In Situ Generated Silver Nanodot Förster Resonance Energy Transfer Pair Reveals Nanocage Sizes

Characterizing nanocages in macromolecules is one of the keys to understanding various biological activities and further utilizing nanocages for novel materials synthesis. However, fast and straightforward detection of the nanocage size remains challenging. Here, we present a new approach to detect the diameter of a nanocage by Förster resonance energy transfer (FRET) of luminescent silver nanodot pairs with reverse micelles as a model. Silver nanodot FRET pairs can be generated in situ from a single silver nanodot species with critical energy transfer distances, R₀, of 4.8-6.5 nm. We have applied this approach to clarify the size variation of the water nanocage in nonionic surfactant Triton X-100-based reverse micelles. FRET efficiency decreases as more water is added, indicating that the size of the reverse micelles continuously expands with water content. The silver element in the nanocage also enhances the visualization of the nanocage under cryo-TEM imaging. The diameter of the water nanocage measured with the above approach is consistent with that obtained by cryo-TEM, demonstrating that the FRET measurement of silver nanodots can be a fast and accurate tool to detect nanocage dimensions. The above demonstration allows us to apply our strategy to other protein-based nanocages.