Thermally Stable Magneto-Plasmonic Nanoparticles for SERS with Tunable Plasmon Resonance

Abstract

Bifunctional magneto-plasmonic nanoparticles that exhibit synergistically magnetic and plasmonic properties are advanced substrates for surface-enhanced Raman spectroscopy (SERS) because of their excellent controllability and improved detection potentiality. In this study, composite magneto-plasmonic nanoparticles (Fe3O4@AgNPs) were formed by mixing colloid solutions of 50 nm-sized magnetite nanoparticles with 13 nm-sized silver nanoparticles. After drying of the layer of composite Fe3O4@AgNPs under a strong magnetic field, they outperformed the conventional silver nanoparticles during SERS measurements in terms of signal intensity, spot-to-spot, and sample-to-sample reproducibility. The SERS enhancement factor of Fe3O4@AgNP-adsorbed 4-mercaptobenzoic acid (4-MBA) was estimated to be 3.1 × 107 for a 633 nm excitation. In addition, we show that simply by changing the initial volumes of the colloid solutions, it is possible to control the average density of the silver nanoparticles, which are attached to a single magnetite nanoparticle. UV-Vis and SERS data revealed a possibility to tune the plasmonic resonance frequency of Fe3O4@AgNPs. In this research, the plasmon resonance maximum varied from 470 to 800 nm, suggesting the possibility to choose the most suitable nanoparticle composition for the particular SERS experiment design. We emphasize the increased thermal stability of composite nanoparticles under 532 and 442 nm laser light irradiation compared to that of bare Fe3O4 nanoparticles. The Fe3O4@AgNPs were further characterized by XRD, TEM, and magnetization measurements.

Magneto-plasmonic nanostructures for SERS: magnetite decorated by silver and gold nanoparticles

“…This interaction was described in our previous and other research works. 38,39 Meanwhile, the increase in the concentration of gold nanoparticles resulted in higher intensity of absorption for two visible plasmonic peaks at 550 nm and 720 nm. The explanation for the appearance of these two peaks is the same as for the AgNPs.…”

“…It was previously shown that the magnetic properties of nanoparticles contribute to a higher enhancement factor and narrower distribution of SERS intensities within a single sample and among the samples from different batches. 39 Fig. 8 demonstrates SERS spectra from 4-MBA modified nanoparticles of different compositions.…”

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

“…The wet chemical synthesis approach, outlined in our earlier work, generates magnetite cubes averaging around 50 nm in diameter. 9 The TEM image in Figure 3B demonstrates a uniform magnetite distribution. Conversely, pulsed laser ablation in liquid results in plasmonic nanoparticles of a higher average size with a broader distribution.…”

“…Then, 2.5 mL of 2 M KNO 3 (Reachem, Bratislava, Slovakia), 2.5 mL of 1 M NaOH (Carl Roth GmbH, Karlsruhe, Germany), and 5 mL of 8 mg/mL PEI (M w = 2500; Sigma-Aldrich, Steinheim, Germany) were added and magnetically stirred under a N 2 gas flow at 90 °C for 2 h. After the solution cooled, the magnetic nanoparticles were triple-washed with deionized water and decorated with either silver, gold, or silver−gold alloy nanoparticles according to the procedure described elsewhere. 9 To obtain hybrid nanoparticles (MPNPs), 10 mL of the plasmonic nanoparticles was mixed with 0.8 mL of the Fe 3 O 4 colloidal solution. After a 45 min ultrasound treatment, the decorated nanoparticles (termed Fe 3 O 4 @Ag, Fe 3 O 4 @Au, Fe 3 O 4 @Ag 80 Au 20 , and Fe 3 O 4 @Ag 50 Au 50 ) were collected by using a strong magnet and washed with distilled water three times.…”

Iron Oxide-Au Magneto-Plasmonic Heterostructures: Advances in Their Eco-Friendly Synthesis

“…For the selection and separation of biological and chemical molecules, the most commonly used method is Surface-Enhanced Raman Spectroscopy (SERS). As evidenced by several studies [ 75 , 76 , 77 , 78 ], the use of plasmonic nanoparticles, in particular Au NPs for their high chemical stability and their SPR support in the visible region, can significantly improve the SERS signal both in vitro and in vivo.…”