Manipulating Nanoparticles and Enhancing Spectroscopy with Surface Plasmons

Professor Ken Crozier
Harvard University

Thursday, April 22, 2010 at 3:00pm
Engr IV Maxwell Room 57-124

Abstract
Field enhancement from surface plasmon structures presents new opportunities for optical manipulation and surface enhanced Raman spectroscopy (SERS). We demonstrate the propulsion of gold nanoparticles using surface plasmon polaritons (NanoLetters 9, 2623 (2009)). SPPs are excited on a thin gold film. The resultant evanescent field draws nanoparticles toward the film, where they are propelled along by the optical scattering force. We describe related work on optical tweezers based on holographic diffractive lenses (Fresnel zone plates). We show that these offer comparable performance to conventional optical tweezers (APL 92, 071112 (2008)), but with considerably smaller footprints. We present an array of zone plates integrated into a microfluidic chip, capable of analysis of nearly 200 000 fluorescent drops per second (Lab on a Chip, in press). We describe our work on metal nanoparticle substrates for SERS. Arrays of metal nanoparticles are often used for SERS, but the interactions between nanoparticles are frequently overlooked. We demonstrate that periodic metal nanoparticle arrays can exhibit spectrally-narrow surface plasmon resonances, with numerical simulations predicting considerably enhanced optical near-fields (APL 93, 181108 (2008)). To conclude, we describe a novel SERS substrate consisting of a metal nanoparticle array separated from a gold film by a thin SiO2 spacer (Opt Lett 34, 244 (2009)). We show that the double plasmon resonances of these structures enable field enhancement at both pump and Stokes frequencies (ACS Nano, in press).

Biography
Ken Crozier is a John Loeb Associate Professor of the Natural Sciences at Harvard University. He received his undergraduate degrees in Electrical Engineering and Physics at the University of Melbourne, Australia. He was awarded the L.R. East Medal (university medal in engineering) by the University of Melbourne. He received his PhD in Electrical Engineering from Stanford University in 2003. He was a recipient of an NSF CAREER award in 2008.