Meining Zhang

Vertically Aligned Carbon Nanotube-Sheathed Carbon Fibers as Pristine Microelectrodes for Selective Monitoring of Ascorbate in Vivo

Using as-synthesized vertically aligned carbon nanotube-sheathed carbon fibers (VACNT-CFs) as microelectrodes without any postsynthesis functionalization, we have developed in this study a new method for in vivo monitoring of ascorbate with high selectivity and reproducibility. The VACNT-CFs are formed via pyrolysis of iron phthalocyanine (FePc) on the carbon fiber support. After electrochemical pretreatment in 1.0 M NaOH solution, the pristine VACNT-CF microelectrodes exhibit typical microelectrode behavior with fast electron transfer kinetics for electrochemical oxidation of ascorbate and are useful for selective ascorbate monitoring even with other electroactive species (e.g., dopamine, uric acid, and 5-hydroxytryptamine) coexisting in rat brain. Pristine VACNT-CFs are further demonstrated to be a reliable and stable microelectrode for in vivo recording of the dynamic increase of ascorbate evoked by intracerebral infusion of glutamate. Use of a pristine VACNT-CF microelectrode can effectively avoid any manual electrode modification and is free from person-to-person and/or electrode-to-electrode deviations intrinsically associated with conventional CF electrode fabrication, which often involves electrode surface modification with randomly distributed CNTs or other pretreatments, and hence allows easy fabrication of highly selective, reproducible, and stable microelectrodes even by nonelectrochemists. Thus, this study offers a new and reliable platform for in vivo monitoring of neurochemicals (e.g., ascorbate) to largely facilitate future studies on the neurochemical processes involved in various physiological events.

Enzyme-based amperometric biosensors for continuous and on-line monitoring of cerebral extracellular microdialysate.

Analytical systems integrating in vivo microdialysis sampling with enzyme-based electrochemical biosensor detection have been increasingly accepted to be a new technique for continuous and on-line monitoring of biologically important species. Extensive interests in such integrated on-line analytical systems have suggested that these systems are very useful for physiological and pathological investigations. This review mainly focuses on the principle, development and striking applications of the enzyme-based amperometric biosensors integrated with in vivo microdialysis for continuous and on-line monitoring of cerebral extracellular fluid in recent years.

Platinized Aligned Carbon Nanotube-Sheathed Carbon Fiber Microelectrodes for In Vivo Amperometric Monitoring of Oxygen

The abnormal level of O2 could disturb various neurochemical processes and even induce neural injury and brain dysfunction. In order to assess critical roles of O2 in the neurochemical processes, it is essential to perform in vivo monitoring of the dynamic changes of O2. In this study, we develop a new electrochemical method for selectively monitoring O2 in vivo, using platinized vertically aligned carbon nanotube (VACNT)-sheathed carbon fibers (Pt/VACNT-CFs) as the electrodes. The VACNT-sheathed CFs (VACNT-CFs) are produced via the pyrolysis of iron phthalocyanine (FePc) on the surface of CFs, followed by electrochemical deposition of platinum nanoparticles to form Pt/VACNT-CFs. The resulting Pt/VACNT-CF microelectrodes exhibit fast overall kinetics for the O2 reduction via a four-electron reduction process without the formation of toxic H2O2 intermediate. Consequently, effective and selective electrochemical methods are developed for the measurements of O2 in rat brain with the Pt/VACNT-CF microelectrodes, even in the presence of some species at their physiological levels, such as ascorbic acid, dopamine, uric acid, 5-hydroxytryptamine, and of the O2 fluctuation in rat brain in the early stage of global cerebral ischemia/reperfusion, mild hyperoxia, and hypoxia induced by exposing the animal, for a short time, to O2 and N2, respectively, and hindfeet pinch. The use of VACNT-CF as the support for Pt effectively improves the stability of Pt, as compared with the bare CF support, while the FePc pyrolysis ensures the VACNT-CFs to be reproducibly produced. Thus, this study offers a novel and reliable strategy for preparing new microelectrodes for in vivo monitoring of O2 in various physiological processes with a high sensitivity and selectivity.

In Vivo Analysis with Electrochemical Sensors and Biosensors

Tongfang Xiao,†,‡ Fei Wu,†,‡ Jie Hao,†,‡ Meining Zhang,†,‡ Ping Yu,†,‡ and Lanqun Mao*,†,‡ †Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Analytical Chemistry for Living Biosystems and Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China ‡University of Chinese Academy of Sciences, Beijing 100049, China ■ CONTENTS Electrochemical Sensors A Differential Pulse Voltammetry B Fast Scan Cyclic Voltammetry B Amperometry Based on Unique Redox Property of Neurochemicals D Ascorbate D DA E O2 F NO F Hydrogen Peroxide F Hydrogen Sulfide G Electrochemical Biosensors G Oxidase-Based Electrochemical Biosensors G Dehydrogenase-Based Electrochemical Biosensors I Multienzyme-Based Electrochemical Biosensors J Aptamer-Based Biosensor for ATP J Conclusion K Author Information K Corresponding Author K ORCID K Notes K Biographies K Acknowledgments L References L

In Vivo Monitoring of H2O2 with Polydopamine and Prussian Blue-coated Microelectrode

In vivo monitoring of hydrogen peroxide (H2O2) in the brain is of importance for understanding the function of both reactive oxygen species (ROS) and signal transmission. Producing a robust microelectrode for in vivo measurement of H2O2 is challenging due to the complex brain environment and the instability of electrocatalysts employed for the reduction of H2O2. Here, we develop a new kind of microelectrode for in vivo monitoring of H2O2, which is prepared by, first, electrodeposition of Prussian blue (PB) onto carbon nanotube (CNT) assembled carbon fiber microelectrodes (CFEs) and then overcoating of the CFEs with a thin membrane of polydopamine (PDA) through self-polymerization. Scanning electron microscopic and X-ray proton spectroscopic results confirm the formation of PDA/PB/CNT/CFEs. The PDA membrane enables PB-based electrodes to show high stability in both in vitro and in vivo studies and to stably catalyze the electrochemical reduction of H2O2. The microelectrode is selective for in vivo measurements of H2O2, interference-free from O2 and other electroactive species coexisting in the brain. These properties, along with good linearity, high biocompatibility, and stability toward H2O2, substantially enable the microelectrode to track H2O2 changes in vivo during electrical stimulation and microinfusion of H2O2 and drug, which demonstrates that the microelectrode could be well suited for in vivo monitoring of dynamic changes of H2O2 in rat brain.

Protein Pretreatment of Microelectrodes Enables in Vivo Electrochemical Measurements with Easy Precalibration and Interference-Free from Proteins.

In vivo electrochemistry is one powerful strategy for probing brain chemistry. However, the decreases in sensitivity mainly caused by the adsorption of proteins onto electrode surface in short-term in vivo measurements unfortunately render great challenges in both electrode calibration and selectivity against the alternation of proteins. In this study, we observe that the pretreatment of carbon fiber microelectrodes (CFEs) with bovine serum albumin (BSA) would offer a simple but effective strategy to the challenges mentioned above. We verify our strategy for dopamine (DA) with conventionally used CFEs and for ascorbate with our previously developed carbon nanotube-modified CFEs. We find that, in artificial cerebral spinal fluid (aCSF) solution containing BSA, the current responses of the microelectrodes equilibrate shortly and the results for precalibration carried out in this solution are found to be almost the same as those for the postcalibration in pure aCSF. This observation offers a new solution to electrode calibration for in vivo measurements with a technical simplicity. Furthermore, we find that the use of BSA pretreated CFEs to replace bare CFEs would minimize the interference from the alternation of proteins in the brain. This study offers a new general and effective approach to in vivo electrochemistry with a high reliability and a simplified procedure.

Renewable and Ultralong Nanoelectrochemical Sensor: Nanoskiving Fabrication and Application for Monitoring Cell Release.

Nanoscaled electrode has been attracting increasing attention because of striking fundamentals and practical applications. Usually, the nanoscaled electrode is fabricated by manual or photo or electron-beam lithography, which is not easy to reproducibly fabricate with simple equipment. In this paper, a cost-effective method, nanoskiving, is developed to fabricate an ultralong nanowire electrode (ULNE). The ULNE is reproducibly obtained by simply sectioning a sandwich epoxy block with a Au film. The width of ULNE could be down to nanometer dependence on the thickness of the Au film, while the length could reach to the millimeter. Thus, the created Au ULNE shows steady-state microamperometric current, characteristic of the nanoelectrode array attributed to its macroscopic length and nanoscaled width without considering the overlap of the diffusion layer of the neighboring nanoelectrode. The electrodeposited Pt/Au ULNE displays unusual electrocatalytic performance toward both the oxidation and reduction of hydrogen peroxide and, as a nanosensor, gives rise to high sensitivity and selectivity of monitoring hydrogen peroxide released from cells stimulated by ascorbic acid.