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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.

Biofuel cells are often limited by the current density produced by the cathode; this is especially true when such fuel cells are scaled down to fit a desired application. Herein, we created a computational model to examine the effects of carbon nanotube (CNT) connectivity and surface activity on the current density of a biofuel cell cathode. The model was motivated by the creation of a novel contact lens biofuel cell that, although more stable and biocompatible than previously reported designs, was cathode limited.The device produced a maximum current density of 22 ± 4 µA cm -2 , and a maximum power density of 2.4 ± 0.9 µW cm -2 (at 0.163 V) with an open-circuit voltage of 0.44 ± 0.08 V. Computational results showed that in a Nafion film containing 1.6% CNTs by volume, less than 20% of the CNT fibers were connected to the electrode, assuming a planar electrode. The simulations predicted that a three-fold increase in CNT loading would lead to a roughly two-fold increase in total CNT connectivity. The simulations further estimated that for the CNTs connected to the electrode, only 21% of their sidewalls were contributing to cathodic current, meaning that the remaining surfaces were not electrochemically active. Given the low bilirubin oxidase (BOD) enzyme surface concentration, which was experimentally found to be 1.24 x 10 -13 mol cm -2 , it is likely that large portions of the CNT surfaces are not connected to enzymes. This result validates the push by the research community to increase BOD and laccase adsorption/orientation to CNT surfaces.

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In this article, we detail a paper‐based three‐electrode electrochemical biosensor using a mitochondria modified Toray carbon paper working electrode. Cyclic voltammetry performed on the paper‐based biosensor and similar electrodes in a common laboratory setup (not in an integrated paper‐based device) compare favorably. In addition, instant detection of malathion with a detection limit of 20 nM by cyclic voltammetry is demonstrated, showing the device can potentially be used as a portable platform for pesticides detection.

Increasing demand for self-powered wearable sensors has spurred an urgent need to develop energy harvesting systems that can reliably and sufficiently power these devices. Within the last decade, reverse electrowetting-on-dielectric (REWOD)-based mechanical motion energy harvesting has been developed, where an electrolyte is modulated (repeatedly squeezed) between two dissimilar electrodes under an externally applied mechanical force to generate an AC current. In this work, we explored various combinations of electrolyte concentrations, dielectrics, and dielectric thicknesses to generate maximum output power employing REWOD energy harvester. With the objective of implementing a fully self-powered wearable sensor, a “zero applied-bias-voltage” approach was adopted. Three different concentrations of sodium chloride aqueous solutions (NaCl-0.1 M, NaCl-0.5 M, and NaCl-1.0 M) were used as electrolytes. Likewise, electrodes were fabricated with three different dielectric thicknesses (100 nm, 150 nm, and 200 nm) of Al2O3 and SiO2 with an additional layer of CYTOP for surface hydrophobicity. The REWOD energy harvester and its electrode–electrolyte layers were modeled using lumped components that include a resistor, a capacitor, and a current source representing the harvester. Without using any external bias voltage, AC current generation with a power density of 53.3 nW/cm2 was demonstrated at an external excitation frequency of 3 Hz with an optimal external load. The experimental results were analytically verified using the derived theoretical model. Superior performance of the harvester in terms of the figure-of-merit comparing previously reported works is demonstrated. The novelty of this work lies in the combination of an analytical modeling method and experimental validation that together can be used to increase the REWOD harvested power extensively without requiring any external bias voltage.

This paper describes the design and testing of a microfluidic biofuel cell that uses a flow-through bioanode and an air-breathing cathode. The bioanode is Toray carbon paper with glucose dehydrogenase (GDH), multi-walled carbon nanotubes (MWCNTs), and methylene green immobilized within a hydrogel. The cathode consists of a commercially available air-breathing platinum cathode hot pressed to a Nafion membrane. All remaining biofuel cell components were laser-cut from poly(methyl methacrylate) (PMMA) and silicone sheets. Half-cell experiments indicate that cathode variability limits the biofuel cell. An examination of flow rate effects on the biofuel cell showed that the current density increased sharply up to about 1 mL/min. Tested at this flow rate, the flow-through biofuel cell achieved a maximum current and power density of 705 μA/cm2 and 146 μW/cm2. This was a 6% and 29% improvement in the current and power density, respectively, compared to the previously demonstrated bioanode without flow. Fuel utilization was calculated based on the measured current and by measuring UV-Vis absorbance of the reduced form of hydroxybenzhydrazide. The maximum fuel utilization was 5.8% at a flow rate of 0.05 mL/min. Finally, a numerical model of the biofuel cell was designed and its results compare favorably to actual data.

Non-electroactive neurotransmitters such as glutamate, acetylcholine, choline, and adenosine play a critical role in proper activity of living organisms, particularly in the nervous system. While enzyme-based sensing of this type of neurotransmitter has been a research interest for years, non-enzymatic approaches are gaining more attention because of their stability and low cost. Accordingly, this focused review aims to give a summary of the state of the art of non-enzymatic electrochemical sensors used for detection of neurotransmitter that lack an electrochemically active component. In place of using enzymes, transition metal materials such as those based on nickel show an acceptable level of catalytic activity for neurotransmitter sensing. They benefit from fast electron transport properties and high surface energy and their catalytic activity can be much improved if their surface is modified with nanomaterials such as carbon nanotubes and platinum nanoparticles. However, a general comparison reveals that the performance of non-enzymatic biosensors is still lower than those that use enzyme-based methods. Nevertheless, their excellent stability demonstrates that non-enzymatic neurotransmitter sensors warrant additional research in order to advance them toward becoming an acceptable replacement for the more expensive enzyme-based sensors.