Broad-Band Fluorescence Enhancement of QDs Captured in the Hotspot of DNA Origami Nanonantennas

The integration of the DNA origami technique with plasmonic nanostructures has led to the development of optical antennas capable of significantly enhancing the excitation and emission rates of proximal fluorophores by offering precise control over their spatial positioning. However, despite these advancements, conventional fluorophores still face challenges due to their susceptibility to photobleaching. This limitation highlights the need for more stable alternatives. Quantum dots (QDs), also known as "artificial atoms", emerge as a promising candidate, offering an array of distinctive size-dependent spectral qualities, encompassing broad absorption ranges, tight emission bands, adjustable fluorescence, and better photostability. The pivotal challenge is ensuring the QDs' precise placement within plasmonic hotspots to unlock maximal signal enhancement. To tackle this, we used DNA origami-based NanoAntennas with Cleared HOtSpots (NACHOS) to successfully incorporate divalent DNA-tagged QDs of different sizes within the hotspot of two 100 nm silver nanoparticles. Known for their broad-band optical properties, silver nanoparticles enabled fluorescence enhancement for three spectrally different QDs, with more than 100-fold enhancement for the smallest QDs, alongside a reduction in their fluorescence lifetime. This integration deepens our understanding of nanoscale interactions and charts a path for the development of advanced plasmonic devices, establishing a robust framework for tailored bioassays.