Organic Molecular Probe Enabled Ionic Current Rectification toward Subcellular Detection of Glutathione with High Selectivity, Sensitivity, and Recyclability

Glass nano/micron pipette-based ion current rectification sensing technology for single cell/in vivo analysis

Glass nano/micron pipettes, owing to their easy preparation, unique confined space at the tip, and modifiable inner surface of the tip, can capture the ion current signal caused by a single entity, making them widely used in the construction of highly sensitive and highly selective electrochemical sensors for single entity analysis. Compared with other solid-state nanopores, their conical nano-tip causes less damage to cells when inserted into them, thereby becoming a powerful tool for the in situ analysis of important substances in cells. However, glass nanopipettes have some shortcomings, such as poor mechanical properties, difficulty in precise preparation (aperture less than 50 nm), and easy blockage during complex real sample detection, limiting their practicability. Therefore, in recent years, researchers have conducted a series of studies on glass micropipettes. Ionic current rectification technology is a novel electrochemical analysis technique. Compared with traditional electrochemical analysis methods, it does not generate redox products during the detection process; therefore, it can not only be used for the determination of non-electrochemically active substances, but also causes less damage to the cell/living body in situ analysis, becoming a powerful analysis technology for the in situ analysis of cells/in vivo in recent years. In this review, we summarize the preparation and functionalization of glass nano/micron pipettes and introduce the sensing mechanisms of two electrochemical sensing platforms constructed using glass nano/micron pipette-based ion current rectification sensing technology as well as their applications in single cell/in vivo analysis, existing problems, and future prospects.

Nanosensors Monitor Intracellular GSH Depletion: GSH Triggers Cu(II) for Tumor Imaging and Inhibition

Glutathione (GSH) is the primary antioxidant in cells, and GSH consumption will break the redox balance in cells. Based on this, a method that uses high concentrations of GSH in the tumor microenvironment to trigger the redox reaction of Cu(II) to generate copper nanoprobes with fluorescence and tumor growth inhibition properties is proposed. The nanoprobe mainly exists in the form of Cu(I) and catalyzes the decomposition of hydrogen peroxide into hydroxyl radicals. At the same time, a simple and controllable carbon micro-nano electrode is used to construct a single-cell sensing platform, which enable the detection of glutathione content in single living cells after Cu(II) treatment, providing an excellent example for detecting single-cell biomolecules.

Quantification of MicroRNA in a Single Living Cell via Ionic Current Rectification-Based Nanopore for Triple Negative Breast Cancer Diagnosis

Accurate analysis of microRNAs (miRNAs) at the single-cell level is extremely important for deeply understanding their multiple and intricate biological functions. Despite some advancements in analyzing single-cell miRNAs, challenges such as intracellular interferences and insufficient detection limits still remain. In this work, an ultrasensitive nanopore sensor for quantitative single-cell miRNA-155 detection is constructed based on ionic current rectification (ICR) coupled with enzyme-free catalytic hairpin assembly (CHA). Benefiting from the enzyme-free CHA amplification strategy, the detection limit of the nanopore sensor for miRNA-155 reaches 10 fM and the nanopore sensor is more adaptable to complex intracellular environments. With the nanopore sensor, the concentration of miRNA-155 in living single cells is quantified to realize the early diagnosis of triple-negative breast cancer (TNBC). Furthermore, the nanopore sensor can be applied in screening anticancer drugs by tracking the expression level of miRNA-155. This work provides an adaptive and universal method for quantitatively analyzing intracellular miRNAs, which will greatly improve our understanding of cell heterogeneity and provide a more reliable scientific basis for exploring major diseases at the single-cell level.

In situ monitoring of cytoplasmic dopamine levels by noble metals decorated carbon fiber tips

Dopamine (DA), a catecholamine neurotransmitter, is crucial in brain signal transmission. Monitoring cytoplasmic DA levels can reflect changes in metabolic factors and provide valuable information for researching the mechanisms involved in neurodegenerative diseases. However, the in-situ detection of intracellular DA is constrained by its low contents in small-sized single cells. In this work, we report that noble metal (Au, Pt)-modified carbon fiber micro-nanoelectrodes are capable of real-time detection of DA in single cells with excellent sensitivity, selectivity, and anti-contamination capabilities. Notably, noble metals can be modified on the electrode surface through electrochemical deposition to enhance the conductivity of the electrode and the oxidation current of DA by 50 %. The nanosensors can work stably and continuously in rat adrenal pheochromocytoma cells (PC12) to monitor changes in DA levels upon K+ stimulation. The functionalized carbon fibers based nanosensors will provide excellent prospects for DA analysis in the brains of living animals.

Application and outlook of electrochemical technology in single-cell analysis

Cellular heterogeneity, especially in some important diseased cells like tumor cells, acts as an invisible driver for disease development like cancer progression in the tumor ecosystem, contributing to differences in the macroscopic and microscopic detection of disease lesions like tumors. Traditional analysis techniques choose group information masked by the mean as the analysis sample, making it difficult to achieve precise diagnosis and target treatment, on which could be shed light via the single-cell level determination/bioanalysis. Hence, in this article we have reviewed the special characteristic differences among various kinds of typical single-cell bioanalysis strategies and electrochemical techniques, and then focused on the recent advance and special bio-applications of electrochemiluminescence and micro-nano electrochemical sensing mediated in single-cell bioimaging & bioanalysis. Especially, we have summarized the relevant research exploration of the possibility to establish the in-situ single-cell electrochemical methods to detect cell heterogeneity through determination of specific biomolecules and bioimaging of some important biological processes. Eventually, this review has explored some important advances of electrochemical single-cell detection techniques for the real-time cellular bioimaging and diagnostics of some disease lesions like tumors. It raises the possibility to provide the specific in-situ platform to exploit the versatile, sensitive, and high-resolution electrochemical single-cell analysis for the promising biomedical applications like rapid tracing of some disease lesions or in vivo bioimaging for precise cancer theranostics.

A Fast and Reversible Responsive Bionic Transmembrane Nanochannel for Dynamic Single-Cell Quantification of Glutathione

Biological channels can rapidly and continuously modulate ion transport behaviors in response to external stimuli, which play essential roles in manipulating physiological and pathological processes in cells. Here, to mimic the biological channels, a bionic nanochannel is developed by synergizing a cationic silicon-substituted rhodamine (SiRh) with a glass nanopipette for transmembrane single-cell quantification. Taking the fast and reversible nucleophilic addition reaction between glutathione (GSH) and SiRh, the bionic nanochannel shows a fast and reversible response to GSH, with its inner-surface charges changing between positive and negative charges, leading to a distinct and reversible switch in ionic current rectification (ICR). With the bionic nanochannel, spatiotemporal-resolved operation is performed to quantify endogenous GSH in a single cell, allowing for monitoring of intracellular GSH fluctuation in tumor cells upon photodynamic therapy and ferroptosis. Our results demonstrate that it is a feasible tool for in situ quantification of the endogenous GSH in single cells, which may be adapted to addressing other endogenous biomolecules in single cells by usage of other stimuli-responsive probes.

Real-Time Monitoring of Exosomes Secretion from Single Cell Using Dual-Nanopore Biosensors

Exosomes secreted from cells carry rich information from their parent cells, representing a promising biomarker for investigation of diseases. We develop a dual-nanopore biosensor using DNA aptamers to specifically recognize CD63 protein on the exosome's surface, which enables label-free exosome detection based on ionic current change. The sensor allows for sensitive detection of exosomes with a detection limit of 3.4 × 10⁶ particles/mL. The dual-nanopore biosensor was able to form an intrapipette electric circuit for ionic current measurement due to its unique structure, which is crucial to achieve detection of exosome secretion from a single cell. We utilized a microwell array chip to entrap a single cell into a confined microwell with small volume, enabling the accumulation of exosomes with high concentration. The dual-nanopore biosensor was positioned into the microwell with a single cell, and monitoring of exosome secretion from a single cell in different cell lines and under different stimulations has been achieved. Our design may provide a useful platform for developing nanopore biosensors for detecting cell secretions from a single living cell.