Self-assembly
of colloidal nanoparticles has generated tremendous
interest due to its widespread applications in structural colorations,
sensors, and optoelectronics. Despite numerous strategies being developed
to fabricate sophisticated structures, the heterogeneous self-assembly
of a single type of nanoparticle in one step remains challenging.
Here, facilitated by spatial confinement induced by a skin layer in
a drying droplet, we achieve the heterogeneous self-assembly of a
single type of nanoparticle by quickly evaporating a colloid-poly
(ethylene glycol) (PEG) droplet. During the drying process, a skin
layer forms at the droplet surface. The resultant spatial confinement
assembles nanoparticles into face-centered-cubic (FCC) lattices with
(111) and (100) plane orientations, generating binary bandgaps and
two structural colors. The self-assembly of nanoparticles can be regulated
by varying the PEG concentration so that FCC lattices with homo- or
heterogeneous orientation planes can be prepared on demand. Besides,
the approach is applicable for diverse droplet shapes, various substrates,
and different nanoparticles. The one-pot general strategy breaks the
requirements for multiple types of building blocks and predesigned
substrates, extending the fundamental understanding underlying colloidal
self-assembly.