A microfluidic device (1) comprises a substrate (10) transparent for imaging and having a plurality of spatially defined and separated cell channels (20) having a dimension to accommodate cells in monolayer. A respective first end (22) of the cell channels(20) is in fluid connection with a flow input channel (30) having a first end (32) in fluid connection with a first fluid port (31) and a second end (34) in fluid connection with a second fluid port (33). A respective second end (24) of the cell channels (20) is in fluid connection with a first end (42) of a respective wash channel (40) having a second end (44) in fluid connection with a flow output channel (50). The flow output channel (50) is in fluid connection with a third fluid port (51). The wash channels (40) have a dimension too small to accommodate the cells.