The co-assembly of charged nanoparticles with oppositely charged
molecular ions has emerged as a promising technique in the fabrication
of nanoparticle superstructures. However, the underlying mechanism
behind these molecular ions in mediating the repulsion between these
charged nanoparticles remains elusive. Herein, coarse-grained molecular
dynamics simulations are used to elucidate the effects of valency, shape
and size of molecular anions on their co-assembly with gold
nanoparticles coated with positively charged ligands. The findings
suggest that the valency, shape and size of molecular anions
significantly influence the repulsion and aggregating dynamics among
these positively charged nanoparticles. Moreover, the free energy
calculations reveal that ring-shaped molecular anions with higher
valencies and larger sizes are more effective at reducing the repulsion
between these gold nanoparticles and thus enhance the stability of the
aggregate. This study contributes to a better understanding of the
critical roles of valence, shape and size of ions in mediating the
electrostatic co-assembly of nanoparticles with oppositely charged ions
and it also guides the future design of DNA templates and DNA origami in
co-assembly with oppositely charged nanoparticles.