Assembly for picking up cell material from the surface of a culture medium in a culture dish , said assembly comprising: - a picking tool device comprising a picking tool holder of electrically conducting material, said picking tool holder being mounted to the picking tool device in an electrically insulated manner, said picking tool holder holding a picking tool made of electrically conducting material, said picking tool being held by the picking tool holder in an electrically conducting manner, said picking tool holder being electrically connected to a first electrical lead ; - a culture dish made of electrically insulating material; - a support for supporting the culture dish having an annular element made of electrically conducting material surrounding a culture dish support portion of electrically insulating material, the annular element being electrically connected to a second electrical lead ; - a positioning device for positioning the picking tool in a starting position above the culture dish and for lowering and raising the picking tool towards and away from the culture dish , respectively; - a controller for controlling the movement of the positioning device ; - an oscillator circuit connected with the first and second electrical leads and configured to provide a signal representing an oscillation frequency characterized by an electrical capacity of a measuring circuit that comprises the first electrical lead, the picking tool holder , the picking tool , the second electrical lead , the support , and the culture dish ; - a comparator for performing a comparison of the oscillation frequency during lowering of the picking tool with a start oscillation frequency and for providing a comparison signal indicative of said comparison, said controller controlling the movement of the positioning device at least based on the comparison signal. - a picking tool device comprising a picking tool holder of electrically conducting material, said picking tool holder being mounted to the picking tool device in an electrically insulated manner, said picking tool holder holding a picking tool made of electrically conducting material, said picking tool being held by the picking tool holder in an electrically conducting manner, said picking tool holder being electrically connected to a first electrical lead ; - a culture dish made of electrically insulating material; - a support for supporting the culture dish having an annular element made of electrically conducting material surrounding a culture dish support portion of electrically insulating material, the annular element being electrically connected to a second electrical lead ; - a positioning device for positioning the picking tool in a starting position above the culture dish and for lowering and raising the picking tool towards and away from the culture dish , respectively; - a controller for controlling the movement of the positioning device ; - an oscillator circuit connected with the first and second electrical leads and configured to provide a signal representing an oscillation frequency characterized by an electrical capacity of a measuring circuit that comprises the first electrical lead, the picking tool holder , the picking tool , the second electrical lead , the support , and the culture dish ; - a comparator for performing a comparison of the oscillation frequency during lowering of the picking tool with a start oscillation frequency and for providing a comparison signal indicative of said comparison, said controller controlling the movement of the positioning device at least based on the comparison signal. <EOS>