Metal-coated magnetic nanoparticles for surface enhanced Raman scattering studies

Abstract

We report the optimization and usage of surfactantless, water dispersible Ag and Au-coated γ -Fe 2 O 3 nanoparticles for applications in surface-enhanced Raman scattering (SERS). These nanoparticles, with plasmonic as well as super paramagnetic properties exhibit Raman enhancement factors of the order of 10 6 (10 5 ) for Ag (Au) coating, which are on par with the conventional Ag and Au nanoparticles. Raman markers like 2-naphthalenethiol, rhodamine-B and rhodamine-6G have been adsorbed to these nanoparticles and tested for nonresonant SERS at low concentrations. Further, to confirm the robustness of Ag-coated nanoparticles, we have performed temperaturedependent SERS in the temperature range of 77-473 K. The adsorbed molecules exhibit stable SERS spectra except at temperatures >323 K, where the thermal desorption of test molecule (naphthalenethiol) were evident. The magnetic properties of these nanoparticles combined with SERS provide a wide range of applications.

Synthesis and properties of magnetic-optical core–shell nanoparticles

“…27, 28, 33, 39, 49, 50 NH 2 OH is known to promote Au 3+ surface catalyzed reduction. 51 Thus, Au atoms are deposited only on the surfaces of IO NPs rather than forming self-nucleated Au NPs.…”

Surface enhanced Raman spectroscopy (SERS) for in vitro diagnostic testing at the point of care

“…When functionalized with sensing ligands, this allows for faster, more automated washing steps while also preventing sample sedimentation often seen with repeated centrifugation [29,163]. Magnetic nanoparticles can also provide a plasmonic response when coated in gold or silver [164], therefore improving SERS enhancement capabilities [165][166][167]. Many groups have facilitated this technique for improving clinical chemistry techniques recently, such as Wang et al who used aptamers immobilized onto silvercoated magnetic nanoparticles along with a secondary SERS active gold nanoprobe coated with another aptamer to capture and quantify bacterial cells down to 10 cells/ml [168].…”

Ferric plasmonic nanoparticles, aptamers, and magnetofluidic chips: toward the development of diagnostic surface-enhanced Raman spectroscopy assays

“…Finally, the particles were centrifuged three times to wash and redispersed in 6 mL of 5 mM sodium citrate. Silver-coated ferrite nanoparticles (Ag@Fe 2 O 3 ) were prepared using a coprecipitation method for the synthesis of the particle core and glucose reduction to coat with silver as described by Kumar et al 23 and Mandal et al, 24 respectively. Briefly, a stock solution of maghemite (γ-Fe 2 O 3 ) nanoparticles was prepared by adding 25 mL of an acidified iron salt solution (0.4 M Fe 2þ , 0.8 M Fe 3þ , 1 M HCl) drop-wise to 250 mL of 1.5 M NaOH at 50°C under vigorous nonmagnetic stirring.…”