Highly cooperative behavior of peptide nucleic acid-linked DNA-modified gold-nanopartide and comb-polymer aggregates

An experiment was conducted to show that peptide nucleic acid (PNA)-linked gold nanoparticles (AuNP)-DNA and polymer-DNA hybrid aggregates display sharp melting transitions when compared with unmodified PNA-DNA duplexes. The melting behavior of unmodified PNA:DNA duplexes of the same sequence were examined to create a basis for comparison. The duplexes of the same sequence display opposite T_m dependence on salt concentration. The presence of PNA-linked aggregates was indicated by a associated color change from red to blue, which arises from a dampening and shifting of the AuNP surface plasmon band. An unusual and general salt dependence of the melting temperature of PNA:DNA duplexes within a hybrid aggregate was recovered, which is the reverse of the trend observed in unmodified PNA:DNA duplexes. The closely spaced duplexes inside the aggregates leads to the positive salt-dependent behavior, which in turn, leads in cooperative interactions between neighboring duplexes.