Improved antibody loading on self-assembled graphene oxide films for using in surface plasmon resonance immunosensors

Immunoassays are important for the diagnosis of many diseases. Efficient methods for the immobilization of the biorecognition elements is a relevant subject because the antibody loading is directly related to the detection range and sensitivity. Here different self-assembled films were explored to take advantage of polar oxygenated groups from graphene oxide (GO) structure. Surface plasmon resonance (SPR) sensors were modified with different GO self-assembled films and compared to the well-established thiol-functionalization with 11-MUA (11-mercaptoundecanoic acid). Self-assembled cysteamine/GO functionalized sensor (Cys-GO(SA)) provided the highest protein loading (7.66 x 10(-12) mol cm(-2) against 1.29 x 10(-11) mol cm(-2) for the traditional thiolfunctionalization). The Langmuir-Blodgett (LB) films of GO were composed of aggregates and empty spaces, which hindered the antibody anchoring (around 6.38 x 10(-12) to 3.45 x 10(-12) mol cm(-2)). The SPR response of the Cys-GO(SA)-modified sensor to the 4.0 ng mL(-1) PSA was 125% higher than the thiol-functionalized sensor at the same concentration. This result indicates a simple and promising surface modification strategy for many important applications, not limited to SPR sensors, but for all immunoreaction-based assays as enzyme-linked immunosorbent assay (ELISA), electrochemical (e.g. amperometric and impedimetric) and quartz crystal microbalance (QCM) based sensors.