A method of individually releasing from an entity one or more members of a sub-group of biological units included in a heterogeneous group of biological units is provided. The method includes binding the group of biological units including the sub-group of biological units to the entity via a linker. Following binding, the location of the one or more members on the entity is determined. Once the location is determined, a localized physical pulse is applied to the one or more members. The localized physical pulse individually releases the one or more members from the entity by dissociating the linker.