A microfluidic device for extracting target objects from a sample comprising: an aliquotting segment comprising a sample inlet channel, a first buffer inlet channel, a sample waste channel, and an aliquot delivery channel fluidly coupled at a fluid junction, the sample inlet channel and first buffer inlet channel in fluid communication with an inlet end of the fluid junction and the sample waste channel and aliquot delivery channel in fluid communication with an outlet end of the fluid junction, the aliquotting segment further comprising a second buffer inlet channel and a normally open valve, the second buffer inlet channel coupled to the fluid junction between the sample inlet channel and the sample waste channel, and the normally open valve operably coupled to the second buffer inlet channel; and a trapping segment in fluid communication with the aliquotting segment, the trapping segment comprising a trapping chamber, a plurality of trapping structures, a collection channel, and a waste channel, wherein the trapping structures are disposed in the trapping chamber, and wherein the collection channel and the waste channel are in fluid communication with the trapping chamber; characterized in that the normally open valve operably coupled to the second buffer inlet channel is open until an actuator is energized to close it; and wherein the normally open valve comprises a valve structure formed across the width of the second buffer inlet channel and a deformable material disposed over at least a portion of the second buffer inlet channel in the area of the valve structure, wherein the deformable material is sealed over the second buffer inlet channel portion except in the area of the valve structure, thereby forming a covered second buffer inlet channel portion that permits fluid to flow over the valve structure. an aliquotting segment comprising a sample inlet channel, a first buffer inlet channel, a sample waste channel, and an aliquot delivery channel fluidly coupled at a fluid junction, the sample inlet channel and first buffer inlet channel in fluid communication with an inlet end of the fluid junction and the sample waste channel and aliquot delivery channel in fluid communication with an outlet end of the fluid junction, the aliquotting segment further comprising a second buffer inlet channel and a normally open valve, the second buffer inlet channel coupled to the fluid junction between the sample inlet channel and the sample waste channel, and the normally open valve operably coupled to the second buffer inlet channel; and a trapping segment in fluid communication with the aliquotting segment, the trapping segment comprising a trapping chamber, a plurality of trapping structures, a collection channel, and a waste channel, wherein the trapping structures are disposed in the trapping chamber, and wherein the collection channel and the waste channel are in fluid communication with the trapping chamber; characterized in that the normally open valve operably coupled to the second buffer inlet channel is open until an actuator is energized to close it; and wherein the normally open valve comprises a valve structure formed across the width of the second buffer inlet channel and a deformable material disposed over at least a portion of the second buffer inlet channel in the area of the valve structure, wherein the deformable material is sealed over the second buffer inlet channel portion except in the area of the valve structure, thereby forming a covered second buffer inlet channel portion that permits fluid to flow over the valve structure.