A method of manipulating particles suspended within a fluid droplet using a microfluidic system including a piezo-electric substrate (1) and a wave generation means (3) for generating a wave within the piezoelectric substrate (1), and a working surface (2) through which the wave can be distributed and upon which fluid droplets (9) can be located, the method including locating one or more droplets of fluid on the working surface (2), varying the power applied to the wave generation means (3) or varying the distribution of the wave across the working surface (2), such that particles (1 1) suspended within the fluid droplet (9) are either dispersed within the droplet or concentrated in an area within the droplet in dependence on the power or wave distribution applied by the wave generation means (3) to the piezoelectric substrate (1), or to facilitate rotation of the fluid within said fluid droplets (9) located jn the path of the wave.