(383c) Award Submission: Encapsulation of Particle Ensembles in Graphene Nanosacks As a New Route to Multifunctional Materials

Encapsulation of Particle Ensembles in Graphene Nanosacks as a

New Route to Multifunctional Materials

Yantao Chen, Fei Guo, Yang Qiu, Edward Walsh, Robert Hurt, et al.

Brown University

A major goal in the nanosynthesis field is the fabrication of hybrid nanostructures with multiple functions for use in smart materials, biomedical diagnostics, and theranostics. Hybrid nanostructures may be designed for combinations of photonic, magnetic, radiological, mechano-responsive, catalytic, and/or targeted delivery behaviors, and the designs typically require complex multistep chemical synthesis. Recent reports of a continuous, scalable aerosol process for graphene encapsulation of nanoparticles may provide a new route to such hybrids if different types of particles can be simultaneously wrapped.
Here we demonstrate a systematic way to create multifunctional hybrid materials through aerosol-phase graphene encapsulation of ensembles of simple uni-functional nanoparticles. We first develop a general theory of aerosol encapsulation based on pH-dependent colloidal interactions in drying microdroplets. It is shown that a wide range of cargo particles can be encapsulated, including some that are colloidally unstable alone, because of association with the highly-charged, stable graphene oxide sheets. High pH is shown to be a favorable operating regime for the aerosol encapsulation process because it leads to particle/sheet electrostatic repulsion, colloidal stability, and low proton activity that limits dissolution of metal and metal-oxide nanoparticles. The cargo-filled graphene nanosacks are also shown to be open structures that rapidly release soluble salt cargoes when reintroduced into water, but can be partially sealed by filler addition during synthesis to achieve slow release profiles of interest in controlled release or theranostic applications.
Finally we demonstrate an example multifunctional material by fabricating graphene/Au/Fe3O4 and graphene/BaTiO3/Fe3O4 ternary particles as MRI/CT multimodal imaging probes. The graphene/Au/Fe3O4 probe is magnetically responsive and shows excellent MRI and CT contrast in CMC gel suspensions at low
concentrations ranging from 0.05â??2000 μg/ml based on tests using full-scale clinical
scanners. Graphene nanosack encapsulation is shown to be a flexible approach for the fabrication of multimodal bioimaging probes and possible theranostic devices.