Facile synthesis of Au nanoparticle-coated Fe3O4 magnetic composite nanospheres and their application in SERS detection of malachite green

Abstract

A facile method for synthesizing Au nanoparticle-coated Fe₃O₄ magnetic composite nanospheres (Fe₃O₄@Au MCS) via seed-mediated growth and iterative reduction is reported. The nanospheres were then successfully used to detect malachite green (MG) residues in water bodies via surface-enhanced Raman scattering (SERS) technique. Fe₃O₄@Au MCS has excellent optical properties and superparamagnetism; it can be dispersed into the solution to fully adsorb target molecules and then collected with a magnet to increase the molecular density and the number of SERS hot spots. Magnetic enrichment was superior to conventional detection method. The limit of detection for MG was 10^-7 M and the enhancement factor was 1.1 × 10⁵. The logarithm of the SERS intensity of the characteristic peak at 1618 cm^-1 exhibited a linear relationship with the logarithm of the MG concentration over the range of 10^-3- 10^-7 M, with a correlation coefficient of 0.966. The Fe₃O₄@Au MCS had good uniformity of SERS signals, with a 18.59% relative standard deviation for the SERS intensity. MG detection in aquaculture water conformed with the established quantitative regulations. The SERS spectrum calculated with density function theory for MG adsorbed on Fe₃O₄@Au MCS was very close to the experimental spectrum, which verified enhancement by the substrate. Overall, Fe₃O₄@Au MCS enabled ultrasensitive, quantitative SERS detection of MG.

Keywords: Density functional theory (DFT); Fe(3)O(4)@Au nanocomposite material; Magnetic enrichment; Malachite green (MG); Surface-enhanced Raman scattering (SERS).