This was harnessed in an early assay of ours, where we lowered the limit of detection (LOD) of a cancer biomarker (prostate specific antigen, PSA) via the controlled overgrowth of Ag on Au nanostars.32 In other work we developed a plasmonic ELISA, where enzyme-mediated growth of AuNPs allowed extremely sensitive detection of HIV-1 capsid antigen p24.33 Similar to conventional ELISA, p24 was first captured on the plates using capture antibodies (human monoclonal anti-p24); then primary and secondary antibodies were added to link p24 to streptavidin–catalase conjugates selectively. This evidence concerns the gene KLK3 and cancer.