Carboxyl-functionalized graphene oxide composites as SPR biosensors with enhanced sensitivity for immunoaffinity detection

This work demonstrates the excellent potential of carboxyl-functionalized graphene oxide (GO–COOH) composites to form biocompatible surfaces on sensing films for use in surface plasmon resonance (SPR)-based immunoaffinity biosensors. Carboxyl-functionalization of graphene carbon can modulate its visible spectrum, and can therefore be used to improve and control the plasmonic coupling mechanism. The binding properties of the molecules between a sensing film and a protein were elucidated at various flow rates of those molecules. The bio-specific binding interaction among the molecules was investigated by performing an antigen and antibody affinity immunoassay. The results thus obtained revealed that the overall affinity binding value, K_A, of the Au/GO–COOH chip can be significantly enhanced by up to ∼5.15 times that of the Au/GO chip. With respect to the shifts of the SPR angles of the chips, the affinity immunoassay interaction at a BSA concentration of 1 μg/ml for an Au/GO-COOH chip, an Au/GO chip and a traditional SPR chip are 35.5 m°, 9.128 m° and 8.816 m°, respectively. The enhancement of the antigen-antibody interaction of the Au/GO–COOH chip cause this chip to become four times as sensitive to the SPR angle shift and to have the lowest antibody detection limit of 0.01 pg/ml. These results indicate the potential of the chip in detecting specific proteins, and the development of real-time in vivo blood analysis and diagnosis based on cancer tumor markers.