Electrochemical immunosensors for cancer biomarker with signal amplification based on ferrocene functionalized iron oxide nanoparticles

Ultrasensitive sandwich type electrochemical immunosensors for the detection of cancer biomarker prostate specific antigen (PSA) is described which uses graphene sheet (GS) sensor platform and ferrocene functionalized iron oxide (Fe3O4) as label. To fabricate the labels, dopamine (DA) was first anchored onto Fe3O4 surface followed by conjugating ferrocene monocarboxylic acid (FC) and secondary-antibody (Ab2) onto Fe3O4 through the amino groups of DA (DA-Fe3O4-FC-Ab2). The great amount of DA molecules anchored onto Fe3O4 surface increased the immobilization of FC and Ab2 onto the Fe3O4 nanoparticle, which in turn increased the sensitivity of the immunosensor. GS used as biosensor platform increased the surface area to capture a great amount of primary antibodies (Ab1) and the good conductivity of GS enhanced the detection sensitivity to FC. Using the redox current of FC as signal, the immunosensor displays high sensitivity, wide linear range (0.01–40 ng/mL), low detection limit (2 pg/mL), good reproducibility and stability. In addition, this method could be extended to the immobilization of other interesting materials (fluorescence dyes) onto Fe3O4 for preparing various kinds of labels to meet the different requirements in immunoassays.