A　new　digital　multimeter　(DMM)-based　immunosensing　system　was　designed　for　quantitative　monitoring　of　biomarker　(prostate-specific　antigen,　PSA　used　in　this　case)　by　coupling　with　an　external　capacitor　and　an　enzymatic　catalytic　reaction.　The　system　consisted　of　a　salt　bridge-linked　reaction　cell　and　a　capacitor/DMM-joined　electronic　circuit.　A　sandwich-type　immunoreaction　with　target　PSA　between　the　immobilized　primary　antibody　and　glucose　oxidase　(GOx)-labeled　detection　antibody　was　initially　carried　out　in　one　of　the　two　half-cells.　Accompanying　the　sandwiched　immunocomplex,　the　conjugated　GOx　could　catalyze　the　oxidation　of　glucose,　simultaneously　resulting　in　the　conversion　of　[Fe(CN)6]3-　to　[Fe(CN)6]4-.　The　difference　in　the　concentrations　of　[Fe(CN)6]3-/[Fe(CN)6]4-　in　two　half-cells　automatically　produced　a　voltage　that　was　utilized　to　charge　an　external　capacitor.　With　the　closing　circuit　switch,　the　capacitor　discharged　through　the　DMM,　which　could　provide　a　high　instantaneous　current.　Under　the　optimal　conditions,　the　resulting　currents　was　indirectly　proportional　to　the　concentration　of　target　PSA　in　the　dynamic　range　of　0.05-7ngmL-1　with　a　detection　limit　(LOD)　of　6pgmL-1.　The　reproducibility,　precision,　and　selectivity　were　acceptable.　In　addition,　the　methodology　was　validated　by　analyzing　12　clinical　serum　specimens,　receiving　a　good　accordance　with　the　referenced　values　for　the　detection　of　PSA.　©　2013　Elsevier　B.V.