Abstract: A portable device for sampling fluid. The device has a puncture device attached to a housing which has an interior and exterior wall. The housing is in fluid communication with the syringe and contains a filtration device comprised of at least one U-shaped hollow fiber membrane. The device also includes a collection chamber. Also in the device is a sensing device including a further hollow fiber membrane the first and second ends each connected to a first and second plug. Each of the plugs contacts the interior wall of the housing. The further hollow fiber membrane contains a sensing agent. The device is arranged so that a sample is collected through the puncture device and is passed through the filtration device where is it passed through the one or more U-shaped hollow fiber membrane to the collection chamber. From the collection chamber it is passed through the hollow fiber membrane which contains the sensing agent device before being passed to a syringe.