A wearable and flexible lactic-acid/O2 biofuel cell with an enhanced air-breathing biocathode.

The performance of biocathode in an enzymatic biofuel cell (EBFC) in the real application is somehow overlooked. Herein, a wearable and flexible lactic-acid/O2 EBFC enhanced with an air-breathing biocathode is designed to solve the limitation of biocathode that arises from the low solubility and slow mass transfer of the dissolved oxygen. To improve the oxygen supply efficiency for the air-breathing biocathode, a superhydrophobic base electrode creating an efficient air-solid-liquid triphase interface is developed. The designed EBFC with an 'island-bridge' configuration is integrated by assembling the current collectors of air-breathing biocathode and bioanode on a commercial laminating film (LF) screen-printed with a noninterfering circuit. It is found that the biocathode/bioanode area ratio should exceed 9:1 so that the designed EBFC (1A//9C) can achieve the optimal performance. This EBFC delivers an open circuit voltage of ca. 0.75 V and outputs a maximum power density of ca. 1.78 mW cm-2. In addition, a scaled-up EBFC (total bioanode area: 1.5 cm2) successfully powers a self-developed low-power device of heartrate in the pulse operation mode when applied on a volunteer's arm.

Tailoring Galactose Oxidase for Self-Powered Benzyl Alcohol Sensing.

Benzyl alcohol (BnOH) is a widely-used preservative in a variety of cosmetics, but the excess addition (≥1.0 %) may cause strong symptoms such as nausea, gastrointestinal irritation, convulsion, even death, making it crucial to monitor and control the addition quantity. Herein, we have developed a test-strip-like BnOH detection method via tailoring a galactose oxidase (GOase) towards BnOH oxidation and preparing a self-powered electrochromic strip for BnOH concentration visualization. A double-substituted GOase variant (Y329S/R330F), on the basis of the reported GOase M1 , has been obtained by semi-rational design with a 24.6-fold improved activity towards BnOH compared to GOase M1 . The GOase Y329S/R330F electrode has a response to BnOH with a linear range of 0.04 to 3.25 mM (R2 =0.9985), a sensitivity of 122.78 µA mM-1 cm-2 , and a detection limit of 0.03 mM (S/N=3). Coupling an electrochromic Prussian blue (PB) cathode helps the successful sensing visualization without any further power supply. The present sensing is more convenient and user-friendly than the generally used gas chromatography (GC) and high performance liquid chromatography (HPLC), and brings a more accessible solution to the field of quality controlling.

A miniaturized bionic ocean-battery mimicking the structure of marine microbial ecosystems.

Marine microbial ecosystems can be viewed as a huge ocean-battery charged by solar energy. It provides a model for fabricating bio-solar cell, a bioelectrochemical system that converts light into electricity. Here, we fabricate a bio-solar cell consisting of a four-species microbial community by mimicking the ecological structure of marine microbial ecosystems. We demonstrate such ecological structure consisting of primary producer, primary degrader, and ultimate consumers is essential for achieving high power density and stability. Furthermore, the four-species microbial community is assembled into a spatial-temporally compacted cell using conductive hydrogel as a sediment-like anaerobic matrix, forming a miniaturized bionic ocean-battery. This battery directly converts light into electricity with a maximum power of 380 µW and stably operates for over one month. Reproducing the photoelectric conversion function of marine microbial ecosystems in this bionic battery overcomes the sluggish and network-like electron transfer, showing the biotechnological potential of synthetic microbial ecology.

An Enzymatic Biosensor for the Detection of D-2-Hydroxyglutaric Acid in Serum and Urine.

D-2-hydroxyglutaric acid (D2HG) is overproduced as a result of the D-2-hydroxyglutaric aciduria and relevant cancers, caused by gene mutation. Accurate analysis of D2HG could help rapid diagnosis of these diseases and allow for timely treatment. In this work, a D-2-hydroxyglutarate dehydrogenase from Ralstonia solanacearum (RsD2HGDH) is cloned and recombinantly expressed. This enzyme features the direct electron transfer to chemical electron mediators (such as methylene blue (MB)) in the absence of additional coenzymes. Therefore, NAD+, a natural electron acceptor for the commercial D2HGDH and usually known for being unstable and difficult for immobilization can be avoided in the preparation of biosensors. The RsD2HGDH and MB are co-immobilized on a two-dimensional material, Ti3C2 MXene, followed by drop-coating on the gold screen-printed electrode (AuSPE) to construct a compact and portable biosensor. The D2HG in samples can be catalyzed by RsD2HGDH, where the current change is measured by chronoamperometry at -0.23 V. The biosensor shows a D2HG detection range of 0.5 to 120 µM (R2 = 0.9974) with a sensitivity of 22.26 µA mM-1 cm-2 and a detection limit of 0.1 µM (S/N = 3). The biosensor retains 72.52% performance of its incipient state after 30 days of storage. The samples of D2HG-containing fetal bovine serum and artificial urine were analyzed with the recovery of 99.56% to 106.83% and 97.30% to 102.47% further indicating the great application potential of our portable D2HG biosensor.

A shriveled rectangular carbon tube with the concave surface for high-performance enzymatic glucose/O2 biofuel cells.

In this study, a novel carbon tube was prepared by carbonizing a rectangular polypyrrole (RPPy) tube at a high temperature for the construction of enzymatic biofuel cells with high performance. SEM and TEM images clearly showed that the initial PPy presented a rectangular tube shape, while the carbonized PPy became a shriveled rectangular tube with a concave surface, which might be beneficial for enzyme immobilization and electrochemical applications. The glucose oxidase (GOx)- or laccase (Lac)-modified electrodes based on carbonized RPPy exhibited excellent bioelectrochemical performance. In addition, a biofuel cell (GOx, glucose/O2, Lac) was assembled, and the open-circuit voltage reached 1.16 V. The maximum power density was measured to 0.350 mW cm-2, which correlated to the gravimetric power density of 0.265 mW mg-1 (per mg of GOx) at 0.85 V. The constant-current discharge method was used to further evaluate the continuous discharge capacity. The discharge time reached 49.9 h at a discharge current of 0.2 mA before the voltage was lower than 0.8 V. Furthermore, three of the fabricated biofuel cells in series were able to continually light up a white light-emitting diode (LED) whose turn-on voltage was ca. 2.4 V for more than 48 h. This study suggests that carbonized conducting polymers may become a useful electrode material for the development of enzymatic biofuel cells.

A novel three-dimensional carbonized PANI1600@CNTs network for enhanced enzymatic biofuel cell.

A novel three-dimensional (3D) carbon composite of PANI1600@CNTs with rhizobium-like structure is prepared by in-situ polymerization of aniline monomers around and along the functionalized carbon nanotubes (CNTs) and then carbonized at 1600°C for enzymatic biofuel cells (EBFCs). The SEM and TEM images clearly show that the carbonized PANI grew seamlessly on the surface of CNTs and presented the rhizobium-like structure. The carbonized PANI acts like conductive "glue" and connects the adjacent tubes together, which can assemble the CNTs into a 3D network. The PANI1600@CNTs composite modified glassy carbon electrodes based on glucose oxidase (GOx) and laccase (Lac) exhibit high electrochemical performance. A glucose//O2 EBFC constitutes of the fabricated anode and cathode performs a maximum power density of 1.12mWcm-2 at 0.45V. Furthermore, three of the fabricated EBFCs in series are able to lightening up a yellow light-emitting diode (LED) whose turn-on voltage is about at 1.8V. This work may be helpful for exploiting novel substrates by carbonizing the composites of conducting polymer with nano materials at high-temperature for immobilization of enzymes in the EBFCs or biosensor fields.

Graphene oxide-supported carbon nanofiber-like network derived from polyaniline: A novel composite for enhanced glucose oxidase bioelectrode performance.

A three-dimensional architecture of PANI@GO hybrid was synthesized via in-situ polymerization of aniline monomers on the surface of graphene oxide (GO) and carbonized at 1600°C. The SEM images showed that surfaces of planar GO were covered by a compact nanofiber-like polyaniline (PANI) layer which presented an interconnected network. Nanofiber-like PANI on the GO surface was mostly preserved and became the carbon nanofibers (CNFs) after carbonization. The TEM images showed that the carbonized PANI grew seamlessly on the GO surface and served as conductive "network" between interlayers of GO. The carbonized PANI@GO hybrid was used to modify a glassy carbon electrode (GCE) based on GOx, resulting in efficient direct electron transfer (DET) and excellent bio-catalytic performance. In addition, a glucose/O2 fuel cell constructed using Nafion/GOx/PANI1600@GO/GCE as the anode and an E-TEK Pt/C modified GCE as the cathode generated a maximum power density of 0.756mWcm-2 at 0.42V. Findings in this study may be helpful for exploiting novel materials for immobilization of enzymes through carbonizing conducting polymers or their composites with inorganic materials at high temperature for applications in enzymatic biofuel cells or biosensors.

Three-dimensional Co3O4@MWNTs nanocomposite with enhanced electrochemical performance for nonenzymatic glucose biosensors and biofuel cells.

Three-dimensional nanoarchitectures of Co3O4@multi-walled carbon nanotubes (Co3O4@MWNTs) were synthesized via a one-step process with hydrothermal growth of Co3O4 nanoparticles onto MWNTs. The structure and morphology of the Co3O4@MWNTs were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller, scanning electron microscopy and transmission electron microscopy. The electrocatalytic mechanism of the Co3O4@MWNTs was studied by X-ray photoelectron spectroscopy and cyclic voltammetry. Co3O4@MWNTs exhibited high electrocatalytic activity towards glucose oxidation in alkaline medium and could be used in nonenzymatic electrochemical devices for glucose oxidation. The open circuit voltage of the nonenzymatic glucose/O2 fuel cell was 0.68 V, with a maximum power density of 0.22 mW cm-2 at 0.30 V. The excellent electrochemical properties, low cost, and facile preparation of Co3O4@MWNTs demonstrate the potential of strongly coupled oxide/nanocarbon hybrid as effective electrocatalyst in glucose fuel cells and biosensors.

Hexagonal NiS nanobelts as advanced cathode materials for rechargeable Al-ion batteries.

Hexagonal NiS nanobelts served as novel cathode materials for rechargeable Al-ion batteries based on an AlCl3/[EMIm]Cl ionic liquid electrolyte system. The nano-banded structure of the materials can facilitate the electrolyte immersion and enhance Al(3+) diffusion. The hexagonal NiS nanobelt based cathodes exhibit high storage capacity, good cyclability and low overpotential.