Dielectrophoretic tweezers as a platform for molecular force spectroscopy in a highly parallel format

Miniaturization has driven down the cost of tools used in bioanalysis and diagnostics, with single molecules becoming the ultimate detection limit. Our aim is to build a force-spectroscopy-on-a-chip device that can detect and manipulate many (millions) single molecules in parallel. We demonstrate placement of single DNA molecules on a surface with controlled spacing and subsequent attachment of microscopic force probes to those molecules. We used dielectrophoresis (DEP) in a simple planar-electrode geometry as a form of molecular force spectroscopy in a highly parallel format. We determined the approximate crossover frequency between negative and positive DEP using electrodes without dielectric microstructures - a simplification over standard experimental methods involving quadrupoles or optical trapping. We applied the DEP tweezers to the stretching of a short DNA oligomer and detected its extension using total-internal reflection fluorescence microscopy. The combination of a simple device fabrication, molecule-bead alignment, uniform distribution of high axial forces, and simultaneous detection of molecular extensions makes DEP tweezers ideal for highly parallel detection of stretching or unbinding of biomolecules.