Surface functionalized perovskite nanocrystals: a design strategy for organelle-specific fluorescence lifetime multiplexing.

Fluorescent molecules or materials with high photoluminescence quantum yields and stability towards photobleaching are ideally suited for multiplex imaging. Despite complying with such properties, perovskite nanocrystals (Pv-NCs) are rarely used for bioimaging owing to their toxicity and limited stability in aqueous media and towards human physiology. We aim to address these deficiencies by designing core-shell structures with Pv-NCs as the core and surface-engineered silica as the shell (SiO 2 @Pv-NCs) since silica is recognized as a biologically benign carrier material and is known to be excreted through urine. The post-grafting methodology is adopted for developing [SiO 2 @Pv-NCs]tpm and [SiO 2 @Pv-NCs]tsy (tpm: triphenylphosphonium ion, tsy: tosylsulfonamide) for specific imaging of mitochondria and endoplasmic reticulum (ER) of the live HeLa cell, respectively. A subtle difference in their average fluorescence decay times ([SiO 2 @Pv-NCs]tpm: tpm τ av = 3.1 ns and [SiO 2 @Pv-NCs]tsy: tsy τ av = 2.1 ns) is used for demonstrating a rare example of perovskite nanocrystals in fluorescence lifetime multiplex imaging.