Supplementary Video 7

Study of effect of optical trapping on diatoms. After manipulation and alignment the trap (8.4 mW) and detection beam were switched on at t = 00:30 and off at t = 02:20, yielding an exposure of 110 s that matches the protocol used for viscosity measurements; the beams were focused at the centre of the cell. The cell remained morphologically intact and excluded trypan blue throughout a subsequent 15-min observation.