Biomedical sensors using metal nanoparticles hold great promise for the early detection of disease. But the current class of sensors has little or no shelf life, and creating and using them is expensive.
Srikanth Singamaneni, PhD, assistant professor of materials science in the School of Engineering & Applied Science at Washington University in St. Louis, plans to develop a low-cost biosensor that is more stable, sensitive and specific with funds from a Faculty Early Career Development (CAREER) Award he has received from the National Science Foundation.
The prestigious awards support junior faculty who model the role of teacher-scholars through outstanding research, excellent education and the integration of education and research within the context of the mission of their organizations. Singamaneni, who focuses on biomedical applications of plasmonic nanostructures, is the 19th faculty member from the School of Engineering & Applied Science to receive a CAREER award since 1996.
With the five-year, $400,000 award, Singamaneni plans to create a novel class of biosensors based on self-assembled clusters of metal nanoparticles that have been imprinted with artificial antibodies specific to target biomarkers, which can be indicators of disease. The goal of the work is twofold: to clarify the nature of artificial antibody-antigen interactions, which will enable him and his team to devise new methods to identify monoclonal artificial antibodies that are highly specific to the target biochemical substances; and to design and fabricate self-assembled, hierarchical metal nanoparticle cluster arrays, which will serve as highly sensitive optical sensors and integrate artificial antibodies with such plasmonic nanocluster arrays.
"We intend to gain some fundamental understanding of how these artificial antibody interactions are happening," he says. "In particular, we are interested in identifying the physical and chemical factors that dictate the selectivity of the artificial antibodies. We're hoping that these experiments will help us to improve the specificity and sensitivity of these sensors we're trying to build."
Most of the previous work related to plasmonic biosensors is based on natural antibodies as target recognition elements. While these sensors are very sensitive and offer great promise for point-of-care diagnostics, natural antibodies have a short shelf life and are expensive and time-consuming to develop and apply. Addressing these issues, Singamaneni and the team used artificial antibodies to create the plasmonic biosensors. Artificial antibodies have been fabricated by a method called surface molecular imprinting.
This process involves attaching the target proteins to the surface of gold nanorods, then adding small molecules around the proteins to form a polymer layer around the outside of the nanorods. The target proteins are removed to leave cavities on the surface of the nanorods. When the nanorods with the artificial antibodies are exposed to a substance, such as urine, that contains the target protein, those proteins settle into the cavities. These antibodies are polyclonal antibodies, which can bind to a nanoparticle in any orientation.
In the new work funded by the CAREER award, Singamaneni plans to use a similar process, but this time use polyhistidine-tagged proteins to ensure that the artificial antibodies will bind to the nanoparticle in a very precise orientation, similar to a puzzle piece fitting into a jigsaw puzzle. This process would create monoclonal antibodies, or very specific antibodies designed to target a specific recognition site of the target protein.
"If we are successful, this will be the first time anyone has created monoclonal artificial antibodies on plasmonic nanostructures," Singamaneni says.
In addition, Singamaneni plans to study the binding interaction between the artificial antibodies and antigens at the molecular level using a technique called surface force spectroscopy.
"Our previous work of fabricating artificial antibodies directly on plasmonic nanostructures was a pioneering work – we were the first to do it," Singamaneni says. "That's why with this new class of sensors, we need to understand the basic science associated with it. We are trying to go after the unknowns so that the fundamental understanding that we gain through this project is applicable to almost any kind of protein-artificial antibody combination."
In another part of the project, Singamaneni plans to invite one or two high-school science teachers to spend a summer working in his lab to be immersed in nanotechnology. At the end of the two summers, Singamaneni, the teachers, and representatives of the university's Institute for School Partnership will formulate a curriculum to teach nanotechnology in Kindergarten through 12th grade.
"We are also hoping to develop a nanotechnology kit that we can market nationwide," he says. "Students would be able to work with nanoparticles in solutions with different pH so that they will see changes in colors. This will prompt discussion and get them interested in nanotechnology."
The School of Engineering & Applied Science at Washington University in St. Louis focuses intellectual efforts through a new convergence paradigm and builds on strengths, particularly as applied to medicine and health, energy and environment, entrepreneurship and security. With 82 tenured/tenure-track and 40 additional full-time faculty, 1,300 undergraduate students, 700 graduate students and more than 23,000 alumni, we are working to leverage our partnerships with academic and industry partners — across disciplines and across the world — to contribute to solving the greatest global challenges of the 21st century.
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