title: Mechanically Tunable Hollow Silica Ultrathin Nanoshells for Ultrasound Contrast Agents.
abstract: Perfluoropentane (PFP) gas filled biodegradable iron-doped silica nanoshells have been demonstrated as long-lived ultrasound contrast agents. Nanoshells are synthesized by a sol-gel process with tetramethyl orthosilicate (TMOS) and iron ethoxide. Substituting a fraction of the TMOS with R-substituted trialkoxysilanes produces ultrathin nanoshells with varying shell thicknesses and morphologies composed of fused nanoflakes. The ultrathin nanoshells had continuous ultrasound Doppler imaging lifetimes exceeding 3 hours, were twice as bright using contrast specific imaging, and had decreased pressure thresholds compared to control nanoshells synthesized with just TMOS. Transmission electron microscopy (TEM) showed that the R-group substituted trialkoxysilanes could reduce the mechanically critical nanoshell layer to 1.4 nm. These ultrathin nanoshells have the mechanical behavior of weakly linked nanoflakes but the chemical stability of silica. The synthesis can be adapted for general fabrication of three-dimensional nanostructures composed of nanoflakes, which have thicknesses from 1.4-3.8 nm and diameters from 2-23 nm.
authors.affiliation: Materials Sciences and Engineering Program, University of California, San Diego.
authors.forename: A
authors.initials: A
authors.lastname: Liberman
authors.affiliation: Department of Nanoengineering, University of California, San Diego.
authors.forename: J
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, TX 75080.
authors.forename: N
authors.initials: N
authors.lastname: Lu
authors.affiliation: Department of Nanoengineering, University of California, San Diego.
authors.forename: R D
authors.initials: RD
authors.lastname: Viveros
authors.affiliation: Department of Chemistry and Biochemistry, University of California, San Diego.
authors.forename: C A
authors.initials: CA
authors.lastname: Allen
authors.affiliation: Department of Radiology, University of California, San Diego.
authors.forename: R F
authors.initials: RF
authors.lastname: Mattrey
authors.affiliation: Moores Cancer Center, University of California, San Diego.
authors.forename: S L
authors.initials: SL
authors.lastname: Blair
authors.affiliation: Department of Chemistry and Biochemistry, University of California, San Diego.
authors.forename: W C
authors.initials: WC
authors.lastname: Trogler
authors.affiliation: Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, TX 75080.
authors.forename: M J
authors.initials: MJ
authors.lastname: Kim
authors.affiliation: Department of Chemistry and Biochemistry, University of California, San Diego.
authors.forename: A C
authors.initials: AC
authors.lastname: Kummel
keywords: Biomedical Imaging; Core/Shell Nanoparticles; Nanoflakes; Silica; Sol-gel