The present invention provides methods and devices for screening a single cell or a small group of cells for a desired biological activity. A shielding layer is located above andor below the region where the resistor group andor the signal interconnection layer are located. The plunger rod includes a stopper of which at least a portion can be embedded in the passageway of the cap to form a plug in the cap. The lid member has one end turnably supported by the case main body and the other end fastened to the case main body by a screw when the aperture is closed.