1. A method of obtaining nucleic acid from a cell sample, the method comprising: (a) providing a sample comprising a plurality of cells suspended in solution; (b) physically isolating one or more cells of the sample within a microfluidic flow channel by a process that comprises flowing the solution partially through a first and a second valve in the microfluidic flow channel while the first and second valves are open, and then closing the first and second valves such that a part of the solution containing the one or more cells is isolated therebetween; (c) exposing the one or more cells in the part of the solution that was isolated between the first and the second valves in step (b) to a lysis chemical while said cell(s) are valved off from other cells in the sample, thereby releasing nucleic acid from the isolated cells; and (d) amplifying at least a portion of a nucleic acid released in step (c), wherein steps (b), (c) and (d) are performed in a microfluidic device.