Multivalent Cation-Induced Actuation of DNA-Mediated Colloidal Superlattices

Nanoparticles functionalized with DNA can assemble into
ordered
superlattices with defined crystal habits through programmable DNA
“bonds”. Here, we examine the interactions of multivalent
cations with these DNA bonds as a chemical approach for actuating
colloidal superlattices. Multivalent cations alter DNA structure on
the molecular scale, enabling the DNA “bond length”
to be reversibly altered between 17 and 3 nm, ultimately leading to
changes in the overall dimensions of the micrometer-sized superlattice.
The identity, charge, and concentration of the cations each control
the extent of actuation, with Ni2+ capable of inducing
a remarkable >65% reversible change in crystal volume. In addition,
these cations can increase “bond strength”, as evidenced
by superlattice thermal stability enhancements of >60 °C relative
to systems without multivalent cations. Molecular dynamics simulations
provide insight into the conformational changes in DNA structure as
the bond length approaches 3 nm and show that cations that screen
the negative charge on the DNA backbone more effectively cause greater
crystal contraction. Taken together, the use of multivalent cations
represents a powerful strategy to alter superlattice structure and
stability, which can impact diverse applications through dynamic control
of material properties, including the optical, magnetic, and mechanical
properties.