Development of in-situ Raman diagnosis technique of eosinophil esophagitis

The spectra of the live tissue with blood flow measured with 785 nm-excitation light showed a very weak signal due to hemoglobin (Hb). It suggested the possibility to detect eosinophil accumulation in the tissue with the 785 nm-excitation light. The excitation wavelength of 633 nm induced strong fluorescence of sapphire glass that is a material of the ball lens of BHRP (Ball lens top hollow optical fiber Raman probe). On the other hand, the previous study suggested that eosinophil including eosinophil peroxidase (EPO) that showed a strong resonance Raman effect with 633 nm-excitation light. The purpose of the present study is to collect basic information and to evaluate the viability of Raman spectroscopic analysis for the detection of eosinophil accumulation in the live esophagus. BHRP with a sapphire ball lens with 500 µm diameter was applied for measurement of live esophagus tissue of a mouse. In this study, Raman spectra of eosinophil were measured with 633 and 785 nm-excitation. The Raman spectra of eosinophil showed a strong contribution of EPO, suggested that a heme chromophore in EPO had pre-resonance enhancement via Q band with the 785 nm-excitation light. Principal component analysis (PCA) is applied for the analysis of Raman spectra of eosinophil, erythrocyte and other granulocytes. Eosinophil was successfully discriminated from other blood cells in the PCA score plots built for the datasets of the spectra measured with 633 and 785 nm-excitation wavelengths. Consequently, our study demonstrates that Raman spectroscopy with 785 nm-excitation had high viability for in situ analysis of eosinophilic esophagitis (EoE).