A lid for a well plate is provided. A pin penetrates the lid and projects
downwardly into a well of the well plate. An electrical charge is applied
to the pin and an electrical charge of opposite polarity is applied to an
electrically conductive portion of a corresponding well, generating a
small flow of electrical current and corresponding electrical fields
within the well. Charged materials, such as DNA, selectably are attracted
to the pin and segregated from the liquid sample.