A microfluidic device (1) comprising, a pallet, having a first surface (4a) and second, opposite, surface (4b); the first surface (4a) having defined therein, a main channel (5), and one or more inlet subsidiary channels (6a,6b) each of which is in fluid communication with the main channel (5) at a first junction (7) which is located at one end of the main channel (5), and corresponding one or more outlet subsidiary channels (8a,8b) each of which is in fluid communication with the main channel (5) at a second junction (9) which is located an second, opposite, end of the main channel (5); wherein the depth (‘d’) of the one or more inlet subsidiary channels (6a,6b) and the depth (‘χ’) of the one or more outlet subsidiary channels (8a,8b) is less than the depth (‘f) of the main channel (5) so that there is step (106a,106b, 108a, 108b) defined at the first junction (7) and at the second junction (9); the second, opposite, surface (4b) having defined therein a groove (15) which can receive a means for generating a magnetic field, wherein the groove (15) is aligned with, and extends parallel to, the main channel (5). There is further provided a corresponding assembly and method of extracting ferromagnetic, paramagnetic and/or diamagnetic particles from a sample.