Boron-doped Diamond Microelectrodes Research Articles

All-Diamond Boron-Doped Microelectrodes for Neurochemical Sensing with Fast-Scan Cyclic Voltammetry.

Neurochemical sensing with implantable devices has gained remarkable attention over the last few decades. A promising area of this research is the progress of novel electrodes as electrochemical tools for neurotransmitter detection in the brain. The boron-doped diamond (BDD) electrode is one such candidate that previously has been reported for its excellent electrochemical properties, including a wide working potential, superior chemical inertness and mechanical stability, good biocompatibility and resistance to fouling. Meanwhile, limited research has been conducted on the BDD as a microelectrode for neurochemical detection. Our team has developed a freestanding, all diamond microelectrode consisting of a boron-doped polycrystalline diamond core, encapsulated in an insulating polycrystalline diamond shell, with a cleaved planar tip for electrochemical sensing. This all-diamond electrode is advantageous due to its - (1) batch fabrication using wafer technology that eliminates traditional hand fabrication errors and inconsistencies, (2) absence of metal-based wires, or foundations, to improve biocompatibility and flexibility, and (3) sp 3 carbon surface with resistance to biofouling, i.e. adsorption of proteins or unwanted molecules at the electrode surface in a biological environment that impedes overall electrode performance. Here, we provide findings on further in vitro testing and development of the freestanding boron-doped diamond microelectrode (BDDME) for neurotransmitter detection using fast scan cyclic voltammetry (FSCV). In this report, we elaborate on - 1) an updated fabrication scheme and work flow to generate all diamond BDDMEs, 2) slow scan cyclic voltammetry measurements of reference and target analytes to understand basic electrochemical behavior of the electrode, and 3) FSCV characterization of common neurotransmitters, and overall favorability of serotonin (5-HT) detection. The BDDME showed a 2-fold increased FSCV response for 5-HT in comparison to dopamine (DA), with a limit of detection of 0.16 µM for 5-HT and 0.26 µM for DA. These results are intended to expand on the development of the next generation BDDME and guide future in vivo experiments, adding to the growing body of literature on implantable devices for neurochemical sensing.

Evaluation of In Vitro Serotonin-Induced Electrochemical Fouling Performance of Boron Doped Diamond Microelectrode Using Fast-Scan Cyclic Voltammetry.

Fast-scan cyclic voltammetry (FSCV) is an electrochemical sensing technique that can be used for neurochemical sensing with high spatiotemporal resolution. Carbon fiber microelectrodes (CFMEs) are traditionally used as FSCV sensors. However, CFMEs are prone to electrochemical fouling caused by oxidative byproducts of repeated serotonin (5-HT) exposure, which makes them less suitable as chronic 5-HT sensors. Our team is developing a boron-doped diamond microelectrode (BDDME) that has previously been shown to be relatively resistant to fouling caused by protein adsorption (biofouling). We sought to determine if this BDDME exhibits resistance to electrochemical fouling, which we explored on electrodes fabricated with either femtosecond laser cutting or physical cleaving. We recorded the oxidation current response after 25 repeated injections of 5-HT in a flow-injection cell and compared the current drop from the first with the last injection. The 5-HT responses were compared with dopamine (DA), a neurochemical that is known to produce minimal fouling oxidative byproducts and has a stable repeated response. Physical cleaving of the BDDME yielded a reduction in fouling due to 5-HT compared with the CFME and the femtosecond laser cut BDDME. However, the femtosecond laser cut BDDME exhibited a large increase in sensitivity over the cleaved BDDME. An extended stability analysis was conducted for all device types following 5-HT fouling tests. This analysis demonstrated an improvement in the long-term stability of boron-doped diamond over CFMEs, as well as a diminishing sensitivity of the laser-cut BDDME over time. This work reports the electrochemical fouling performance of the BDDME when it is repeatedly exposed to DA or 5-HT, which informs the development of a chronic, diamond-based electrochemical sensor for long-term neurotransmitter measurements in vivo.

Amperometry approach curve profiling to understand the regulatory mechanisms governing the concentration of intestinal extracellular serotonin

Enterochromaffin (EC) cells located within the intestinal mucosal epithelium release serotonin (5-HT) to regulate motility tones, barrier function and the immune system. Electroanalytical methodologies have been able to monitor steady state basal extracellular 5-HT levels but are unable to provide insight into how these levels are influenced by key regulatory processes such as release and uptake. We established a new measurement approach, amperometry approach curve profiling, which monitors the extracellular 5-HT level at different electrode–tissue (E–T) distances. Analysis of the current profile can provide information on contributions of regulatory components on the observed extracellular 5-HT level. Measurements were conducted from ex vivo murine ileum and colon using a boron-doped diamond (BDD) microelectrode. Amperometry approach curve profiling coupled with classical pharmacology demonstrated that extracellular 5-HT levels were significantly lower in the colon when compared to the ileum. This difference was due to a greater degree of activity of the 5-HT transporter (SERT) and a reduced amount of 5-HT released from colonic EC cells. The presence of an inhibitory 5-HT4 autoreceptor was observed in the colon, where a 40% increase in extracellular 5-HT was the half maximal inhibitory concentration for activation of the autoreceptor. This novel electroanalytical approach allows estimates of release and re-uptake and their contribution to 5-HT extracellular concentration from intestinal tissue be obtained from a single series of measurements.

Real-Time Measurement of Antiglaucoma Drugs in Porcine Eyes Using Boron-Doped Diamond Microelectrodes.

The primary treatment for glaucoma, the most common cause of intermediate vision impairment, involves administering ocular hypotensive drugs in the form of topical eye drops. Observing real-time changes in the drugs that pass through the cornea and reach the anterior chamber of the eye is crucial for improving and developing safe, reliable, and effective medical treatments. Traditional methods for measuring temporal changes in drug concentrations in the aqueous humor employ separation analyzers such as LC-MS/MS. However, this technique requires multiple measurements on the eyes of various test subjects to track changes over time with a high temporal resolution. To address this issue, we have developed a measurement method that employs boron-doped diamond (BDD) microelectrodes to monitor real-time drug concentrations in the anterior chamber of the eye. First, we confirmed the electrochemical reactivity of 13 antiglaucoma drugs in a phosphate buffer solution with a pH of 7.4. Next, we optimized the method for continuous measurement of timolol maleate (TIM), a sympathetic beta-receptor antagonist, and generated calibration curves for each BDD microelectrode using aqueous humor collected from enucleated porcine eyes. We successfully demonstrated the continuous ex vivo monitoring of TIM concentrations in the anterior chambers of these enucleated porcine eyes. The results indicate that changes in intracameral TIM concentrations can be monitored through electrochemical measurements using BDD microelectrodes. This technique holds promise for future advancements in optimizing glaucoma treatment and drug administration strategies.

Preparation of boron-doped diamond microelectrodes to determine the distribution size of platinum nanoparticles using current transient method

Boron-doped diamond (BDD) microelectrodes were prepared to investigate the correlation of hydrazine oxidation current responses with Pt nanoparticle (Pt NP) size distribution. The BDD film was grown on the surface of a tungsten needle with a diameter of 25 µm. An average particle size of around 5 µm BDD crystalline was successfully synthesized using a microwave plasma-assisted chemical vapor deposition technique. The Raman spectrum confirmed the presence of diamond formation as indicated by peaks corresponding to C-C sp3 bonds, while X-ray photoelectron spectroscopy spectrum showed the presence of C-H and C-OH bonds on the surface of the BDD microelectrode. Meanwhile the Pt nanoparticles was synthesized through reduction reaction of PtCl62- solution using NaBH4 with citric acid as the capping agent. Particles size between 4.46 to 4.78 nm were observed by using TEM measurements. The BDD microelectrodes were utilized to investigate the relationship between Pt nanoparticle size distribution and the current generated from the oxidation reaction of 15 mM hydrazine in a 50 mM phosphate buffer solution pH 7.4 in the presence of 1.0 mL nanoparticle solutions. A current range of 5 and 6 nA with a noise level of 0.15 nA was observed showing a good correlation with the particle sizes of Pt NPs. Comparison was also performed with the measurements using Au microelectrodes, indicated that the prepared BDD microelectrodes is promising for the measurements of nanoparticle sizes distribution, especially Pt NPs.

In Vitro Biofouling Performance of Boron-Doped Diamond Microelectrodes for Serotonin Detection Using Fast-Scan Cyclic Voltammetry.

Neurotransmitter release is important to study in order to better understand neurological diseases and treatment approaches. Serotonin is a neurotransmitter known to play key roles in the etiology of neuropsychiatric disorders. Fast-scan cyclic voltammetry (FSCV) has enabled the detection of neurochemicals, including serotonin, on a sub-second timescale via the well-established carbon fiber microelectrode (CFME). However, poor chronic stability and biofouling, i.e., the adsorption of interferent proteins to the electrode surface upon implantation, pose challenges in the natural physiological environment. We have recently developed a uniquely designed, freestanding, all-diamond boron-doped diamond microelectrode (BDDME) for electrochemical measurements. Key potential advantages of the device include customizable electrode site layouts, a wider working potential window, improved stability, and resistance to biofouling. Here, we present a first report on the electrochemical behavior of the BDDME in comparison with CFME by investigating in vitro serotonin (5-HT) responses with varying FSCV waveform parameters and biofouling conditions. While the CFME delivered lower limits of detection, we also found that BDDMEs showed more sustained 5-HT responses to increasing or changing FSCV waveform-switching potential and frequency, as well as to higher analyte concentrations. Biofouling-induced current reductions were significantly less pronounced at the BDDME when using a "Jackson" waveform compared to CFMEs. These findings are important steps towards the development and optimization of the BDDME as a chronically implanted biosensor for in vivo neurotransmitter detection.

In Vitro Monitoring of Nitric Oxide Release in the Mouse Colon Using a Boron-Doped Diamond Microelectrode Modified with Platinum Nanoparticles and Nafion.

This research reports on the preparation of a boron-doped diamond microelectrode modified with platinum nanoparticles and Nafion and its application for detecting nitric oxide (NO) in vitro in the mouse colon. Platinum nanoparticle deposition was performed potentiodynamically using a 2.0 mmol L-1 potassium hexachloroplatinate solution and cycling from -0.2 to 1.3 V vs Ag/AgCl at 0.01 V s-1 for 10 cycles. The Nafion overlayer was applied by immersion in a solution containing 2.5% (w/v) colloidal Nafion and drying overnight at 55 °C in a humid environment. The optimal microelectrode preparation conditions were chosen based on the electrode response for NO oxidation as well as rejection of nitrite (NO2-) oxidation, the main interferent in the electrochemical detection of NO in biological media. Detection figures of merit include a sensitivity of 16.7 ± 2.7 mA M-1 cm-2 (n = 3 electrodes), a detection limit of 0.5 μmol L-1 (S/N = 3), and an electrode response reproducibility of 2.5% (RSD). Electrical stimulation and continuous amperometry were used to measure NO release from myenteric ganglia in wild-type male and female mice in response to an increasing number of electrical stimuli to study nitrergic signaling in the colon. We also present preliminary data regarding the use of optogenetics to selectively stimulate nitrergic myenteric neurons using blue light stimulation with a goal of understanding how inhibitory neuromuscular signaling is involved in the myenteric plexus circuitry that controls intestinal motility.

Ultrasensitive Diamond Microelectrode Application in the Detection of Ca2+ Transport by AnnexinA5-Containing Nanostructured Liposomes.

This report describes the innovative application of high sensitivity Boron-doped nanocrystalline diamond microelectrodes for tracking small changes in Ca2+ concentration due to binding to Annexin-A5 inserted into the lipid bilayer of liposomes (proteoliposomes), which could not be assessed using common Ca2+ selective electrodes. Dispensing proteoliposomes to an electrolyte containing 1 mM Ca2+ resulted in a potential jump that decreased with time, reaching the baseline level after ~300 s, suggesting that Ca2+ ions were incorporated into the vesicle compartment and were no longer detected by the microelectrode. This behavior was not observed when liposomes (vesicles without AnxA5) were dispensed in the presence of Ca2+. The ion transport appears Ca2+-selective, since dispensing proteoliposomes in the presence of Mg2+ did not result in potential drop. The experimental conditions were adjusted to ensure an excess of Ca2+, thus confirming that the potential reduction was not only due to the binding of Ca2+ to AnxA5 but to the transfer of ions to the lumen of the proteoliposomes. Ca2+ uptake stopped immediately after the addition of EDTA. Therefore, our data provide evidence of selective Ca2+ transport into the proteoliposomes and support the possible function of AnxA5 as a hydrophilic pore once incorporated into lipid membrane, mediating the mineralization initiation process occurring in matrix vesicles.

In vitro electrochemical measurement of serotonin release in the human jejunum mucosa using a diamond microelectrode.

We report herein on the use of a boron-doped diamond microelectrode (DME) to record oxidation currents in vitro associated with the release of serotonin from enterochromaffin cells in the epithelium of the human intestinal mucosa. Continuous amperometric measurements were made as a function of distance (ln current vs. distance) from the tissue surface in human jejunum specimens. The results demonstrate the capabilities of the DME for the stable and reproducible detection of serotonin in the complex environment of the human tissue. Serotonin release was evoked by the shearing force of a continuously flowing Krebs buffer solution at 36 °C with the tissue pinned down in a flow bath. Reproducible currents with distance were recorded for serotonin oxidation. Increased oxidation currents were observed in the presence of the selective serotonin reuptake inhibitor, fluoxetine, indicating that a significant fraction of the amperometric current recorded is attributable to serotonin oxidation. The nominal reciprocal slope, |slope-1|, of the ln current vs. distance plots increased from 270 ± 25 μm-1 in Krebs buffer (N = 3) to 471 ± 65 μm-1 during fluoxetine addition (N = 3), reflective of a reduced rate of reuptake in the presence of the SERT antagonist. The paper reports on the characterization of the diamond microelectrodes and the in vitro electrochemical measurement data.

Cyclic and differential pulse voltammetry investigations of an iodine contrast product using microelectrode of BDD

This work deals with the electrochemical behavior and detection of an iodine contrast product using microelectrode. For this, cyclic voltammetry and differential pulse were used for behavior study and detection, respectively. In this work, a boron-doped diamond (BDD) microelectrode was used. Cyclic voltammetry showed that the oxidation peak of iohexol (IHX) appeared at a potential of 1.655 V/ESM in H 2 SO 4 medium (0.1 M). The electrooxidation process of IHX is irreversible, controlled by diffusion combined par adsorption, and can undergo direct and/or indirect oxidation. In addition, using the differential pulse voltammetry technique, the peak oxidation current shows a linear relationship with the IHX concentration between 4 µmol/L and 74.35 µ mol/L. The calculated limit of detection (LOD) and limit of quantification (LOQ) are 1.953 µmol/L and 6.511 µmol/L, respectively. Recovery rates ranging from 95% to 99% in the presence of interfering compounds (inorganic compounds with concentrations 300 times higher than that of IHX). In addition, the DDB successfully recovered the concentration (20 µmol/L) of IHX dissolved with paracetamol concentrations ranging from 31 µmol/L to 149.66 µmol/L. These results suggest that the BDD can be used as a practical sensor to detect and quantify trace amounts of IHX.

Detection of Lead (II) on a Boron-doped Diamond Electrode by Differential Pulse Anodic Stripping Voltammetry

Lead, even in low concentrations, can be dangerous and toxic to humans and their environment. Due to the toxicity of this metal, an electroanalytical method has been developed for the direct quantitative determination of Pb2+. The Pb2+ detection was performed using Differential Pulse Anodic Stripping Voltammetry. The quantification of Pb2+ by these electrochemical methods was carried out on a boron-doped diamondmicro electrode in HNO3 medium (0.01 M). This work made it possible to efficiently detect lead with a detection limit equal to 0.052 μM and a quantification limit equal to 0.173 μM. This method made it possible to selectively detect and quantify the Pb2+ in the presence of other metals such as Cd2+ and Cu2+. In the presence of other metals, a recovery rate of 94.53% was observed. This value is close to the recovery rate obtained (98.6%) when the Pb2+ is alone in electrolyte.

(Invited) Diamond Based Chemical/Biochemical Sensors: State-of-the-Art and Perspectives

Diamond is grown in some laboratories by either HPHT process or Plasma-Enhanced Chemical Vapor Deposition (MP-CVD) since a few decades. Single crystal diamond exhibits outstanding properties including a high optical transparency over a broad electromagnetic spectrum, high thermal conductivity approx. five times higher than copper, and acoustic wave velocity close to 19 000 m.s-1. It displays also remarkable mechanical properties with e.g. a Young’s modulus exceeding 1000 GPa along with high resistance to fracture, to name a few. Some of these properties remain also remarkable in its polycrystalline form when compare to most other materials. Furthermore, diamond can be doped with nitrogen or boron during growth, offering electrical properties from semiconducting to quasi-metallic regimes. When heavily doped with boron (~2.1021 cm-3), the so-called Boron Doped Diamond (BDD) electrodes become attractive electrodes featuring a high potential window > 3V in water and low double-layer capacitance. Moreover, diamond is extremely resilient to corrosion and more generally to chemical attacks. It is also biocompatible, which makes it very attractive for in-vivo sensing applications. Finally, the carbon nature of the diamond offers wide opportunities for surface grafting of chemical or biochemical functional groups through highly stable covalent carbon-carbon bonding. These properties can be exploited advantageously to enhance the analytical performances and stability of chemical/biochemical sensors and have motivated our research over the last 15 years. Our work focuses mainly on polycrystalline diamond thin films that can be grown typically on inches silicon substrates, thus offering access to some clean-room processes and potentially large-scale production.Several processes were elaborated to micro-pattern diamond layers in order to design chemical transducers such as gravimetric MEMS devices, electrodes, field effect transistors, etc. Diamond microstructures may also be transferred to flexible parylene or polyimide substrates, thus making them attractive e.g. for wearable sensors and implantable medical electrodes. Further techniques have also been developed to enhance the active surface area of diamond transducer surfaces at the nanoscale and thus increase drastically the sensitivity of the resulting sensors by multiplying the number of active sites. Here diamond is typically grown onto well-chosen high aspect ratio templates that can withstand the growth conditions of diamond in high-density hydrogen plasma. Most of these methods have been “standardized”. They involve clean-room processing including dry etching, photolithography, and so on and forth. As examples, heavily doped diamond electrodes were developed successfully both as macro- and micro-electrodes for biomedical, pharmaceutical or foodstuff analysis applications. These applications benefit both from the high analytical performances of diamond electrodes in particular due to their low background signals and high reactivity, and high stability and reliability. BDD electrodes may also be modified with transition metal nanoparticles to enhance their catalytic behavior. From this concept, diamond multi-electrode arrays were designed for chemical patterns identification, for instance for sensory analysis of coffee, or for the monitoring of environmental pollutants. BDD electrodes offer also significant advantages in electrochemiluminescence (ECL) techniques, which are being investigated for various applications ranging from foodstuff analysis to narcotics detection. A key benefit of BDD electrodes for all of the above applications is certainly that they can be electrochemically reactivated following fouling, sometimes directly in the analytical medium, to maintain high reactivity thus opening the way to reusable sensors and online monitoring. Besides, BDD microelectrode arrays have also been transferred to flexible substrates for neural stimulation and recording, along with in-vivo neuromodulators measurements. Finally, diamond based MEMS devices (microcantilevers, SAW sensors) take advantage both of the mechanical properties of diamond, along with steady carbon interface for convenient bio-functionalization. Our work here focused mainly on the detection of odorant molecules, using biomolecular receptors involved in olfaction in Nature as sensitive layers, including Odorant Binding Proteins (OBPs), Major Urinary Proteins (MUPs) and Olfactory Receptors (OR). Multisensor array instrumentations were developed around this concept, for applications ranging from breathe analysis to security applications.

Electrical transport measurements for superconducting sulfur hydrides using boron-doped diamond electrodes on beveled diamond anvil

A diamond anvil cell (DAC) has become an effective tool for investigating physical phenomena that occur at extremely high pressure, such as high-transition temperature superconductivity. Electrical transport measurements, which are used to characterize one of the most important properties of superconducting materials, are difficult to perform using conventional DACs. The available sample space in conventional DACs is very small and there is an added risk of electrode deformation under extreme operating conditions. To overcome these limitations, we herein report the fabrication of a boron-doped diamond microelectrode and undoped diamond insulation on a beveled culet surface of a diamond anvil. Using the newly developed DAC, we have performed in-situ electrical transport measurements on sulfur hydride H2S, which is a well-known precursor of the pressure-induced, high-transition temperature superconducting sulfur hydride, H3S. These measurements conducted under high pressures up to 192 GPa, indicated the presence of a multi-step superconducting transition, which we have attributed to elemental sulfur and possibly HS2.

In Vivo Real-Time Simultaneous Examination of Drug Kinetics at Two Separate Locations Using Boron-Doped Diamond Microelectrodes.

Methylcobalamin, which is used for the clinical treatment of patients with neuropathy, can have an impact on the sensorineural components associated with the cochlea, and it is possible that the auditory threshold in a certain population of patients with deafness may be recovered. Nonetheless, it remains uncertain whether the action site of methylcobalamin is localized inside or outside the cochlea and which cellular or tissue element is targeted by the drug. In the present work, we developed a method to realize in vivo real-time simultaneous examination of the drug kinetics in two separate locations using boron-doped diamond microelectrodes. First, the analytical performance of methylcobalamin was studied and the measurement protocol was optimized in vitro. Then, the optimized protocol was applied to carry out real-time measurements inside the cochlea and the leg muscle in live guinea pigs while systemically administering methylcobalamin. The results showed that the methylcobalamin concentration in the cochlea was below the limit of detection for the microelectrodes or the drug did not reach the cochlea, whereas the compound clearly reached the leg muscle.

Flexible, diamond-based microelectrodes fabricated using the diamond growth side for neural sensing

Diamond possesses many favorable properties for biochemical sensors, including biocompatibility, chemical inertness, resistance to biofouling, an extremely wide potential window, and low double-layer capacitance. The hardness of diamond, however, has hindered its applications in neural implants due to the mechanical property mismatch between diamond and soft nervous tissues. Here, we present a flexible, diamond-based microelectrode probe consisting of multichannel boron-doped polycrystalline diamond (BDD) microelectrodes on a soft Parylene C substrate. We developed and optimized a wafer-scale fabrication approach that allows the use of the growth side of the BDD thin film as the sensing surface. Compared to the nucleation surface, the BDD growth side exhibited a rougher morphology, a higher sp3 content, a wider water potential window, and a lower background current. The dopamine (DA) sensing capability of the BDD growth surface electrodes was validated in a 1.0 mM DA solution, which shows better sensitivity and stability than the BDD nucleation surface electrodes. The results of these comparative studies suggest that using the BDD growth surface for making implantable microelectrodes has significant advantages in terms of the sensitivity, selectivity, and stability of a neural implant. Furthermore, we validated the functionality of the BDD growth side electrodes for neural recordings both in vitro and in vivo. The biocompatibility of the microcrystalline diamond film was also assessed in vitro using rat cortical neuron cultures.

Application of spike sorting algorithm to neuronal signals originated from boron doped diamond micro-electrode arrays.

In this work we report on the implementation of methods for data processing signals from microelectrode arrays (MEA) and the application of these methods for signals originated from two types of MEAs to detect putative neurons and sort them into subpopulations. We recorded electrical signals from firing neurons using titanium nitride (TiN) and boron doped diamond (BDD) MEAs. In previous research, we have shown that these methods have the capacity to detect neurons using commercially-available TiN-MEAs. We have managed to cultivate and record hippocampal neurons for the first time using a newly developed custom-made multichannel BDD-MEA with 20 recording sites. We have analysed the signals with the algorithms developed and employed them to inspect firing bursts and enable spike sorting. We did not observe any significant difference between BDD- and TiN-MEAs over the parameters, which estimated spike shape variability per each detected neuron. This result supports the hypothesis that we have detected real neurons, rather than noise, in the BDD-MEA signal. BDD materials with suitable mechanical, electrical and biocompatibility properties have a large potential in novel therapies for treatments of neural pathologies, such as deep brain stimulation in Parkinson's disease.

Advancing Electrochemical Microsensor Technologies Using Carbon Nanomaterials for Chronic Dopamine Detection

Analytical microsensors that can reliably detect (bio)molecules in real-time long-term represent one of the greatest challenges for health and environmental monitoring. Developing such microsensors with high sensitivity and selectivity in minimally prepared complex samples is especially difficult. In recent years, the application of nanomaterials and advanced fabrication methods to microsensing has demonstrated major enhancements in key microsensor performance metrics and their ease of integration into miniaturized microelectrode microarray sensor platforms. In this work, we report the electrochemical response of a boron-doped ultrananocrystalline diamond (BDUNCD) microelectrode during long-term dopamine (DA) detection. Specifically, changes to its electrochemical activity and electroactive area due to DA-by products and surface oxidation are studied via scanning electron microscopy, energy dispersive spectroscopy, electrochemical impedance spectroscopy and silver deposition imaging (SDI). The fouling studies with amperometry (AM) and fast scan cyclic voltammetry (FSCV) methods suggest that the microelectrodes are heavily fouled due to poor DA-dopamine-o-quinone cyclization rates followed by a combination of polymer formation and major changes in their surface chemistry. SDI data confirms the presence of the insulating polymer with sparsely-distributed tiny electroactive regions. This resulted in severely distorted DA signals and a 90% loss in signal starting as early as 3 hrs for AM and a 56% loss at 6.5 hrs for FSCV. This underscores the need for cleaning of the fouled microelectrodes if they have to be used long-term. Out of the three in vivo suitable electrochemical cycling cleaning waveforms investigated, the standard waveform (-0.4 V to +1.0 V) provides the best cleaned surface with a fully retained voltammogram shape, no hysteresis, no DA signal loss (a 90±0.72 nA increase) and the smallest charge transfer resistance value of 0.4±0.02 MW even after 6.5 hrs of monitoring. Most importantly, this is the same waveform that is widely used for in vivo detection with carbon fiber microelectrodes. Future work to test these microelectrodes for more than 24 hrs of DA detection is anticipated.

Surface Fouling of Ultrananocrystalline Diamond Microelectrodes during Dopamine Detection: Improving Lifetime via Electrochemical Cycling.

In this work, we report the electrochemical response of a boron-doped ultrananocrystalline diamond (BDUNCD) microelectrode during long-term dopamine (DA) detection. Specifically, changes to its electrochemical activity and electroactive area due to DA byproducts and surface oxidation are studied via scanning electron microscopy, energy dispersive spectroscopy, electrochemical impedance spectroscopy, and silver deposition imaging (SDI). The fouling studies with amperometry (AM) and fast scan cyclic voltammetry (FSCV) methods suggest that the microelectrodes are heavily fouled due to poor DA-dopamine- o-quinone cyclization rates followed by a combination of polymer formation and major changes in their surface chemistry. SDI data confirms the presence of the insulating polymer with sparsely distributed tiny electroactive regions. This resulted in severely distorted DA signals and a 90% loss in signal starting as early as 3 h for AM and a 56% loss at 6.5 h for FSCV. This underscores the need for cleaning of the fouled microelectrodes if they have to be used long-term. Out of the three in vivo suitable electrochemical cycling cleaning waveforms investigated, the standard waveform (-0.4 V to +1.0 V) provides the best cleaned surface with a fully retained voltammogram shape, no hysteresis, no DA signal loss (a 90 ± 0.72 nA increase), and the smallest charge transfer resistance value of 0.4 ± 0.02 MΩ even after 6.5 h of monitoring. Most importantly, this is the same waveform that is widely used for in vivo detection with carbon fiber microelectrodes. Future work to test these microelectrodes for more than 24 h of DA detection is anticipated.

Electrochemical measurement of lamotrigine using boron-doped diamond electrodes

In this paper we report on a study of the electrochemical behavior of lamotrigine (LTG) using boron-doped diamond (BDD) electrodes. Cyclic voltammetry of LTG in a phosphate buffer solution exhibited an oxidation signal at ca. +1.4 V (vs. Ag/AgCl). A reduction signal at −0.5 to −1.0 V (vs. Ag/AgCl) was observed only after oxidation of LTG. The oxidation signal was due to polymerization of LTG adsorbed on the BDD electrode, while the reduction signal was a consequence of a process involving the reduction of the azo group in the LTG-oxidized product. Continuous measurements of LTG aiming at in vivo monitoring were successfully investigated and an optimized chronoamperometry technique, in which the BDD microelectrode was clamped to the LTG oxidation potential (+1.4 V) for 2 s, then to the LTG reduction potential (−0.6 V) for 2 s, was implemented. The limits of detection (S/N = 3) were estimated to be 29 nM and 130 nM for the oxidation and reduction of LTG, respectively. The use of this chronoamperometry technique enables a high temporal resolution of 4 s for LTG measurements. BDD microelectrodes, therefore, are the ideal electrodes for performing continuous in vivo measurements of LTG.

Detection of neurochemicals with enhanced sensitivity and selectivity via hybrid multiwall carbon nanotube-ultrananocrystalline diamond microelectrodes.

Abnormal neurochemical signaling is often the underlying cause of brain disorders. Electrochemical microsensors are widely used to monitor neurochemicals with high spatial-temporal resolution. However, they rely on carbon fiber microelectrodes that often limit their sensing performance. In this study, we demonstrate the potential of a hybrid multiwall carbon nanotube (MWCNT) film modified boron-doped ultrananocrystalline diamond (UNCD) microelectrode (250 μm diameter) microsensor for improved detection of dopamine (DA) in the presence of common interferents. A series of modified microelectrodes with varying film thicknesses were microfabricated by electrophoretic deposition (EPD) and characterized by scanning electron microscopy, x-ray photoelectron spectroscopy, electrochemical impedance spectroscopy (EIS) and silver deposition imaging. Using cyclic voltammetry, the 100-nm "thin" film microelectrode produced the most favorable combination of DA sensitivity value of 36 ±2% μA/μM/cm2 with a linear range of 33 nM to 1 μM and a limit of detection (LOD) of 9.5 ± 1.2% nM. The EIS spectra of these microelectrodes revealed three regions with inhomogeneous pore geometry and differing impedance values and electrochemical activity, which was found to be film thickness dependent. Using differential pulse voltammetry, the modified microelectrode showed excellent selectivity by exhibiting three distinct peaks for the DA, serotonin and excess ascorbic acid in a ternary mixture. These results provide two key benefits: first, remarkable improvements in DA sensitivity (>125-fold), selectivity (>2000-fold) and LOD (>180-fold), second, these MWCNTs can be selectively coated with a simple, scalable and low cost EPD process for highly multiplexed microsensor technologies. These advances offer considerable promise for further progress in chemical neurosciences.