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>>> Enzymatic Biofuel Cells for Self-Powered, Controlled Drug Release
Self-powered drug-delivery systems based on conductive polymers (CPs) that eliminate the need for external power sources are of significant interest for use in clinical applications. Osmium redox polymer-mediated glucose/O2 enzymatic biofuel cells (EBFCs) were prepared with an additional CP−drug layer on the cathode. On discharging the EBFCs in the presence of glucose and dioxygen, model drug compounds incorporated in the CP layer were rapidly released with negligible amounts released when the EBFCs were held at open circuit. Controlled and ex situ release of three model compounds, ibuprofen (IBU), fluorescein (FLU), and 4′,6-diamidino-2-phenylindole (DAPI), was achieved with this self-powered drug-release system. DAPI released in situ in cell culture media was incorporated into retinal pigment epithelium (RPE) cells. This work demonstrates a proof-of-concept responsive drug-release system that may be used in implantable devices.
https://doi.org/10.1021/acs.chemrev.9b00115
Chem. Rev. 2019, 119, 16, 9509-9558
The ever-increasing demands for clean and sustainable energy sources combined with rapid advances in biointegrated portable or implantable electronic devices have stimulated intensive research activities in enzymatic (bio)fuel cells (EFCs). The use of renewable biocatalysts, the utilization of abundant green, safe, and high energy density fuels, together with the capability of working at modest and biocompatible conditions make EFCs promising as next generation alternative power sources. However, the main challenges (low energy density, relatively low power density, poor operational stability, and limited voltage output) hinder future applications of EFCs. This review aims at exploring the underlying mechanism of EFCs and providing possible practical strategies, methodologies and insights to tackle these issues. First, this review summarizes approaches in achieving high energy densities in EFCs, particularly, employing enzyme cascades for the deep/complete oxidation of fuels. Second, strategies for increasing power densities in EFCs, including increasing enzyme activities, facilitating electron transfers, employing nanomaterials, and designing more efficient enzyme-electrode interfaces, are described. The potential of EFCs/(super)capacitor combination is discussed. Third, the review evaluates a range of strategies for improving the stability of EFCs, including the use of different enzyme immobilization approaches, tuning enzyme properties, designing protective matrixes, and using microbial surface displaying enzymes. Fourth, approaches for the improvement of the cell voltage of EFCs are highlighted. Finally, future developments and a prospective on EFCs are envisioned.
>>>Use of polymer coatings to enhance the response of redox‐polymer‐mediated electrodes
The successful use of biosensors requires that the sensor can operate over abroad enough linear range that encompasses the physiological concentration of the substrate of interest. A polymer coating layer functioning as a mass transport barrier is typically used to expand the linear range of biosensors, with however, the concomitant disadvantage of a reduction in the response. Effects of a poly(acrylic acid) (PAA) coating layer on the response of a glassy carbon electrode modified with an Os redox polymer and lactate oxidase (LOx) were evaluated. The coating layer resulted in an expanded linear range from 7 to 15 mM, doubled catalytic response towards the oxidation of 35 mM lactate and improved operational stability. Detailed voltammetry studies revealed that the coating layer can improve the amount of the redox polymer that is available as a mediator, leading to the increased catalytic response at high concentrations of substrate. Similar results were obtained with other polymer layers (polystyrene sulfonate (PSS), poly(diallyldimethyl‐ammonium chloride) (PDADMAC) and poly(3,4‐ethylenedioxythiophene) (PEDOT)) and with the enzymes, glucose oxidase and bilirubin oxidase demonstrating the general nature of the method.
The integration of supercapacitors with enzymatic biofuel cells (BFCs) can be used to prepare hybrid devices in order to harvest significantly higher power output. In this study, a supercapacitor/biofuel cell hybrid device was prepared by the immobilisation of redox enzymes with electrodeposited poly(3,4-ethylenedioxythiophene) (PEDOT) and the Os redox polymer. Once charged by the internal BFC, the device can be discharged as a supercapacitor at a current density of 2 mA cm-2 providing a maximum power density of 608.8 μW cm-2, an increase of a factor of 468 when compared to the power output from the BFC itself. The device could be used as a pulse generator, mimicking a cardiac pacemaker delivering pulses of 10 μA for 0.5 ms at a frequency of 0.2 Hz.
Enzymatic biofuel cells (BFCs) utilizing oxidoreductases as electrocatalysts can be used to generate electricity from fuels such as sugars or alcohols in combination with dioxygen. BFCs are of interest as power sources for biosensors, medical implants (e.g. insulin pumps, cardiac pacemakers), and other devices.
An oxygen-independent and membrane-less glucose biobattery was prepared that consists of a dealloyed nanoporous gold (NPG) supported glucose dehydrogenase (GDH) bioanode, immobilised with the assistance of conductive polymer/Os redox polymer composites, and a solid-state NPG/MnO2 cathode. The potential of the discharged MnO2 could be recovered, enabling a proof-of-concept biobattery/supercapacitor hybrid device. The resulting device exhibited a stable performance for 50 cycles of self-recovery and galvanostatic discharge as a supercapacitor at 0.1 mA cm−2 over a period of 25 h. The device could be discharged at current densities up to 2 mA cm−2 supplying a maximum instantaneous power density of 676 μW cm−2, which is 294 times higher than that from the biobattery alone. A mechanism for the recovery of the potential of the cathode, analogous to that of RuO2 (Electrochim. Acta 42(23), 3541–3552) is described.
>>> Nanoporous Gold-Based Biofuel Cells on Contact Lenses
A lactate/O2 enzymatic biofuel cell (EBFC) was prepared as a potential power source for wearable microelectronic devices. Mechanically stable and flexible nanoporous gold (NPG) electrodes were prepared using an electrochemical dealloying method consisting of a pre-anodization process and a subsequent electrochemical cleaning step. Bioanodes were prepared by the electrodeposition of an Os polymer and Pediococcus sp. lactate oxidase onto the NPG electrode. The electrocatalytic response to lactate could be tuned by adjusting the deposition time. Bilirubin oxidase from Myrothecium verrucaria was covalently attached to a diazonium-modified NPG surface. A flexible EBFC was prepared by placing the electrodes between two commercially available contact lenses to avoid direct contact with the eye. When tested in air-equilibrated artificial tear solutions (3 mM lactate), a maximum power density of 1.7 ± 0.1 μW cm-2 and an open-circuit voltage of 380 ± 28 mV were obtained, values slightly lower than those obtained in phosphate buffer solution (2.4 ± 0.2 μW cm-2 and 455 ± 21 mV, respectively). The decrease was mainly attributed to interference from ascorbate. After 5.5 h of operation, the EBFC retained 20% of the initial power output.
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