2.5. Investigation of Individual Chromophore Absorption in the Tissue

Absorption of red or near-infrared photons by cytochrome C oxidase (unit IV of the mitochondrial respiratory chain) has been established by prior works [44,45]. In this section, we investigated the absorption by CCO at 630 nm, 700 nm, and 810 nm wavelengths, which can cause its activation and may lead to photobiomodulation in the gray matter [44]. Besides CCO, we also investigated other major chromophores in the gray matter along with the investigation of water absorption. Chromophores present in the gray matter that were investigated in this section are as follows:

Oxyhemoglobin

Deoxyhemoglobin

Cytochrome c oxidase(reduced and oxidized state)

Lipid

Figure 2 [46], Figure 3 [47], Figure 4 [48] and Figure 5 [49] shows the absorption spectra of two states of hemoglobin, two states of cytochrome c oxidase and lipid respectively. In Figure 4, the main plot shows the absorbance due to 4.9 μM of CCO and the inset shows the absorbance due to five times the concentration of CCO [48].

Water absorption spectrum.

Lipid absorption spectrum.

Cytochrome c Oxidase absorption spectrum.

Hemoglobin absorption spectrum.