Label-free tetra-modal molecular imaging of living cells with CARS, SHG, THG and TSFG (coherent anti-Stokes Raman scattering, second harmonic generation, third harmonic generation and third-order sum frequency generation)

We have developed a new multimodal molecular imaging system that combines CARS (coherent anti-Stokes Raman scattering), SHG (second harmonic generation), THG (third harmonic generation) and multiplex TSFG (third-order sum frequency generation) using a subnanosecond white-light laser source. Molecular composition and their distribution in living cells are clearly visualized with different contrast enhancements through different mechanisms of CARS, SHG, THG and TSFG. A correlation image of CARS and TSF reveals that the TSF signal is generated predominantly from lipid droplets inside a cell as well as the peripheral cell wall.