Single-Carbon-Fiber-Powered Microsensor for In Vivo Neurochemical Sensing with High Neuronal Compatibility

The development of new principles and techniques with high neuronal compatibility for quantitatively monitoring the dynamics of neurochemicals is essential for deciphering brain chemistry and function but remains a great challenge. We herein report a neuron-compatible method for in vivo neurochemical sensing by powering a single carbon fiber through spontaneous bipolar electrochemistry as a new sensing platform. By using ascorbic acid as a model target to prove the concept, we found that the single-carbon-fiber-powered microsensor exhibited a good response, high stability and, more importantly, excellent neuronal compatibility. The microsensor was also highly compatible with electrophysiological recording, thus enabling the synchronous recording of both chemical and electrical signals. The sensing principle could be developed for in vivo monitoring of various neurochemicals in the future by rationally designing and tuning the electrochemical reactions at the two poles of the carbon fiber.     

Recent progress in improving the performance of in vivo electrochemical microsensor based on materials

In vivo monitoring of neurochemicals is important for exploring the mechanism and function of the central nervous system. In vivo electrochemical microsensor benefiting from high temporal and spatial resolution has been demonstrated to be one effective strategy for neurochemical detection. However, due to the complex biological environment, microsensor faces huge challenges in sensitivity, selectivity, stability, and biocompatibility. Materials with good electron-transfer, rough surface, and easy functionalization are widely used to enhance the performance of microsensor. In this review, we summarize the recent progress in improving the performance of in vivo electrochemical microsensor based on materials.     

A Generalizable and Noncovalent Strategy for Interfacing Aptamers with a Microelectrode for the Selective Sensing of Neurotransmitters In Vivo

The selective sensing of neurochemicals is essential for understanding the chemical basis of brain function and pathology. Interfacing the excellent recognition features of aptamers with in vivo compatible carbon fiber microelectrode (CFE)-based electroanalytical systems offers a plausible means to achieve this end. However, this is challenging in terms of coupling chemistry, stability, and versatility. Here, we present a new interfacial functionalization strategy based on the assembly of aptamer cholesterol amphiphiles (aptCAs) on the alkyl chain-functionalized CFE. The noncovalent cholesterol-alkyl chain interactions effectively immobilize aptamers onto the CFE surface, allowing the generation of a highly selective system for probing neurochemical dynamics in living systems and opening up a vast array of new opportunities for designing in vivo sensors for exploring brain chemistry.     

快捷两步法制备金纳米电极用于活体多巴胺检测

用微电极进行活体检测神经化学物质属于侵入式分析,会对脑组织产生不可避免的损伤,进而在生理上产生一些信号干扰检测过程. 减小电极的尺寸对于减小对脑组织的损伤非常重要. 该研究报道了一种新型制备金纳米电极的方法并将其用于活体鼠脑内多巴胺分析研究. 这种金纳米电极的制备过程包含两步：1）通过离子溅射在毛细管的尖端覆盖一层金种子;2）把覆盖有金种子的毛细管浸入氯金酸和盐酸羟胺混合溶液中湿法沉积生成连续导电金膜. 制备好的纳米电极尖端约300 ~ 400 nm. 该金纳米电极可以应用于多巴胺的检测,并且在多巴胺浓度1.0 ~ 56.0 μmol·L^-1范围内有很好的线性响应,最低检测限低至0.14 μmol·L^-1（信噪比=3）. 该金纳米电极具有优异的电化学性能,可以成功的应用于检测鼠脑纹状体儿茶酚胺的释放.     

Recent advances in development of devices and probes for sensing and imaging in the brain

As the most important part of the central nervous system, the brain is extremely complex in structure and function. In vivo analysis of chemical signals is an essential way to investigate brain activity and function. Although functional magnetic resonance imaging(fMRI) or electrophysiology can be used to record brain activity, they are usually limited by low spatiotemporal fidelity or the difficulty of distinguishing the contributions of various neurochemicals. In addition, the development of in vivo biosensors with high selectivity and accuracy is essential to understand the roles that neurochemicals play in the brain. In this review, we focus on the development of instruments and devices for recording chemical signals in the live brain. Meanwhile,the strategies for development of electrochemical and fluorescent probes with high selectivity, high accuracy and good stability are also summarized. In particular, this review highlighted the contributions of our research group to this field. The development of techniques and probes enable us to understand the brain structure and function, and the mechanism of brain diseases, providing the solution for preventing and treating brain diseases.     

Electrochemical characterization of 17β-estradiol with fast-scan cyclic voltammetry

We have developed a sensitive and stable electrochemical method for 17β-estradiol (E2) detection using fast-scan cyclic voltammetry (FSCV). Recently, E2 was proposed to function as a rapid synaptocrine signaling molecule in the brain; however, methods to directly monitor subsecond fluctuations in E2 are currently unavailable, limiting our understanding of the dynamics and mechanism of rapid E2 release. FSCV at carbon-fiber microelectrodes enables subsecond detection of electroactive neurochemicals directly in tissues like the brain. Here, we have electrochemically characterized E2 using FSCV for use in a tissue matrix. The limit of detection of E2 is 31.2±2.5 nM with FSCV, which will enable low nanomolar fluctuations in extracellular E2 to be monitored with hundred millisecond temporal resolution. We also identify specific parameters for waveform modification to improve future detection. This method will significantly improve E2 sensing capabilities and will have far-reaching impacts on improving our understanding of dynamic E2 signaling in the brain.     

Implantable optical fiber microelectrode with anti-biofouling ability for in vivo photoelectrochemical analysis

In-situ monitoring of neurochemicals is of vital importance for the understanding of brain functions. Microelectrode-based photoelectrochemical (PEC) sensing has emerged as a promising tool for in vivo analysis since it inherits the merits of both optical and electrochemical methods. However, the in-situ excitation of photoactive materials on the photoelectrode in living body is still a challenge because of limited tissue penetration depth of light. To circumvent this problem, we herein developed an implantable optical fiber (OF)-based microelectrode for in vivo PEC analysis. The working electrode was constructed by coating Au film as conducting layer and CdS@ZnO as photoactive material on a micron-sized OF, which was free of the limitation of light penetration in biological tissues. Further decoration of an anti-biofouling layer on the surface made the sensor robust in biosamples. It was successfully applied for monitoring Cu²⁺ level in three different brain regions in the rat model of cerebral ischemia/reperfusion.     

Use of poly(ester-sulfonic acid) film-coated electrodes as amperometric detectors in flow injection analysis

Within the past several years significant advances have been made towards the development and incorporation of chemically modified electrodes as selective detectors for high performance liquid chromatography and flow injection analysis. In many cases the chemically modified electrode systems closely approach the “ideal” detector specifications of chemical and mechanical stability along with a significant linear response region. This paper will discuss the characterization and incorporation of ionomeric poly(ester-sulfonic acid) coated electrodes as nonaqueous electrochemical detectors. The orientation of the electrodes in the detector system as well as the increased sensitivity levels to 10⁻¹⁰ g ml⁻¹ for cationic species and 10⁻⁹ g ml⁻¹ for neutral species will be presented. Also the applicability of the ionomer coated electrodes as nonelectrolyte detectors achieved a reproducible response with detection limits to 10⁻⁶ g ml⁻¹. Overall this system performed as well as, or better than, more specialized and expensive thin layer electrochemical detectors.     

Galvanic Redox Potentiometry for Fouling-Free and Stable Serotonin Sensing in a Living Animal Brain

Serotonin (5-HT) is a major neurotransmitter broadly involved in many aspects of feeling and behavior. Although its electro-activity makes it a promising candidate for electrochemical sensing, the persistent generation of fouling layers on the electrode by its oxidation products presents a hurdle for reliable sensing. Here, we present a fouling-free 5-HT sensor based on galvanic redox potentiometry. The sensor efficiently minimizes electrode fouling as revealed by in situ Raman spectroscopy, ensuring a less than 3 % signal change in a 2 hour continuous experiment, whereas amperometric sensors losing 90 % within 30 min. Most importantly, the sensor is highly amenable for in vivo studies, permitting real-time 5-HT monitoring, and supporting the mechanism associated with serotonin release in brain. Our system offers an effective way for sensing different neurochemicals having significant fouling issues, thus facilitating the molecular-level understanding of brain function.     

Multi-Spatiotemporal Probing of Neurochemical Events by Advanced Electrochemical Sensing Methods

Neurochemical events involving biosignals of different time and space dimensionalities constitute the complex basis of neurological functions and diseases. In view of this fact, electrochemical measurements enabling real-time quantification of neurochemicals at multiple levels of spatiotemporal resolution can provide informative clues to decode the molecular networks bridging vesicles and brains. This Minireview focuses on how scientific questions regarding the properties of single vesicles, neurotransmitter release kinetics, interstitial neurochemical dynamics, and multisignal interconnections in vivo have driven the design of electrochemical nano/microsensors, sensing interface engineering, and signal/data processing. An outlook for the future frontline in this realm will also be provided.     

New trends in the electrochemical sensing of dopamine

Since the early 70s electrochemistry has been used as a powerful analytical technique for monitoring electroactive species in living organisms. In particular, after extremely rapid evolution of new micro and nanotechnology it has been established as an invaluable technique ranging from experiments in vivo to measurement of exocytosis during communication between cells under in vitro conditions. This review highlights recent advances in the development of electrochemical sensors for selective sensing of one of the most important neurotransmitters—dopamine. Dopamine is an electroactive catecholamine neurotransmitter, abundant in the mammalian central nervous system, affecting both cognitive and behavioral functions of living organisms. We have not attempted to cover a large time-span nor to be comprehensive in presenting the vast literature devoted to electrochemical dopamine sensing. Instead, we have focused on the last five years, describing recent progress as well as showing some problems and directions for future development.     

Bioinspired NC Coated BM-ZIF for Electrochemical Monitoring of Adrenaline from Blood and Pharmaceutical Samples

Herein, we have developed highly sensitive and selective non-enzymatic bioinspired polydopamine derived nitrogen rich carbon (NC) coated bimetallic zeolitic imidazolate framework (BM-ZIF) electrochemical sensor via simple hydrothermal approach for monitoring adrenaline (AD) from COVID-19 quarantined person blood and pharmaceutical sample. The designed NC-BM-ZIF electrode shows excellent sensitive and selective performance towards AD monitoring with detection limit (LOD) of 0.01 nM and 0.1931 μA/nM/cm² sensitivity over a wide linear range of 50–1625 nM. To the best of our knowledge, this is the first study of using of NC-BM-ZIF electrode for the electrochemical sensing of AD from quarantined person blood and pharmaceutical sample.     

A mitochondria-targeted fluorescent probe for ratiometric detection of hypochlorite in living cells

A new fl uorescent probe 1 was designed for mitochondrial localization and ratiometric detection of hypochlorite in living cells. It is noteworthy that a high Pearson’s co-localization coeffi cient (Rr) we have obtained was calculated to be 0.97.     

非电活性分子的活体电化学分析进展

发展非电活性分子的活体电化学分析方法,对于解析这些物质在生理过程和病理过程中的作用具有重要研究意义. 本综述从三种分析策略出发,简要介绍了最近活体电化学传感器的研究进展：1）设计和筛选高选择性配体,通过将特异性的化学反应转换成电化学信号,发展了新型的非电活性分子的活体分析;2）利用微型孔道里的整流效应,结合特异性配体,建立了非电活性分子的新型分析平台;3）结合微电极阵列技术及同时分析多种输出信号的新型分析模式,实现活体中的多种非电活性物质的同时分析.     

A Fast HPLC Analysis Of Catecholamines and Indoleamines in Avian Brain Tissue

Abstract

A fast HPLC method for the determination of monoamine levels in avian brain tissue, using a short 3 micron column and electrochemical detection, is presented. This system simultaneously analyzes 18 catecholamines, indoleamines, metabolites, and internal standards, without further sample preparation, in 20 minutes. Contrary to reports involving the mammalian species, incubation of the tissue homogenate with ascorbate oxidase and/or urate oxidase does not significantly alter the analysis under the reported conditions. The assay was used to evaluate differences in the neurochemical content of brain tissue from chickens divergently selected for 42 day exponential growth rate.     

Electrochemical Detection of Superoxide Anion Released by Living Cells by Manganese(III) Tetraphenyl Porphine as Superoxide Dismutase Mimic

Superoxide anion, one of the most active reactive oxygen species, is associated with the development of many diseases. So monitoring superoxide anion in living cells is of great significance for the pathological research of many diseases. In this work, a new non-enzymatic sensor for the detection of superoxide anion(O₂^·-) was developed, which was fabricated by the nanocomposites composed of manganese(III) tetraphenyl porphine(MnTPP) as super-oxide dismutase mimic and electrochemical reduced graphene oxide(ERGO) as electrode support material to modify the glassy carbon electrode(GCE). The electrochemical behavior of the fabricated electrode(MnTPP/ERGO/GCE) was performed by electrochemical impedance spectroscopy(EIS) and cyclic voltammetry(CV), which revealed that MnTPP/ERGO/GCE possessed good catalytic ability to the electrochemical reduction of O₂^·-. The MnTPP/ERGO/GCE showed excellent electroanalysis performance towards O₂^·- using the technique of differential pulse voltammetry(DPV) with a linear relationship in the range of 0.2-110.0 μmol/L, a sensitivity of 445 μA·L·mmol^-1·cm^-2 and a detection limit of 0.039 μmol/L(S/N=3). The real-time monitoring of O₂^·- from MCF-7 breast cancer cells stimulated by zymosan was realized in this work, which indicates that the MnTPP/ERGO/GCE hold potential application for electrochemical quantification of superoxide anions in biological applications.     

An Electrochemical Biosensor with Dual Signal Outputs: Toward Simultaneous Quantification of pH and O2 in the Brain upon Ischemia and in a Tumor during Cancer Starvation Therapy

Herein, we develop a novel method for designing electrochemical biosensors with both current and potential signal outputs for the simultaneous determination of two species in a living system. Oxygen (O₂) and pH, simple and very important species, are employed as model molecules. By designing and synthesizing a new molecule, Hemin‐aminoferrocene (Hemin‐Fc), we create a single electrochemical biosensor for simultaneous detection and ratiometric quantification of O₂ and pH in the brain. The reduction peak current of the hemin group increases with the concentration of O₂ from 1.3 to 200.6 μm . Meanwhile, the peak potential positively shifts with decreasing pH from 8.0 to 5.5, resulting in the simultaneous determination of O₂ and pH. The Fc group can serve as an internal reference for ratiometric biosensing because its current and potential signals remain almost constant with variations of O₂ and pH. The developed biosensor has high temporal and spatial resolutions, as well as remarkable selectivity and accuracy, and is successfully applied in the real‐time quantification of O₂ and pH in the brain upon ischemia, as well as in tumor during cancer therapy.     

An Online Electrochemical System for Continuous Measurement of Glutamate with Signal Amplification by Enzymatic Substrate Cycling

This study demonstrates a new online electrochemical system (OECS) for continuous monitoring of glutamate by efficiently integrating in vivo microdialysis and selective electrochemical detection with an enhanced sensitivity through enzymatic substrate cycling. We find that the involvement of enzymatic substrate cycling in the biosensing scheme remarkably increases the sensitivity of the OECS toward the measurements of glutamate. Moreover, the OECS demonstrated here is stable, reproducible, and selective and could thus be potentially useful for continuous monitoring of glutamate release in central nervous system. This study essentially offers a new approach to the continuous measurements of cerebral glutamate release, which is believed to find interesting applications in understanding the molecular basis underlying brain functions.     

Sensitive analysis of blood for amodiaquine and three metabolites by high-performance liquid chromatography with electrochemical detection

A high-performance liquid chromatographic method using oxidative electrochemical detection has been developed for selective and sensitive quantification of the antimalarial drug amodiaquine and three of its metabolites in the blood of dosed individuals. The method requires only one extraction step and has detection limits of 1 ng/ml for amodiaquine and its metabolites desethylamodiaquine and bisdesethylamodiaquine and 3 ng/ml for 2-hydroxydesethylamodiaquine. Minor modification of the mobile phase preserves the chromatographic separation and allows ultraviolet spectroscopic detection, which, although appreciably less sensitive, permits monitoring of levels of amodiaquine and the three metabolites in blood and urine samples if an electrochemical detector is unavailable. Levels of amodiaquine and the three metabolites were determined for two volunteers undergoing a nine-week chemoprophylactic regimen in connection with travel to a malarious area. Data are included to compare the in vitro antimalarial activities against three strains of Plasmodium falciparum of amodiaquine and the three metabolites considered.     

Simple and rapid detection of Alternaria alternata using an excreted redox-active species

Airborne fungi pose a serious threat to public health. Alternaria alternata (A. alternata) is a fungus that has been associated with the development of asthma. Detection using redox-active species excreted from fungi is an effective method for a simple electrochemical fungal biosensor. The achievable electrochemical signal in most fungi, however, is exceptionally low because of the low amount of excreted redox-active species and their slow excretion rates. Herein, we report that A. alternata excretes an exceptionally large amount of a redox-active species that can be used for sensitive and selective detection of A. alternata. The excretion rate is enhanced in Tris buffer, and the electrochemical-chemical redox cycling involving excreted redox-active species significantly increases the electrochemical signals. Only A. alternata among five common airborne fungi provides large electrochemical signals, which allows selective detection of A. alternata. The calculated detection limit for A. alternata is ~20 spores/mL with an incubation period of 10 min, indicating that the detection method is highly sensitive and rapid. The detection method does not require complicated procedures or harsh pretreatment and is optimal for point-of-care testing of A. alternata.