Roger Dettloff, Danielle Leiske, Andrea Chow, Javier Farinas
A label-free method for DNA sequencing based on the principle of the Millikan oil drop experiment was developed. This sequencing-by-synthesis approach sensed increases in bead charge as nucleotides were added by a polymerase to DNA templates attached to beads. The balance between an electrical force, which was dependent on the number of nucleotide charges on a bead, and opposing hydrodynamic drag and restoring tether forces resulted in a bead velocity that was a function of the number of nucleotides attached to the bead. The velocity of beads tethered via a polymer to a microfluidic channel and subjected to an oscillating electric field was measured using dark-field microscopy and used to determine how many nucleotides were incorporated during each sequencing-by-synthesis cycle. Increases in bead velocity of ∼ 1% were reliably detected during DNA polymerization allowing for sequencing of short DNA templates. The method could lead to a low-cost, high-throughput sequencing platform that could enable routine sequencing in medical applications.
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