Semi-circular microgrooves to observe active movements of individual Navicula pavillardii cells

► Semi-circular looped grooves were effective to observe single diatom cell movements. ► Stimulation of the same cell was successfully observed using the grooves. ► The mechanical limit of the velocity of the diatom cells was around 19 μm/s. ► Frictional force between the cell body and the wall of a groove was negligible. ► A simple model of the cell motion in the semi-circular grooves was proposed.