Detection Of Cdte Quantum Dots In Living Cells: Two-photon Excitation

To effectively image living cells with quantum dots(QDs),particularly for those cells containing high content of native fluorophores,the two-photon excitation(TPE) with a femto-second 800 nm laser was employed and compared with the single-photon excitations(SPE) of 405 nm and 488 nm in BY-2 Tobacco(BY-2-T) and human hepatocellular carcinoma(QGY) cells,respectively.The 405 nm SPE produced the bright photoluminescence(PL) signals of cellular QDs but also induced a strong autofluorescence(AF) from the native fluorophores like flavins in cells.The AF occupied about 30%and 13%of the total signals detected in QD imaging channel in the BY-2-T and QGY cells,respectively.With the excitation of 488 nm SPE, the PL signals were lower than those excited with the 405 nm SPE,although the AF signals were also reduced.The 800 nm TPE generated the best PL images of intracellular QDs with the highest signal ratio of PL to AF,because the two-photon absorption cross section of QDs is much higher than that of the native fluorophores.By means of the TPE,the reliable cellular imaging with QDs,even for the cells having the high AF background,can be achieved.The 800 nm TPE can acquire reliable PL images of cellular QDs by effectively suppressing the AF from native fluorophores in living cells,no matter in mammalian cells or in Tobacco cells with the high content flavoprotein.While with SPE,the AF influence seems unavoidable, producing artificial component in obtained QD images to some extents depending on the fluorophore content in cells.Our results suggest that 800 nm TPE is a feasible and suitable approach for cellular imaging with QDs.In addition,the 800 nm fs laser may produce the least damaging effect on cells when appropriate power is used.