Peptides constructed from a-helical subunits of the Lac repressor protein (Lacl) were designed then tailored to achieve particular binding kinetics and dissociation constants for plasmid DNA purification and detection. Surface plasmon resonance was employed for quantification and characterization of the binding of double stranded Escherichia coli plasmid DNA (pUC19) via the lac operon (lacO) to "biomimics" of the DNA binding domain of Lacl. Equilibrium dissociation constants (K-D), association (k(a)), and dissociation rates (k(d)) for the interaction between a suite of peptide sequences and pUC19 were determined. KD values measured for the binding of pUC19 to the 47mer, 27mer, 16mer, and 14mer peptides were 8.8 +/- 1.3 X 10(-10) M, 7.2 +/-0.6 X 10(-10) M, 4.5 +/- 0.5 X 10(-8) M, and 6.2 +/- 0.9 X 10(-6) M, respectively. These findings show that affinity peptides, composed of subunits from a naturally occurring operon-repressor interaction, can be designed to achieve binding characteristics suitable for affinity chromatography and biosensor devices. (c) 2008 American Institute of Chemical Engineers AIChE J, 55: 505-515, 2009