A microfluidic device includes a substrate and a cover. The substrate has an inlet port, a first microchannel, one or more parking loops, a second microchannel and an outlet port for each microchannel network. The first microchannel is connected to the inlet port, the second microchannel is connected to the outlet port, the parking loops are connected between the first and second microchannels. Each parking loop includes a parking loop inlet, a parking loop output, a fluidic trap connected between the parking loop inlet and the parking loop outlet, and a bypass microchannel connected to the parking loop inlet and the parking loop outlet. The cover is attached to a top of the substrate and has an inlet opening and an outlet opening through the cover for each microchannel network. The inlet and outlet openings of the cover are disposed above the inlet and outlet ports in the substrate.