Magnetic nanoparticle enhanced surface plasmon resonance sensor for estradiol analysis

An enhanced surface plasmon resonance (SPR) biosensor system using magnetic nanoparticles as amplifying element was developed for the real-time determination of estradiol (E-2) based on indirect competition method. The anti-estradiol monoclonal antibody (E-2-mAb) was conjugated with the magnetic nanoparticles (MNPs) via protein A for signal amplification to improve the detection sensitivity. The chitosan, spin-coated on the sensor chip surface, was used to immobilize the antigen (E-2-BSA) by glutaraldehyde. The chitosan could significantly improve the performance and stability of the immobilized E-2-BSA. During the detection, E2-BSA competed with E2 in samples for binding with the E-2-mAb-MNPs conjugates. Then the SPR response decreased in the presence of E-2 because E-2 prevented the combination of E-2-mAb-MNPs conjugates and E-2-BSA. In other words, the response of SPR sensor was inversely proportional to E-2 concentration. Assay parameters, such as the amount of antibody and MNPs, the amount of immobilized E2-BSA and E-2-mAb-MNPs concentration, were optimized in detail and E-2-spiked milk samples were detected. A good linear relationship was obtained between inhibition and lgC(E-2) ranging from 1.95 to 2000 ng/mL and the limit of detection (LOD) was 0.81 ng/mL. The result implied that the detection sensitivity was improved compared with the traditionnal sensor without magnetic nanoparticles. Meanwhile, an ELISA method was conducted to detect E-2 in milk as comparation with the enhanced SPR method, and the results indicated that these two methods had good consistency. The present study demonstrated a presumable general way and the enhanced sensors possessed a promising application for detection of various kinds of small molecules. (C) 2017 Elsevier B.V. All rights reserved.