Label free gravimetric detection of epidermal growth factor receptor by antibody immobilization on quartz crystal microbalance

An efficient and simple method for the detection of epidermal growth factor receptor (EGFR) using anti-EGFR immobilized quartz crystal microbalance (QCM) was developed. The immobilization of anti-EGFR on the gold surface of QCM electrode was constructed by a self-assembled monolayer (SAM) of thiosalicylic acid followed by the activation of 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). In order to assess the sensitivity of QCM, two analytical procedures namely, dip-and-dry and flow cell methods were investigated. Two different antibody immobilization patterns such as chemical cross-linking and site-specific via protein G were attempted. Accordingly, protein G mediated antibody immobilization controls the quantity and orientation of the antibody molecules on the electrode surface for its high affinity to antigens. Thus, a similar immobilization strategy was utilized for the flow-cell analysis of real-time binding of EGFR. A linear relationship was observed between the frequency shift and different EGFR concentrations (0.01-10 μg mL−1). The stepwise assembly of the immunosensor was characterized by quartz crystal microbalance. It was also demonstrated that, the prepared sensor surface was stable enough to withstand the repeated surface regeneration with 0.1 M NaOH.