Nanoprojectile Secondary Ion Mass Spectrometry for Analysis of Extracellular Vesicles
Dmitriy S. Verkhoturov, Bruno P. Crulhas, Michael J. Eller, Yong Duk Han, Stanislav V. Verkhoturov, Yordanos Bisrat, Alexander Revzin, E. A. Schweikert
Abstract
We describe a technique based on secondary ion mass spectrometry with nanoprojectiles (NP-SIMS) for determining the protein content of extracellular vesicles, EVs, via tagged antibodies. The technique uses individual gold nanoprojectiles (e.g., Au4004+ and Au28008+), separated in time and space, to bombard a surface. For each projectile impact (10–20 nm in diameter), the co-emitted molecules are mass analyzed and recorded as an individual mass spectrum. Examining these individual mass spectra for co-localized species allows for nanoscale mass spectrometry to be performed. The high lateral resolution of this technique is well suited for analyzing nano-objects. SIMS is generally limited to analyzing small molecules (below ∼1500 Da); therefore, we evaluated three molecules (eosin, erythrosine, and BHHTEGST) as prospective mass spectrometry tags. We tested these on a model surface comprising a mixture of all three tags conjugated to antibodies and found that NP-SIMS could detect all three tags from a single projectile impact. Applying the method, we tagged two surface proteins common in urinary EVs, CD63 and CD81, with anti-CD63–erythrosine and anti-CD81–BHHTEGST. We found that NP-SIMS could determine the relative abundance of the two proteins and required only a few hundred or thousand EVs in the analysis region to detect the presence of the tagged antibodies.