Photothermal_optical_microscopy
Photothermal optical microscopy / "photothermal single particle microscopy" is a technique that is based on detection of non-fluorescent labels. It relies on absorption properties of labels (gold nanoparticles, semiconductor nanocrystals, etc.), and can be realized on a conventional microscope using a resonant modulated heating beam, non-resonant probe beam and lock-in detection of photothermal signals from a single nanoparticle. It is the extension of the macroscopic photothermal spectroscopy to the nanoscopic domain. The high sensitivity and selectivity of photothermal microscopy allows even the detection of single molecules by their absorption. Similar to Fluorescence Correlation Spectroscopy (FCS), the photothermal signal may be recorded with respect to time to study the diffusion and advection characteristics of absorbing nanoparticles in a solution. This technique is called photothermal correlation spectroscopy (PhoCS).