Dynamic photothermal interferometric phase microscopy

We present our latest advances in highly dynamic photothermal interferometric phase microscopy for quantitative, selective contrast imaging. Gold nanoparticles can be bio-functionalized to bind specific cells. When stimulating gold nanoparticles at their plasmon-peak wavelength, local increase of temperature occurs due to plasmon resonance. This causes a rapid change of optical phase of the light beam interacting with the sample. These phase changes can be recorded by interferometric phase microscopy and analyzed to form a photothermal image of the binding sites of the nanoparticles in the cells. Furthermore, by increasing the excitation laser light, one can deplete certain cells at will. Usually, the analysis of the photothermal signals utilizes a Fourier transform, which is computational time consuming. This makes photothermal imaging not suitable for applications requiring dynamic imaging or real-time quantitative analysis, such as for analyzing and sorting cells during their fast flow. For this goal, we have developed new algorithms, based on discrete Fourier transform variants, enabling fast analysis of photothermal signals from nanoparticles in live and highly dynamic cells. For the first time, video-rate photothermal signals are obtained, which forms the basis for real-time interferometric phase microscopy with molecular specificity. This technique holds great potential for using photothermal imaging in flow cytometry.