Using Nanoscale Interdigitated Electrode Arrays to Detect Biomolecules

Diseases such as cancer and tuberculosis are still the leading causes of death in the world. Conventional methods of detecting such diseases are expensive, time consuming, incapable of on-site detection as they require skilled personnel and laboratory equipment for operation. This project aims to design and construct an inexpensive and portable biosensor to detect biomolecules associated with these diseases, which would greatly benefit diagnosis and containment.

Electrochemical Impedance Spectroscopy (EIS) is a method in which the target analytes are bound to a set of electrodes, creating a measurable change in capacitance. Interdigitated Electrode Arrays (IDAs) were used in this project due to their optimal geometry for the highest possible sensitivity. A majority of existing research on IDA sensors use a less sensitive microscale IDA, but for this project, the IDA fabrication step was avoided by modifying inexpensive and commercially available SAW chips to utilize their built-in nanoscale IDAs. Both salt molecules and specific DNA strands were tested, to investigate the sensitivity and effectiveness of the device.

Capacitance changes were measured using a probe system during salt measurements, but was replaced with a much more accessible capacitance sensor in later DNA tests. Four different salt solutions with concentrations ranging from 0.1mM/L to 100mM/L were dropped onto the modified SAW chip and it was concluded that because the sensor was able to detect even the lowest concentration of salt with a 0.005pf deviation, it had a high sensitivity. The next phase of the project involved immobilizing capture probe DNA strands onto the electrode surface using dry adsorption and dropping a solution containing complementary/non-complementary DNA onto the SAW chip. The surface was then washed with DI water to remove any non-attached particles. Qualitative observations were recorded with a microscope, and it was shown that the complementary DNA caused an increase of capacitance over the probe-modified SAW chip, while the non-complementary DNA caused a decrease.

It was concluded that the device created had a high performance with high sensitivity, range, and instant detection speed. In addition, the device was kept very accessible, being inexpensive and easy to use. The DNA detection of this project is still ongoing, but current results suggest that the device is capable of differentiating between strands of DNA.