Glucose oxidase and 1-butyl-3-methylimidazolium deposited by AC-electrophoresis on Pt as a glucose bioanode for biofuel cells

Fabrication of glucose bioelectrochemical sensor based on Au@Pd core-shell supported by carboxylated graphene oxide

The study presents a novel electrochemical glucose biosensor based on glucose oxidase (GOx) immobilized on Au@Pd core-shell nanoparticles supported on carboxylated graphene oxide (cGO). The immobilization of GOx was achieved by cross-linking the chitosan biopolymer (CS) including Au@Pd/cGO and glutaraldehyde (GA) on a glassy carbon electrode. The analytical performance of GCE/Au@Pd/cGO-CS/GA/GOx was investigated using amperometry. The biosensor had fast response time (5.2 ± 0.9 s), a satisfactory linear determination range between 2.0 × 10^-5 and 4.2 × 10^-3 M, and limit of detection of 10.4 μM. The apparent Michaelis-Menten constant (K_app) was calculated as 3.04 mM. The fabricated biosensor also exhibited good repeatability, reproducibility, and storage stability. No interfering signals from dopamine, uric acid, ascorbic acid, paracetamol, folic acid, mannose, sucrose, and fructose were observed. The large electroactive surface area of carboxylated graphene oxide is a promising candidate for sensor preparation.

A pH-Sensitive, Stretchable, Antibacterial Artificial Tongue Based on MXene Cross-Linked Ionogel

Dehydration has always been a confusing problem for a hydrogel exposed to air, which restricts its application in practical detection. While an ionogel with unique properties can lock water molecules efficiently due to its low vapor pressure, the design and development of an ionogel with excellent water-locking properties and stability to achieve satisfactory detection are thus highly desirable. In this work, a pH-sensitive, stretchable, antibacterial, and stable ionogel artificial tongue was fabricated through dual cross-linking. The artificial tongue consisted of MXene as a cross-linking agent, phenol red as an indicator, gelatin, N-(2-hydroxyethyl) acrylamide, and 1-butyl-3-methylimidazolium chloride as the three-dimensional polymer network. A small quantity of MXene was used as a cross-linker the first time to promote the initiator in the system to generate free radicals, accelerating the reaction process and the multilevel linkage among the polymers. Meanwhile, the indicator phenol red was introduced into the ionogel successfully for the first time, showing great stability in 5 weeks. After evaluation by the Brand-Altman analysis, it was found that the method of pH measurement using ionogels had good consistency with the pH meter measurement method. Additionally, the prepared ionogel presented excellent water retention, mechanical stretchability, antibacterial property, and stability, as well as good test results in the test of artificial simulated saliva, demonstrating great potential in clinical applications.

A high performance nanocomposite based bioanode for biofuel cell and biosensor application

Herein, to improve the current density and sensitivity for biofuel cell and glucose sensing application, a bioanode based on redox polymer (PEI-Fc) binding polydopamine (PDA) coated MWCNTs (PEI-Fc/PDA/MWCNTs) nanocomposite and glucose oxidase (GOD) was fabricated. PDA/MWCNTs nanocomposite was prepared by spontaneous self-polymerization of dopamine on MWCNTs surface and the PEI-Fc/PDA/MWCNTs nanocomposite was prepared by a simple self-assembly method. The PEI-Fc/PDA/MWCNTs nanocomposite and the resulting bioanode were fully characterized. A maximum current density of 0.73 mA cm^-2 at the resulting bioanode was obtained by linear sweep voltammetry (LSV) at the scan rate of 50 mV s^-1 with 20 mM glucose concentration. Moreover, a linear range up to 4 mM, a high sensitivity of 57.2 μA mM^-1 cm^-2, a fast response time reaching 95% of the steady current (2 s) and a low limit of detection (0.024 mM) were achieved. The amperometric method demonstrated both the sensitivity and the stability of the bioanode for glucose-sensing was improved by the employed PDA layer. Finally, the biosensor was used for glucose detection in human serum samples showing good recoveries. This study proposed an excellent functional material prepared by a facile self-assembled method for applying in biofuel cells and second-generation biosensors.

Formation of Free-Standing Inverse Opals with Gradient Pores

We demonstrate the fabrication of free-standing inverse opals with gradient pores via a combination of electrophoresis and electroplating techniques. Our processing scheme starts with the preparation of multilayer colloidal crystals by conducting sequential electrophoresis with polystyrene (PS) microspheres in different sizes (300, 600, and 1000 nm). The critical factors affecting the stacking of individual colloidal crystals are discussed and relevant electrophoresis parameters are identified so the larger PS microspheres are assembled successively atop of smaller ones in an orderly manner. In total, we construct multilayer colloidal crystals with vertical stacking of microspheres in 300/600, 300/1000, and 300/600/1000 nm sequences. The inverse opals with gradient pores are produced by galvanostatic plating of Ni, followed by the selective removal of colloidal template. Images from scanning electron microscopy exhibit ideal multilayer close-packed structures with well-defined boundaries among different layers. Results from porometer analysis reveal the size of bottlenecks consistent with those of interconnected pore channels from inverse opals of smallest PS microspheres. Mechanical properties determined by nanoindentation tests indicate significant improvements for multilayer inverse opals as compared to those of conventional single-layer inverse opals.

Kraton based polymeric nanocomposite bioanode for the application in a biofuel cell

The objective of this work is to introduce a nanocomposite based bioanode for biofuel cell application. The as-prepared Kraton/MWCNTs nanocomposite was used as a current enhancer and ferritin (Frt) as a mediator between glucose oxidase (GOx) and the electrode surface. The hybrid anode achieved enzymatic oxidation of glucose by the nanocomposite reflecting an efficient energy conversion from glucose. The resulting Kraton/MWCNTs/Frt/GOx bioande exhibited good catalytic activity towards glucose oxidation along with excellent stability. The maximum current density attained by the bioanode is 1.14 mA cm^-2 at the optimum glucose concentration of 60 mM. This enzymatic strategy can be employed to develop other polysaccharide or oligosaccharide fuel cells in which glucose oxidation is involved.

Direct electrochemistry and bioelectrocatalysis of glucose oxidase in CS/CNC film and its application in glucose biosensing and biofuel cells

Due to their unique physicochemical properties, carbon nanochips (CNCs) have been used for studies of the direct electrochemical and electrocatalytic properties of oxidoreductase.

Cross-linked glucose oxidase clusters for biofuel cell anode catalysts

The efficient localization of increased levels of active enzymes onto conducting scaffolds is important for the development of enzyme-based biofuel cells. Cross-linked enzyme clusters (CEC) of glucose oxidase (GOx) constrained to functionalized carbon nanotubes (CEC-CNTs) were generated in order to evaluate the potential of using CECs for developing GOx-based bioanodes functioning via direct electron transfer from the GOx active site to the CNT scaffold. CEC-CNTs generated from several weight-to-weight ratios of GOx:CNT were examined for comparable catalytic activity to free GOx into the solution, with CEC-CNTs generated from a 100% GOx solution displaying the greatest enzymatic activity. Scanning transmission electron microscopic analysis of CEC-CNTs generated from 100% GOx to CNT (wt/wt) ratios revealed that CEC clusters of ∼78 µm2 localized to the CNT surface. Electrochemical analysis indicates that the enzyme is engaged in direct electron transfer, and biofuel cells generated using GOx CEC-CNT bioanodes were observed to have a peak power density of ∼180 µW cm(-2). These data indicate that the generation of nano-to-micro-sized active enzyme clusters is an attractive option for the design of enzyme-specific biofuel cell powered implantable devices.