Assemblies and methods for screening sample fluids

There is provided an assembly, useable to screen sample fluids for predefined molecules, the comprising, a needle unit comprising n hollow needles, wherein n is greater than one; a flow cell unit comprising m flow cells, wherein m is greater than one, each flow cell having an input and an output, and a test surface on which ligands can be provided; a first selector valve unit which is fluidly connected between the needle unit and flow cell unit, which is operable to selectively fluidly connect any one of the n hollow needles with the m flow cells in the flow cell unit; a pumping means which is selectively operable to provide negative pressure; a second selector valve unit which is fluidly connected between the pumping means and the output of each flow cell. There are further provided methods of screening sample fluids for predefined molecule.