Probing Nanocolloids–Nanochannel Electrokinetic Interaction by Impedance Spectroscopy: A New Biosensing Platform

We have designed and tested a combined nanochannel/nanocolloid biomolecule sensing platform based on a fundamental analysis of the underlying electrokinetic phenomena. The nanochannels are bounded by two micro-reservoirs to which the sample with dispersed nanocolloids are introduced. The nanocolloids are then driven electrophoretically, electro-osmotically or dielectrophoretically into the channel. Depending on the relative dimensions of the nanochannel cross-section, the nanocolloid size and the presence of hybridized molecules on the nanocolloids, the nanocolloids can accumulate at the nanochannel's entrance, pass through the nanochannel or even form a close-packed structure within the nanochannel [BMF 3 012001 (2009)]. Due to the small dimension of the channel, these events can significantly change the complex cross-channel impedance signal, as detected by the same microelectrodes that drove the nanocolloids into the nanochannels. Besides these non-linear characteristics associated with the nanocolloids, the nanochannels exhibit significant non-linear electrical responses of their own, such as vortex instability (PRL 101, 254501 (2008)), non-linear I-V curve (PRE 79, 046305 (2009)), voltage gating, channel cross-talk and current rectification effects. Understanding and being able to selectively filter and amplify the pertinent non-linear impedance signatures of this nanocolloid-nanochannel platform will be shown to provide sensitive biomolecular detection.