We report on the dynamic control over the orientation of short oligonucleotide strands which are tethered to gold surfaces in electrolyte solution. By applying alternating electrical bias potentials to the supporting electrodes we are able to induce a switching of the layer conformation between a "lying" and a "standing" state, simultaneously monitored in a contactless mode by fluorescence techniques. We demonstrate that our electrooptical experiments allow for an in-depth investigation of the intriguing molecular dynamics of DNA at surfaces and, moreover, how the dynamic response of these switchable biomolecular layers opens new prospects in label-free biosensing.
We report a method to detect label-free oligonucleotide targets. The conformation of surface-tethered probe nucleic acids is modulated by alternating electric fields, which cause the molecules to extend away from or fold onto the biased surface. Binding (hybridization) of targets to the single-stranded probes results in a pronounced enhancement of the layer-height modulation amplitude, monitored optically in real time. The method features an exceptional detection limit of <3 ؋ 10 8 bound targets per cm 2 sensor area. Single base-pair mismatches in the sequences of DNA complements may readily be identified; moreover, binding kinetics and binding affinities can be determined with high accuracy. When driving the DNA to oscillate at frequencies in the kHz regime, distinct switching kinetics are revealed for single-and double-stranded DNA. Molecular dynamics are used to identify the binding state of molecules according to their characteristic kinetic fingerprints by using a chip-compatible detection format.fluorescence ͉ sensor ͉ SNP ͉ affinity ͉ energy transfer
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