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Response of a conductive micromechanical cantilever placed in close proximity to a surface undergoing electrical excitation near the resonance frequency of the cantilever is influenced by the presence of microscopic dielectrics in the gap between the cantilever and the sample surface. The variations of the resonance response of unmodified cantilevers at gap distances below a few hundred nanometers are used to discern biomolecular differences of oligomeric nucleic acids in an array format without the use of extrinsic labels. The resonance response variation paves the way for the development of high throughput detection of biomolecular reactions, such as DNA hybridization reactions or antibody-antigen interactions without the use of external labels, in which the need is only to see the presence or absence of interaction. This dynamic method is simple, does not require immobilizing individual elements on a cantilever array, and is compatible with current generation DNA chips in which DNA spots are deposited in micro- and nanoarray format.