A fluid extraction device (101, 200, 300, 352), comprising: a housing (140, 304) having a fluid passage (158, 307, 358) and a porous medium (184, 302, 370) in said fluid passage (158, 307, 358), wherein said porous medium (184, 302, 370) is capable of moving between a first position to open a space adjacent to said porous medium and a second position to close said space adjacent to said porous medium; and a pressure source in fluid communication with said fluid passage (158, 307, 358), wherein said pressure source is configured to: draw fluid into said fluid passage (158, 307, 358) through said space adjacent to said porous medium (184, 302, 370), wherein upon said fluid being directed into said fluid passage (158, 307, 358), said porous medium (184, 302, 370) is positioned in said first position; and discharge said fluid from said fluid passage (158, 307, 358) through said porous medium (184, 302, 370), wherein upon said fluid being discharged from said fluid passage (158, 307, 358): (i) said porous medium (184, 302, 370) is positioned in said second position, thereby closing said space adjacent to said porous medium (184, 302, 370), and (ii) said porous medium (184, 302, 370) captures nucleic acids from said fluid. a housing (140, 304) having a fluid passage (158, 307, 358) and a porous medium (184, 302, 370) in said fluid passage (158, 307, 358), wherein said porous medium (184, 302, 370) is capable of moving between a first position to open a space adjacent to said porous medium and a second position to close said space adjacent to said porous medium; and a pressure source in fluid communication with said fluid passage (158, 307, 358), wherein said pressure source is configured to: draw fluid into said fluid passage (158, 307, 358) through said space adjacent to said porous medium (184, 302, 370), wherein upon said fluid being directed into said fluid passage (158, 307, 358), said porous medium (184, 302, 370) is positioned in said first position; and discharge said fluid from said fluid passage (158, 307, 358) through said porous medium (184, 302, 370), wherein upon said fluid being discharged from said fluid passage (158, 307, 358): (i) said porous medium (184, 302, 370) is positioned in said second position, thereby closing said space adjacent to said porous medium (184, 302, 370), and (ii) said porous medium (184, 302, 370) captures nucleic acids from said fluid. draw fluid into said fluid passage (158, 307, 358) through said space adjacent to said porous medium (184, 302, 370), wherein upon said fluid being directed into said fluid passage (158, 307, 358), said porous medium (184, 302, 370) is positioned in said first position; and discharge said fluid from said fluid passage (158, 307, 358) through said porous medium (184, 302, 370), wherein upon said fluid being discharged from said fluid passage (158, 307, 358): (i) said porous medium (184, 302, 370) is positioned in said second position, thereby closing said space adjacent to said porous medium (184, 302, 370), and (ii) said porous medium (184, 302, 370) captures nucleic acids from said fluid. (i) said porous medium (184, 302, 370) is positioned in said second position, thereby closing said space adjacent to said porous medium (184, 302, 370), and (ii) said porous medium (184, 302, 370) captures nucleic acids from said fluid.