Magnetic Nanoparticle Enhanced Surface Plasmon Resonance Sensing and Its Application for the Ultrasensitive Detection of Magnetic Nanoparticle-Enriched Small Molecules

Magnetic nanoparticles (MNPs) have been frequently used in bioseparation, but their applicability in bioassays is limited due to their extremely small size so that sensitive detection is difficult to achieve using a general technique. Here, we present an amplification technique using MNPs for an enhanced surface plasmon resonance (SPR) bioassay. The amplification effect of carboxyl group modified Fe3O4 MNPs of two sizes on SPR spectroscopy is first demonstrated by assembling MNPs on amino group modified SPR gold substrate. To further evaluate the feasibility of the use of Fe3O4 MNPs in enhancing a SPR bioassay, a novel SPR sensor based on an indirect competitive inhibition assay (ICIA) is developed for detecting adenosine by employing Fe3O4 MNP−antiadenosine aptamer conjugates as the amplification reagent. The results confirm that Fe3O4 MNPs can be used as a powerful amplification agent to provide a sensitive approach to detect adenosine by SPR within the range of 10−10 000 nM, which is much superior to the detection result obtained by a general SPR sensor. Importantly, the present detection methodology could be easily extended to detect other biomolecules of interest by changing the corresponding aptamer in Fe3O4 MNP−aptamer conjugates. This novel technique not only explores the possibility of the use of SPR spectroscopy in a highly sensitive detection of an MNP-based separation product but also offers a new direction in the use of Fe3O4 MNPs as an amplification agent to design high performance SPR biosensors.