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In-vivo femtonewton-sensing nanotribology of Tradescantia zebrina leaf cell inner surface using roll rotation detection

Accessing the properties of a plant cell interior non-invasively is difficult due to the presence of a cell wall. Nanoparticles larger than 5 nm cannot be readily phagocytosed inside the cell like animal cells. It is here that we realise that Tradescantia zebrina plant cells have prismatic forms of calcium oxalate crystals present inside them naturally. These crystals make a ready choice to study properties of the inner cell surface with the application of optical tweezers. Moreover, out-of-plane rotations in optical tweezers have begun to be explored only recently. The pitch rotation has been detected with high resolution and several applications are explored. In this work, we first study the stable configuration while trapped in linearly polarized optical tweezers and then explore the other out-of-plane configurations to detect the roll rotation at high resolution. Then a micro-rheological analysis is performed to obtain the frictional properties of the inner surface of the plasma membrane of the leaf cell. The size of the particle is about 5 $μ$m along the diagonal, so that the contact length with the surface is about 200 nm. We measure a frictional force of 18.5 pN at a sensitivity of about 200 fN without averaging.