Magnetic Fe3O4@Au composite-enhanced surface plasmon resonance for ultrasensitive detection of magnetic nanoparticle-enriched α-fetoprotein.

Small molecules or analytes present at low concentrations are difficult to detect directly using conventional surface plasmon resonance (SPR) techniques because only small changes in the refractive index of the medium are typically induced by the binding of these analytes. Here, we present an amplification technique using core-shell Fe(3)O(4)@Au magnetic nanoparticles (MNPs) for an SPR bioassay. To evaluate this amplification effect, a novel SPR sensor based on a sandwich immunoassay was developed to detect α-fetoprotein (AFP) by immobilizing a primary AFP antibody (Ab(1)) on the surface of a 3-mercapto-1-propanesulfonate/chitosan-ferrocene/Au NP (MPS/CS-Fc/Au NP) film employing Fe(3)O(4)@Au-AFP secondary antibody conjugates (Fe(3)O(4)@Au-Ab(2)) as the amplification reagent. The stepwise fabrication of the biosensor was characterized using UV-vis spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. A calibration curve of Fe(3)O(4)@Au-Ab(2) conjugates amplification for AFP detection was obtained to yield a correlation in the range of 1.0-200.0 ng mL(-1) with a detection limit of 0.65 ng mL(-1), and a significant increase in sensitivity was therefore afforded through the use of Fe(3)O(4)@Au-Ab(2) conjugates as an amplifier. This magnetic separation and amplification strategy has great potential for the detection of other biomolecules of interest with low interference and high sensitivity by changing the antibody label used in the Fe(3)O(4)@Au-antibody conjugates.