Label-free Mie Scattering Identification of Tumor Tissue Using an Angular Photodiode Array

Tumors differ from normal tissues in several meaningful ways including cellular size, morphology, and protein expression, which will accordingly change the refractive index and the size/morphology of cells. There are also important differences in tissue organization and unique tissue specific cell densities. Instead of time-consuming and labor-intensive histology involving the use of a benchtop microscope, a plot of Mie scattering intensities at fixed wavelength against scattering angle, which we referred to as "Mie spectrum," is suggested as an alternative to identify tumor from normal tissues. An angular photodiode array is developed to measure this Mie spectrum with three different light emitting diodes (blue, green and red) as light sources. The resulting Mie spectra show characteristic peaks for rat colonic tissues, and substantial differences can be found between tumor vs. normal tissues. Two peaks were identified at 120° and 150° scattering angles, potentially representing capillaries and colon cells, respectively. Contributions from crypts and goblet cells, represented by the scattering at 140°, were minimal. Substantial differences between tumor and normal tissues were found with 45°-70° light irradiation angles.