A problem formulation which I modified slightly can be found in [frutos1997demonstration]. This reference also describes the construction of a solution of size 108.
[codishWordDesign]
DNA Word Design: A New Constraint Model and New Results
2016
[tulpan2006effective]
Effective heuristic methods for DNA strand design
Ph.D. thesis, University of British Columbia
2006
[frutos1997demonstration]
Demonstration of a word design strategy for DNA computing on surfaces
Nucleic Acids Research 25(23), 4748–4757,
1997