Metal nanoparticles for microscopy and spectroscopy

Metal nanoparticles interact strongly with light due to a resonant response of their free electrons. These ‘plasmon’ resonances appear as very strong extinction and scattering for particular wavelengths, and result in high enhancements of the local field compared to the incident electric field. In this chapter we introduce the reader to the optical properties of single plasmon particles as well as finite clusters and periodic lattices, and discuss several applications

An optically controlled microscale elevator using plasmonic janus particles

© 2015 American Chemical Society. In this article, we report how Janus particles, composed of a silica sphere with a gold half-shell, can be not only stably trapped by optical tweezers but also displaced controllably along the axis of the laser beam through a complex interplay between optical and thermal forces. Scattering forces orient the asymmetric particle, while strong absorption on the metal side induces a thermal gradient, resulting in particle motion. An increase in the laser power leads to an upward motion of the particle, while a decrease leads to a downward motion. We study this reversible axial displacement, including a hysteretic jump in the particle position that is a result of the complex pattern of a tightly focused laser beam structure above the focal plane. As a first application we simultaneously trap a spherical gold nanoparticle and show that we can control the distance between the two particles inside the trap. This photonic micron-scale >elevator> is a promising tool for thermal force studies, remote sensing, and optical and thermal micromanipulation experiments.Peer Reviewe