Magnetic nanoparticles with fluorescence and affinity for DNA sensing and nucleus staining

Most traditional fluorescent dyes have poor photostability and high toxicity. To address this problem, we modified magnetic nanoparticles (MNPs) with fluorescent Hoechst dye via covalent conjugation. The prepared MNPs were characterized by fluorescence spectrometry, transmission electron microscopy, Fourier transform infrared, and photon correlation spectrometry to verify their optical and chemical properties. Additionally, the pH effects of modification on the amide conjugation between Hoechst dye and MNPs were evaluated to maximize the conjugation efficacy. The Hoechst MNPs could target chromosome DNA and emit fluorescence after ultraviolet light irradiation. The nucleus of human embryonic kidney cells and rabbit corneal epithelial cells could be labeled within 1 min. The modified MNPs exhibited bright fluorescence and retained good magnetic properties. The influences of various parameters, such as salt effect and contact time, on the adsorption isotherms of ssDNA and plasmid DNA were investigated to understand the mechanism of nucleus labeling. The DNA adsorption behaviors of Hoechst MNPs followed the Langmuir isotherm model and the pseudo-second order kinetic model. The maximum adsorption values of ssDNA and pDNA were 1034 and 252 μg mg^-1 MNP, respectively, which were higher than those in the literature. The fluorescent properties and the specific DNA bind capacity make the developed MNPs promising for fluorescent labeling and DNA separation.