Anthracene-modified pyrenes immobilized on carbon nanotubes for direct electroreduction of O2 by laccase

A self-powered amperometric lactate biosensor based on lactate oxidase immobilized in dimethylferrocene-modified LPEI

Lactate is an important biomarker due to its excessive production by the body during anerobic metabolism. Existing methods for electrochemical lactate detection require the use of an external power source to supply a positive potential to the working electrode of a given device. Herein we describe a self-powered amperometric lactate biosensor that utilizes a dimethylferrocene-modified linear poly(ethylenimine) (FcMe2-LPEI) hydrogel to simultaneously immobilize and mediate electron transfer from lactate oxidase (LOx) at the anode and a previously described enzymatic cathode. Operating as a half-cell, the FcMe2-LPEI electrode material generates a jmax of 1.51 ± 0.13 mAcm(-2) with a KM of 1.6 ± 0.1 mM and a sensitivity of 400 ± 20 μAcm(-2)mM(-1) while operating with an applied potential of 0.3 V vs. SCE. When coupled with an enzymatic biocathode, the self-powered biosensor has a detection range between 0mM and 5mM lactate with a sensitivity of 45 ± 6 μAcm(-2)mM(-1). Additionally, the FcMe2-LPEI/LOx-based self-powered sensor is capable of generating a power density of 122 ± 5 μWcm(-2) with a current density of 657 ± 17 μAcm(-2) and an open circuit potential of 0.57 ± 0.01 V, which is sufficient to act as a supplemental power source for additional small electronic devices.

Rational design of quinones for high power density biofuel cells

Enzymatic fuel cells (EFCs) are devices that can produce electrical energy by enzymatic oxidation of energy-dense fuels (such as glucose). When considering bioanode construction for EFCs, it is desirable to use a system with a low onset potential and high catalytic current density. While these two properties are typically mutually exclusive, merging these two properties will significantly enhance EFC performance. We present the rational design and preparation of an alternative naphthoquinone-based redox polymer hydrogel that is able to facilitate enzymatic glucose oxidation at low oxidation potentials while simultaneously producing high catalytic current densities. When coupled with an enzymatic biocathode, the resulting glucose/O2 EFC possessed an open-circuit potential of 0.864 ± 0.006 V, with an associated maximum current density of 5.4 ± 0.5 mA cm-2. Moreover, the EFC delivered its maximum power density (2.3 ± 0.2 mW cm-2) at a high operational potential of 0.55 V.

Voltammetric immunosensor assembled on carbon-pyrenyl nanostructures for clinical diagnosis of type of diabetes

Herein we report the first serum insulin voltammetric immunosensor for diagnosis of type 1 and type 2 diabetic disorders. The sensor is composed of multiwalled carbon nanotube-pyrenebutyric acid frameworks on edge plane pyrolytic graphite electrodes (PGE/MWNT/Py) to which an anti-insulin antibody was covalently attached. The detection of picomolar levels of serum insulin binding to the surface antibody was achieved by monitoring the decrease in voltammetric current signals of a redox probe taken in the electrolyte solution. This method offered a detection limit of 15 pM for free insulin present in serum. This detection limit was further lowered to 5 pM by designing serum insulin conjugates with poly(acrylic acid)-functionalized magnetite nanoparticles (100 nm hydrodynamic diameter) and detecting the binding of MNP-serum insulin conjugate to the surface insulin-antibody on PGE/MWNT/Py electrodes. When tested on real patient serum samples, the sensor accurately measured insulin levels. To our knowledge, this is the first report of a voltammetric immunosensor capable of both diagnosing and distinguishing the type of diabetes based on serum insulin levels in diabetic patients.

Contact lens biofuel cell tested in a synthetic tear solution

A contact lens biofuel cell was fabricated using buckypaper electrodes cured on a silicone elastomer soft contact lens. The buckypaper anode consisted of poly(methylene green) and a hydrogel matrix containing lactate dehydrogenase and nicotinamide adenine dinucleotide hydrate (NAD(+)). The buckypaper cathode was modified with 1-pyrenemethyl anthracene-2-carboxylate, and then bilirubin oxidase was immobilized within a polymer. Contact lens biofuel cell testing was performed in a synthetic tear solution at 35°C. The open circuit voltage was 0.413±0.06 V and the maximum current and power density were 61.3±2.9 µA cm(-2) and 8.01±1.4 µWc m(-2), respectively. Continuous operation for 17h revealed anode instability as output current rapidly decreased in the first 4h and then stabilized for the next 13 h. The contact lens biofuel cell presented here is a step toward achieving self-powered electronic contact lenses and ocular devices with an integrated power source.

Hybrid microfluidic fuel cell based on Laccase/C and AuAg/C electrodes

A hybrid glucose microfluidic fuel cell composed of an enzymatic cathode (Laccase/ABTS/C) and an inorganic anode (AuAg/C) was developed and tested. The enzymatic cathode was prepared by adsorption of 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and Laccase on Vulcan XC-72, which act as a redox mediator, enzymatic catalyst and support, respectively. The Laccase/ABTS/C composite was characterised by Fourier Transform Infrared (FTIR) Spectroscopy, streaming current measurements (Zeta potential) and cyclic voltammetry. The AuAg/C anode catalyst was characterised by Transmission electron microscopy (TEM) and cyclic voltammetry. The hybrid microfluidic fuel cell exhibited excellent performance with a maximum power density value (i.e., 0.45 mW cm(-2)) that is the highest reported to date. The cell also exhibited acceptable stability over the course of several days. In addition, a Mexican endemic Laccase was used as the biocathode electrode and evaluated in the hybrid microfluidic fuel cell generating 0.5 mW cm(-2) of maximum power density.

Effect of enzymatic orientation through the use of syringaldazine molecules on multiple multi-copper oxidase enzymes

The effect of proper enzyme orientation at the electrode surface was explored for two multi-copper oxygen reducing enzymes: Bilirubin Oxidase (BOx) and Laccase (Lac).

Surfactant-assisted direct electron transfer between multi-copper oxidases and carbon nanotube-based porous electrodes

The pre-treatment of carbon nanotube-based nanostructured porous electrodes with surfactant enhanced the efficiency of direct electron transfer of multi-copper oxidases.