title: Sub-monolayer silver loss from large gold nanospheres detected by surface plasmon resonance in the sigmoidal region.
abstract: Nanosilver becomes labile upon entering the human body or the environment. This lability creates silver species with antimicrobial properties that make nanosilver attractive as active components in many consumer products, wound dressings, and agricultural applications. Because lability depends strongly on morphology, it is imperative to use a material with constant lability throughout kinetic studies so that accurate lability data can be acquired with efficient detection. Here 2.5nm thick silver was coated onto 90-nm diameter gold nanosphere cores and this surface silver layer was gradually removed by either chemical or X-ray radiation etching. The most sensitive region of a sigmoidal surface plasmon resonance (SPR) response as a function of silver thickness was found for the first time between 0.9- and 1.6-nm thick silver, revealing a new nanosilver standard for lability studies. The SPR peak position detection sensitivity is 8nm (SPR peak shift)/nm (silver thickness change) within this steepest region of the plasmon response curve whereas outside, sensitivity drops to 1nm/nm. Since the centroid of SPR profiles can be discerned with 0.25nm precision, the 8-nm/nm sensitivity means it is possible to detect a 0.3-angstrom or sub-monolayer change in silver thickness. The SPR response simulated by discrete dipole approximation (DDA) was an identical sigmoidal function between 0 and 2nm of silver coating. These findings were supported by several other analytical measurements, which confirmed no silver recoating during these etching processes.
authors.affiliation: Department of Chemistry, University of California, Davis, CA 95616, United States.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Lien
authors.affiliation: Department of Chemistry, University of California, Davis, CA 95616, United States.
authors.forename: Kristin A
authors.initials: KA
authors.lastname: Peck
authors.affiliation: Department of Chemistry, University of California, Davis, CA 95616, United States.
authors.forename: Mengqi
authors.initials: M
authors.lastname: Su
authors.affiliation: Department of Chemistry, University of California, Davis, CA 95616, United States. Electronic address: tguo@ucdavis.edu.
authors.forename: Ting
authors.initials: T
authors.lastname: Guo
mesh_terms: D006046:Gold / Q000737:chemistry*; D015394:Molecular Structure; D054118:Nanospheres / Q000737:chemistry*; D010316:Particle Size; D012834:Silver / Q000737:chemistry*; D020349:Surface Plasmon Resonance; D013499:Surface Properties
chemical_list: D012834:Silver; D006046:Gold
keywords: Core-shell nanoparticles; Exponential phase; Nanosilver; SPR sensing; SPR-thickness response; Sigmoidal response; Surface plasmon resonance (SPR); Surface silver; Thin silver shell