Electroactive dendrimer-encapsulated silver nanoparticles for sensing low-abundance proteins with signal amplification

Abstract

A new electrochemical immunoassay strategy with signal amplification was designed for sensitive detection of free prostate-specific antigen (fPSA), using electroactive silver-mediated poly(amidoamine) (PAMAM) dendrimer nanostructures as molecular tags on the polyclonal rabbit anti-human PSA antibody (pAb₁)-modified screen-printed carbon electrode (SPCE). The molecular tag was first synthesized and functionalized with monoclonal mouse anti-human prostate-specific antibody (mAb₂). In the presence of target fPSA, a specific sandwich-type immunocomplex was formed on the functionalized SPCE, and the carried silver nanoparticles could directly catalyze the reduction of hydrogen peroxide in the detection solution without the participation of bioactive enzymes. Compared with silver nanoparticles alone, the presence of PAMAM dendrimer increased the immobilized amount of silver nanotags and enhanced the detectable signal of the electrochemical immunoassay. Two labeling protocols including silver nanoparticle-labeled mAb₂ and silver-PAMAM-labeled mAb₂ were implemented for the detection of fPSA, and improved analytical features were achieved with the silver-PAMAM labeling. Under the optimal conditions, the developed immunoassay enabled the determination of target fPSA with a wide dynamic range of 0.005–5.0 ng mL⁻¹ and a detection limit (LOD) of 1.0 pg mL⁻¹ (S/N = 3). The simple preparation and strong attachment of silver-PAMAM nanostructures with pAb₂ resulted in a good repeatability and intermediate reproducibility down to 7.5%. In addition, the accuracy of the electrochemical immunoassay was evaluated for the detection of 7 clinical serum specimens, achieved in good accordance with the referenced enzyme-linked immunosorbent assay (ELISA) method.