An Optimized Positive Staining Protocol Method for Clear Visualization of Extracellular Vesicles by TEM Using Uranyless and Lead Citrate

Transmission electron microscopy (TEM) is widely used for visualizing extracellular vesicles (EVs) due to its nanometer-scale resolution. However, existing sample preparation protocols often lack sufficient methodological detail, requiring researchers to rely on trial-and-error approaches to achieve high-quality images. Here, we report an optimized positive-staining method that utilizes the sequential application of Uranyless and lead citrate with an intermediate buffered wash. This approach yields high image contrast, preserves EV morphology, and significantly reduces background artifacts. Staining specificity and elemental localization were confirmed using Energy-Dispersive X-ray Spectroscopy (EDS). The protocol is reproducible and robust, offering a reliable framework for EV structural analysis and potentially serving as a reference standard for TEM-based EV imaging.