A microfluidic device comprises a substrate transparent for imaging and having a plurality of spatially defined and separated cell channels having a dimension to accommodate cells in monolayer. A respective first end of the cell channels is in fluid connection with a flow input channel having a first end in fluid connection with a first fluid port and a second end in fluid connection with a second fluid port. A respective second end of the cell channels is in fluid connection with a first end of a respective wash channel having a second end in fluid connection with a flow output channel. The flow output channel is in fluid connection with a third fluid port. The wash channels have a dimension too small to accommodate the cells.