Influence of different primary ion species on the secondary ion emission from PNA/DNA biosensor surfaces

Abstract

AbstractIn recent publications, the use of time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) for a detailed examination of the immobilization process of peptide nucleic acid (PNA) and its hybridization capability to label‐free complementary DNA fragments has been described. Unlabeled single‐stranded DNA was hybridized to biosensor surfaces containing both complementary and noncomplementary PNA sequences. The hybridization of complementary DNA could readily be identified by detecting phosphate‐related molecules from the DNA backbone such as PO3−.Extending previous measurements on hybridized DNA surfaces using different primary ions and energies, additional ion species have been applied for a more detailed evaluation of the secondary ion emission behavior under static SIMS conditions. The large number of available primary ion species allowed for a comparison between results achieved with ‘classic’ monoatomic and polyatomic ions (such as Ar+, Ga+, Xe+ and SF5+) and bismuth primary ions up to cluster sizes of seven constituents. It was found that the use of polyatomic primary ions in general resulted in a significant increase of secondary ion yields and secondary ion formation efficiencies of DNA‐specific fragments, while the highest values could be achieved with large bismuth cluster ions. It can also be shown that nonlinear effects in projectile‐surface‐excitation are partly responsible for the observed enhancements of yield and efficiency under polyatomic bombardment.It can be concluded that large bismuth cluster ions are the best choice for detecting hybridized DNA on PNA biosensor chips. Their application optimizes analysis conditions under which TOF‐SIMS provides a useful method for label‐free DNA diagnostics. Copyright © 2008 John Wiley & Sons, Ltd.