Magnetic nanoparticle enhanced surface plasmon resonance sensor for estradiol analysis

Abstract 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, E 2 -BSA competed with E 2 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 E 2 -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.