Probing elasticity of soft bio-material through optical nanoindentation

We report a radiation pressure-driven atomic force microscopy (AFM)-like nanoindentation tip, where incident waves undergo total internal reflection at two surfaces, enhancing radiation pressure by four times compared to normal incidence. This significantly improves energy efficiency and enables nanometric precision using interferometric detection of tip–sample contact. The method assesses the elasticity of AFM tips, soft polymers, and biological samples like human skin, facilitating optically driven nanoindentation with sharp conical tips. Additionally, we measured the elasticity of skin layers formed during milk drying, demonstrating its versatility. Numerical simulations under realistic conditions closely matched experimental results, ensuring high repeatability across various elastic moduli. This technique holds great potential for characterizing soft biological materials.