Two-photon excited cellular autofluorescence induced by cw and femtosecond NIR microradiation

We report the first two-photon excited autofluorescence measurements in single cells induced by continuous wave NIR laser microbeams. In particular we demonstrate NIR-excited NAD(P)H fluorescence of motile spermatozoa in a single-beam gradient force optical trap ('optical tweezers'). In addition, two-photon NIR excited autofluorescence imaging and 'tau- mapping' of CHO cells was performed with laser scanning microradiation of a tunable femtosecond-Ti:sapphire laser. Cellular response on autofluorescence to two-photon absorption of NIR radiation was compared with exposure to UVA light (one-photon absorption).