Hybrid magnetic nanoparticle/nanogold clusters and their distance-dependent metal-enhanced fluorescence effect via DNA hybridization

Abstract

To improve the metal-enhanced fluorescence (MEF) effect of nanogolds (AuNPs) and accurately detect specific DNA sequences via DNA hybridization, novel hybrid magnetic nanoparticles/nanogold clusters (HMNCs) were designed based on finite-difference time-domain simulation results and prepared by using Fe₃O₄ and nanogolds. The nanogolds outside the HMNC were then conjugated with thiol-terminated DNA molecules, thus DNA modified-HMNCs (DNA–HMNCs) were obtained. The size distributions of these nanostructures were measured by a Malvern size analyzer, and their morphology was observed via transmission electron microscopy (TEM). The ultraviolet (UV)-visible (vis) absorption spectra of the samples were recorded with a UV-2600 spectrophotometer. Fluorescence spectra and the MEF effect were recorded using a spectrophotofluorometer, and lifetimes were determined using a time-correlated single photon counting apparatus. The prepared HMNCs were stable in aqueous solutions and had an average diameter of 87 ± 3.2 nm, with six to eight AuNPs around a single Fe₃O₄ nanoparticle. Fluorescein isothiocyanate (FITC) tagged DNA–HMNC conjugates exhibited a significant MEF effect and could accurately detect specific DNA sequences after DNA hybridization. This result indicates their various potential applications in sensors and biomedical fields.