  The possibility of prescribing local interactions between nano- and
microscopic components that direct them to assemble in a predictable fashion is
a central goal of nanotechnology research. In this article we advance a new
paradigm in which self-assembly of DNA-functionalized colloidal particles is
programmed using linker oligonucleotides dispersed in solution. We find a phase
diagram that is surprisingly rich compared to phase diagrams typical of other
DNA-functionalized colloidal particles that interact by direct hybridization,
including a re-entrant melting transition upon increasing linker concentration,
and show that multiple linker species can be combined together to prescribe
many interactions simultaneously. A new theory predicts the observed phase
behavior quantitatively without any fitting parameters. Taken together, these
experiments and model lay the groundwork for future research in programmable
self-assembly, enabling the possibility of programming the hundreds of specific
interactions needed to assemble fully-addressable, mesoscopic structures, while
also expanding our fundamental understanding of the unique phase behavior
possible in colloidal suspensions.
