Surface plasmon fluorescence immunoassay of free prostate-specific antigen in human plasma at the femtomolar level

This study describes the development of a surface plasmon fluorescence spectroscopy (SPFS)-based sandwich immunoassay, for the detection of free prostate-specific antigen (f-PSA). The commercial CM5 chip (Biacore) was integrated into the SPFS-based assay making use of its three-dimensionally extended dextran architecture, which offers a large protein retention capacity and alleviates the metal-induced fluorescence quenching. The performance of the f-PSA assay was investigated in buffer and in human plasma, respectively. In the human plasma, the limit of detection of f-PSA was estimated to be ~80 fM for 40 min of contact time, which adequately meets clinical requirements.