About the design of oligo-chips

On a very small surface, a chip, several thousands of oligonucleotides, having a length between 20 and 25 bases, can be synthesized. The actual technology to manufacture in parallel these high-density oligo-chips is photolithography using masks to select the oligos on which one base, among A, T, G or C, must be added. The problems tackled here deal with the possibility, with a unique series of masks, to synthesize each oligonucleotide in different ways, such that two copies of the same one are realized with different subsequences of masks.