In-vitro monitoring of redox state of cytochrome oxidase in bone by optical coherence quantitation based on low-coherence interferometry

Abstract

We present optical coherence quantitation technique to monitor the redox state of mitochondria enzyme Cytochrome oxidase (CytOx) in bone tissue by the use of optical coherence tomography (OCT) system. Superluminescent diode (SLD) with its peak emission wavelength ((lambda) = 820nm) on the absorption band of oxidized form of CytOx was used in the experiments. The reflectance returning from the liquid phantoms (naphthol green B with intralipid) and bone tissue specimens (periosteum of calvaria from newborn rats) as a function of penetration depth was used to quantify the absorption changes of the sample. Absorption coefficients of naphthol green B were accurately quantified by the linear relationship between attenuation coefficients from the slopes of the reflected signals and naphthol green B concentration. The results show that the attenuation coefficient decreases in periosteums as CytOx is reduced by sodium dithionite, demonstrating the feasibility of this method to quantify the redox state of tissues studied. A 70% +/- 7% (n=4) reduction of attenuation coefficients in periosteums was clearly observed with redox change of CytOx after 5 min reduction. In addition, the results demonstrate that the OCT system is also capable of imaging the calvaria tomographically with a resolution at 9 microns, which could only be previously obtained by the conventional excisional biopsy.