June 17, 2013 weblog
Combined team of physicists and biologists build Lyme disease detector using carbon nanotube sensor
(Phys.org) —A team made up of researchers from both the physics and biology departments at the University of Pennsylvania has succeeded in building a Lyme disease detector using a carbon nanotube sensor. In their paper published in the journal Biosensors and Bioelectronics, the team describes the process they used to make the device and how it works.
Lyme disease is an infection caused by several types of bacteria—generally tick-borne, the disease can cause permanent nerve damage if not detected early. Currently patients must undergo a two-stage process as part of a diagnosis. The first is called an ELISA assay—it uses antibodies and color changes to identify substances. Because it tends to sometimes produce false positives, patients must also undergo what is known as a Western blot test—a test for the specific bacteria that cause the disease. It too tends to result in the occasional false positive however, which is why researchers continue to look for a more accurate way to detect the presence of the bacteria that causes the disease.
In this new effort, the research team grew a large array of carbon nanotubes for use as sensors. Then using a new covalent-chemistry technique they developed they attached antibody proteins to the nanotubes. The antibodies attract and capture a type of protein found in the flagellum of bacteria that are the source of Lyme disease. The adhered protein causes a change in the how well the nanotube sensors are able to conduct electricity. By measuring changes in voltage, the researchers can determine if the bacteria are present in a single drop of blood.
Besides being more accurate than the current method of testing for Lyme disease, the new device also can give researchers a better idea of how highly concentrated the antigens are in a patient—allowing doctors to prescribe the right amount of medicine for treatment. The nanotube based detector can also detect the presence of the bacteria much earlier than the current method, helping to prevent nerve damage and other health problems.
The new sensor isn't ready to be used by doctors just yet of course, it must be put through rigorous testing first. Also, the team believes they can improve their detector by making it sensitive to just the pieces of the antibodies that are responsible for antigen bonding, instead of the whole protein.
We examined the potential of antibody-functionalized single-walled carbon nanotube (SWNT) field-effect transistors (FETs) to use as a fast and accurate sensor for a Lyme disease antigen. Biosensors were fabricated on oxidized silicon wafers using chemical vapor deposition grown carbon nanotubes that were functionalized using diazonium salts. Attachment of Borrelia burgdorferi (Lyme) flagellar antibodies to the nanotubes was verified by atomic force microscopy and electronic measurements. A reproducible shift in the turn-off voltage of the semiconducting SWNT FETs was seen upon incubation with B. burgdorferi flagellar antigen, indicative of the nanotube FET being locally gated by the residues of flagellar protein bound to the antibody. This sensor effectively detected antigen in buffer at concentrations as low as 1 ng/ml, and the response varied strongly over a concentration range coinciding with levels of clinical interest. Generalizable binding chemistry gives this biosensing platform the potential to be expanded to monitor other relevant antigens, enabling a multiple vector sensor for Lyme disease. The speed and sensitivity of this biosensor make it an ideal candidate for development as a medical diagnostic test.
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