Tailor-designed AC electro-osmotic (AC-EO) stagnation flows are used to convect bioparticles globally from a bulk solution to localized dielectrophoretic (DEP) traps that are aligned at flow stagnation points. The multi-scale trap, with a typical trapping time of seconds for a one cc sample, is several orders of magnitude faster than conventional DEP traps and earlier AC-EO traps with disjoint electrodes. A novel serpentine wire resistor loop capable of sustaining a high field, up to 20,000 V/cm, is fabricated to produce strong AC electro-osmotic flow with two separated stagnation lines, one aligned with the field minimum and one with the field maximum. The continuous loop design allows a large applied voltage without inducing Faradaic electrode reactions. Particles are trapped within seconds at one of the traps depending on whether they suffer negative or positive DEP (n-DEP, p-DEP). The particles can also be rapidly released from their respective traps (and recaptured in the opposite traps) by varying the frequency of the applied AC field below particle-distinct cross-over frequencies. Zwitter ion addition to the buffer allows further geometric and frequency alignments of the AC-EO and DEP motions. The same device hence allows fast trapping, detection sorting and characterization of a sample with realistic conductivity, volume and bacteria count.

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