Lab research may aid characterization and development of nanoparticles and sensing applications

July 12, 2010—The development of a full spectral, in-flow Raman instrument created by LANL researchers is a powerful new tool for nanomaterials development. The instrument has uses beyond traditional biological applications of flow cytometry. The capability could have an expanded role in the characterization and development of nanoparticles and sensing applications. In research that appears on the May 5 cover of the Journal of the American Chemical Societyi>, a LANL team that includes Steve Doorn of the Center for Integrated Nanotechnologies (MPA-CINT); Greg Goddard, John Martin, James Freyer, Steven Grave, and Robb Habbersett of Advanced Measurement Science, (B-9); and Leif Brown and Christina Brady of Chemical Diagnostics and Engineering (C-CDE) reports on this new capability.

Plasmonic nanoparticles functionalized with molecular dyes can be designed to provide stable and intense surface enhanced Raman (SERS) spectral fingerprint signatures. Changing the adsorbed dye molecule can vary the spectral signature of these "SERS tags," thus providing a route to advanced multiplexing in sensing applications. Such spectral tags have potential for applications in bioassays and imaging. However, development of the spectral tags has been limited by the lack of rapid, high-throughput characterization tools to correlate the observed spectral responses with particle structure for feedback into synthesis optimization.

The research team demonstrated flow-based instrumentation that directly addresses this problem. The new approach uses a modified flow cytometry platform to acquire full, high-resolution Raman spectra of single SERS-tag particles in applications-relevant detection times of 20 microseconds. Particle analysis rates can be as high as 100s to 1,000s of particles per second. The ability to compare spectral signatures and intensities for individual particles over large populations is needed to advance particle development and gain a fundamental understanding of their properties. By combining the Raman spectral measurements with simultaneously measured Rayleigh scattering intensities, variability in spectral response can be directly correlated to differences in SERS-tag geometries. The ability to measure SERS-tag properties at the single-particle level enables studies of new fundamental behaviors, including the first demonstration of SERS signal saturation and the occurrence of sub-populations of spectral response within a single nanoparticle preparation batch.

The new capability will aid the Laboratory's development of SERS tags for next generation bioassays by providing rapid feedback on synthesis strategies for spectral tag optimization. It also will allow a first-time direct particle-by-particle comparison of SERS response for different nanoparticle architectures. In addition, the unique sorting capability of flow cytometry will enable isolation of selected particle populations to permit analysis of SERS enhancements. LANL's Laboratory Directed Research and Development (LDRD) program funded the research. The technical contact is Steve Doorn.