which not only accommodates a large amount of Ru(bpy)₃²⁺ but also confines the spatial diffusion of active species. Therefore, the Ru(bpy)₃²⁺-loaded Cu₃(HHTP)₂ nanocomplex (Ru@CuMOF) as an ECL emitter exhibits an enhanced ECL efficiency. The ECL resonance energy transfer (ECL-RET) was accomplished by combining Ru@CuMOF used as a donor with gold nanoparticles-functionalized graphene oxide nanosheets (GO-Au) utilized as an acceptor. This should be ascribed to the fact that the ECL emission spectrum of Ru@CuMOF shows the strongest signal intensity at 615 nm, overlapping with the absorption spectrum of GO-Au at 580-680 nm. Targeted detection of CRP in human serum samples was achieved by the sandwich-type immunosensor based on the ECL-RET mechanism with a 0.26 pg mL^-1 detection limit. The electro-activated hybrids of Cu₃(HHTP)₂ and ECL emitters provide a new sensing strategy for the high-sensitivity detection of disease markers.

A Novel Method for the Fabrication of Antibacterial Stainless Steel with Uniform Silver Dispersions by Silver Nanoparticle/Polyethyleneimine Composites

Only a few studies have so far focused on the addition of silver to SS316L alloys by conventional sintering methods. Unfortunately, the metallurgical process of silver-containing antimicrobial SS is greatly limited due to the extremely low solubility of silver in iron and its tendency to precipitate at the grain boundaries, resulting in an inhomogeneous distribution of the antimicrobial phase and loss of antimicrobial properties. In this work, we present a novel approach to fabricate antibacterial stainless steel 316L by functional polyethyleneimine-glutaraldehyde copolymer (PEI-co-GA/Ag catalyst) composites. PEI is a highly branched cationic polymer, which makes it exhibit very good adhesion on the surface of the substrate. Unlike the effect of the conventional silver mirror reaction, the introduction of functional polymers can effectively improve the adhesion and distribution of Ag particles on the surface of 316LSS. It can be seen from the SEM images that a large number of silver particles are retained and well dispersed in 316LSS after sintering. PEI-co-GA/Ag 316LSS exhibits excellent antimicrobial properties and does not release free silver ions to affect the surrounding environment. Furthermore, the probable mechanism for the influence of the functional composites on the enhancement of adhesion is also proposed. The formation of a large number of hydrogen bonds and van der Waals forces, as well as the negative zeta potential of the 316LSS surface, can effectively enable the formation of a tight attraction between the Cu layer and the surface of 316LSS. These results meet our expectations of designing passive antimicrobial properties on the contact surface of medical devices.

Biomimetic Polylactic Acid Electrospun Fibers Grafted with Polyethyleneimine for Highly Efficient Methyl Orange and Cr(VI) Removal

The rapid growth of industrialization has resulted in the release of large quantities of pollutants into the environment, especially dyes and heavy metals, which are environmentally hazardous for humans and animals. It is considered as the most promising and environmentally friendly route to develop green materials by using the green modification method, which has no negative impact on the environment. In this work, the green material of polylactic acid (PLA) was used as the substrate material, and a novel modification method of polydopamine (PDA)-assisted polyethyleneimine (PEI) grafting was developed. The electrospun PLA fibers are mainly composed of stereocomplex crystallites, which were achieved via the electrospinning of poly(l-lactic acid) and poly(d-lactic acid). The water-soluble PEI was grafted onto the PDA-modified PLA fibers through the glutaraldehyde-assisted cross-linking reaction. The prepared composite fibers can be degraded, which is environmentally friendly and meets the requirements of sustainable development. The potential application of such PLA composite fibers in wastewater treatment was intensively evaluated. The results show that at appropriate fabrication conditions (PDA concentration of 3 g·L^-1 and a PEI molecular weight of 70,000 g·mol^-1), the composite fibers exhibit the maximum adsorption capacities of 612 and 398.41 mg·g^-1 for methyl orange (MO) and hexavalent chromium [Cr(VI)], respectively. Simultaneously, about 64.79% of Cr(VI) adsorbed on the composite fibers was reduced to Cr(III). The above results show that the PLA composite fibers have a good development prospect in the field of wastewater treatment.

Reversible Adsorption and Detachment of Saccharomyces cerevisiae on Thermoresponsive Poly(N-isopropylacrylamide)-Grafted Fibers for Continuous Immobilized Fermentation

Biofilm-mediated continuous fermentation with cells immobilized has gained much attention in recent years. In this study, thermoresponsive poly(N-isopropylacrylamide)-grafted cotton fibers (PNIPAM-CF) were prepared via an improved surface-initiated atom transfer radical polymerization. The modification process imparted switchable wettability to the surface while maintaining the thermal stability and biocompatibility of the CF. During the ethanol transformation, the rapid, reversible cell adsorption and detachment of Saccharomyces cerevisiae were performed through the modulation of wettability, displaying the enhancement of immobilized biomass and immobilization efficiency from 2.20 g/L and 59.43% to 2.81 g/L and 93.32%, respectively. Moreover, the biofilm adsorption matched well with the Freundlich model, indicating that multilayer adhesion was the main mode of biofilm formation. Based on the accumulation of the biofilm, the fabrication and utilization of PNIPAM-CF improved the efficiency of continuous immobilized fermentation, making the ethanol production reach 26.34 g/L in the sixth batch of fermentation. Meanwhile, wettability regulation further enhanced the reusability of the carrier. Therefore, the findings of this study revealed that the application of smart materials in cell immobilization systems had broad prospects for achieving sustainable and continuous catalysis.

Stabilizing bienzymatic cascade catalysis via immobilization in ZIF-8/GO composites obtained by GO assisted co-growth

Enzyme catalysis has clear advantages in the process of oxidizing glucose to produce gluconic acid. In the enzyme cascade, the improvement of the cascade efficiency is desired but challenging. Graphene oxide (GO) and ZIF-8 composites as enzyme support offer the promising opportunity that not only the cascade efficiency can be improved by control the distance between two enzymes, but also the stability can be improved. Here, a new strategy of GO assisted co-growth of ZIF-8 and enzyme was carried in a one-pot synthesis. Glucose oxidase&catalase immobilized in the ZIF-8/GO composites can obtain 98% residual activity after 15 days of storage with almost no enzyme shedding. The residual activity is still higher than 75% after 5 repeated uses. The presented method of controllable growth of metal organic frameworks on 2D nanosheet can also be extended for renewable energy devices, gas storage and separation of small molecules.