Daniel Evans and Dr. Aaron Hawkins, Electrical and Computer Engineering
At the current time, the most sensitive detection methods for biological molecules are based on fluorescent tags. This requires the use of optical sources and detectors as well as the introduction of a fluorophore that can be attached to a molecule of interest. In light of these challenges, my research goal was to create a sensitive method of detection based on electrical impedance measurements rather than optical measurements. In theory, this technique has the potential for providing a detection method that can be easily implemented on multiple parallel channels on a microfluidic chip.
My research was centered on being able to develop a method of detecting biological molecules in a microfluidic channel based on impedance measurements. Microfluidic channels have the potential of making “lab on a chip” technologies viable. Microfluidic channels are currently being fabricated in the Integrated Microelectronics Laboratory in the Clyde Building at Brigham Young University. The BYU channels can be made very small and with high densities on a chip. Electrical impedance measurements require only metal electrodes that can be attached above and below a channel.
The first step in my research was to attach the metal electrodes above and below the channel and reservoirs at both ends of the channel. This process turned out to be much more complicated than previously anticipated due to the small size of the microfluidic channels. After much experimentation with different types of solder paste and silver epoxy, a systemic procedure for attaching the electrodes was developed and documented. Attaching the reservoirs at the ends of the channel also proved to be a challenging task. I finally discovered that small rings of doubled sided tape could be used to hold the reservoirs in place. Additional strength was required so I developed a technique of applying epoxy around the base of the reservoirs after it was attached with the double sided tape.
The next step was to use the reservoirs to insert salt water of varying electrical conductivities into the channels. The purpose of this was to test our microfluidic detection structures. The salt water solutions with varying conductivities simulated different biological molecules. In order to perform these tests I had to know the exact conductivity of the salt water we were inserting into the microfluidic channels. To accomplish this I invented a clever technique to measure the conductivity of salt water. After troubleshooting our setup we were able to obtain experimental results that matched our expectations. We discovered that our system did not function is electric potential difference between the two electrodes was less than 2 voltages. We also discovered that our system had a very linear response at voltage differences greater than 3 volts. This was the expected behavior of the system and is what we wanted.
The third step was to modify an existing program that controlled the lab equipment. This program facilitated taking of thousands of measurements in a few seconds. The existing program which was modified was written using a visual programming language known as LabVIEW. After attempting to modify the existing LabVIEW program it became apparent that creating an entirely new program to perform the desired functions would be easier. A new program was created that controlled a function generator, spectrum analyzer, and a DC power supply. The collected data was saved to a file and than post processed using Matlab.
The next step was to use our new setup to measure the time it took for our salt water that was inserted into the reservoir to be detected by our electrodes. In theory if the channel was filled with de-ionized water and salt water was added to one of the reservoirs an increase in the conductivity of the channel should be detected as time went on. Our major problem was that this was not always the case. Sometimes produce the desired expected results but sometimes no change could be detected. I believe the problem was that the solutions we were putting into the channel were not being moved through the channel. The channel itself appeared to be stagnant which consequently ruined our hope of detecting molecules as they passed by the electrodes. Some technique must be developed to move the solutions through the channel.
The final step was to use the reservoirs to run amino acids through the microfluidic channel and try to measure the instant they passed by the electrodes. This step was never attempted because of less than satisfactory results with the salt water.
We still have not obtained the results that we need in order to publish a paper. Research is on going to develop a way to move molecules through the channel. Significant accomplishments were made but lots of research work still remains to be done.
I was able to develop and document procedures to attached electrodes and reservoirs to the mircofluidic channels. I was able to detect changes in the conductivity of the channel depending on the solution that was inside. I was able to write a program that controlled several bench top pieces of equipment in order to take automated measurements.