RESUMO
Immobilization of enzymes is one of the protein engineering methods used to improve their thermal and long-term stabilities. Immobilized pectinase has become an essential biocatalyst for optimization in the food processing industry. Herein, nanostructured magnetic nanoparticles were prepared in situ for use as supports to immobilize pectinase. The structural, morphological, optical and magnetic features and the chemical compositions of the nanoparticles were characterized. Nanoparticle agglomeration and low porosity were observed due to the synthetic conditions. These nanoparticles exhibited superparamagnetic behavior, which is desirable for biotechnological applications. The maximum retention rate for the enzyme was observed at pH 4.5 with a value of 1179.3 U/mgNP (units per milligram of nanoparticle), which was equivalent to a 65.6% efficiency. The free and immobilized pectinase were affected by the pH and temperature. The long-term instability caused 40% and 32% decreases in the specific activities of the free and immobilized pectinase, respectively. The effects of immobilization were analyzed with kinetic and thermodynamic studies. These results indicated a significant affinity for the substrate, a decreased reaction rate, and improved thermal stability of the immobilized pectinase. The reusability of the immobilized pectinase was preserved effectively during cycling, with only a 21.2% decrease in activity observed from the first to the last use. Therefore, alternative magnetic nanoparticles are presented for immobilizing and maintaining the thermostability of pectinase.
RESUMO
Nanostructured Zn1-xYbxO (0.0 ≤ x ≤ 0.1) powders were prepared by the solution method using polyvinyl alcohol (PVA) and sucrose. The effect of the ytterbium doping content on the structural, morphological, optical and antimicrobial properties was analyzed. X-ray diffraction (XRD) analysis revealed that the hexagonal wurtzite structure was retained, and no secondary phases due to doping were observed. The crystallite size was under 20 nm for all the Zn1-xYbxO (0.0 ≤ x ≤ 0.1) powders. The optical band gap was calculated, and the results revealed that this value increased with the ytterbium content, and the Eg values varied from 3.06 to 3.10 eV. The surface chemistry of the powders was analyzed using X-ray photoelectron spectroscopy (XPS), and the results confirmed the oxidation state of ytterbium as 3+ for all the samples. Zn1-xYbxO (0.0 ≤ x ≤ 0.1) nanoparticles were tested as antimicrobial agents against Staphylococcus aureus and Escherichia coli, resulting in a potential antimicrobial effect at most of the tested concentrations. These results were used in an artificial neural network (ANN). The results showed that it is possible to generate a model capable of forecasting the absorbance with good precision (error of 1-2%).
Assuntos
Anti-Infecciosos , Nanopartículas , Óxido de Zinco , Antibacterianos/farmacologia , Anti-Infecciosos/farmacologia , Escherichia coli , Staphylococcus aureus , Óxido de Zinco/farmacologiaRESUMO
Improving enzyme immobilization with high loading capacity and achieving direct electron transfer (DET) between the enzyme and the electrode surface is key to designing highly sensitive enzymatic electrochemical biosensors. Herein, we report a novel approach based on the selective modification of the outer surface of halloysite nanotubes (HNTs) that supports silver nanoparticles (AgNPs) to obtain a hybrid nanocomposite. AgNPs of about 10 nm average size could be uniformly supported on silane-modified HNTs through in situ reduction of Ag+ ions. The resultant nanocomposite shows an excellent support capability for the effective immobilization and electrical wiring of redox enzyme glucose oxidase (GOx). The GOx immobilized HNT/AgNPs were deposited on the glassy carbon electrode (GCE) and utilized for the bioelectrocatalyzed electrochemical detection of glucose. The GOx modified composite electrodes show glucose sensitivity as high as 5.1 µA mM-1 cm-2, which is higher than for the electrodes prepared without surface functionalization.