Rapid Voltammetric Measurements at Conducting Polymer Microelectrodes Using Ultralow-Capacitance Poly(3,4-ethylenedioxythiophene):Tosylate

Conductive PEDOT:PSS copolymer electrode coatings for selective detection of dopamine in ex vivo mouse brain slices

A novel voltammetric sensor was developed to selectively determine dopamine (DA) concentration in the presence of ascorbic acid (AA) and 3,4-dihydroxyphenylacetic acid (DOPAC). This sensor utilizes a modified pencil graphite electrode (PGE) coated with a newly synthesized poly (3,4-ethylene dioxythiophene) (PEDOT):poly (styrene sulfonate-co-2-(3-(6-Methyl-4-oxo-1,4-dihydropyrimidin-2-yl) ureido) ethyl methacrylate) (P(SS-co-UPyMA)) composite. The PEDOT:P(SS-co-UPyMA) (PPU) composite was characterized using nuclear magnetic resonance, X-ray photoelectron, and Raman spectroscopies. The PPU-coated PGE was characterized using electrochemical techniques, including cyclic and differential pulse voltammetry. Compared to uncoated, PPU-coated PGE demonstrated improved sensitivity and selectivity for DA. The sensor exhibited a dynamic linear range of 0.1-300 μM for DA, with a detection limit of 44.4 nM (S/N = 3). Additionally, the PPU-coated PGE showed high reproducibility and storage stability for four weeks. To demonstrate its practical applicability, the PPU-coated PGE sensor was used for ex vivo brain slice samples from control and Parkinson's disease model mice.

Electrical percolation in extrinsically conducting, poly(ε-decalactone) composite neural interface materials

By providing a bidirectional communication channel between neural tissues and a biomedical device, it is envisaged that neural interfaces will be fundamental in the future diagnosis and treatment of neurological disorders. Due to the mechanical mismatch between neural tissue and metallic neural electrodes, soft electrically conducting materials are of great benefit in promoting chronic device functionality. In this study, carbon nanotubes (CNT), silver nanowires (AgNW) and poly(hydroxymethyl 3,4-ethylenedioxythiophene) microspheres (MSP) were employed as conducting fillers within a poly(ε-decalactone) (EDL) matrix, to form a soft and electrically conducting composite. The effect of a filler type on the electrical percolation threshold, and composite biocompatibility was investigated in vitro. EDL-based composites exhibited favourable electrochemical characteristics: EDL/CNT-the lowest film resistance (1.2 ± 0.3 kΩ), EDL/AgNW-the highest charge storage capacity (10.7 ± 0.3 mC cm- 2), and EDL/MSP-the highest interphase capacitance (1478.4 ± 92.4 µF cm-2). All investigated composite surfaces were found to be biocompatible, and to reduce the presence of reactive astrocytes relative to control electrodes. The results of this work clearly demonstrated the ability of high aspect ratio structures to form an extended percolation network within a polyester matrix, resulting in the formulation of composites with advantageous mechanical, electrochemical and biocompatibility properties.

A Smart Tongue Depressor-Based Biosensor for Glucose

The development of new bioelectronic platforms for direct interactions with oral fluid could open up significant opportunities for healthcare monitoring. A tongue depressor is a widely used medical tool that is inserted into the mouth, where it comes into close contact with saliva. Glucose is a typical salivary biomarker. Herein, we report—for the first time—a tongue depressor-based biosensor for the detection of glucose in both phosphate buffer and real human saliva. Carbon nanotubes (CNTs) are attractive electronic materials, with excellent electrochemical properties. The sensor is constructed by printing CNTs and silver/silver chloride (Ag/AgCl) to form three electrodes in an electrochemical cell: Working, reference, and counter electrodes. The enzyme glucose oxidase (GOD) is immobilized on the working electrode. The glucose detection performance of the sensor is excellent, with a detection range of 7.3 μM to 6 mM. The glucose detection time is about 3 min. The discretion between healthy people’s and simulated diabetic patients’ salivary samples is clear and easy to tell. We anticipate that the biosensor could open up new opportunities for the monitoring of salivary biomarkers and advance healthcare applications.

Purine Functional Group Type and Placement Modulate the Interaction with Carbon-Fiber Microelectrodes

Purine detection in the brain with fast-scan cyclic voltammetry (FSCV) at carbon-fiber microelectrodes (CFME) has become increasingly popular over the past decade; despite the growing interest, an in-depth analysis of how purines interact with the CFME at fast-scan rates has not been investigated. Here, we show how the functional group type and placement in the purine ring modulate sensitivity, electron transfer kinetics, and adsorption on the carbon-fiber surface. Similar investigations of catecholamine interaction at CFME with FSCV have informed the development of novel catecholamine-based sensors and is needed for purine-based sensors. We tested purine bases with either amino, carbonyl, or both functional groups substituted at different positions on the ring and an unsubstituted purine. Unsubstituted purine showed very little to no interaction with the electrode surface, indicating that functional groups are important for interaction at the CFME. Purine nucleosides and nucleotides, like adenosine, guanosine, and adenosine triphosphate, are most often probed using FSCV due to their rich extracellular signaling modalities in the brain. Because of this, the extent to which the ribose and triphosphate groups affect the purine-CFME interaction was also evaluated. Amino functional groups facilitated the interaction of purine analogues with CFME more than carbonyl groups, permitting strong adsorption and high surface coverage. Ribose and triphosphate groups decreased the oxidative current and slowed the interaction at the electrode which is likely due to steric effects and electrostatic repulsion. This work provides insight into the factors that affect purine-CFME interaction and conditions to consider when developing purine-targeted sensors for FSCV.

Review: New insights into optimizing chemical and 3D surface structures of carbon electrodes for neurotransmitter detection

The carbon-fiber microelectrode has been used for decades as a neurotransmitter sensor. Recently, new strategies have been developed for making carbon electrodes, including using carbon nanomaterials or pyrolyzing photoresist etched by nanolithography or 3D printing. This review summarizes how chemical and 3D surface structures of new carbon electrodes are optimized for neurotransmitter detection. There are effects of the chemical structure that are advantageous and nanomaterials are used ranging from carbon nanotube (CNT) to graphene to nanodiamond. Functionalization of these materials promotes surface oxide groups that adsorb dopamine and dopants introduce defect sites good for electron transfer. Polymer coatings such as poly(3,4-ethylenedioxythiophene) (PEDOT) or Nafion also enhance the selectivity, particularly for dopamine over ascorbic acid. Changing the 3D surface structure of an electrode increases current by adding more surface area. If the surface structure has roughness or pores on the micron scale, the electrode also acts as a thin layer cell, momentarily trapping the analyte for redox cycling. Vertically-aligned CNTs as well as lithographically-made or 3D printed pillar arrays act as thin layer cells, producing more reversible cyclic voltammograms. A better understanding of how chemical and surface structure affects electrochemistry enables rational design of electrodes. New carbon electrodes are being tested in vivo and strategies to reduce biofouling are being developed. Future studies should test the robustness for long term implantation, explore electrochemical properties of neurotransmitters beyond dopamine, and combine optimized chemical and physical structures for real-time monitoring of neurotransmitters.