Detection of Three Different Estrogens in Milk Employing SPR Sensors Based on Double Signal Amplification Using Graphene

Abstract

A double signal enhanced surface plasmon resonance (SPR) biosensor system was developed, which involved graphene-based magnetic dispersion solid-phase extraction (MDSPE) and carboxylated graphene oxide (GO-COOH) materials as amplifying elements in order to achieve real-time determinations of estradiol (E2), diethylstilboestrol (DES), and bisphenol A (BPA) via an indirect competition method. In this work, the graphene-based MDSPE materials were synthesized using the chemical co-precipitation method, with a maximum enrichment efficiency of 500 times. To improve the detection sensitivity, the complete antigen (E2-BSA, DES-BSA, and BPA-BSA) was conjugated on the GO-COOH-modified gold chips for signal amplification. Furthermore, the GO-COOH materials could also significantly improve the performance and stability of the immobilized E2-BSA, DES-BSA, or BPA-BSA conjugations. Real-time SPR signals were obtained while mixing the targets (E2, DES, BPA) with anti-target monoclonal antibodies (E2-mAb, DES-mAb, BPA-mAb) at a 1:1 volume ratio. After optimizing the experimental conditions, the minimum detection limits (LOD) of E2, DES, and BPA were 3.605 × 10−6 ng/mL, 2.901 × 10−6 ng/mL, and 5.169 × 10−5 ng/mL, respectively. This simple, accurate, and stable method combined the advantages of two types of graphene materials to simplify the complicated pre-treatment and detection procedures. This study demonstrates a presumable and general method for detecting estrogen-like small molecules in the environment and in food.