Electroanalysis of Brain and Cells

In vivo analysis of chemical signals in practical brain environment and cells is an essential way to investigate brain function and brain activity mapping 1. The major obstacle to understanding the roles that biomolecules play in the brain and cells is a lack of reliable and efficient methods for in vivo analysis 2. In parallel with the development of brain and cell imaging, brain and cells electroanalysis has emerged out of the toolbox due to its nature of high spatiotemporal resolution and ease of operation. Up to date, various electroanalytical methods through smartly combined with functionalization of electrode interface and the design of probe have been applied to monitor the dynamics of chemicals in biological systems 3. The complex living environment with lots of interferences, and the trace amount of many chemical species in brain and cells are the primary challenges to accurate measurement in brain and cells. In order to solve these problems, a variety of specific recognition probes were designed and synthesized, and proposed the synergistic strategy of molecular recognition and micro/nano electrode interface design to greatly improve the selectivity of in vivo determination 4. In this research topic, Zhang et al. reviewed the recent progress for detection of H2S in brain and cell and briefly expound the principle of methods with the comparison of the different methods between analytical performance and temporal resolution. Tang et al. developed immunosensor for detection of alphafetorprotein in hepatocellular carcinoma based on the readout of electric potential triggered by antigen-antibody reaction. Qi and Lu et al. constructed the aptasensors based on specific aptamer recognitions to realize the selective and sensitive detection of serotonin. Moreover, Zhang et al. explored an electrochemical platform to electrochemically detect tyrosinase in cells based on functionalized alumina nanochannels via chemically specific reaction between phenolic hydroxyl groups of tyramine and tyrosinase. Monitoring neuronal signaling with chemical expression involved in long-term physiological and pathological changes in vivo holds the key to dissecting the complex molecular mechanisms of pathogenesis. Fouling is a key issue to limit the practical application of electrochemical sensors in both in vitro and in vivo analysis 5. Numerous methods and materials have been developed to minimize the fouling effect in past decades. Recently, in combination with graphene oxide microbands, a new anti-biofouling microfiber array was created by Tian group to quantify extracellular Ca2+ concentrations with reversible response together with neuro activity across multi-regions in the mammalian brain for 60 days 6. In this Research Topic, Su et al. reviewed the surface antifouling strategies including self-assembled monolayer, antifouling polymers, porous coating, in-situ electrochemical and photocatalytic cleaning and gave a brief summary of antifouling mechanisms, advantages and challenges of each strategy. Cellular heterogeneity presents a major challenge in understanding the relationship between cells of particular genotype and response in disease. Elucidating cellular diversity and heterogeneity is helpful to unravel the pathways associated with disease states. Thus, in order to elucidate the cell-to-cell differences during the biochemical processes, single-cell analysis is necessary and significant. To date, electrochemical methods have been demonstrated to be a useful technique for single-cell analysis 7. Compared with other biological analyses, single-cell analysis requires higher sensitivity and signal-to-noise ratio, which can be achieved by regulating the sensing interface. The emergence of nanomaterials provides the possibility to build a more efficient sensing platform. In this Research Topic, two mini-reviews were well organized by Wang, and Liu et al., in which recent advances in development of nanostructure interface for label-free single-cell analysis, and electrochemiluminescence single-cell analysis were introduced and discussed. Li et al. investigated whether and how cisplatin regulates the release of neurotransmitter during exocytosis in single chromaffin cells using single cell amperometry. They found that cisplatin reduces the amount of transmitter released during exocytosis by reducing the duration of the exocytotic events and the stability of the initial fusion pore formed during exocytosis. Photoelectrochemical (PEC) detection is a novel emerging and fast developing technique with incidence light as exciting resource and electrical current as readout signal, which can be performed without external bias potential, avoiding extra electrical stimulation of living cells, thus is expected to be a promising strategy to implement reliable in vivo detection in living body 8. The photosensitive material, which converts the excitation light into an output electrical signal, is the key component of a PEC sensor. Though plenty of efforts have been devoted to investigating the photosensitive materials, most current PEC sensors were excited by ultraviolet-visible light with the intrinsic limitation of short penetration, which hampers their future applications in bioanalysis. Near-infrared (NIR) light-driven photoelectrochemical sensing is a highly promising, especially for in situ bioanalysis due to the deep penetration capability and minimal invasiveness of NIR light,. Here, a minireview by Zhou et al. focused on NIR light-responsive materials including upper- conversion nanoparticles, quantum dots, TiO2 photonic crystals, and organic dyes. Additionally, they also summarized the application of NIR-PEC sensing for metal ions, biomacromolecules, and cancer cells and in vivo detection in animals. Inspired by recent remarkable advancements in engineering the micro/nano electrode interface, electrochemical analysis in single cell, and photoelectrochemical biosensor, we may foresee that electroanalysis is a promising and powerful tool for deeply elucidating the physiological and pathological processes involved in brain events and cells. The articles on this research topic show how the electrochemical application in brain and cells expands by combining electrochemical/photoelectrochemical measurements with rational designing of specific elements and smart tailoring of nanostructure. These investigations will be useful and favorable to further developing and establishing the highly efficient approaches for electrochemical measurement of chemical information in biological systems, and deeply understanding the biological events involved in brain and cells. Limin Zhang composed and wrote the editorial, Yang Tian, and Zhonghai Zhang reviewed it. All authors approved the final version of the manuscript. We are grateful to all the authors and reviewers for their valuable input to this research topic and editorial office of the journal for giving us the opportunity to guest edit this collection and for their professional assistance. Finally, we hope readers will enjoy this article collection as much as we have.