A microfluidic device (100) comprises: a reaction chamber (102); at least a first and a second supply channel (110a, 110b) for allowing transport of a first fluid and a second fluid, respectively, from a fluid supply source (112a, 112b) into the reaction chamber (102), wherein each of the first and the second supply channels (110a, 110b) comprises a side drain (114a, 114b) connected to the supply channel (110a, 110b) between the fluid supply source (112a, 112b) and the reaction chamber (102), wherein the side drain (114a, 114b) is configured to prevent undesired diffusion of the fluid in the ...