Probing fluid-cells-substrate nanoscale interactions using digital holographic interferometry and WiMTiP sensor

Measuring surface deformation is of great interest in areas including physics, material science, surface engineering, and biology. Among many, non-intrusive optical methods have advantages. We proposed a new method for measuring nano-deformation by combining a wrinkle-free nm thin film in polymer (WiMTiP) nano-strain sensor and Mach-Zehnder interferometry. A nm-thick smooth reflective thin film embedded in a polymer matrix acts as a flexible mirror and subsequently reflects a collimated coherent light to form the perturbed objective beam. It interferes with the unperturbed reference beam to form an interferogram. Any stress acting on the sensor deforms the embedded flexible mirror as changes in fringe spacings and subsequently encodes the deformation. To extract the deformation from interference pattern, a novel integration method, a.k.a. local-growing omni-directional integration is introduced whereby multiple integration paths with various lengths are generated to perform path integrations. Three applications will be discussed including the wetting of sessile water droplets over functional surfaces, the evaporation of droplets on soft surfaces, and cancer cell detection using WiMTiP microfluidic platform.