Optical reprogramming and optical characterization of cells using femtosecond lasers

Stem cell research attracts considerable attention in developmental biol-ogy, nanobiotechnology, and medicine. Since Maksimow's landmark hypothesis on stem cells in 1909, hundreds of thousands of reports have been published in biol-ogy, medicine and biotechnology regarding stem cells, evidence of their considerable worth as a major research subject. Artificial stem cells such as 'induced pluripotent stem cells' (iPS cells), which mor-phologically and functionally resemble embryonic stem cells have been generated through the reprogramming of somatic cells for research purposes. Typically, opti-cal techniques such as light microscopy in combination with fluorescent markers are applied, sometimes accompanied with fluorescence-activated cell sorting (FACS), to characterize and isolate both tissue-specific stem and iPS cells. To date, modern laser-based techniques such as nonlinear multiphoton microscopy and optical transfection using femtosecond lasers are only used in a fe w laboratories. The application of inno-vative femtosecond laser techniques in stem cell research shall be the subject of this chapter. Of particular focus is the application of femtosecond laser microscopy (i) for imaging and characterization of stem cells with high spatial sub-cellular resolution; (ii) as a nanoscalpel for optical cleaning; and (iii) for transfection and optical repro-gramming of cells.