title: Focused-ion-beam-fabricated Au nanorods coupled with Ag nanoparticles used as surface-enhanced Raman scattering-active substrate for analyzing trace melamine constituents in solution.
abstract: A well-ordered Au-nanorod array with a controlled tip ring diameter (Au_NRsd) was fabricated using the focused ion beam method. Au_NRsd was then coupled with Ag nanoparticles (Ag NPs) to bridge the gaps among Au nanorods. The effect of surface-enhanced Raman scattering (SERS) on Au_NRsd and Ag NPs/Au_NRsd was particularly verified using crystal violet (CV) as the molecular probe. Raman intensity obtained from a characteristic peak of CV on Au_NRsd was estimated by an enhancement factor of ≈10(7) in magnitude, which increased ≈10(12) in magnitude for that on Ag NPs/Au_NRsd. A highly SERS-active Ag NPs/Au_NRsd was furthermore applied for the detection of melamine (MEL) at very low concentrations. Raman-active peaks of MEL (10(-3) to 10(-12)M) in water or milk solution upon Au_NRsd or Ag NPs/Au_NRsd were well distinguished. The peaks at 680 and 702 cm(-1) for MEL molecules were found suitable to be used as the index for sensing low-concentration MEL in a varied solution, while that at 1051 cm(-1) was practical to interpret MEL molecules in water or milk solution bonded with Au (i.e., Au_NRsd) or Ag (i.e., Ag NPs/Au_NRsd) surface. At the interface of Ag NPs/Au_NRsd and MEL molecules in milk solution, a laser-induced electromagnetic field or hotspot effect was produced and competent to sense low-concentration MEL molecules interacting with Ag and Au surfaces. Accordingly, Ag NPs/Au_NRsd is very promising to be used as a fast and sensitive tool for screening MEL in complex matrices such as adulteration in e.g., food and pharmaceutical products.
authors.affiliation: Department of Materials Science and Engineering, National Cheng Kung University, 1 University Road, Tainan 70101, Taiwan.
authors.forename: Kundan
authors.initials: K
authors.lastname: Sivashanmugan
authors.forename: Jiunn-Der
authors.initials: JD
authors.lastname: Liao
authors.forename: Bernard Haochih
authors.initials: BH
authors.lastname: Liu
authors.forename: Chih-Kai
authors.initials: CK
authors.lastname: Yao
mesh_terms: D000818:Animals; D002417:Cattle; D006046:Gold / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D053768:Metal Nanoparticles / Q000737:chemistry*; D008892:Milk / Q000737:chemistry; D043942:Nanotubes / Q000737:chemistry*; D010316:Particle Size; D012834:Silver / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D014227:Triazines / Q000032:analysis*; D014867:Water / Q000737:chemistry
chemical_list: D007477:Ions; D012996:Solutions; D014227:Triazines; D014867:Water; D012834:Silver; D006046:Gold; C011907:melamine
keywords: Ag nanoparticles; Au-nanorods; Focused ion beam; Melamine; Surface-enhanced Raman scattering