† Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095
‡ California NanoSystems Institute, University of California, Los Angeles, California 90095
§ Department of Craniofacial Biology, MUSC College of Dental Medicine, Charleston, South Carolina 29425
FEI Company, 5350 NE Dawson Creek Drive, Hillsboro, Oregon 97124
School of Dentistry and Dental Research Institute, University of California, Los Angeles, California 90095
¶ International Center for Materials Nanoarchitectonics Satellite (MANA), National Institute for Materials Science (NIMS), Tsukuba 305-0047, JapanAll living systems contain naturally occurring nanoparticles with unique structural, biochemical, and mechanical characteristics. Specifically, human saliva exosomes secreted by normal cells into saliva via exocytosis are novel biomarkers showing tumor-antigen enrichment during oral cancer. Here we show the substructure of single human saliva exosomes, using a new ultrasensitive low force atomic force microscopy (AFM) exhibiting substructural organization unresolvable in electron microscopy. We correlate the data with field emission scanning electron microscopy (FESEM) and AFM images to interpret the nanoscale structures of exosomes under varying forces. Single exosomes reveal reversible mechanical deformation displaying distinct elastic, 70−100 nm trilobed membrane with substructures carrying specific transmembrane receptors. Further, we imaged and investigated, using force spectroscopy with antiCD63 IgG functionalized AFM tips, highly specific and sensitive detection of antigenCD63, potentially useful cancer markers on individual exosomes. The quantitative nanoscale morphological, biomechanical, and surface biomolecular properties of single saliva exosomes are critical for the applications of exosomes for cancer diagnosis and as a model for developing new cell delivery systems.