Colorimetric detection of cancer biomarker based on pH induced color change

A simple, easy, colorimetric immunoassay for cancer biomarker prostate specific antigen (PSA) is reported based on pH induced color change. Glutathione functionalized gold nanoparticles (Glu-AuNPs) were prepared and used as label for the immunoassay, while dopamine anchored Fe3O4 (DA-Fe3O4) was selected to immobilize anti-PSA antibody (Ab1). AuNPs and Fe3O4 were further assembled into immuno-complex in the presence of PSA. After the separation of the immuno-complex using magnet, the left AuNPs was mixed with methyl red solution and displaying colors. Different colors corresponding to different concentrations of PSA can be directly detected with eyes. This novel immunoassay has great potential to the detection of other cancer biomarkers.