Effect of electrode configuration on the sensitivity of nucleic acid detection in a non-planar, flow-through, porous interdigitated electrode.

Electrical impedance spectroscopy (EIS) sensors, though rapid and cost-effective, often suffer from poor sensitivity. EIS sensors modified with carbon-based transducers show a higher conductance, thereby increasing the sensitivity of the sensor toward biomolecules such as DNA. However, the EIS spectra are compromised by the parasitic capacitance of the electric double layer (EDL). Here, a new shear-enhanced, flow-through nonporous, nonplanar interdigitated microelectrode sensor has been fabricated that shifts the EDL capacitor to high frequencies. Enhanced convective transport in this sensor disrupts the diffusion dynamics of the EDL, shifting its EIS spectra to high frequency. Concomitantly, the DNA detection signal shifts to high frequency, making the sensor very sensitive and rapid with a high signal to noise ratio. The device consists of a microfluidic channel sandwiched between two sets of top and bottom interdigitated microelectrodes. One of the sets of microelectrodes is packed with carbon-based transducer material such as carboxylated single-walled carbon nanotube (SWCNT). Multiple parametric studies of three different electrode configurations of the sensor along with different carbon-based transducer materials are undertaken to understand the fundamental physics and electrochemistry. Sensors packed with SWCNT show femtomolar detection sensitivity from all the different electrode configurations for a short target-DNA. A 20-fold jump in the signal is noticed from the unique working electrode configuration in contrast to the other electrode configurations. This demonstrates the potential of the sensor to have a significant increase in detection sensitivity for DNA and other biomolecules.