Application of coaxial beam photothermal microscopy to the analysis of a single biological cell in water

Photothermal microscopy, with the excitation and probe beams coaxial under a microscope, was shown to provide highly sensitive absorptiometry for micro-objects. The signal dependence on the modulation frequency showed that the detected signal was photothermally generated. In addition, the thermal lens effect of the microparticle itself was expected to be dominant, judging from the signal dependence on the focal point of the excitation and probe beams. This method was applied to the measurement of a single, stained biological cell in water. The results suggested that the method could measure a trace amount of chemical species in a living biological cell.