The full lac binding region peptide and its subunits were investigated as potential ligands either for the affinity immobilization and purification of plasmid DNA or for detection purposes such as in a BioMEMS device. Affinities and mechanisms for lacI peptides binding to pUC19 plasmid DNA were examined through measurement of binding isotherm and maximum binding capacity. In addition, the effects of elution, different binding buffers, and ionic strength are examined with the aim of optimising binding and elution conditions and of assistance to the affinity purification of plasmid DNA.