Quantitative index imaging of coculture cells by scanning focused refractive index microscopy.

We report the quantitative refractive index (RI) imaging of cocultured cells in their living environment by scanning focused refractive index microscopy (SFRIM). Mouse microglial cells and synovial cells are cocultured on the top surface of a trapezoid prism. The RI imaging of living cells is obtained in a reflection-type method. The RI information is deduced with the simple derivative total internal reflection method, where a complex retrieval algorithm or reconstruction process is unnecessary. The outline of each cell is determined according to the RI value compared with that of the immersion liquid. The cocultured cells can be discriminated in the RI image. The measurement is nondestructive and label-free. The experimental results prove that SFRIM is a promising tool in the field of biological optics.

Measurement of complex refractive index of turbid media by scanning focused refractive index.

We present the application of scanning focused refractive index microscopy in the complex refractive index measurement of turbid media. An extra standard scattering layer is placed in front of the detector to perform scattering transformation on the reflected light. The principle of the scattering transformation is elaborated theoretically. The influence of the sample scattering is deeply and effectively suppressed experimentally. As a proof of the feasibility and accuracy of the proposed method, we demonstrate experimental data of 20% and 30% Intralipid solutions that are commonly used as phantom media for light propagation studies.

Scanning focused refractive-index microscopy.

We present a novel scanning focused refractive-index microscopy (SFRIM) technique to obtain the refractive index (RI) profiles of objects. The method uses a focused laser as the light source, and combines the derivative total reflection method (DTRM), projection magnification, and scanning technique together. SFRIM is able to determine RIs with an accuracy of 0.002, and the central spatial resolution achieved is 1 µm, which is smaller than the size of the focal spot. The results of measurements carried out on cedar oil and a gradient-refractive-index (GRIN) lens agree well with theoretical expectations, verifying the accuracy of SFRIM. Furthermore, using SFRIM, to the best of our knowledge we have extracted for the first time the RI profile of a periodically modulated photosensitive gelatin sample. SFRIM is the first RI profile-resolved reflected light microscopy technique that can be applied to scattering and absorbing samples. SFRIM enables the possibility of performing RI profile measurements in a variety of applications, including optical waveguides, photosensitive materials and devices, photorefractive effect studies, and RI imaging in biomedical fields.