Shadow Electrochemiluminescence Microscopy of Single Mitochondria

Call to action to properly utilize electron microscopy to measure organelles to monitor disease

This review provides an overview of the current methods for quantifying mitochondrial ultrastructure, including cristae morphology, mitochondrial contact sites, and recycling machinery and a guide to utilizing electron microscopy to effectively measure these organelles. Quantitative analysis of mitochondrial ultrastructure is essential for understanding mitochondrial biology and developing therapeutic strategies for mitochondrial-related diseases. Techniques such as transmission electron microscopy (TEM) and serial block face-scanning electron microscopy, as well as how they can be combined with other techniques including confocal microscopy, super-resolution microscopy, and correlative light and electron microscopy are discussed. Beyond their limitations and challenges, we also offer specific magnifications that may be best suited for TEM analysis of mitochondrial, endoplasmic reticulum, and recycling machinery. Finally, perspectives on future quantification methods are offered.

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.

Direct Visualization of Nanoconfinement Effect on Nanoreactor via Electrochemiluminescence Microscopy

Nanoconfinement in mesoporous nanoarchitectures could dramatically change molecular transport and reaction kinetics during electrochemical process. A molecular-level understanding of nanoconfinement and mass transport is critical for the applications, but a proper route to study it is lacking. Herein, we develop a single nanoreactor electrochemiluminescence (SNECL) microscopy based on Ru(bpy)₃ ²⁺ -loaded mesoporous silica nanoparticle to directly visualize in situ nanoconfinement-enhanced electrochemical reactions at the single molecule level. Meanwhile, mass transport capability of single nanoreactor, reflected as long decay time and recovery ability, is monitored and simulated with a high spatial resolution. The nanoconfinement effects in our system also enable imaging single proteins on cellular membrane. Our SNECL approach may pave the way to decipher the nanoconfinement effects during electrochemical process, and build bridges between mesoporous nanoarchitectures and potential electrochemical applications.

Operando Imaging of Chemical Activity on Gold Plates with Single-Molecule Electrochemiluminescence Microscopy

Classical electrochemical characterization tools cannot avoid averaging between the active reaction sites and their support, thus obscuring their intrinsic roles. Single-molecule electrochemical techniques are thus in high demand. Here, we demonstrate super-resolution imaging of Ru(bpy)₃ ²⁺ based reactions on Au plates using single-molecule electrochemiluminescence microscopy. By converting electrochemical signals into optical signals, we manage to achieve the ultimate sensitivity of single-entity chemistry, that is directly resolving the single photons from individual electrochemical reactions. High spatial resolution, up to 37 nm, further enables mapping Au chemical activity and the reaction kinetics. The spatiotemporally resolved dynamic structure-activity relationship on Au plates shows that the restructuring of catalysts plays an important role in determining the reactivity. Our approach may lead to gaining new insights towards evaluating and designing electrocatalytic systems.