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 (E2) based on indirect competition method. The anti-estradiol monoclonal antibody (E2-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 (E2-BSA) by glutaraldehyde. The chitosan could significantly improve the performance and stability of the immobilized E2-BSA. During the detection, E2-BSA competed with E2 in samples for binding with the E2-mAb-MNPs conjugates. Then the SPR response decreased in the presence of E2 because E2 prevented the combination of E2-mAb-MNPs conjugates and E2-BSA. In other words, the response of SPR sensor was inversely proportional to E2 concentration. Assay parameters, such as the amount of antibody and MNPs, the amount of immobilized E2-BSA and E2-mAb-MNPs concentration, were optimized in detail and E2-spiked milk samples were detected. A good linear relationship was obtained between inhibition and lgC(E2) ranging from 1.95 to 2000ng/mL and the limit of detection (LOD) was 0.81ng/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 E2 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.