Lab researchers develop simple method to prepare nanostructured metals for sensing applications

June 2, 2010—Ping Xu, Nathan H. Mack, Sea-Ho Jeon, and Hsing-Lin Wang of the Lab's Physical Chemistry and Applied Spectroscopy group, Stephen Doorn of Center for Integrated Nanotechnology, and collaborators at the Harbin Institute of Technology in China have developed a novel synthetic platform for nanomaterials by using the conjugated polymer, polyaniline (PANI), as a reductive substrate.

Nanomaterials have potential in surface-enhanced Raman scattering (SERS) applications for ultrasensitive detection of chemical and biological molecules. However, fabricating the required nanomaterial platforms with controlled structures, homogeneity, and complexity is technically challenging. In their research, the Lab scientists tailored the surface chemistry to chemically deposit a wide range of nanostructured metals with various size, structures, and morphologies.

They used polyaniline for direct chemical reduction of metal ions to prepare metal nanostructures with well-defined morphology and size on gold-supported PANI membranes. This simple method enables fabrication of homogeneous silver (Ag) nanosheet assemblies with a well-defined three-dimensional structure on PANI membranes. The silver nanosheets that form the 3D structures are actually single thin-silver layers assembled by uniform silver nanoparticles. The thickness and size of the silver nanosheet layers can be modulated with the reaction time. The fabricated hybrid metal nanostructures display uniform surface-enhanced Raman scattering (SERS) responses throughout the entire surface area, with an average enhancement factor of 10⁶-10⁷.

The researchers conclude that the desired strong SERS response probably results from an electromagnetic enhancement that is common in metal structures with sharp edges, intersections, and bifurcations, where nanoscaled roughness generates high local fields. The nanocavities formed by the silver nanosheet stacks and the junctions and gaps between neighboring silver nanoparticles may serve as effective SERS electromagnetic hot spots. The highly uniform, enhanced SERS response throughout the nanomaterial assembly shows promise for application to sensitive detection of chemical and biological molecules.

Langmuir ASAP published the work online. The National Nanotechnology Entrepreneur Development Center, DOE Office of Basic Energy Sciences, and LANL Laboratory Directed Research and Development (LDRD) supported various aspects of the research.