# The optoelectric tunability effect of structurally patterned Fe3O4-Au assembly on Rhodamine 6G signals under Magneto-SERS measurements

## TL;DR

Researchers developed a tunable magneto-plasmonic system using Fe3O4-Au colloids to enhance Raman signals of Rhodamine 6G under magnetic fields.

## Contribution

A micro-patterned Fe3O4-Au thin film was created to demonstrate optoelectric tunability and enhanced SERS performance with magnetic field influence.

## Key findings

- A single Fe3O4-Au thin film with varying concentration ratios showed different optoelectronic behaviors.
- An external magnetic field increased R6G Raman peak intensity by 133% and improved spectral resolution.
- Magnetic polarization of Fe3O4 influenced Au plasmon electrons, tuning nearby analyte vibrations.

## Abstract

The magneto-plasmonic tunability property of magnetite-gold complex (Fe3O4-Au) colloids has garnered significant interest in bio-sensory applications like surface-enhanced Raman spectroscopy (SERS). In many studies, this tunability does not only depend on the external magnetic field contribution but also on the concentration ratio between Fe3O4 and Au. This would require multiple preparation of Fe3O4-Au colloidal badges. In this study, a magnetically stimulated Fe3O4-Au colloidal suspension in polyvinyl alcohol was spin-coated, forming a micro-patterned thin film on a silicon wafer substrate for assessing the SERS vibrational signal response of Rhodamine 6G (R6G). The varying concentration ratio between Fe3O4 and Au across three regions of interest within the single cast resulted in differing optoelectronic behaviour. Such was observed from diffuse reflectance UV-Vis-NIR spectroscopy measurements, and its impact on different Raman signals of R6G. The introduction of an external magnetic field also led to approximately 133% higher peak intensity and improved spectral resolution of R6G under SERS measurements. This implies that the magnetic field polarization of Fe3O4 domain electrons influences plasmon electrons of Au nanoparticles leading to tuning of electronic-influenced vibrations of nearby analyte molecules. The variability of nanoparticle concentration ratios, configurations and the magneto-optoelectronic effect of this design template, provide flexibility and tunability in diagnosing biomolecule signals under SERS.

The online version contains supplementary material available at 10.1038/s41598-025-21536-y.