Applications and immobilization strategies of the copper-centred laccase enzyme : a review

DATA AVAILABILITY STATEMENT: No data was used for the research described in the article.Laccase is a multi-copper enzyme widely expressed in fungi, higher plants, and bacteria which facilitates the direct reduction of molecular oxygen to water (without hydrogen peroxide production) accompanied by the oxidation of an electron donor. Laccase has attracted attention in biotechnological applications due to its non-specificity and use of molecular oxygen as secondary substrate. This review discusses different applications of laccase in various sectors of food, paper and pulp, waste water treatment, pharmaceuticals, sensors, and fuel cells. Despite the many advantages of laccase, challenges such as high cost due to its non-reusability, instability in harsh environmental conditions, and proteolysis are often encountered in its application. One of the approaches used to minimize these challenges is immobilization. The various methods used to immobilize laccase and the different supports used are further extensively discussed in this review.The National Research Foundation (NRF) of South Africa.https://www.cell.com/heliyonChemical Engineerin

Silver–zinc oxide nanocomposite antiseptic from the extract of Bidens pilosa

Silver nanoparticles (Ag-NPs), zinc oxide (ZnO-NPs) and zinc oxide–silver (ZnO–Ag-NPs) were biosynthesized based on the rich matrix of alkaloids, flavones, tannins capping/stabilizing agents present in Bidens pilosa extract. Different plant parts-root, leaf and seed ware used to prepare the plant extract for synthesis. Also, zinc and silver nitrate salts were used as precursor materials. The surface plasmon peaks (SPR) based on the UV–Vis results for the Ag-NPs, ZnO-NPs were located between 408–411 and 365–450 nm respectively. The SPR peaks for the Ag–ZnO-NPs occurred at 300–450 nm indicating both blue and red shifts. The Ag–ZnO-NPs SPR shifts were associated with possible nanoparticle size reduction and change in dielectric constant of the synthesis medium. Raman measurement peaks at 356, 484, 1350, 1578, 2435 cm−1 associated with OH, –C==C–, –C–O, S=O, =C–H moieties indicated successful capping. Nanoparticle yield was temperature dependent and optimal yield could not be tied to a particular plant part as source of extract. Tunneling electron microscope results showed Ag-NPs and ZnO-NPs were globular/spherical with a diameter range of 2–20 nm. Interestingly, ZnO-NPs TEM displayed isolated miniaturized globular nanoparticles (< 2 nm) which then joined up to form a large donut shaped structure indicating different formation mechanisms for the nanoparticles. XRD results showed the Ag-NPs, ZnO-NPs and the Ag–ZnO-NPs particles were crystalline in nature

Recent Advances in Applications of Oxidases and Peroxidases Polymer-Based Enzyme Biocatalysts in Sensing and Wastewater Treatment: A Review

Oxidase and peroxidase enzymes have attracted attention in various biotechnological industries due to their ease of synthesis, wide range of applications, and operation under mild conditions. Their applicability, however, is limited by their poor stability in harsher conditions and their non-reusability. As a result, several approaches such as enzyme engineering, medium engineering, and enzyme immobilization have been used to improve the enzyme properties. Several materials have been used as supports for these enzymes to increase their stability and reusability. This review focusses on the immobilization of oxidase and peroxidase enzymes on metal and metal oxide nanoparticle-polymer composite supports and the different methods used to achieve the immobilization. The application of the enzyme-metal/metal oxide-polymer biocatalysts in biosensing of hydrogen peroxide, glucose, pesticides, and herbicides as well as blood components such as cholesterol, urea, dopamine, and xanthine have been extensively reviewed. The application of the biocatalysts in wastewater treatment through degradation of dyes, pesticides, and other organic compounds has also been discussed

Electroconductive Polyaniline&ndash;Ag-ZnO Green Nanocomposite Material

Metal-conducting polyaniline (PANI)-based nanocomposite materials have attracted attention in various applications due to their synergism of electrical, mechanical, and optical properties of the initial components. Herein, metal-PANI nanocomposites, including silver nanoparticle-polyaniline (AgNP-PANI), zinc oxide nanoparticle-polyaniline (ZnONP-PANI), and silver-zinc oxide nanoparticle-polyaniline (Ag&ndash;ZnONP-PANI), were prepared using the two processes. Nanocomposite-based electrode platforms were prepared by depositing AgNPs, ZnONPs, or Ag&ndash;ZnONPs on a PANI modified glass carbon electrode (GCE) in the presence of 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide/N-Hydroxysuccinimide (EDC/NHS, 1:2) as coupling agents. The incorporation of AgNPs, ZnONPs, and Ag&ndash;ZnONPs onto PANI was confirmed by UV-Vis spectrophotometry, which showed five absorbance bands at 216 nm, 412 nm, 464 nm, 550 nm, and 831 nm (i.e., transition of &pi;-&pi;*, &pi;-polaron band transition, polaron-&pi;* electronic transition, and AgNPs). The FTIR characteristic signatures of the nanocomposite materials exhibited stretching arising from C&ndash;H aromatic, C&ndash;O, and C&ndash;N stretching mode for benzenoid rings, and =C&ndash;H plane bending vibration formed during protonation. The CV voltammograms of the nanocomposite materials showed a quasi-reversible behavior with increased redox current response. Notably, AgNP&ndash;PANI&ndash;GCE electrode showed the highest conductivity, which was attributed the high conductivity of silver. The increase in peak currents exhibited by the composites shows that AgNPs and ZnONPs improve the electrical properties of PANI, and they could be potential candidates for electrochemical applications

Synthesis and Assessment of Antimicrobial Composites of Ag Nanoparticles or AgNO₃ and Egg Shell Membranes

Engineering research has been expanded by the advent of material fusion, which has led to the development of composites that are more reliable and cost-effective. This investigation aims to utilise this concept to promote a circular economy by maximizing the adsorption of silver nanoparticles and silver nitrate onto recycled chicken eggshell membranes, resulting in optimized antimicrobial silver/eggshell membrane composites. The pH, time, concentration, and adsorption temperatures were optimized. It was confirmed that these composites were excellent candidates for use in antimicrobial applications. The silver nanoparticles were produced through chemical synthesis using sodium borohydride as a reducing agent and through adsorption/surface reduction of silver nitrate on eggshell membranes. The composites were thoroughly characterized by various techniques, including spectrophotometry, atomic absorption spectrometry, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, as well as agar well diffusion and MTT assay. The results indicate that silver/eggshell membrane composites with excellent antimicrobial properties were produced using both silver nanoparticles and silver nitrate at a pH of 6, 25 °C, and after 48 h of agitation. These materials exhibited remarkable antimicrobial activity against Pseudomonas aeruginosa and Bacillus subtilis, resulting in 27.77% and 15.34% cell death, respectively