Ultra high-density oligomer arrays and method of production thereof

A method of producing an oligomer array, comprising:

• (a) providing a substrate with a plurality of recesses;
• (b) stochastically placing a first particle with a first molecule within a recess, wherein a plurality of first particles are respectively placed in different recesses of the substrate without determining in advance which particle will be placed at which location of the array;
• (c) releasing the first molecule from the first particle;
• (d) binding the first molecule to a second molecule while forming an oligomer, wherein the second molecule is immobilized within the recess;
• (e) repeating (b) to (d) while elongating the oligomer;
• wherein at least a first particle comprises a detectable marker.