Mechanical properties of biological cells can be utilized as an inherent, label-free biomarker to indicate the physiological and pathological changes of cells. Characterization of cell deformability has been found to be useful to distinguish healthy and unhealthy cells for disease diagnosis. In this thesis, we focus on developing optofluidic cell stretchers using optical tweezers and interference patterns in microfluidic channels for non-contact cell mechanical characterization.

We develop an optofluidic cell stretcher based on a “tweeze-and-drag” mechanism using a periodically blocked optical tweezer in a microfluidic channel. Our stretcher enables a cell-stretching throughput of ~1.5 cells/s, which is much higher than conventional optical stretchers (~1 cell/min) and static t...[ Read more ]

Mechanical properties of biological cells can be utilized as an inherent, label-free biomarker to indicate the physiological and pathological changes of cells. Characterization of cell deformability has been found to be useful to distinguish healthy and unhealthy cells for disease diagnosis. In this thesis, we focus on developing optofluidic cell stretchers using optical tweezers and interference patterns in microfluidic channels for non-contact cell mechanical characterization.

We develop an optofluidic cell stretcher based on a “tweeze-and-drag” mechanism using a periodically blocked optical tweezer in a microfluidic channel. Our stretcher enables a cell-stretching throughput of ~1.5 cells/s, which is much higher than conventional optical stretchers (~1 cell/min) and static testing techniques. We estimated the spring constant of red blood cells to be ~14.9 μN/m. We also distinguish healthy and unhealthy (glutaraldehyde-treated) cells based on their different mechanical responses. We further study optofluidic cell stretchers using two optical tweezers in a microfluidic channel, which potentially enables a higher characterization throughput and a more flexible way to induce cell deformation for mechanical characterization.

We develop a beam-shaping technique for optical lattice generation by inventing the vertically embedded multimode-interference (MMI) polymer waveguides on a silicon chip. We demonstrate the generation of various two-dimensional optical lattices spanning from 4×4 to 10×10 arrays. We demonstrate that longitudinally offsetting the waveguide bottom end-face from the focused beam waist allows a simple way of tuning the effective waveguide length to satisfy the self-imaging condition for optical lattice generation.

Based on the optical lattices generated by the vertically embedded MMI polymer waveguides, we demonstrate optofluidic cell stretchers in an optofluidic chip. Leveraging the parallel stretching in multiple rows of a 5×5 optical lattice, our stretcher enables a characterization throughput of ~ 6 cells/s. We also distinguish healthy and unhealthy cells (glutaraldehyde-treated) based on their different mechanical responses.