From bird flu to H1N1, outbreaks of fast-spreading viral diseases in recent years have sparked concern of pandemics similar to the 1918 Spanish flu that caused more than 50 million deaths. A significant fraction of today’s viral threats are viruses that use RNA to replicate and often produce symptoms that are not virus-specific, making them difficult to diagnose. Among them are hemorrhagic fever viruses, such as Ebola and Marburg, which could be used as bio-warfare agents. Critical to identifying and containing future epidemics of RNA-based viruses is the development of rapid, sensitive diagnostic techniques that healthcare providers can quickly deploy at multiple sites.
Traditional virus diagnostic tools such as ELISA and polymerase chain reaction (PCR) remain strong diagnostic options, but they require significant infrastructure and sample preparation time. Now a team of researchers led by Boston University Assistant Professors Hatice Altug (ECE) and John Connor (Microbiology, BUSM) has introduced a novel biosensor that directly detects live viruses from biological media with little to no sample preparation.
Partly funded through the Boston University Photonics Center and the U.S. Army Research Laboratory (ARL), and working in collaboration with the U.S. Army Medical Research Institute for Infectious Diseases, the team has demonstrated reliable detection of hemorrhagic fever virus surrogates (i.e. for the Ebola virus) and poxviruses (such as monkeypox or smallpox) in ordinary biological laboratory settings. The researchers report on this breakthrough in the November 5 online edition of Nano Letters.
“Our platform can be easily adapted for point-of-care diagnostics to detect a broad range of viral pathogens in resource-limited clinical settings at the far corners of the world, in defense and homeland security applications as well as in civilian settings such as airports,” said Altug. “By enabling ultra-portable and fast detection, our technology can directly impact the course of our reaction against bio-terrorism threats and dramatically improve our capability to confine viral outbreaks.”
Connor noted an additional, significant advantage of the new technology. “It will be relatively easy to develop a diagnostic device that simultaneously tests for several different viruses,” he observed. “This could be extremely helpful in providing the proper diagnosis.”
The new biosensor is the first to detect intact viruses by exploiting plasmonic nanohole arrays (PNAs), or arrays of apertures with diameters of about 250 to 350 nanometers on metallic films, that transmit light more strongly at certain wavelengths. When a live virus in a sample solution, such as blood or serum, binds to the sensor surface, the effective refractive index in the close vicinity of the sensor changes, causing a detectable shift in the resonance frequency of the light transmitted through the nanoholes. The magnitude of that shift reveals the presence and the concentration of the virus in the solution.
“Unlike PCR and ELISA approaches, our method does not require enzymatic amplification of a signal or fluorescent tagging of a product, so samples can be read immediately following pathogen binding,” said Altug. Ahmet Yanik, Altug’s research associate who conducted the experiments, added, “Our platform can detect not only the presence of the intact viruses in the analyzed samples, but also indicate the intensity of the infection process.”
The researchers are now working on a highly portable version of their biosensor platform using microfluidic technology designed for use in the field with minimal human interference. They plan to subject the platform to initial tests on samples containing Ebola, Marburg and other hemorrhagic fever viruses in the U.S., followed by additional tests in resource-limited countries in Africa where outbreaks of hemorrhagic fever occur.