Controllable Fe₃O₄/Au substrate for surface-enhanced infrared absorption spectroscopy

In this paper, the Fe₃O₄/Au nanocomposites were fabricated and employed as surface-enhanced infrared absorption (SEIRA) substrates. The superparamagnetic nature of Fe₃O₄/Au nanocomposites makes them suitable for controlled magnetic manipulation. The infrared absorption enhancements of Fe₃O₄/Au composite were improved as the magnetic field intensity increasing both for mercaptobenzoic acid and nitrobenzoic acid probe molecules. When the magnetic field intensities increase to 280 mT, the infrared enhancement could raise up to 3.3 and 10.7 times for -SH and -NO₂ groups, respectively. The enhancement is due to the synergy of localized surface plasmon resonance of Au and the magnetism of Fe₃O₄. Under the strong magnetic field, the superparamagnetic Fe₃O₄/Au nanoparticles are highly concentrated, leading to the increase number of SEIRA "active sites" and the surface density of Au nanoparticles. The synergistic effects of both Fe₃O₄ and Au nanoparticles make the composites an excellent SEIRA substrate. In addition, the Fe₃O₄/Au nanocomposites were also utilized to determine the thiol and thione tautomers in -SH based molecules.