  Top-down fabricated nanoantenna architectures of both metallic and dielectric
materials demonstrated powerful functionalities for Raman and fluorescence
enhancement with relevance to single molecule sensing, while inducing
directionality of chromophore emission with implications for single photon
sources. Herein, we synthesize the smallest bowtie nanoantenna by selective
tip-to-tip fusion of two tetrahedral colloidal quantum dots (CQDs) forming a
dimer. While the tetrahedral monomers emit non-polarized light, the bowtie
architecture manifests nanoantenna functionality of enhanced emission
polarization along the bowtie axis as predicted theoretically and revealed by
single particle spectroscopy. Theory also predicts the formation of an
electric-field hotspot at the bowtie epicenter. This is utilized for selective
light induced photocatalytic metal growth at that location, unlike growth on
the free tips in dark conditions thus demonstrating the bowtie dimer
functionality as a photochemical reaction center. Our findings pave a path for
additional bottom-up bowtie architectures applicable in optics, sensing and
photocatalysis.
