Microwell array integrating nanoelectrodes for coupled opto-electrochemical monitorings of single mitochondria

Nanozyme-Enhanced Electrochemical Biosensors: Mechanisms and Applications

Nanozymes, as innovative materials, have demonstrated remarkable potential in the field of electrochemical biosensors. This article provides an overview of the mechanisms and extensive practical applications of nanozymes in electrochemical biosensors. First, the definition and characteristics of nanozymes are introduced, emphasizing their significant role in constructing efficient sensors. Subsequently, several common categories of nanozyme materials are delved into, including metal-based, carbon-based, metal-organic framework, and layered double hydroxide nanostructures, discussing their applications in electrochemical biosensors. Regarding their mechanisms, two key roles of nanozymes are particularly focused in electrochemical biosensors: selective enhancement and signal amplification, which crucially support the enhancement of sensor performance. In terms of practical applications, the widespread use of nanozyme-based electrochemical biosensors are showcased in various domains. From detecting biomolecules, pollutants, nucleic acids, proteins, to cells, providing robust means for high-sensitivity detection. Furthermore, insights into the future development of nanozyme-based electrochemical biosensors is provided, encompassing improvements and optimizations of nanozyme materials, innovative sensor design and integration, and the expansion of application fields through interdisciplinary collaboration. In conclusion, this article systematically presents the mechanisms and applications of nanozymes in electrochemical biosensors, offering valuable references and prospects for research and development in this field.

Recent advances of nanopore technique in single cell analysis

Single cells and their dynamic behavior are closely related to biological research. Monitoring their dynamic behavior is of great significance for disease prevention. How to achieve rapid and non-destructive monitoring of single cells is a major issue that needs to be solved urgently. As an emerging technology, nanopores have been proven to enable non-destructive and label-free detection of single cells. The structural properties of nanopores enable a high degree of sensitivity and accuracy during analysis. In this article, we summarize and classify the different types of solid-state nanopores that can be used for single-cell detection and illustrate their specific applications depending on the size of the analyte. In addition, their research progress in material transport and microenvironment monitoring is also highlighted. Finally, a brief summary of existing research challenges and future trends in nanopore single-cell analysis is tentatively provided.

Click-Chemistry-Enabled Nanopipettes for the Capture and Dynamic Analysis of a Single Mitochondrion inside One Living Cell

The in-depth study of single cells requires the dynamically molecular information in one particular nanometer-sized organelle in a living cell, which is difficult to achieve using current methods. Due to high efficiency of click chemistry, a new nanoelectrode-based pipette architecture with dibenzocyclooctyne at the tip is designed to realize fast conjugation with azide group-containing triphenylphosphine, which targets mitochondrial membranes. The covalent binding of one mitochondrion at the tip of the nanopipette allows a small region of the membrane to be isolated on the Pt surface inside the nanopipette. Therefore, the release of reactive oxygen species (ROS) from the mitochondrion is monitored, which is not interfered by the species present in the cytosol. The dynamic tracking of ROS release from one mitochondrion reveals the distinctive "ROS-induced ROS release" within the mitochondria. Further study of RSL3-induced ferroptosis using nanopipettes provides direct evidence for supporting the noninvolvement of glutathione peroxidase 4 in the mitochondria during RSL3-induced ROS generation, which has not previously been observed at the single-mitochondrion level. Eventually, this established strategy should overcome the existing challenge of the dynamic measurement of one special organelle in the complicated intracellular environment, which opens a new direction for electroanalysis in subcellular analysis.

Dual-mode biosensor platform based on synergistic effects of dual-functional hybrid nanomaterials

Detection of biomarkers is very vital in the prevention, diagnosis and treatment of diseases. However, due to the poor accuracy and sensitivity of the constructed biosensors, we are now facing great challenges. In addressing these problems, nanohybrid-based dual mode biosensors including optical-optical, optical-electrochemical and electrochemical-electrochemical have been developed to detect various biomarkers. Integrating the merits of nanomaterials with abundant active sites, synergy and excellent physicochemical properties, many bi-functional nanohybrids have been reasonable designed and controllable preparation, which applied to the construction dual mode biosensors. Despite the significant progress, further efforts are still needed to develop dual mode biosensors and ensure their practical application by using portable digital devices. Therefore, the present review summarizes an in-depth evaluation of the bi-functional nanohybrids assisted dual mode biosensing platform of biomarkers. We are hoping this review could inspire further concepts in developing novel dual mode biosensors for possible detection application.

Electroanalysis at a Single Giant Vesicle Generating Enzymatically a Reactive Oxygen Species

In the framework of artificial or synthetic cell development, giant liposomes are common basic structures. Their enclosed membrane allows encapsulating proteins, DNA, reactants, etc., while its phospholipid nature allows some exchanges with the surrounding medium. Biochemical reactions induced inside giant liposomes or vesicles are often monitored or imaged by fluorescence microscopy techniques. Here, we show that electrochemistry performed with ultramicroelectrodes is perfectly suitable to monitor an enzymatic reaction occurring in a single giant unilamellar vesicle. Glucose oxidase (GOx) was microinjected inside individual vesicles containing 1 mM glucose. H₂O₂ was thus generated in the vesicle and progressively diffused across the membrane toward the surrounding environment. An ultramicroelectrode sensitive to H₂O₂ (black platinum-modified carbon surface) was placed next to the membrane and provided a direct detection of the hydrogen peroxide flux generated by the enzyme activity. Electrochemistry offered a highly sensitive (in situ detection), selective (potential applied at the electrode), time-resolved analysis (chronoamperometry) of the GOx activity over an hour duration, without modifying the internal giant unilamellar vesicles (GUV) medium. These results demonstrate that electroanalysis with microsensors is well adapted and complementary to fluorescence microscopy to sense enzymatic activities, for instance, generating reactive oxygen species, at single vesicles further used to develop artificial cells.

Shadow Electrochemiluminescence Microscopy of Single Mitochondria

Mitochondria are the subcellular bioenergetic organelles. The analysis of their morphology and topology is essential to provide useful information on their activity and metabolism. Herein, we report a label-free shadow electrochemiluminescence (ECL) microscopy based on the spatial confinement of the ECL-emitting reactive layer to image single living mitochondria deposited on the electrode surface. The ECL mechanism of the freely-diffusing [Ru(bpy)₃ ]²⁺ dye with the sacrificial tri-n-propylamine coreactant restrains the light-emitting region to a micrometric thickness allowing to visualize individual mitochondria with a remarkable sharp negative optical contrast. The imaging approach named "shadow ECL" (SECL) reflects the negative imprint of the local diffusional hindrance of the ECL reagents by each mitochondrion. The statistical analysis of the colocalization of the shadow ECL spots with the functional mitochondria revealed by classical fluorescent biomarkers, MitoTracker Deep Red and the endogenous intramitochondrial NADH, validates the reported methodology. The versatility and extreme sensitivity of the approach are further demonstrated by visualizing single mitochondria, which remain hardly detectable with the usual biomarkers. Finally, by alleviating problems of photobleaching and phototoxicity associated with conventional microscopy methods, SECL microscopy should find promising applications in the imaging of subcellular structures.

Microwell Array Based Opto-Electrochemical Detections Revealing Co-Adaptation of Rheological Properties and Oxygen Metabolism in Budding Yeast

Microdevices composed of microwell arrays integrating nanoelectrodes (OptoElecWell) are developed to achieve dual high-resolution optical and electrochemical detections on single Saccharomyces cerevisiae yeast cells. Each array consists of 1.6 × 10⁵ microwells measuring 8 µm in diameter and 5 µm height, with a platinum nanoring electrode for in situ electrochemistry, all integrated on a transparent thin wafer for further high-resolution live-cell imaging. After optimizing the filling rate, 32% of cells are effectively trapped within microwells. This allows to analyse S. cerevisiae metabolism associated with basal respiration while simultaneously measuring optically other cellular parameters. In this study, the impact of glucose concentration on respiration and intracellular rheology is focused. It is found that while the oxygen uptake rate decreases with increasing glucose concentration, diffusion of tracer nanoparticles increases. The OptoElecWell-based respiration methodology provides similar results compared to the commercial gold-standard Seahorse XF analyzer, while using 20 times fewer biological samples, paving the way to achieve single cell metabolomics. In addition, it facilitates an optical route to monitor the contents within single cells. The proposed device, in combination with the dual detection analysis, opens up new avenues for measuring cellular metabolism, and relating it to cellular physiological indicators at single cell level.