nanoliter pipette assembly . the assembly includes a housing containing a working fluid in a working fluid chamber therein and includes a moveable piston within the housing , the piston moveable by a linear actuation mechanism for contact with the working fluid . a tip portion is provided that includes a diaphragm deformable to engage an inner portion of the tip . it is preferred that the diaphragm have a projecting three - dimensional structure for direct contact with a liquid .