Detecting HIV at the Molecular Level
Drexel Researchers Develop New Method for HIV Detection Using Nanopores
April 1, 2013 — Researchers at Drexel University are less than five years away from developing a hand-held, point-of-care device that can rapidly detect HIV and certain types of cancer. A rendering of their work will be featured on the cover of the May issue of the journal Small. In an accompanying article, the research team explained how they’re using nanopores to quickly detect HIV antigens at the molecular level.
Traditional HIV tests are usually conducted in two stages. Patients often first learn of results through a rapid HIV test or an ELISA (enzyme-linked immunosorbent assay) test in which patients receive either a “negative” or a “preliminary positive” result in as little as 20 minutes. However, most rapid HIV test must be confirmed with another test called a Western Blot, which often takes days or even weeks and is difficult to perform.
Freedman and the research team believe their method can accurately confirm or deny the presence of HIV antigens in less than two hours, which would replace the need for both rapid HIV tests and the Western Blot.
The benefit to the Drexel research team’s nanopore detection method lies in the number of molecules needed to confirm the presence of HIV. Older methods detect HIV by obtaining a noisy signal coming from millions of molecules, whereas this new method detects single molecules, one at a time, in a consecutive manner. The result is higher resolution sensing while using a lower concentration of molecules, which in turn leads to more rapid detection than previous technologies.
“This is really transformative. The novel bioanalytical platform enables us to allow characterization of HIV envelop proteins, especially for understanding the role of gp120 in drug resistance to viral inhibitors. Such a platform in molecular viral pathogenesis would enable novel investigation of heterogeneity of the pathogen population over the course of infection and disease progression or in response to drugs. In addition, we will be able to develop a fast, inexpensive HIV point-of-care device at the early stage”, said MinJun Kim, associate professor in the Mechanical Engineering and Mechanics Department and Principal Investigator of the project.
Development of this detection technology was conducted by Kevin Freedman, Ph.D. candidate in the Department of Chemical and Biological Engineering and Rosemary Bastian, Ph.D. candidate with the School of Biomedical Engineering, under the direction of MinJun Kim, an associate professor in the Mechanical Engineering and Mechanics Department and Principal Investigator on the project, and Irwin Chaiken, a professor with the Department of Biochemistry and Molecular Biology.
Kevin Freedman is the lead author of the research group’s paper featured in the Journal Small.
How does this device work?
The device is relatively simple. The functional sensing component of the device is a single nanopore
, which is essentially a hole within a very thin membrane; similar to a piece of paper with a small hole in it. The membrane is suspended on a silicon chip which is fabricated by the research team inside a clean room environment. An electrolyte solution is added to both sides, so you now have ions that float around on each side of the opening [nanopore]. When we applied an electric field, the ions in the solution move in the direction of the electric field. You can measure how many ions are going through the small opening by measuring the ionic current using custom electrodes. The molecule used to make the sensing specific to HIV proteins is called an antibody which binds specifically to a protein called gp120. When an antibody is added to one side of the membrane, it moves through the nanopore thereby blocking ions from entering the pore for a very short period of time. Once this signal is achieved, a patient sample can be mixed with the same antibody which then binds to the HIV proteins. When this larger complex moves through the pore, more ions are displaced causing even less current to be recorded. By examining the shape of that reduction you can determine the properties of the HIV protein and determine whether a person is HIV positive or healthy.
How do you detect HIV specifically?
The main molecule protein used is an antibody. You can design antibodies to bind any protein. In this case, we used an antibody that binds specifically to HIV antigens. That’s how we detect HIV specifically.
Why did you choose HIV?
We used HIV as a proof of concept, but you can essentially use our device to sense any disease protein marker. HIV is so prevalent in the world and the ability to have trained personnel with a laboratory in the middle of nowhere is kind of hard, so the need is very high. Also, we worked closely with collaborators here at Drexel who have a lot of expertise with HIV. They were able to answer a lot of our questions about the biochemistry of the proteins we were detecting.
So this method could be used to detect other diseases, such as certain types of cancers?
The methods that we employ could potentially use two different antibodies to detect several different diseases at a time, such as two different types of antigens for HIV or certain types of cancer. Essentially, you could do an entire biochemical panel of someone’s blood using our method. So it’s much more robust in that aspect. The only thing that really changes is the molecules that we use for detection.
What are the benefits to adopting this technique?
With this technique, we have the ability to gather more information in a shorter amount of time. It’s extremely beneficial. We can work in much lower concentrations, which allow us to detect things earlier and a lot of benefits come from that. For example, when you treat HIV and cancers, it’s more productive when it’s treated earlier on allowing the treatment to work more efficiently. Also, the voltage applied is very low, so the power requirements are low, offering the potential of a battery operated device that can be used in developing regions of the world. Compared to other techniques, you won’t really need to be trained to work in a laboratory to use it.
How far are we from seeing this type of device used by medical doctors?
One to five years. The device is very much in the early stages, but we hope to make it in to a lab-on-a- chip type technology. Ultimately, we hope to be able to package this in to a point-of-care device that can become an efficient input/output for detecting HIV [or other diseases], something that can be kept on a patient bedside to get results right away or to take in to a non-hospital setting such as developing countries.
What’s been the biggest challenge?
Convincing biochemists that this a good technique. Unless you’re familiar with nanopores and the signals that you get, convincing more traditional scientists to trust it is probably the biggest thing.
What was your reaction when you made the cover of Small?
I was very excited. Based on how well the images turned out, I had high expectations though. Nevertheless, I was still surprised and very happy that we were going to be on the cover.