Magnetically-controllable hollow multi-shell magnetite spheres as stable and reusable SERS substrates

Abstract

This study successfully synthesized magnetically-manipulatable and reusable SERS active buoyant substrates, i.e. Ag@SiO 2 @Fe 3 O 4 composite hollow spheres. The composites comprised mesoscopic hollow spheres with a Fe 3 O 4 inner shell of 15-30 nm in thickness and strong ferromagnetism, which were synthesized using spray pyrolysis and the subsequent reduction, and a SiO 2 outer shell to maintain the stability of Fe 3 O 4 , as well as Ag nanoparticles on the sphere surface providing localized surface plasmon resonance. The coercive field (H c ) of bare Fe 3 O 4 hollow sphere reached 200 Oe, and the saturation magnetization (M s ) was 130 emu/g at 300 K, which was at least 30% higher than the reported values no matter in bulk or nanoscales. Compared to composite spheres with Fe 3 O 4 solid cores, the SERS signal intensity of hollow structures was 2.6 times greater, which could be attributed to the buoyancy of hollow structure which contribute to more interaction with the target analytes. Under external magnetic field, these ferromagnetic hollow composites can be concentrated and separated easily, resulting in a more augmented SERS effect (about 1.5 times higher than those collected without applying magnetic field). This study also demonstrated the possibility to reuse those composites for SERS measurements.

Magnetic MOF Substrates for the Rapid and Sensitive Surface-Enhanced Raman Scattering Detection of Uranyl

“…Magnetic SERS substrates have been extensively used for the detection of contaminants because the analytes can be easily separated and enriched from the sample. Further, the SERS intensity can be enhanced with an external magnet. − To verify the influence of an external magnetic field, 10 points were randomly selected on the substrate with or without using a magnet. By placing an external magnet under the silicon wafer (Figure c), the FA@ZIF-8 substrate was concentrated in the center of the droplet.…”

SERS hotspot engineering using external field assembly of a plasmonic magnetic nanocomposite with high sensitivity and uniformity

“…The uniformity of SERS signals was approximately 10fold, and the signal intensity was approximately 27-fold higher aer modulating the substrate distribution with magnets, consistent with previous reports. [11][12][13]25 In the absence of magnetic modulation, the widely separated nanoparticles resulted in a scattered and inhomogeneous hotspot distribution. By contrast, the presence of an external magnetic eld decreased the spacing between the FA particles, leading to plasma formation on the surface of the substrate and enhanced electromagnetic elds between the AuNPs.…”

“…The ability to reuse magnetic nanoparticles (MNPs) not only promotes economic efficiency but also aligns with ecological sustainability by reducing both costs and the environmental impact. [4][5][6][7][8][9][10][11][12][13][14][15][16] Despite its potential, the practical application of magnetic SERS in realworld scenarios is hampered by a trio of formidable challenges: the inconsistent reproducibility across different batches, concerns over substrate stability, and the inherent nonuniformity of hotspot distribution. 17 To address these issues, recent advances have shied focus toward the integration of plasmonic magnetic nanocomposites with external elds to manipulate hotspot formation and positioning.…”

Composites of ZIF-67 MOF Nanostructures and CoFe2O4 Magnetic Nanospheres Both Decorated with Ag Nanoparticles as SERS Carboxylesterase 1 Sandwich Assay Immunosensors

“…The combination of magnetic materials and precious metals Au and Ag, due to their good magnetic properties, can not only achieve rapid separation and easy recycling but also achieve high detection sensitivity. 6 Fan et al 7 reported a magneto-plasmonic Ag−Fe 3 O 4 nanocomposite that could modulate and enhance the SERS activity, but the inhomogeneous distribution of AgNPs resulted in unsatisfactory repeatability and reproducibility of the SERS signal. Han et al 8 prepared recyclable magnetic Fe 3 O 4 @Au core−shell nanocomposites as SERS substrates and used them for thiram detection, but the detection sensitivity was insufficient.…”

“…Unfortunately, it is difficult to separate and recycle Au (Ag) from the solution and recycle it. The combination of magnetic materials and precious metals Au and Ag, due to their good magnetic properties, can not only achieve rapid separation and easy recycling but also achieve high detection sensitivity …”