Characterizing Metal Nanoparticle Nanoassemblies
EMSL Project ID
3382
Abstract
Raman spectroscopy is capable of providing highly resolved vibrational information at room temperature and does not suffer from rapid photobleaching. However, Raman scattering is an extremely inefficient process with scattering cross sections (~10-30 cm2 per molecule) approximately 14 orders of magnitude smaller than the absorption cross sections (~10-16 cm2 per molecule) of fluorescent dye molecules. To achieve single-molecule sensitivity, the normal Raman scattering efficiency must be enhanced 1014 fold or more. Such enormous degrees of enhancement have been achieved using silver and gold nanoparticles. These particles are relatively large (>50 nm in diameter), faceted nanocrystals that are able to enhance the Raman scattering cross sections of adsorbed analyte molecules by as much as 1015 fold. This large enhancement allows both the detection and identification of single, nonfluorescent molecules. Currently, the overall molecular detection efficiency of these studies has been relatively low (<10% analyte molecules detected/analyte molecules in sample) because not all molecules are adsorbed, not all adsorbed molecules are surface-enhanced, and not all nanoparticles are SERS-active. Great strides towards producing efficient and reliable SERS-substrates can thus be made by improving nanoparticle synthesis, separation, and assembly methods. Our focus is on developing novel synthesis and assembly strategies to create highly SERS-active nanostructures to make ultrasensitive analytical measurements.
New strategies are required if highly SERS-active substrates are to be efficiently and reliably constructed. Our approach is to utilize preformed “scaffolds” such as latex microspheres or viral capsids to assemble preformed Ag or Ag-cladded Au nanoparticles into discrete nanostructures for ultrasensitive SERS spectroscopy. Students in my research group have successfully used such an approach to create SERS-active Ag/microsphere assemblies with improved detection efficiency. Improving SERS-active nanostructures by controlling nanometer-scale architecture will dramatically impact the analytical utility of SERS and facilitate SM-SERS studies.
A key component that my research group lacks at Western Washington University is the ability to fully characterize these SERS-active nanostructures using state-of-the-art microscopy techniques. Specifically, we propose obtaining electron micrographs of our Ag/microsphere assemblies using the scanning electron microscopes at the Interfacial and Nanoscale Science Facility (INSF). These nanostructures will first be prepared in my research laboratory at Western. Once a set of samples is compiled, I would take the samples to the INSF and analyze the sample under the guidance of an INSF staff member. Sample preparation and waste generation will be minimal.
Project Details
Project type
Exploratory Research
Start Date
2003-02-26
End Date
2005-03-25
Status
Closed
Released Data Link
Team
Principal Investigator