Synthesis and attachment of polymide nucleic acid on gold surface

Abstract

Two novel thiol-modified polyamide nucleic acids (PNA) were synthesized by solid phase peptide synthesis and directly attached on gold coated quartz crystals by self assembly monolayer (SAM) formation via S atom for detection of DNA hybridization. The amount of immobilized PNA and the extent of DNA hybridization were detected by quartz crystal microbalance (QCM) which is an extremely sensitive mass sensor. From the result, it can be demonstrated that the amount of immobilized PNA on the gold electrode increased with the PNA concentration. The blocking step is critical to the success of subsequent DNA hybridization. The optimal immobilization condition is PNA concentration: 1.0 M and immobilization time: 24 h and the optimal hybridization condition is DNA concentration: 50 M, sodium phosphate buffer pH 7 concentration: 0.5 mM and hybridization time: 1 h. Moreover, the effect of pH and ionic strength were also investigated. Hybridization of immobilized PNA with perfect matched and mismatched DNA sequences were observed to determine the specificity of hybridization. The QCM results indicated that the binding affinity of PNA immobilized on the gold surface with target DNA is extremely dependent on the nucleobases of PNA and DNA. Finally, single mismatch discrimination has been achieved by a combination of PNA with QCM technique.