title: Influence of Surfactant Bilayers on the Refractive Index Sensitivity and Catalytic Properties of Anisotropic Gold Nanoparticles.
abstract: Shape-controlled synthesis of gold nanoparticles generally involves the use of surfactants, typically cetyltrimethylammonium (CTAX, X = Cl(-) , Br(-)), to regulate the nucleation growth process and to obtain colloidally stable nanoparticles. The surfactants adsorb on the nanoparticle surface making further functionalization difficult and therefore limit their use in many applications. Herein, the influence of CTAX on nanoparticle sensitivity to local dielectric environment changes is reported. It is shown, both experimentally and theoretically, that the CTAX bilayer significantly reduces the refractive index (RI) sensitivity of anisotropic gold nanoparticles such as nanocubes and concave nanocubes, nanorods, and nanoprisms. The RI sensitivity can be increased by up to 40% by removing the surfactant layer from nanoparticles immobilized on a solid substrate using oxygen plasma treatment. This increase compensates for the otherwise problematic decrease in RI sensitivity caused by the substrate effect. Moreover, the removal of the surfactants both facilitates nanoparticle biofunctionalization and significantly improves their catalytic properties. The strategy presented herein is a simple yet effective universal method for enhancing the RI sensitivity of CTAX-stabilized gold nanoparticles and increasing their potential as transducers in nanoplasmonic sensors, as well as in catalytic and biomedical applications.
authors.affiliation: Division of Molecular Physics, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83, Linköping, Sweden.
authors.forename: Erik
authors.initials: E
authors.lastname: Martinsson
authors.affiliation: Department of Chemistry and Materials Science and Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA.|School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore.
authors.forename: Mohammad M
authors.initials: MM
authors.lastname: Shahjamali
authors.affiliation: Department of Chemistry and Materials Science and Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Large
authors.affiliation: Department of Chemistry and Materials Science and Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA.
authors.forename: Negin
authors.initials: N
authors.lastname: Zaraee
authors.affiliation: Department of Chemistry and Materials Science and Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Department of Chemistry and Materials Science and Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA.
authors.forename: George C
authors.initials: GC
authors.lastname: Schatz
authors.affiliation: Department of Chemistry and Materials Science and Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA.
authors.forename: Chad A
authors.initials: CA
authors.lastname: Mirkin
authors.affiliation: Division of Molecular Physics, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83, Linköping, Sweden.
authors.forename: Daniel
authors.initials: D
authors.lastname: Aili
keywords: catalysis; cetyltrimethylammonium; finite-difference time-domain; localized surface plasmon resonance; oxygen plasma