An Aligned Multi-Walled Carbon Nanotube Based DNA Biosensor

The research in this project represents a step towards the development of ultra-sensitive biosensors that will provide label-free, direct real-time electronic detection of DNA hybridization between surface immobilized single strand DNAs on multi-walled carbon nanotubes (MWCNTs) and target single strand DNA from a given bioagent. Simply put the nucleotide base pairs of DNA attached to the MWCNT will bind with complementary nucleotide base pairs of DNA from the bio or chemical agent to be detected. After successful hybridization, electrical properties such as resistance and conductivity of the MWCNT/DNA sensing element will change from its nominal values prior to the detection resulting in an electrically detectable output signal. The proposed research is high risk, but the potential payoff is tremendous. Successful results have the potential to catalyze rapid and innovative advances not only pathogen detection, but also other important areas including genomics, proteomics, and biomedical diagnostics. The desired target level of sensor sensitivity to achieve is considerably higher than traditional fluorescent and hybridization assays.

Currently a prototype MWCNT based DNA bio-sensor is being fabricated using surface micromachining techniques. The prototype sensor has been fabricated on a glass substrate. Gold electrical traces, contacts, and triangular electrodes are patterned on the glass substrate in order to align the MWCNT/DNA sensing elements through a process called AC dielectrophoresis. The MWCNT/DNA mixture is mixed with DI water and surfactant called Nanosperse, sonicated for a given time period in an ultra sonic bath, and then dispersed between the gold electrodes by using a micropipett. Once the mixture has been applied in the gap region between the electrodes the AC power supply/function generator is turned on and the proper peak to peak AC voltage and frequency is selected that will result in alignment. After a given period of time at a particular frequency and peak-to-peak voltage, alignment of the suspended MWCNT/DNA particles occurs resulting in electrical connection between the gold electrodes on each side of the gap. This biosensor will hopefully be integrated into a microfluidic system along with a CNT shear stress sensor to accurately detect biological agents and measure extremely low flow rates.