Abstract
DNA conformational and mechanical properties play a significant role in determining DNA protein interactions and hybridization efficiency. Counterions differently screen the electrostatic charge carried by the DNA backbone affecting its curvature and flexibility. In order to improve the understanding of DNA conformation in crowded cellular environments and for the realization of more efficient biosensors, we analyse the collective response of DNA brushes to changes of ionic strength. We report here about an atomic force microscopy (AFM) study of the ionic effects on single stranded (ssDNA) confined monolayers tethered on ultra flat gold surfaces. We realized via Nanografting, an AFM-based lithography, micrometer sized brushes of short ssDNAs with controlled, variable surface density, confined inside a biorepellent self-assembled monolayer. Varying concentration and salt species (NaCl, KCl, CaCl2) inside the AFM liquid cell we monitored with high precision the corresponding ssDNA brush height variations. We will show the measured height can be related to scaling law of salt concentration with an exponent α =-1/6, in agreement with the theory of polyelectrolyte brush.
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