title: Light-Directed Reversible Assembly of Plasmonic Nanoparticles Using Plasmon-Enhanced Thermophoresis.
abstract: Reversible assembly of plasmonic nanoparticles can be used to modulate their structural, electrical, and optical properties. Common and versatile tools in nanoparticle manipulation and assembly are optical tweezers, but these require tightly focused and high-power (10-100 mW/μm2) laser beams with precise optical alignment, which significantly hinders their applications. Here we present light-directed reversible assembly of plasmonic nanoparticles with a power intensity below 0.1 mW/μm2. Our experiments and simulations reveal that such a low-power assembly is enabled by thermophoretic migration of nanoparticles due to the plasmon-enhanced photothermal effect and the associated enhanced local electric field over a plasmonic substrate. With software-controlled laser beams, we demonstrate parallel and dynamic manipulation of multiple nanoparticle assemblies. Interestingly, the assemblies formed over plasmonic substrates can be subsequently transported to nonplasmonic substrates. As an example application, we selected surface-enhanced Raman scattering spectroscopy, with tunable sensitivity. The advantages provided by plasmonic assembly of nanoparticles are the following: (1) low-power, reversible nanoparticle assembly, (2) applicability to nanoparticles with arbitrary morphology, and (3) use of simple optics. Our plasmon-enhanced thermophoretic technique will facilitate further development and application of dynamic nanoparticle assemblies, including biomolecular analyses in their native environment and smart drug delivery.
authors.forename: Linhan
authors.initials: L
authors.lastname: Lin
authors.forename: Xiaolei
authors.initials: X
authors.lastname: Peng
authors.forename: Mingsong
authors.initials: M
authors.lastname: Wang
authors.affiliation: Bionanoplasmonics Laboratory, CIC biomaGUNE , Paseo de Miramón 182, 20009 Donostia, San Sebastián, Spain.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Scarabelli
authors.affiliation: Department of Engineering Science and Mechanics, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Zhangming
authors.initials: Z
authors.lastname: Mao
authors.affiliation: Bionanoplasmonics Laboratory, CIC biomaGUNE , Paseo de Miramón 182, 20009 Donostia, San Sebastián, Spain.|Ikerbasque, Basque Foundation for Science , 48013 Bilbao, Spain.|CIBER de Bioingeniería, Biomateriales y Nanomedicina, CIBER-BBN , 20009 Donostia, San Sebastián, Spain.
authors.forename: Luis M
authors.initials: LM
authors.lastname: Liz-Marzán
authors.forename: Michael F
authors.initials: MF
authors.lastname: Becker
authors.forename: Yuebing
authors.initials: Y
authors.lastname: Zheng
keywords: nanoparticle trapping; photothermal effect; reversible nanoparticle assembly; surface plasmons; surface-enhanced Raman scattering; thermophoresis