Molecular dielectrophoresis (DEP) is employed to rapidly (<ms) trap ssDNA molecules in a flowing solution to a cusp-shaped nanocolloid assembly on a chip with a locally amplified AC electric field gradient. By tuning AC field frequency and DNA DEP mobility relative to its electrophoretic mobility due to electrostatic repulsion from like-charged nanocolloids, mismatch-specific binding of DNA molecules at the cusp is achieved by the converging flow, with a concentration factor about 6 orders of magnitude higher than the bulk, thus allowing fluorescent quantification of concentrated DNAs at the singularity in a generic buffer, at room temperature within a minute. Optimum flow rate and the corresponding hybridization rate change by nearly a factor of 2 with a single mismatch in the 26 base docking sequence and are also sensitive to the mismatch location. This dielectrophoresis and shear enhanced pico-molar sensitivity and SNP selectivity can hence be used for field-use DNA detection/identification.