(391a) A Mismatch-Discriminating Open-Flow Carbon Nanotube Electrochemical DNA Sensor

The development of detection devices according to market demands needs to be rapid, sensitive, low cost and portable for easy accessibility to consumers. Conventional lab based assays although offer single molecule sensitivity, employ bulky and expensive fluorescent detection units that require qualified professional for their operations. Herein, we present an open-flow diagnostic chip that allows for the examination of a large volume (~100 microliter) sample with a small number of target molecules. The unit has a simple electrochemical impedance-based DNA biosensor with dielectrophoretic entrainment of multiwall carbon nanotubes (MWNT) across interdigital electrodes to produce maximum hydrodynamic shear force. The nanotube backbone is functionalized with a complementary probe to study DNA hybridization within a microfluidic chip. This is achieved by linking an amino functionalized single-stranded DNA probe onto carboxylated MWNTs by using water-soluble carbodiimide chemistry by crosslinking ?NH2 and ?COOH groups. Before and after hybridization with the complementary DNA sequences, a change of impedance is observed due to docking of DNA on the surface of CNT. It is observed that the flow within the chip creates a large enough shear force to differentiate three-base mismatches when compared with DNA from targeted species and a closely related congeneric species having mismatches at positions 12, 21 and 22 of the 26 base tag sequences (reading from 5' to 3', respectively). Typically in most electrochemical impedance devices with DNA tagging on electrodes shows a Randle circuit wherein the double layer capacitance dominates near the detection frequency range complicating the measurement of hybridization events. Previous studies implemented various novel methods to overcome this limitation. However, in our case, the impedance characteristics show a Warburg Impedance at a high frequency, without interference from the parasitic double layer thus allowing a quantitative and qualitative scrutiny of the hybridization-sensitive charge transfer reaction on the MWNT. The detection time for the device is only 20 minutes. Thus, we demonstrate for the first time, a rapid and sensitive detection of hybridization events at picomolar (pM) concentrations of target DNA with shear enhanced discrimination in a label-free CNT based microfluidic platform.