Magneto-Plasmonic Nanoparticles Generated by Laser Ablation of Layered Fe/Au and Fe/Au/Fe Composite Films for SERS Application

Abstract

Magneto-plasmonic nanoparticles were fabricated using a 1064 nm picosecond-pulsed laser for ablation of Fe/Au and Fe/Au/Fe composite thin films in acetone. Nanoparticles were characterized by electron microscopy, ultraviolet-visible (UV-VIS) absorption, and Raman spectroscopy. Hybrid nanoparticles were arranged on an aluminum substrate by a magnetic field for application in surface-enhanced Raman spectroscopy (SERS). Transmission electron microscopy and energy dispersive spectroscopy analysis revealed the spherical core-shell (Au-Fe) structure of nanoparticles. Raman spectroscopy of bare magneto-plasmonic nanoparticles confirmed the presence of magnetite (Fe3O4) without any impurities from maghemite or hematite. In addition, resonantly enhanced carbon-based bands were detected in Raman spectra. Plasmonic properties of hybrid nanoparticles were probed by SERS using the adsorbed biomolecule adenine. Based on analysis of experimental spectra and density functional theory modeling, the difference in SERS spectra of adsorbed adenine on laser-ablated Au and magneto-plasmonic nanoparticles was explained by the binding of adenine to the Fe3O4 structure at hybrid nanoparticles. The hybrid nanoparticles are free from organic stabilizers, and because of the biocompatibility of the magnetic shell and SERS activity of the plasmonic gold core, they can be widely applied in the construction of biosensors and biomedicine applications.

Multiwavelength SERS of Magneto-Plasmonic Nanoparticles Obtained by Combined Laser Ablation and Solvothermal Methods

“…The most intense band at 731–733 cm –1 is associated with ring breathing motion, and its position is characteristic of Ag surface-adsorbed molecules rather than bulk adenine, whose Raman band appears around 723 cm –1 . , No such band was observed in the given concentration window of our experiment. Other notable bands included 625 cm –1 , assigned to ν­(C–C) mixed with the in-plane bending of adenine rings; 958 cm –1 , related to NH 2 rocking coupled with C–N stretching; 1331 cm –1 , assigned to ν­(C–N) and β­(CH); and 1398 cm –1 , related to ν­(C–C) and β­(CH). ,− The mode at 668 cm –1 is associated with the stretching motion of Fe–O of magnetite. No additional iron oxide phases, such as maghemite (broad spectral features at 350, 500, and 700 cm –1 ) or hematite (290 and 412 cm –1 ), were recognized from the spectra .…”

“…32 Organic solutions, however, contaminate the plasmonic nanoparticles with carbon species originating from the laser-induced thermal decomposition of the solvent. 31 In this study, we propose an MPNP synthesis method in which the plasmonic part is obtained by PLAL in saline water and the magnetic part is obtained by a wet chemistry synthesis method. Polyethylenimine mediates the nanoparticle attachment and formation of the hybrid MPNP structure.…”

“…Therefore, only a narrow concentration window of plasmonic material is practical for SERS. , Another issue with MPNP production using PLAL is that the ablation of an iron target is limited to organic solutions because ablation in water results in the formation of weak magnetization iron oxides, such as maghemite . Organic solutions, however, contaminate the plasmonic nanoparticles with carbon species originating from the laser-induced thermal decomposition of the solvent …”

“…There are several approaches for generating hybrid bimetallic nanoparticles by PLAL, e.g., the sequential ablation of two metal targets in the same liquid medium, which leads to the mixing and coalescence of two different material nanoparticles, although the quality of the process may sometimes be limited . Another way is to use layered thin films of different metals, which results in alloyed and complex nanostructures as the core–shell. ,− However, the alloying and dual structure formation are challenging to manage, and PLAL more often results in a mixture of different nanoparticle types, which translates into poor SERS enhancement. For example, MPNPs prepared by Fe and Au multilayer laser ablation exhibited an enhancement factor of 5.8 × 10 4 for the 4-mercaptobenzoic acid (4-MBA) reporter molecule .…”

“…Another way is to use layered thin films of different metals, which results in alloyed and complex nanostructures as the core–shell. ,− However, the alloying and dual structure formation are challenging to manage, and PLAL more often results in a mixture of different nanoparticle types, which translates into poor SERS enhancement. For example, MPNPs prepared by Fe and Au multilayer laser ablation exhibited an enhancement factor of 5.8 × 10 4 for the 4-mercaptobenzoic acid (4-MBA) reporter molecule . Moreover, in a bimetallic alloy having Au/Ag and Fe components, the LSPR was found to sharply decline with increasingly higher Fe concentrations (above approximately 15%).…”