Redox-filled Carbon-Fiber Microelectrodes for Single-Cell Exocytosis

Real-time calcium uptake monitoring of a single renal cancer cell based on an all-solid-state potentiometric microsensor

Introduction: In addition to many cellular processes, Ca2+ is also involved in tumor initiation, progression, angiogenesis, and metastasis. The development of new tools for single-cell Ca2+ measurement could open a new avenue for cancer therapy.

Methods: The all-solid-state calcium ion-selective microelectrode (Ca2+-ISμE) based on carbon fiber modified with PEDOT (PSS) as solid-contact was developed in this work, and the characteristics of the Ca2+-ISμE have also been investigated.

Results: The Ca2+-ISμE exhibits a stable Nernstian response in CaCl2 solutions in the active range of 1.0 × 10−8 - 3.1 × 10−3 M with a low detection limit of 8.9 × 10−9 M. The Ca2+-ISμE can be connected to a patch clamp to fabricate a single-cell analysis platform for in vivo calcium monitoring of a single renal carcinoma cell. The calcium signal decreased significantly (8.6 ± 3.2 mV, n = 3) with severe fluctuations of 5.9 ± 1.8 mV when the concentration of K+ in the tumor microenvironment is up to 20 mM.

Discussion: The results indicate a severe cell response of a single renal carcinoma cell under high K+ stimuli. The detection system could also be used for single-cell analysis of other ions by changing different ion-selective membranes with high temporal resolution.

Microelectrode-Based Electrochemical Sensing Technology for in Vivo Detection of Dopamine: Recent Developments and Future Prospects

Dopamine (DA) is an essential type of neurotransmitter in the central nervous system. DA neurons usually exist as nuclei which are mainly found in the ventral tegmental area (VTN) and substantia nigra pars compacta (SNc). Parkinson's disease, epilepsy, schizophrenia and other diseases are all related to the abnormal metabolism of DA. Compared with traditional DA detection methods such as spectrophotometry and electrophoresis, electrochemical sensing technology has high detection efficiency, high sensitivity, fast and convenient real-time detection, which is recognized as the most effective method for measuring neurotransmitters in vivo. The working electrode of an electrochemical sensor can be generally divided into the conventional electrode and the microelectrode according to its size. The microelectrode shows excellent properties such as high sensitivity, high temporal resolution, and high spatial resolution while detecting DA, which makes it possible to detect neurotransmitters in vivo. In order to further investigate the role of DA in regulating action, emotion, and cognition, and to further clarify the relationship between DA abnormalities or lack and neurological diseases such as Parkinson, more and more researchers apply microelectrode-based electrochemistry sensing technology to detect DA in vivo. This article reviews recent applications of microelectrodes and the latest researches in DA detection in vivo, focusing on the following three types of microelectrodes: (1) non-nanomaterial-modified carbon fiber microelectrodes (CFE); (2) nanomaterial-modified microelectrodes; (3) microelectrode arrays (MEA).

A microfluidic platform for continuous monitoring of dopamine homeostasis in dopaminergic cells

Homeostasis of dopamine, a classical neurotransmitter, is a key indicator of neuronal health. Dysfunction in the regulation of dopamine is implicated in a long list of neurological disorders, including addiction, depression, and neurodegeneration. The existing methods used to evaluate dopamine homeostasis in vitro are inconvenient and do not allow for continuous non-destructive measurement. In response to this challenge, we introduce an integrated microfluidic system that combines dopaminergic cell culture and differentiation with electroanalytical measurements of extracellular dopamine in real-time at any point during an assay. We used the system to examine the behavior of differentiated SH-SY5Y cells upon exposure to four dopamine transporter ant/agonists (cocaine, ketamine, epigallocatechin gallate, and amphetamine) and study their pharmacokinetics. The IC₅₀ values of cocaine, ketamine, and epigallocatechin gallate were determined to be (average ± standard deviation) 3.7 ± 1.1 µM, 51.4 ± 17.9 µM, and 2.6 ± 0.8 µM, respectively. Furthermore, we used the new system to study amphetamine-mediated dopamine release to probe the related phenomena of dopamine transporter-mediated reverse-transport and dopamine release from vesicles. We propose that this platform, which is the first platform to simultaneously evaluate uptake and release, could be useful to screen for drugs and other agents that target dopaminergic neurons and the function of the dopamine transporter. More broadly, this platform should be adaptable for any application that could benefit from high-temporal resolution electroanalysis combined with multi-day cell culture using small numbers of cells.

Static and Dynamic Measurement of Dopamine Adsorption in Carbon Fiber Microelectrodes Using Electrochemical Impedance Spectroscopy

In this study, electrochemical impedance spectroscopy was used for the first time to study the adsorption of dopamine in carbon fiber microelectrodes. In order to show a proof-of-concept, static and dynamic measurements were taken at potentials ranging from -0.4 to 0.8 V versus Ag|AgCl to demonstrate the versatility of this technique to study dopamine without the need of its oxidation. We used electrochemical impedance spectroscopy and single frequency electrochemical impedance to measure different concentrations of dopamine as low as 1 nM. Moreover, the capacitance of the microelectrodes surface was found to decrease due to dopamine adsorption, which is dependent on its concentration. The effect of dissolved oxygen and electrochemical oxidation of the surface in the detection of dopamine was also studied. Nonoxidized and oxidized carbon fiber microelectrodes were prepared and characterized by optical microscopy, scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. Optimum working parameters of the electrodes, such as frequency and voltage, were obtained for better measurement. Electrochemical impedance of dopamine was determined at different concentration, voltages, and frequencies. Finally, dynamic experiments were conducted using a flow cell and single frequency impedance in order to study continuous and real-time measurements of dopamine.

Ferricyanide-backfilled cylindrical carbon fiber microelectrodes for in vivo analysis with high stability and low polarized potential

A ferricyanide-backfilled cylindrical carbon fiber microelectrode of high stability and low polarized potential was fabricated and used for in vivo analysis.