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Neurotransmitters are important chemical messengers in the nervous system that play a crucial role in physiological and physical health. Abnormal levels of neurotransmitters have been correlated with physical, psychotic, and neurodegenerative diseases such as Alzheimer’s, Parkinson’s, dementia, addiction, depression, and schizophrenia. Although multiple neurotechnological approaches have been reported in the literature, the detection and monitoring of neurotransmitters in the brain remains a challenge and continues to garner significant attention. Neurotechnology that provides high-throughput, as well as fast and specific quantification of target analytes in the brain, without negatively impacting the implanted region is highly desired for the monitoring of the complex intercommunication of neurotransmitters. Therefore, it is crucial to develop clinical assessment techniques that are sensitive and reliable to monitor and modulate these chemical messengers and screen diseases. This review focuses on summarizing the current electrochemical measurement techniques that are capable of sensing neurotransmitters with high temporal resolution in real time. Advanced neurotransmitter sensing platforms that integrate nanomaterials and biorecognition elements are explored.

•By modifying FSCV components, simultaneous fMRI data can be acquired with minimal imaging artifacts.•We detect and quantify evoked dopamine and/or tissue oxygen changes using FSCV during BOLD fMRI.•FSCV-fMRI is used to derive a neurotransmitter-inclusive hemodynamic response function (HRF).•Dopamine-derived HRFs can identify brain regions that encode dopamine release amplitude. The vascular contributions of neurotransmitters to the hemodynamic response are gaining more attention in neuroimaging studies, as many neurotransmitters are vasomodulatory. To date, well-established electrochemical techniques that detect neurotransmission in high magnetic field environments are limited. Here, we propose an experimental setting enabling simultaneous fast-scan cyclic voltammetry (FSCV) and blood oxygenation level-dependent functional magnetic imaging (BOLD fMRI) to measure both local tissue oxygen and dopamine responses, and global BOLD changes, respectively. By using MR-compatible materials and the proposed data acquisition schemes, FSCV detected physiological analyte concentrations with high temporal resolution and spatial specificity inside of a 9.4 T MRI bore. We found that tissue oxygen and BOLD correlate strongly, and brain regions that encode dopamine amplitude differences can be identified via modeling simultaneously acquired dopamine FSCV and BOLD fMRI time-courses. This technique provides complementary neurochemical and hemodynamic information and expands the scope of studying the influence of local neurotransmitter release over the entire brain.

Detailed studies of the electrochemical oxygen reduction reaction (ORR) on catalyst materials are crucial to improving the performance of different electrochemical energy conversion and storage systems (e.g., fuel cells and batteries), as well as numerous chemical synthesis processes. In the effort to reduce the loading of expensive platinum group metal (PGM)-based catalysts for ORR in the electrochemical systems, many carbon-based catalysts have already shown promising results and numerous investigations on those catalysts are in progress. Most of these studies show the catalyst materials’ ORR performance as current density data obtained through the rotating disk electrode (RDE), rotating ring-disk electrode (RRDE) experiments taking cyclic voltammograms (CV) or linear sweep voltammograms (LSV) approaches. However, the provided descriptions or interpretations of those data curves are often ambiguous and recondite which can lead to an erroneous understanding of the ORR phenomenon in those specific systems and inaccurate characterization of the catalyst materials. In this paper, we presented a study of ORR on a newly developed carbon-based catalyst, the nitrogen-doped graphene/metal-organic framework (N-G/MOF), through RDE and RRDE experiments in both alkaline and acidic mediums, taking the LSV approach. The functions and crucial considerations for the different parts of the RDE/RRDE experiment such as the working electrode, reference electrode, counter electrode, electrolyte, and overall RDE/RRDE process are delineated which can serve as guidelines for the new researchers in this field. Experimentally obtained LSV curves’ shapes and their correlations with the possible ORR reaction pathways within the applied potential range are discussed in depth. We also demonstrated how the presence of hydrogen peroxide (H2O2), a possible intermediate of ORR, in the alkaline electrolyte and the concentration of acid in the acidic electrolyte can maneuver the ORR current density output in compliance with the possible ORR pathways.

Current strategies for optimizing deep brain stimulation (DBS) therapy involve multiple postoperative visits. During each visit, stimulation parameters are adjusted until desired therapeutic effects are achieved and adverse effects are minimized. However, the efficacy of these therapeutic parameters may decline with time due at least in part to disease progression, interactions between the host environment and the electrode, and lead migration. As such, development of closed-loop control systems that can respond to changing neurochemical environments, tailoring DBS therapy to individual patients, is paramount for improving the therapeutic efficacy of DBS. Evidence obtained using electrophysiology and imaging techniques in both animals and humans suggests that DBS works by modulating neural network activity. Recently, animal studies have shown that stimulation-evoked changes in neurotransmitter release that mirror normal physiology are associated with the therapeutic benefits of DBS. Therefore, to fully understand the neurophysiology of DBS and optimize its efficacy, it may be necessary to look beyond conventional electrophysiological analyses and characterize the neurochemical effects of therapeutic and non-therapeutic stimulation. By combining electrochemical monitoring and mathematical modeling techniques, we can potentially replace the trial-and-error process used in clinical programming with deterministic approaches that help attain optimal and stable neurochemical profiles. In this manuscript, we summarize the current understanding of electrophysiological and electrochemical processing for control of neuromodulation therapies. Additionally, we describe a proof-of-principle closed-loop controller that characterizes DBS-evoked dopamine changes to adjust stimulation parameters in a rodent model of DBS. The work described herein represents the initial steps toward achieving a \"smart\" neuroprosthetic system for treatment of neurologic and psychiatric disorders.

The development of efficient H2O2 sensors is crucial because of their multiple functions inside and outside the biological system and the adverse effects that a higher concentration can cause. This work reports a highly sensitive and selective non-enzymatic electrochemical H2O2 sensor achieved through the hybridization of Co3S4 and graphitic carbon nitride nanosheets (GCNNS). The Co3S4 is synthesized via a hydrothermal method, and the bulk g-C3N4 (b-GCN) is prepared by the thermal polycondensation of melamine. The as-prepared b-GCN is exfoliated into nanosheets using solvent exfoliation, and the composite with Co3S4 is formed during nanosheet formation. Compared to the performances of pure components, the hybrid structure demonstrates excellent electroreduction towards H2O2. We investigate the H2O2-sensing performance of the composite by cyclic voltammetry, differential pulse voltammetry, and amperometry. As an amperometric sensor, the Co3S4/GCNNS exhibits high sensitivity over a broad linear range from 10 nM to 1.5 mM H2O2 with a high detection limit of 70 nM and fast response of 3 s. The excellent electrocatalytic properties of the composite strengthen its potential application as a sensor to monitor H2O2 in real samples. The remarkable enhancement of the electrocatalytic activity of the composite for H2O2 reduction is attributed to the synergistic effect between Co3S4 and GCNNS.

Mesolimbic dopamine signaling plays a major role in alcohol and substance use disorders as well as comorbidities such as anxiety and depression. Growing evidence suggests that alcohol drinking is modulated by the function of the dopamine transporter (DAT), which tightly regulates extracellular dopamine concentrations. Adult male rats on a Wistar Han background (DAT+/+) and rats with a partial DAT deletion (DAT+/−) were used in this study. First, using fast‐scan cyclic voltammetry in brain slices containing the nucleus accumbens core from ethanol‐naïve subjects, we measured greater evoked dopamine concentrations and slower dopamine reuptake in DAT+/− rats, consistent with increased dopamine signaling. Next, we measured ethanol drinking using the intermittent access two‐bottle choice paradigm (20% v/v ethanol vs. water) across 5 weeks. DAT+/− rats voluntarily consumed less ethanol during its initial availability (the first 30 min), especially after longer periods of deprivation. In addition, DAT+/− males consumed less ethanol that was adulterated with the bitter tastant quinine. These findings suggest that partial DAT blockade and concomitant increase in brain dopamine levels has potential to reduce drinking and ameliorate alcohol use disorder (AUD). We investigated patterns of ethanol drinking in male rats with partial deletion of dopamine transporters. Compared to wild‐types, DAT+/− animals do not as readily develop alcohol use disorder (AUD)‐like phenotypes.

Development in high-rate electrode materials capable of storing vast amounts of charge in a short duration to decrease charging time and increase power in lithium-ion batteries is an important challenge to address. Here, we introduce a synthesis strategy with a series of composition-controlled NMC cathodes, including LiNi0.2Mn0.6Co0.2O2(NMC262), LiNi0.3Mn0.5Co0.2O2(NMC352), and LiNi0.4Mn0.4Co0.2O2(NMC442). A very high-rate performance was achieved for Mn-rich LiNi0.2Mn0.6Co0.2O2 (NMC262). It has a very high initial discharge capacity of 285 mAh g−1 when charged to 4.7 V at a current of 20 mA g−1 and retains the capacity of 201 mAh g−1 after 100 cycles. It also exhibits an excellent rate capability of 138, and 114 mAh g−1 even at rates of 10 and 15 C (1 C = 240 mA g−1). The high discharge capacities and excellent rate capabilities of Mn-rich LiNi0.2Mn0.6Co0.2O2 cathodes could be ascribed to their structural stability, controlled particle size, high surface area, and suppressed phase transformation from layered to spinel phases, due to low cation mixing and the higher oxidation state of manganese. The cathodic and anodic diffusion coefficient of the NMC262 electrode was determined to be around 4.76 × 10−10 cm2 s−1 and 2.1 × 10−10 cm2 s−1, respectively.

Reactivity of (2E)-3-(3,4-dihydroxyphenyl)prop-2-enoic acid (caffeic acid), classified as a hydroxycinnamic acid (HCA) derivative, toward electrogenerated superoxide radical anion (O2•−) was investigated through cyclic voltammetry, in situ electrolytic electron spin resonance spectrometry, and in situ electrolytic ultraviolet–visible spectrometry in N,N-dimethylformamide (DMF), aided by density functional theory (DFT) calculations. The quasi-reversible redox of dioxygen/O2•− is modified in the presence of caffeic acid, suggesting that O2•− is scavenged by caffeic acid through proton-coupled electron transfer. The reactivities of caffeic acid toward O2•− are mediated by the ortho-diphenol (catechol) moiety rather than by the acryloyl group, as experimentally confirmed in comparative analyses with other HCAs. The electrochemical and DFT results in DMF suggested that a concerted two-proton-coupled electron transfer mechanism proceeds via the catechol moiety. This mechanism embodies the superior kinetics of O2•− scavenging by caffeic acid.

Ammonium thiosulfate leaching is a promising alternative to the conventional cyanide method for extracting gold from ores. However, strategies for recovering gold from the leachate are less commercially used due to its low affinity to gold. The present study investigated the recovery of gold from the leachate using iron oxides (hematite, Fe2O3 or magnetite, Fe3O4). Cementation experiments were conducted by mixing 0.15 g of aluminum powder as an electron donor and 0.15 g of an electron mediator (activated carbon, hematite, or magnetite) in 10 mL of ammonium thiosulfate leachate containing 100 mg/L gold ions and 10 mM cupric ions for 24 h at 25 °C. The results of the solution analysis showed that when activated carbon (AC) was used, the gold was recovered together with copper (recoveries were 99.99% for gold and copper). However, selective gold recovery was observed when iron oxides were used, where the gold and copper recoveries were 89.7% and 21% for hematite and 85.9% and 15.4% for magnetite, respectively. An electrochemical experiment was also conducted to determine the galvanic interaction between the electron donor and electron mediator in a conventional electrochemical setup (hematite/magnetite–Al as the working electrode, Pt as the counter electrode, Ag/AgCl as the reference electrode) in a gold–thiosulfate medium. Cyclic voltammetry showed a gold reduction “shoulder-like” peak at −1.0 V using hematite/Al and magnetite/Al electrodes. Chronoamperometry was conducted and operated at a constant voltage (−1.0 V) determined during cyclic voltammetry and further analyzed using SEM-EDX. The results of the SEM-EDX analysis for the cementation products and electrochemical experiments confirmed that the gold was selectively deposited on the iron oxide surface as an electron mediator.

Conductive polymer actuators and sensors rely on controlled ion transport coupled to a potential/charge change. In order to understand and control such devices, it is of paramount importance to understand the factors that determine ion flux at various conditions, including the synthesis potential. In this work, the ion transport in thinner poly-3,4-ethylenedioxythiophene (PEDOT) films during charge/discharge driven by cyclic voltammetry is studied by consideration of the electrochemical quartz crystal microbalance (EQCM) and the results are compared to the actuation responses of thicker films that have been synthesized with the same conditions in the bending and linear expansion modes. The effects of polymerization potentials of 1.0 V, 1.2 V, and 1.5 V are studied to elucidate how polymerization potential contributes to actuation, as well the involvement of the EQCM. In this work, it is revealed that there is a shift from anion-dominated to mixed to cation-dominated activity with increased synthesis potential. Scanning electron microscopy shows a decrease in porosity for the PEDOT structure with increasing synthesis potential. EQCM analysis of processes taking place at various potentials allows the determination of appropriate potential windows for increased control over devices.