Investigation of pH-dependent DNA-metal ion interactions by surface plasmon resonance

Ni(II) and Zn(II) M-DNA formation and denaturation of double-stranded DNA (dsDNA) by Cd2+ were monitored by surface plasmon resonance (SPR). When exposed to immobilized 30 bp 50% GC dsDNA, Zn2+ and Ni2+ were found to give signals indicative of a conformational change at pH 8.5 but not 7.5, while Mg2+ and Ca2+ caused small changes at both pHs. The concentrations that gave 50% of the maximum responses were 0.06 and 0.50 mM for Zn2+ and Ni2+, respectively. At pH 8.5, Cd2+ denatured over 40% of the dsDNA, while other metals denatured less than 5% of the DNA. Smaller pH-dependent signals were induced by Zn2+, Ni2+ or Cd2+ with 50% GC single-stranded DNA (ssDNA), and with a homopolymer of d(T)30. Homopolymers d(A)30 and d(C)30 showed small signals that were largely independent of pH in the presence of Zn2+ or Ni2+.