(447i) Flame-Spray-Synthesis of Ultrabright, Nanoscale Near-Infrared Fluorescent 2D Copper Silicates for In Vivo Bioimaging

Two-dimensional (2D) copper silicates of the family XCuSi4O10 with X=Ca,Ba,Sr are well known for their stabile and bright fluorescence emission in the near-infrared (NIR) spectrum around 950 nm. Recent advances in dispersing and exfoliating these materials into nanosheets (NS) render them useful as novel nanoscale imaging and labeling agents, as well as for chemical sensing applications. So far, various synthesis routes are available for the production of bulk copper silicates, however, the scalable synthesis of nanosheets remains challenging.

Here, we introduce the method of flame-spray-pyrolysis (FSP) for the production of various copper silicates. This approach yields nanoscale metal oxide particles, which, following annealing, transform into the desired 2D crystal lattice. The obtained copper silicates are ultrabright with a photoluminescence quantum yield ranging from 11% to 32%, allowing rapid imaging of exfoliated nanosheets at video rates >178 frames per second (fps) in a stand-off approach (>20 cm). These promising luminescence properties offer a route to next generation bioimaging in the second NIR (NIR-II) spectral window, e.g. shown for in vivo localization-based tracking of luminescent nanosheets in the mouse brain for super-resolution structural imaging of the vasculature and measuring blood flow velocity. Overall, the tunable FSP-synthesis of 2D copper-silicates gives access to precise control over chemical composition, crystal phase and fluorescence quantum yield and fluorescence lifetime (40-80 µs), creating highly luminescent nanosheets for NIR bioimaging.