Sensitive electrochemical immunosensor for cancer biomarker with signal enhancement based on nitrodopamine-functionalized iron oxide nanoparticles

A novel electrochemical immunosensor for sensitive detection of cancer biomarker prostate specific antigen (PSA) based on nitrodopamine (NDA) functionalized iron oxide nanoparticles (NDA-Fe3O4) is described. NDA-Fe3O4 was used both for the immobilization of primary anti-PSA antibody (Ab1) and as secondary anti-PSA antibody (Ab2) label. For the preparation of the label, mediator thionine (TH) was first conjugated onto NDA-Fe3O4 based on the amino groups of NDA, and then the amino group of TH was used to immobilize horseradish peroxidase (HRP) and Ab2. Due to the high amount of NDA anchored onto Fe3O4 surface, the loading of antibodies as well as mediator and enzyme onto NDA-Fe3O4 was substantially increased, which increased the sensitivity of the immunosensor. The resulting immunosensor displayed a wide range of linear response (0.005-50 ng/mL), low detection limit (4 pg/mL), good reproducibility and stability. The immunosensor was used to detect the PSA contents in serum samples with satisfactory results.