Graphene has been widely employed in immunodiagnostics [1-4] due to its increased surface area, low cost and high electrical conductivity. It is a two-dimensional planar sheet of sp2-bonded carbon atoms packed densely in a honeycomb crystal lattice. Although graphene has been synthesized by numerous procedures, its mass production is done by chemical vapor deposition (CVD) and chemical or thermal reduction of graphene oxide. There have been significant advances in the chemical modification of graphene, preparation of graphene nanocomposites and biomolecular immobilization strategies, where researchers have induced specific functional groups on graphene and bound it to the specific biomolecules.
Graphene nano platelets are commercially-available crystalline or flake form of graphite that consists of many graphene sheets stacked together. We have recently developed graphene nano platelets (GNPs)-based sandwich enzyme-linked immunosorbent assay (ELISA) procedure for the highly sensitive detection of human lipocalin-2 (LCN2) .GNPs, mixed with 3-aminopropyltriethoxysilane (APTES), were functionalized on 96-well microtiter plate (MTP) and bound covalently to the anti- LCN2 antibodies. The increased surface area provided by the GNPs-functionalization led to higher antibody immobilization density, which was responsible for significant signal enhancement that led to the highly sensitive detection of LCN2 in plasma, serum and whole blood. The dynamic range of the assay was 0.6-5120pg/ml, while the limit of detection was 0.5pg/ml. The developed assay had 80-fold higher analytical sensitivity and 3-fold lesser immunoassay duration than the commercial ELISA. Moreover, the antibody-bound MTPs were found to be highly stable for 8 weeks, which is appropriate for healthcare and industrial applications.
Graphene has been widely used for the detection of a wide range of analytes .It has immense potential for electrochemical biosensors as it enables the direct electron transfer between enzyme and electrode surface . Graphene-functionalized electrodes have superior analytical performance with negligible interference from physiological substances and drug metabolites, and excellent anti-biofouling [6,7].The intrinsic peroxidase activity of graphene oxide (GO) has been employed to develop a naked-eye colorimetric immunoassay for the detection of prostate specific antigen (PSA) . The capture anti-PSA antibody was immobilized onto the surface of magnetic bead, while the secondary anti-PSA antibody was bound to GO (GO-Ab2).