First entities consisting in cells or microorganisms (BIO) and second entities consisting in compounds or compound units, carried typically by microbeads (BEAD), are trapped selectively within closed movable potential cages (S1) by means of dielectrophoretic force generated by mutually opposed electrodes (M1, M2). The cages are set in relative motion so as to bring about the interaction of selected first and second entities, causing the cages containing them to fuse, whereupon results are obtained preferably by reinstating the original cages and/or observing previously empty adjacent cages. The procedure takes place in a device (DE) with two separate chambers (F, FL) connected one to the other by way of a narrow passage (D) and finished with respective selectively controllable inlets and outlets (I1, I2; O1, O2) through which a liquid or semi-liquid buffer (L) can be pumped in or out.