Efficient Electrochemical Microsensor for the Simultaneous Measurement of Hydrogen Peroxide and Ascorbic Acid in Living Brains.

Hydrogen peroxide (H2O2) and ascorbic acid (AA), acting as two significant indicative species, correlate with the oxidative stress status in living brains, which have historically been considered to be involved mainly in neurodegenerative disorders such as Alzheimer's disease, Huntington's disease, and Parkinson's disease (PD). The development of efficient biosensors for the simultaneous measurement of their levels in living brains is vital to understand their roles played in the brain and their interactive relationship in the progress of these diseases. Herein, a robust ratiometric electrochemical microsensor was rationally designed to realize the determination of H2O2 and AA simultaneously. Therefore, a specific probe was designed and synthesized with both recognition units responsible for reacting with H2O2 to produce a detectable signal on the microsensor and linkage units helping the probe modify onto the carbon substrate. A topping ingredient, single-walled carbon nanotubes (SWCNTs) was added on the surface of the electrode, with the purpose of not only facilitating the oxidation of AA but also absorbing methylene blue (MB), prompting to read out the inner reference signal. This proposed electrochemical microsensor exhibited a robust ability to real-time track H2O2 and AA in linear ranges of 0.5-900 and 10-1000 µM with high selectivity and accuracy, respectively. Eventually, the efficient electrochemical microsensor was successfully applied to the simultaneous measurement of H2O2 and AA in the rat brain, followed by microinjection, and in the PD mouse brain.

Advancements in Brain Research: The In Vivo/In Vitro Electrochemical Detection of Neurochemicals.

Neurochemicals, crucial for nervous system function, influence vital bodily processes and their fluctuations are linked to neurodegenerative diseases and mental health conditions. Monitoring these compounds is pivotal, yet the intricate nature of the central nervous system poses challenges. Researchers have devised methods, notably electrochemical sensing with micro-nanoscale electrodes, offering high-resolution monitoring despite low concentrations and rapid changes. Implantable sensors enable precise detection in brain tissues with minimal damage, while microdialysis-coupled platforms allow in vivo sampling and subsequent in vitro analysis, addressing the selectivity issues seen in other methods. While lacking temporal resolution, techniques like HPLC and CE complement electrochemical sensing's selectivity, particularly for structurally similar neurochemicals. This review covers essential neurochemicals and explores miniaturized electrochemical sensors for brain analysis, emphasizing microdialysis integration. It discusses the pros and cons of these techniques, forecasting electrochemical sensing's future in neuroscience research. Overall, this comprehensive review outlines the evolution, strengths, and potential applications of electrochemical sensing in the study of neurochemicals, offering insights into future advancements in the field.

A portable electrochemical microsensor for in-site measurement of dissolved oxygen and hydrogen sulfide in natural water.

Dissolved oxygen (O2) and hydrogen sulfide (H2S) are two important indicators of water quality, their levels are of intimate dependence and varying over time. It is of great significance to monitoring of dissolved O2 and H2S simultaneously in natural water, yet has not been reported because of lack of effective approaches. In this work, a portable electrochemical microsensor was developed for simultaneously quantifying dissolved O2 and H2S. Here, Pd@Ni nanoparticles (NPs) were self-assembled onto the microelectrode by MXene titanium carbide (Ti3C2Tx), which were of responsibility towards O2 and H2S detection within single electrochemical reduction process. On this regard, Pd NPs facilitated catalyzing the electrochemical reduction of O2, while Ni NPs were employed as recognition element for H2S detection. With the electrochemical reduction sweep, the initial application of a positive voltage rendered the Ni to be oxidized to be Ni ions, contributing to their following capture of surrounding S2- to form nickel sulfide. Nickel sulfide with highly electrochemical activity were capable of generating detecting reduction current. In consequence, the as-designed microsensor can simultaneously determine O2 concentrations ranging from 36 to 318 µM and H2S levels ranging from 0.1 to 2.5 µM with high selectivity. Finally, the portable microsensor was successfully applied to simultaneous detection dissolved O2 and H2S in natural water in-site, the results of which were comparable to the classical methods.

Efficient Electrochemical Microsensor for In Vivo Monitoring of H2O2 in PD Mouse Brain: Rational Design and Synthesis of Recognition Molecules.

Hydrogen peroxide (H2O2), one of the most stable and abundant reactive oxygen species (ROS), acting as a modulator of dopaminergic signaling, has been intimately implicated in Parkinson's disease, creating a critical need for the selective quantification of H2O2 in the living brain. Current natural or nanomimic enzyme-based electrochemical methods employed for the determination of H2O2 suffer from inadequate selectivity and stability, due to which the in vivo measurement of H2O2 in the living brain remains a challenge. Herein, a series of 5-(1,2-dithiolan-3-yl)-N-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pentanamide (DBP) derivatives were designed by tuning the substitute groups and sites of a boric acid ester, which served as probes to specifically react with H2O2. Consequently, the reaction products, 5-(1,2-dithiolan-3-yl)-N-(4-hydroxyphen-yl)pentanamide (DHP) derivatives, converted the electrochemical signal from inactive into active. After systematically evaluating their performances, 5-(1,2-dithiolan-3-yl)-N-(3-chloro-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pentanamide (o-Cl-DBP) was finally identified as the optimized probe for H2O2 detection as it revealed the fastest reaction time, the largest current density, and the most negative potential. In addition, electrochemically oxidized graphene oxide (EOGO) was utilized to produce a stable inner reference. The designed electrochemical microsensor provided a ratiometric strategy for real-time tracking of H2O2 in a linear range of 0.5-600 µM with high selectivity and accuracy. Eventually, the efficient electrochemical microsensor was successfully applied to the measurement of H2O2 in Parkinson's disease (PD) mouse brain. The average levels of H2O2 in the cortex, striatum, and hippocampus in the normal mouse and PD mouse were systematically compared for the first time.

In Vivo Monitoring of pH in Subacute PD Mouse Brains with a Ratiometric Electrochemical Microsensor Based on Poly(melamine) Films.

In vivo monitoring of cerebral pH is of great significance because its disturbance is related to some pathological processes such as neurodegenerative diseases, for example, Parkinson's disease (PD). In this study, we developed an electrochemical microsensor based on poly(melamine) (PMel) films for ratiometric monitoring of pH in subacute PD mouse brains. In this microsensor, PMel films were prepared from a simple electropolymerization approach in a melamine-containing solution, serving as the selective pH recognition membrane undergoing a 2H+/2e- process. Meanwhile, electrochemically oxidized graphene oxide (EOGO) produced a built-in correction signal which helped avoid the environmental interference of the complicated brain systems. The potential difference between the peaks generated from EOGO and PMel gradually decreased with the aqueous pH increasing from 4.0 to 9.0, constituting the detection foundation of the ratiometric electrochemical microsensor (REM). The in vitro studies demonstrated that this proposed method exhibited a high sensitivity (a Nernstian response of -61.35 mV/pH) and remarkable selectivity against amino acids, anions, cations, and biochemical and reactive oxygen species coexisting in the brain. Coupled with its excellent stability and reproducibility and good antibiofouling based on short-term detection, the developed REM could serve as a disposable sensor for the determination of cerebral pH in vivo. Its following successful application in the real-time measurement of pH in the striatum, hippocampus, and cortex of rat brains in the events of global cerebral ischemia/reperfusion verified the reliability of this method. Finally, we adopted this robust REM to systematically analyze and compare the average pH in different regions of normal and subacute PD mouse brains.

Progress on the reaction-based methods for detection of endogenous hydrogen sulfide.

Hydrogen sulfide (H2S) is a biologically signaling molecule that mediates a wide range of physiological functions, which is frequently misregulated in numerous pathological processes. As such, measurement of H2S holds great attention due to its unique physiological and pathophysiological roles. Currently, a variety of methods based on the H2S-involved reactions have been reported for detection of endogenous H2S, bearing the advantages of good specificity and high sensitivity. This review describes in detail the types of reactions, their mechanisms, and their applications in biological research, thus hopefully providing some guidelines to the researchers in this field for further investigation.