Method of performing an assay

A method of selecting a biological cell by performing assays on a compound excreted by biological cells, the method being performed using a device, wherein the device comprises:

• a frontside with a plurality of wells;
• and
• a backside wherein each respective well of the plurality of wells comprises a respective bottom provided with a respective through-hole extending from the respective well to the backside,
• wherein the wells of the plurality of wells contain biological cells, and wherein each respective through-hole has smaller dimensions than the biological cells in the plurality of wells and thereby physically retains the biological cells in the wells, wherein at least 10% of the plurality of wells contain only a single biological cell;
• wherein said method comprises:
• contacting the backside of the device with a substrate such that a substantially respective straight passage from each respective through-hole to the substrate is established wherein each respective straight passage is substantially coaxial with each respective through-hole and is substantially perpendicular to the backside, wherein the biological cells excrete a compound in the plurality of wells and following excretion of the compound by the cells in the plurality of wells, the method further comprises:
• transferring a liquid from the plurality of wells via the through-holes to the substrate;
• performing a first assay using the substrate;
• and
• selecting a biological cell from a well of the plurality of wells,
• wherein the device is held in a position with the backside oriented substantially downward between the transferring of the liquid from the plurality of wells to the substrate via the through-holes and performing the first assay using the substrate.