Water-soluble chiral CdSe/CdS dot/rod nanocrystals for two-photon fluorescence lifetime imaging and photodynamic therapy

Compared with traditional organic contrast agents, semiconductor nanocrystals (NCs) have unique optical properties that are vital for biological applications with ultrahigh sensitivities, such as long fluorescence lifetime and large multiphoton absorption (MPA). However, the MPA properties and biological applications of chiral-ligand-stabilized semiconductor NCs have scarcely been reported, which seriously hinders their relevant applications. In this work, we report the aqueous phase transfer of CdSe/CdS dot/rod NCs with the use of cysteine molecules, after which the NCs preserve their high fluorescence quantum yield, long lifetime, and efficient circular dichroism. More importantly, the investigated dot/rod NCs show extremely large two- and three-photon absorption action cross-sections in the first and second biological windows, with maximum values of ∼21 000 GM at 800 nm and ∼4.6 × 10 −78 cm 6 s 2 per photon 2 at 1300 nm, which are among the largest values reported for water-soluble fluorescent nanoparticles. Interestingly, the dot/rod NCs exhibit a high singlet oxygen generation efficiency of 35%. In addition, for the first time, two-photon fluorescence lifetime imaging and photodynamic therapy of the dot/rod NCs were successfully demonstrated. The performed investigation of the optical properties of these water-soluble CdSe/CdS dot/rod NCs indicates that they are promising candidates for nonlinear biological imaging applications. Water-soluble CdSe/CdS nanocrystals stabilized using cysteine molecules exhibit efficient circular dichroism and large multiphoton absorption and show applications in two-photon fluorescence lifetime imaging and photodynamic therapy.