title: Attomolar Level Detection of Raman Molecules with Hierarchical Silver Nanostructures Including Tiny Nanoparticles between Nanosized Gaps Generated in Silver Petals.
abstract: We developed a route for synthesizing Ag nanostructures with tunable morphologies for ultrasensitive surface-enhanced Raman spectroscopy. Through the consecutive addition of three reducing agents (i.e., 4-mercaptobenzoic acid, trisodium citrate, and ascorbic acid) to an aqueous solution of silver nitrate, hierarchical flower-like Ag nanostructures were produced. The nanostructures had Ag petals in which nanosized gaps were generated, and small Ag nanoparticles were incorporated within the gaps. Theoretically, the nanostructures exhibited highly enhanced electric fields in the outer-shell regions where the small Ag nanoparticles were densely located. Combining the enhanced field effect with resonance effect of a Raman-active molecule (methylene blue) at a specific wavelength, measurable Raman signals were obtained at concentrations as low as 100 attomolar (10(-16) M; corresponding to 10(-21) mol). Key factors were discussed for the synthesis of the Ag nanostructures while finely controlling the morphologies of hierarchical Ag nanostructures, thereby modulating the intensity of surface-enhanced resonance Raman spectroscopy (SERRS) signals. Therefore, this synthetic method produces highly promising nanostructures for SERRS-based applications.
authors.affiliation: †School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637457, Singapore.
authors.forename: Anirban
authors.initials: A
authors.lastname: Dandapat
authors.affiliation: ‡School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 689-798, South Korea.
authors.forename: Tae Kyung
authors.initials: TK
authors.lastname: Lee
authors.affiliation: †School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637457, Singapore.
authors.forename: Yiming
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: ‡School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 689-798, South Korea.
authors.forename: Sang Kyu
authors.initials: SK
authors.lastname: Kwak
authors.affiliation: §Department of Chemical Engineering, Hanyang University, Seoul 133-791, South Korea.
authors.forename: Eun Chul
authors.initials: EC
authors.lastname: Cho
authors.affiliation: †School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637457, Singapore.
authors.forename: Dong-Hwan
authors.initials: DH
authors.lastname: Kim
keywords: SERRS; morphology tuning; nanoparticles incorporated branches; silver nanostructures; ultrasensitive detection