A novel biosensor for ultrasensitive detection of prostate-specific antigen (PSA) was established based on gold nanorod (Au NR) dimers assembly. The circular dichroism signal was significantly amplified by a silver shell depositing on the surface of the Au NR dimers. A low limit of detection of 0.076 aM and high specificity were observed within the range of 0.1 to 50 aM target PSA. The developed biosensor has the potential to serve as a general platform for the detection of cancer biomarkers.