Deep tissue imaging approaches by direct capture of two-photon absorption

Multiphoton imaging with fluorescence detection has proven to be a powerful method for moderately deep tissue imaging (less than 1 mm) with molecular specificity. However, many important endogenous biomolecules do not fluoresce (NAD) or have low efficiency (melanin). In this paper two femtosecond pulse shaping methods have been demonstrated to detect two-photon absorption (TPA), instead of fluorescence, with high sensitivity, which opens up a wide range of molecular targets. It also facilitates longer excitation wavelengths, which permit greater tissue penetration. Developing the imaging system by using these new methods will be also discussed.