title: Silver and gold glyconanoparticles for colorimetric bioassays.
abstract: The color changes associated with the aggregation of metal nanoparticles has led to the development of colorimetric-based assays for a variety of target species. We have examined both silver- and gold-based nanoparticles in order to establish whether either metal exhibits optimal characteristics for bioassay development. These silver and gold nanoparticles have been stabilized with a self-assembled monolayer of a mannose derivative (2-mercaptoethyl alpha-d-mannopyranoside) with the aim of inducing aggregation by exploiting the well-known interaction between mannose and the lectin Concanavalin A (Con A). Both metal glyconanoparticles were determined to be ca. 16 nm in diameter (using TEM measurements). Aggregation was observed on addition of Con A to both silver and gold nanoparticles resulting in a shift in the surface plasmon absorption band and a consequent color change of the solution, which was monitored using UV-visible spectrophotometry. Mannose-stabilized silver nanoparticles at a concentration of 3 nM provide an assay for Con A with the largest linear range (between 0.08 and 0.26 microM). Additionally, the kinetic rate of aggregation of the silver-nanoparticle-based bioassay was significantly greater than that of the gold-nanoparticle system. However, in terms of sensitivity, the mannose-stabilized gold-nanoparticle-based assay was optimum with a limit of detection of 0.04 microM Con A, as compared with a value of 0.1 microM obtained for the mannose-stabilized silver nanoparticles. Additionally, a lactose derivative (11-mercapto-3,6,9-trioxaundecyl beta-D-lactoside) was used to stabilize gold nanoparticles to induce aggregation upon addition of the galactose specific lectin Ricinus communis agglutinin (RCA(120)). To examine the specificity of the bioassay, lactose-stabilized gold nanoparticles were mixed with a solution of mannose-stabilized silver nanoparticles to give an aggregation assay capable of detecting two different lectins. When either Con A or RCA(120) was added to the mixed glyconanoparticles, selective recognition of the respective natural ligand was shown by aggregation of a single metal nanoparticle. Centrifugation and removal of the aggregated species enabled further bioassay measurements using the second glyconanoparticle system.
authors.affiliation: School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich, Norfolk, NR4 7TJ United Kingdom.
authors.forename: Claire L
authors.initials: CL
authors.lastname: Schofield
authors.forename: Alan H
authors.initials: AH
authors.lastname: Haines
authors.forename: Robert A
authors.initials: RA
authors.lastname: Field
authors.forename: David A
authors.initials: DA
authors.lastname: Russell
mesh_terms: D000373:Agglutinins / Q000032:analysis; D003124:Colorimetry / Q000379:methods; D003208:Concanavalin A / Q000032:analysis; D006001:Glycoconjugates / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D008024:Ligands; D008358:Mannose / Q000031:analogs & derivatives* / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D012680:Sensitivity and Specificity; D012834:Silver / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D000373:Agglutinins; D006001:Glycoconjugates; D008024:Ligands; D003208:Concanavalin A; D012834:Silver; D006046:Gold; D008358:Mannose