Aug 20, 2009
Nanocomposite route to ultra-sensitive SERS substrates
Surface enhanced Raman spectroscopy (SERS) is a powerful technique for identifying molecules at very low concentrations. This capability is critical for many analytical applications such as forensics, medical diagnostics, drug discovery and chemical development. Extremely large enhancements in the SERS signal can occur when molecules are adsorbed onto suitably rough, noble metal surfaces, which feature appropriate nanostructures and morphologies.
In a recent paper published in Nanotechnology, researchers from the University of Oklahoma, the University of Illinois at Urbana-Champaign and the University of Arkansas at Little Rock (UALR) reported the fabrication of ultra-sensitive, stable SERS substrates that are promising candidates for the direct detection (label-free) and analysis of various biological and chemical samples.
The team uses a novel route to prepare its SERS substrates, which is based on polymer–metal nanocomposites with a specific structure and composition just below the percolation threshold. The neighboring nanoparticles are still quite densely packed, but remain separated by narrow polymer gaps (<1 nm). Such a nanostructure allows the creation of densely packed hot spots where electromagnetic energy can be confined.
The polymer–metal nanocomposites are fabricated by a simple and single-step method of electron-beam-assisted vapor-phase co-deposition. As shown above, the preparation of the SERS substrates is based on a simple plasma-etching process, which removes the polymer structures that allow the formation of metal nanoparticle SERS nano-aggregates with very uniform and controllable inter-particle gaps. The method results in "ideal SERS hot spots" throughout the matrix. These hot spots can be created over very large areas.
The SERS substrate developed by the researchers has a number of major advantages: it is easy to produce, highly reproducible and cheap. The method could be leveraged to develop large-scale spectroscopic-based advanced detector systems for rapid and quantitative detection and analysis of various biological and chemical samples.
The researchers plan to extend their investigations to prepare robust SERS substrates for detecting viral pathogens, chemical and biological warfare agents and explosives. Their goal is to develop portable SERS modules that take advantage of the capabilities of these advanced nanocomposite films.
About the author
Dr Abhijit Biswas is the lead researcher on the project. He is a research fellow based at the University of Oklahoma's Center for Semiconductor Physics in Nanostructures. Previously he worked as a senior scientist in the Office of Electronic Miniaturization at the University of Alaska at Fairbanks. Prof. Alexandru S Biris is the director/chief scientist of the University of Arkansas at Little Rock Nanotechnology Center. Dr Ilker S Bayer is a research assistant professor in the Department of Aerospace Engineering at University of Illinois at Urbana-Champaign. Dr Lloyd A Bumm is an associate professor in the Department of Physics and Astronomy at the University of Oklahoma. Daminda H Dahanayaka is a PhD candidate in the condensed matter research group of Prof. Lloyd A Bumm.