The path that a mesoscopic polarisable particle takes as it flows through a lattice of intensity maxima and minima (optical lattice) depends crucially upon the degree to which it interacts with the lattice. Two particles of dissimilar size, refractive index or even shape will interact in a different manner with such a lattice. Combining this selective interaction with a guiding mechanism has allowed us to achieve lateral separation of particles by all these properties simply by flowing them through an angled optical lattice. We present such particle separation in a variety of three-dimensional optical lattices discussing the importance of parameters such as flow speed, lattice intensity, lattice constant, lattice angle, maxima interconnectivity and flow chamber design. We also present cell sorting with the separation of erythrocytes from lymphocytes and present our flow chamber fabrication methods.