Biosensing with a dual-size plasmonic ruler

Abstract

Nanoplasmonic biosensing is a field of nanotechnology and plasmonics wherein localized sur- face plasmon resonance(LSPR) is utilized in order to detect and measure structures at the nanoscale. This detection is based upon the measurement of the shift of the LSPR peak as induced by the adsorption of the species studied. A nanoplasmonic sensor,comprised of sil- ver nanodisks of two different sizes,as proposed and realised by the Langhammer Group at the department for Chemical Physics at Chalmers University of Technology,was used for the purpose of biosensing.The novel feature of this dual-size ruler is the determination of spatial dimension and refractive index of species adsorbed onto it,by virtue of taking the ratio of the LSPR shifts of the two peaks.Experiments were performed on two different molecular systems: 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine(POPC) with DNA and spherical lipid vesicles,and polylysine(PLL) with silica nanoparticles,with the goal being the deter- mination of the thickness of a thin film composed of these compounds.The experimental results with respect to thickness determination were not solid,although a key configurational change of the POPC bilayer was clearly distinguished. This points at the ruler having the ability and resolution to record structural changes in lipid membranes,which indeed is one of it’s visualized areas of application.In order to provide a solid proof-of-concept,a simpler molecular system should be studied,e.g. a spherically symmetrical nanoparticle deposited on top of POPC.