Optical tweezers can be used to manipulate droplets, vesicles and vesicle membranes, as shown in the example of a sucrose-filled giant unilamellar vesicle (GUV) in Fig. 18.1. In fact, just like with solid particles, it is possible to transport and release droplets and vesicles. Differently from solid particles, though, droplets and vesicles can be brought together and made to coalesce into larger droplets and vesicles in a process where their contents get mixed. By doing so, it is possible to use droplets and vesicles as movable reaction vessels containing tiny amounts of desired reagents for combinatorial chemistry studies using ultrasmall (in the femtolitre range) volumes. These mechanical manipulations can then be coupled to spectroscopic probing techniques in order to measure and understand mixing and coalescence processes as they happen, in real time. In this Chapter, we will review progress in experiments regarding the fusion of droplets and vesicles, the spectro- scopic study of the resulting chemical mixing processes and also the action of optical trapping on the encapsulating vesicle membrane itself.
18.1 Liquid droplets
18.2 Vesicle and membrane manipulation
18.3 Vesicle fusion
18.4 Further reading