Maximizing surface-enhanced Raman scattering sensitivity of surfactant-free Ag-Fe3O4 nanocomposites through optimization of silver nanoparticle density and magnetic self-assembly

Abstract

Magnetic composite nanomaterials consisting of more than two functional constituents have been attracting much research interests due to the realization of multiple functionalities in a single entity. In particular, integration of ferromagnetic oxides and noble metal nanoparticles (NPs) in composites results in simultaneous magnetic activity and optical response where the optical property of the whole system could be modulated by application of an external magnetic field. In this work, we prepared Ag NPs-coated Fe 3 O 4 microspheres as a novel surfactant-free surfaceenhanced Raman scattering (SERS) substrate through a solid-phase thermal decomposition reaction. The SERS sensitivity of the fabricated nanocomposites is maximized by adjusting the size and density of Ag NPs supported on the Fe 3 O 4 microspheres and further increased by magneticfield-directed self-assembly of the composite substrates, with both effects attributed to the efficient generation of plasmonic near-field "hot" spots. At the optimal conditions, the prepared substrate is capable of detecting rhodamine 6G molecules at a concentration down to 10 À12 M, thus demonstrating the great potential of using bifunctional nanocomposites as an excellent candidate for ultra-high sensitive Raman spectroscopy and biosensors. We also reveal the underlying mechanisms responsible for the observed SERS enhancements through full-wave numerical simulations. V C 2013 AIP Publishing LLC. [http://dx

Magnetically Assembled SERS Substrates Composed of Iron–Silver Nanoparticles Obtained by Laser Ablation in Liquid

“…[36,51] However,our experiments showed that light scattering and absorption in the plasmonic spot could be detrimental to SERS analysis, if ac ritical NP concentration threshold was exceeded in the solution depositedfor the magnetic assembly. In this way,w eo bserved a2 8-foldi ncrement of the SERS signal collectedf rom the plasmonic spots, relative to the same NPs spotted on the glass slide without magnetic assembly or to ar eference of nonmagnetic pure Ag NPs.…”

“…[36] Interestingly,t heses ubstrates are achievable in ar eproducible ands calable way,a llowing the preparation of arrays of variable dimensions (varying the The widespreada pplication of surface-enhanced Raman scattering (SERS) would benefit from simple and scalable self-assembly procedures for the realization of plasmonic arrays with ah igh density of electromagnetic hot-spots. [51] In recent years,l aser ablation in liquid (LAL) has emerged as ar eliable approachf or the preparation of magnetic and plasmonic NPs in one step, even with unconventional structures or thermodynamically inhibited compositions. The use of laser ablation in liquid is key to achieving bimetallic NPs in one step with ac lean surface availablef or functionalization with the desired thiolated molecules.…”

Novel Nanobiosensing Using a Focused Laser Beam

“…Because this situation causes the interference signal due to SERS of surfactant molecules, the surfactant-free synthesis of nanoparticles is an important issue in SERS application (Bao et al 2013). We prepared Ag nanoparticles suitable for SERS measurement and optical trapping by an original synthesis method without surfactant.…”

Nanobiosensors and Nanobioanalyses

“…Because this situation causes the interference signal due to SERS of surfactant molecules, the surfactant-free synthesis of nanoparticles is an important issue in SERS application (Bao et al 2013). Because this situation causes the interference signal due to SERS of surfactant molecules, the surfactant-free synthesis of nanoparticles is an important issue in SERS application (Bao et al 2013).…”