High-Sensitivity Enzymatic Glucose Sensor Based on ZnO Urchin-like Nanostructure Modified with Fe3O4 Magnetic Particles

A novel and efficient enzymatic glucose sensor was fabricated based on Fe3O4 magnetic nanoparticles (Fe3O4MNPs)-modified urchin-like ZnO nanoflowers (ZnONFs). ZnONFs were hydrothermally synthesizing on a flexible PET substrate. Fe3O4MNPs were deposited on the surface of the ZnONFs by the drop-coating process. The results showed that the urchin-like ZnONFs provided strong support for enzyme adsorption. For Fe3O4MNPs, it significantly promoted the redox electron transfer from the active center of GOx to the ZnO nanoflowers beneath. More importantly, it promoted the hydrolysis of H2O2, the intermediate product of glucose catalytic reaction, and thus improved the electron yield. The sensitivity of the Nafion/GOx/Fe3O4MNPs/ZnONFs/Au/PET sensor was up to 4.52 μA·mM−1·cm−2, which was improved by 7.93 times more than the Nafion/GOx/ZnONFs/Au/PET sensors (0.57 μA·mM−1·cm−2). The detection limit and linear range were also improved. Additionally, the as-fabricated glucose sensors show strong anti-interference performance in the test environment containing organic compounds (such as urea, uric acid, and ascorbic acid) and inorganic salt (for instance, NaCl and KCl). The glucose sensor’s service life was evaluated, and it can still maintain about 80% detection performance when it was reused about 20 times. Compared with other existing sensors, the as-fabricated glucose sensor exhibits an ultrahigh sensitivity and wide detection range. In addition, the introduction of Fe3O4MNPs optimized the catalytic efficiency from the perspective of the reaction mechanism and provided potential ideas for improving the performance of other enzymatic biosensors.

Pengaruh Radiasi Microwave dan Perlakuan Asam pada Batubara Peringkat Rendah terhadap Perolehan Biosolubilisasi Menggunakan Neurospora intermedia

Abstrak. Biosolubilisasi batubara peringkat rendahmerupakan teknologi yang menjanjikan untuk mendapatkan bahan bakar cair yang ramah lingkungan. Biosolubilisasi batubara peringkat rendah dapat dilakukan dengan menggunakan mikroorganisme seperti Neurospora intermedia yang mampu menghasilkan enzim-enzim pensolubilisasi. Mekanisme biosolubilisasibatubaraterjadikarenaadsorpsienzim-enzim tersebutkepermukaan partikel batubara, sehingga proses perlakuan awal batubara perlu dilakukan untuk memudahkan proses adsorpsi enzim.Penelitian ini dilakukan untuk mengkaji pengaruh perlakuan awal partikel batubara peringkat rendah terhadap struktur batubara dan perolehan biosolubilisasi. Pengaruh perlakuan awal tersebut dikaji dengan membandingkan biosolubilisasi menggunakan partikel batubara tanpa perlakuan awal (B1), perlakuan fisik dengan memberikan radiasi microwave 511 Watt selama 5 menit (B2), perlakuan kimiawi dengan merendam partikel batubara dalam HNO3 8 M selama 48 jam (B3), serta perlakuan kombinasi radiasi microwave selama 5 menit dan HNO3 dengan konsentrasi 2, 4, 6, dan 8 M selama 48 jam (B4, B5, B6, dan B7). Partikel batubara B1 memiliki rentang diameter mesopori sebesar 33,97 Å, sedangkan partikel batubara yang telah mengalami perlakuan awal mengalami peningkatan diameter pori namun masih dalam rentang mesopori. Luas permukaan persatuan massa dan volume pori yang tertinggi diperoleh dari perlakuan B3, masing-masing adalah 44,39 m2/g dan 0,09 cc/g. Hasil analisis proksimat dan ultimat menunjukkan bahwa perlakuan asam dapat mengurangi kandungan karbon terikat. Secara kualitatif dapat terlihat bahwa biosolubilisasi batubara B1, B2, B4, dan B5 tidak terjadi dengan baik, sehingga tidak terdapat cairan hitam sebagai hasil batubara yang tersolubilisasi, sedangkan biosolubilisasi batubara B3, B6, dan B7 menghasilkan cairan hitam sejak hari pertama. Secara kuantitatif, biosolubilisasi batubara peringkat rendah menggunakan perlakuan B3 menghasilkan konsentrasi asam humat dan persentase biosolubilisasi yang tertinggi, masing-masing yaitu 186,1 mmol/L dan 67,8%. Kata kunci: biosolubilisasi batubara, HNO3, Neurospora intermedia, radiasi microwave. Abstract. Effect of Microwave Radiation and Acid Treatment on Low Grade Coal on Biosolubilization Acquisition Using Neurospora intermedia. Bio-solubilization of low rank coal is a promising technology to obtain environmentally friendly liquid fuel. Bio-solubilization can be carried out using microorganism, such as Neurospora intermedia, which is capable to produce solubilizing enzymes. Mechanism of coal bio-solubilization occurs due to enzymes adsorption onto surface of coal, so that the low rank coal pre-treatment is needed to easy enzyme adsorption. This research examines the effects of low rank coal pre-treatment towards coal structure and bio-solubilization yields. The effects of the pre-treatment were studied by comparing the bio-solubilization using coal with the following specification: without treatment (B1), physical pre-treatment of 511 Watt microwave radiation for 5 minutes (B2), chemical pre-treatment using 8 M HNO3 for 48 hours (B3), and pre-treatment with a combination of microwave radiation for 5 minutes and acid treatment using various HNO3 concentration of 2, 4, 6, and 8 M for 48 hours (B4, B5, B6, and B7, respectively). Coal particle of B1 had mesopore diameter range of 33.97 Å, while coal particle with pre-treatment have increased pore diameter, but are still in range of mesopore. The coal obtained by B3 process has the highest specific surface area and pore volume, which were 44.39 m2/g and 0.99 cc/g, respectively. The proximate and ultimate analyses showed that acid treatment reduced fixed carbon contain. Coal bio-solubilization of B1, B2, B4, and B5 by qualitative could not be solubilized and there was no black liquid as a result of solubilized coal, meanwhile, B3, B6, and B7 were solubilized easily since the first day. Bio-solubilization of chemically pre-treatment low rank coal, B3, resulted in the highest humic acid concentration and bio-solubilization percentage i.e. 186.1 mmol/L and 67.8%, respectively. Keywords: coal bio-solubilization, HNO3, microwave radiation, Neurospora intermedia.

Magnetically Responsive PA6 Microparticles with Immobilized Laccase Show High Catalytic Efficiency in the Enzymatic Treatment of Catechol

Herewith we report the first attempt towards non-covalent immobilization of Trametes versicolor laccase on neat and magnetically responsive highly porous polyamide 6 (PA6) microparticles and their application for catechol oxidation. Four polyamide supports, namely neat PA6 and such carrying Fe, phosphate-coated Fe and Fe3O4 cores were synthesized in suspension by activated anionic ring-opening polymerization (AAROP) of ε-caprolactam (ECL). Enzyme adsorption efficiency up to 92% was achieved in the immobilization process. All empty supports and PA6 laccase complexes were characterized by spectral and synchrotron WAXS/SAXS analyses. The activity of the immobilized laccase was evaluated using 2,2’-Azino-bis-(3- ethylbenzothiazoline-6-sulfonic acid (ABTS) and compared to the native enzyme. The PA6 laccase conjugates displayed up to 105% relative activity at room temperature, pH 4, 40 °C and 20 mM ionic strength (citrate buffer). The kinetic parameters of the ABTS oxidation were also determined. The reusability of the immobilized laccase-conjugates was proven for five consecutive oxidation cycles of catechol.

A Hybrid Microbial–Enzymatic Fuel Cell Cathode Overcomes Enzyme Inactivation Limits in Biological Fuel Cells

The construction of optimized biological fuel cells requires a cathode which combines the longevity of a microbial catalyst with the current density of an enzymatic catalyst. Laccase-secreting fungi were grown directly on the cathode of a biological fuel cell to facilitate the exchange of inactive enzymes with active enzymes, with the goal of extending the lifetime of laccase cathodes. Directly incorporating the laccase-producing fungus at the cathode extends the operational lifetime of laccase cathodes while eliminating the need for frequent replenishment of the electrolyte. The hybrid microbial–enzymatic cathode addresses the issue of enzyme inactivation by using the natural ability of fungi to exchange inactive laccases at the cathode with active laccases. Finally, enzyme adsorption was increased through the use of a functionally graded coating containing an optimized ratio of titanium dioxide nanoparticles and single-walled carbon nanotubes. The hybrid microbial–enzymatic fuel cell combines the higher current density of enzymatic fuel cells with the longevity of microbial fuel cells, and demonstrates the feasibility of a self-regenerating fuel cell in which inactive laccases are continuously exchanged with active laccases.

Rational feeding strategies of substrate and enzymes to enzymatic hydrolysis bioreactors

Bioreactors operating in fed-batch mode improve the enzymatic hydrolysis productivity at high biomass loadings. The present work aimed to apply rational feeding strategies of substrates (pretreated sugarcane straw) and enzymes (CellicCtec2?) to achieve sugar titers at industrial levels. The instantaneous substrate concentration was kept constant at 5 % (w/v) along the fed-batch, and the enzyme dosage inside the bioreactor was adjusted so that the reaction rate was not less than a pre-defined value (a percentage of the initial reaction rate - rmin). When r reached values below rmin, enzyme pulses were applied to return the reaction rate to its initial value (r0). The optimized feeding policy indicated a reaction rate maintained at a minimum of 70 % of r0, based on the trade-off between glucose productivity and enzyme saving. Initially, it was possible to process a total of 21 % (w/v) solid load, achieving 160 g/L of glucose concentration and 80 % of glucose yield. It was verified that non-productive enzyme adsorption was the main reason for some reduction of hydrolysis yield regarding the theoretical cellulose-to-glucose conversion. An increment of 30 g/L in the final glucose concentration was achieved when a lignin-blocking additive (soybean protein) was used in the enzymatic hydrolysis.

Direct Electrochemical Enzyme Electron Transfer on Electrodes Modified by Self-Assembled Molecular Monolayers

Self-assembled molecular monolayers (SAMs) have long been recognized as crucial “bridges” between redox enzymes and solid electrode surfaces, on which the enzymes undergo direct electron transfer (DET)—for example, in enzymatic biofuel cells (EBFCs) and biosensors. SAMs possess a wide range of terminal groups that enable productive enzyme adsorption and fine-tuning in favorable orientations on the electrode. The tunneling distance and SAM chain length, and the contacting terminal SAM groups, are the most significant controlling factors in DET-type bioelectrocatalysis. In particular, SAM-modified nanostructured electrode materials have recently been extensively explored to improve the catalytic activity and stability of redox proteins immobilized on electrochemical surfaces. In this report, we present an overview of recent investigations of electrochemical enzyme DET processes on SAMs with a focus on single-crystal and nanoporous gold electrodes. Specifically, we consider the preparation and characterization methods of SAMs, as well as SAM applications in promoting interfacial electrochemical electron transfer of redox proteins and enzymes. The strategic selection of SAMs to accord with the properties of the core redox protein/enzymes is also highlighted.