title: A conformation- and ion-sensitive plasmonic biosensor.
abstract: The versatile optical and biological properties of a localized surface plasmon resonance (LSPR) sensor that responds to protein conformational changes are illustrated. The sensor detects conformational changes in a surface-bound construct of the calcium-sensitive protein calmodulin. Increases in calcium concentration induce a 0.96 nm red shift in the spectral position of the LSPR extinction maximum (λ(max)). Addition of a calcium chelating agent forces the protein to return to its original conformation and is detected as a reversal of the λ(max) shift. As opposed to previous work, this work demonstrates that these conformational changes produce a detectable shift in λ(max) even in the absence of a protein label, with a signal:noise ratio near 500. In addition, the protein conformational changes reversibly switch both the wavelength and intensity of the resonance peak, representing an example of a bimodal plasmonic component that simultaneously relays two distinct forms of optical information. This highly versatile plasmonic device acts as a biological sensor, enabling the detection of calcium ions with a biologically relevant limit of detection of 23 μM, as well as the detection of calmodulin-specific protein ligands.
authors.affiliation: Department of Chemistry, Northwestern University, 2145 North Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: W Paige
authors.initials: WP
authors.lastname: Hall
authors.forename: Justin
authors.initials: J
authors.lastname: Modica
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Anker
authors.forename: Yao
authors.initials: Y
authors.lastname: Lin
authors.forename: Milan
authors.initials: M
authors.lastname: Mrksich
authors.forename: Richard P
authors.initials: RP
authors.lastname: Van Duyne
mesh_terms: D015374:Biosensing Techniques; D002147:Calmodulin / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry; D007477:Ions; D008968:Molecular Conformation; D020349:Surface Plasmon Resonance / Q000295:instrumentation*
chemical_list: D002147:Calmodulin; D002614:Chelating Agents; D007477:Ions