By Mark Dwortzan
Breakthroughs Could Bolster Point-of-Care Diagnosis of Infectious Diseases
Rapid, chip-scale, low-cost detection of viruses and other pathogens is of critical importance in treating infectious diseases, curbing the spread of pandemics and responding to potential bio-warfare agents, but today’s bio-detection technology falls short in many ways. Most diagnostic tests for bacterial and viral diseases are too expensive, time- and labor-intensive to be completed at point-of-care, leading many physicians to overprescribe antibiotics and miss opportunities to contain potentially lethal viral outbreaks.
But a major interdisciplinary research effort now underway at the College of Engineering (ENG) could change all that. In collaboration with researchers at the Boston University School of Medicine (BUSM) and with support from the BU Photonics Center, ENG faculty members and graduate students are advancing groundbreaking, nanoscale techniques to detect and diagnose infectious diseases quickly, easily and inexpensively.
“What’s unique about our efforts to advance bio-detection capability is the ongoing collaboration we have with renowned infectious disease experts and access to experimental facilities at the School of Medicine,” said Professor Selim Ünlü (BME, ECE, MSE). “The novel technologies we’re developing are applicable to a wide range of diseases.”
In pursuing this work, ENG researchers have helped place the Photonics Center at the forefront of groundbreaking research and technology development that addresses critical national defense needs in bio-detection. As a result, the National Science Foundation approved on March 1 the start of an Industry/University Cooperative Research Center for Biophotonic Sensors and Systems (CBSS) at the Photonics Center and the University of California at Davis Center for Biophotonics Science and Technology aimed at accelerating technology transfer and boosting U.S industrial competitiveness in this area. One of 50 such cooperative research centers across the country, CBSS is the only one focused on biophotonic sensors.
In projects organized by the Photonics Center, Ünlü and Assistant Professor Hatice Altug (ECE, MSE) have already produced distinct biosensor platform prototypes that offer dramatic improvements in pathogen detection capability.
Developed by Ünlü’s research group in collaboration with Professor Bennett Goldberg (Physics, BME, ECE, MSE) and the MITRE Corporation, the Interferometric Reflectance Imaging Sensor (IRIS) is a highly sensitive nanoparticle device that can pinpoint single virus and other pathogen particles with unprecedented speed, accuracy and affordability. The shoebox-sized, battery-operated device is the first not only to provide high-throughput detection of single nanoparticles of interest, but also to measure their size—an important factor in confirming the identity of a suspected pathogen.
In a recent study described in Biosensors and Bioelectronics, a research team led by Ünlü, Goldberg and microbiologist John Connor (BUSM) used IRIS to demonstrate fast, user-friendly detection of VSV, a safe-for-humans “surrogate” virus genetically modified to model the behavior of hemorrhagic fever viruses such as Ebola and Marburg. In an earlier experiment conducted at the BU Medical Campus, IRIS also detected and sized individual, 100-nanometer diameter H1N1 virus.
“Our results show highly sensitive and specific virus detection with a simple surface chemistry and minimal sample preparation on a quantitative, label-free, interferometric platform,” said Ünlü. “Detection was rapid, repeatable, and demonstrates the potential of this system for inexpensive clinical and field-capable pathogen diagnostics.”
To detect and size pathogens, IRIS shines light from multi-color LED sources sequentially on nanoparticles bound to the sensor surface, which consists of a silicon dioxide layer atop a silicon substrate. Interference of light reflected from the sensor surface is altered by the presence of the particles, producing a distinct signal that reveals the size of each particle. Configured with a large surface area, the device can capture the telltale interferometric responses, in parallel, of up to a million nanoparticles.
In a separate collaboration with Professor John Connor, Altug’s research group has introduced a different kind of biosensor that rapidly detects live viruses from biological media with little to no sample preparation. Also using VSV, the group’s platform recently demonstrated reliable detection of hemorrhagic fever virus surrogates.
Altug’s new, highly sensitive biosensor platform 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 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 concentration of the virus in the solution.
“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, whose work recently garnered Young Investigator awards from both the Office of Naval Research and the IEEE Photonics Society.
The researchers are now working on a highly portable version of the biosensor platform using nano- and micro-fluidic technology designed for use in the field. They plan to subject the platform to initial tests on samples containing Ebola, Marburg, Lassa and other hemorrhagic fever viruses in the U.S., followed by additional tests in resource-limited countries in Africa where hemorrhagic fever outbreaks have occurred.
Altug has also advanced another biosensor platform that uses an array of gold “nano-antennas” to amplify infrared signals received from protein molecules by a factor of up to 100,000, thereby enabling studies from small samples often available from biological specimens.
Detection and Integration
Biosensor platform development at the College of Engineering spans all departments and reflects a wide range of pathogen detection and sample preparation strategies.
For example, Associate Professor Kamil Ekinci (ME, MSE) and Assistant Professor Luca Dal Negro (ECE, MSE) are advancing platforms that involve light-matter interaction.
Ekinci is designing diving-board-like cantilevers to detect trace amounts of pathogens in a fluid. The textured surfaces of these special cantilevers mitigate the inherent stickiness of water and other fluids, thus optimizing signals received from any pathogens onboard. If a pathogen attaches to one of Ekinci’s vibrating, nanoscale diving boards, the board will become heavier and its resonant frequency will decrease. By bouncing light or radio waves off these boards, he can detect this reduced frequency and thus detect the pathogen.
Dal Negro, using precisely-engineered arrays of metallic and silicon nanoparticles to boost the intensity of optical fields localized on two-dimensional surfaces, is developing a new platform for nanoscale optical sensing that could be used to detect molecules, proteins and harmful bacteria/viruses with greater reliability and lower error rates than current technology.
Two other ENG researchers, Associate Professor Catherine Klapperich (BME, ME, MSE) and Research Assistant Professor Mario Cabodi (BME), are incorporating microfluidic technology in biosensor platforms.
Klapperich is developing a robust, inexpensive, handheld plastic chip that extracts DNA using nanoparticles and could enable rapid, point-of-care diagnostics for infectious diseases such as influenza without the need for electricity or refrigeration. Integrating sample preparation, amplification and detection, this microfluidic chip could be a major step forward in facilitating molecular diagnostics in developing countries. Cabodi is working on the integration of a microfluidic sample preparation chip with interferometric biosensors.
The latter two projects reflect a growing capability and interest among College of Engineering bio-detection researchers to build integrated, point-of-care systems that combine sample preparation with the various sensor platforms they’ve been developing.
“We’re also focused on adapting these systems to detect diseases in resource-limited settings,” said Ünlü. “For instance, we are developing single-virus detection technologies so that HIV, dengue and other diseases can be identified at remote clinics, as well as compact systems for DNA extraction so that samples can be shipped without refrigeration for further diagnostic testing.”