ADSORPTION OF PEPTIDE NUCLEIC-ACID AND DNA DECAMERS AT ELECTRICALLY CHARGED SURFACES

Adsorption behavior of peptide nucleic acid (PNA) and DNA decamers (GT AGATCACT and the complementary sequence) on a mercury surface was stud ied by means of AC impedance measurements at a hanging mercury drop el ectrode. The nucleic acid was first attached to the electrode by adsor ption from a 5-mu l drop of PNA (or DNA) solution, and the electrode w ith the adsorbed nucleic acid layer was then washed and immersed in th e blank background electrolyte where the differential capacity C of th e electrodedouble layer was measured as a function of the applied pote ntial E. It was found that the adsorption behavior of the PNA with an electrically neutral backbone differs greatly from that of the DNA (wi th a negatively charged backbone), whereas the DNA-PNA hybrid shows in termediate behavior. At higher surface coverage PNA molecules associat e at the surface, and the minimum value of C is shifted to negative po tentials because of intermolecular interactions of PNA at the surface, Prolonged exposure of PNA to highly negative potentials does not resu lt in PNA desorption, whereas almost all of the DNA is removed from th e surface at these potentials. Adsorption of PNA decreases with increa sing NaCl concentration in the range from 0 to 50 mM NaCl, in contrast to DNA, the adsorption of which increases under the same conditions.