Tiopronin-Protected Gold Nanoparticles as a Potential Marker for Cryo-EM and Tomography

Gold nanoparticles (AuNPs) and their conjugation to biological samples have numerous potential applications. When combined with cryo-electron microscopy and tomography analysis, AuNPs may provide a versatile and powerful tool to identify and precisely localize proteins even when attached to cellular components. Here, we describe a general and facile approach for the synthesis of homogeneous and stable AuNPs, which can readily be conjugated to a molecule of interest and imaged by cryo-electron tomography (cryo-ET). We demonstrate the synthesis of 2.2 ± 0.45-nm tiopronin-protected AuNPs, followed by their conjugation with recombinant proteins and peptides. Visualization of the ∼2.2-nm gold-tagged peptides by cryo-ET reveals the potential use of this strategy to label and localize accessible proteins in a cellular environment with nanometric resolution. Dahan et al. describe a simple approach towards the synthesis of stable 2.2 ± 0.45-nm tiopronin-protected gold nanoparticles, which can be readily conjugated to a molecule of interest, such as peptides and proteins. Functionalized nanoparticles were used to label integrin receptors in intact platelets and detected using cryo-ET.