Ultrasensitive detection of prostate specific antigen (PSA) has been achieved by applying the field-effect enzymatic detection (FEED) technique to the sandwich immuno-sensing technique. The voltage-controlled intrinsic amplification provided by FEED enabled the detection of PSA contained in serum on the femto-gram/mL level. Two electrochemical approaches used to obtain the amperometric detection signal resulted id similar detection limits and sensitivities. The lowest PSA detection limit achieved was 27 fg mL(-1). The high selectivity of the detection system was reflected in the fact that PSA detection was successful on the fg mL(-1) level, where biological substances other than PSA had a 1-million-fold higher concentration. Electron transfer through the immunological sandwich nanostructure has been observed in the detection of biomarkers. However, our results showed that electron transfer through the nanostructure could be controlled using an external voltage, leading to an ultralow detection limit for PSA. (C) 2013 Elsevier Ltd. All rights reserved.