Two-photon properties of CdSe core ZnS/CdS multishell quantum dots for bioimaging applications

This letter demonstrates that the fluorescence intensity of CdSe-core CdS/ZnS-multishell quantum dots (QDs) in toluene is related via a power-law of similar to 1.9 to the input intensity of femtosecond laser at 5 similar to 130 GW/cm(2). This clearly indicates a broad range of optical intensity of two-photon excitation (TPE). The two-photon absorption (TPA) cross sections of QDs of core-size 2.9, 4.0 and 5.3 nm at 800 nm are 1980, 5680 and 14600 GM, respectively. Furthermore, the log-log plot of CdSe-core diameters versus the TPA cross sections shows the increase with a slope >3, indicating a nonlinear dependent relationship between TPA cross section and size of CdSe-core. The broad optical range of TPE and large TPA cross section make these QDs excellent candidates for two-photon fluorescent microscopy and bioimaging. Based on these two-photon properties of our QDs, we continue to investigate the bioimaging applications with two-photon microscopy. The results of the fluorescence images of living cells with the QDs demonstrate that QDs could be penetrate into cell membrane, then steadily and dispersedly distribute at the cytoplasm, which further indicates such QDs could be excellent candidate for two-photon microscopy applications.