Multi-photon resonance enhancement of third harmonic generation in human oxyhemoglobin and deoxyhemoglobin

Cancer cells require excessive oxygen and nutrition to support their rapid growth, so angiogenesis and decrease of blood oxygen are often associated with areas of cancer development. Current technologies for blood oxygen measurement, however, do not possess high spatial resolution and therefore cannot be used to detect small tumors in their early stage. In this paper, we studied the third harmonic generation (THG) spectra of oxy- and deoxyhemoglobin in the 1170-1365 nm region, which is strongly influenced by the multi-photon resonance effect, especially around the Soret transition band. Our spectroscopic results thus indicate the high potential of THG spectroscopic microscopy for oxygen depletion level measurement of a single red blood cell in vivo. [GRAPHICS] The THG spectrum, measured THG ratio versus the generated THG wavelength, of the oxyhemoglobin sample (black triangles) correlates well with its linear absorbance at third harmonic wavelengths (blue line) around the Soret transition band.