Prostate-specific　antigen　(PSA),　one　of　the　indications　of　possible　prostate　malignancy,　is　used　as　a　biomarker　for　the　diagnosis　and　prognosis　of　prostate　cancer.　Herein,　we　develop　a　new　homogeneous　potentiometric　immunoassay　for　sensitive　detection　of　low-concentration　PSA　without　the　need　of　sample　separation　and　washing　step.　Two　nanostructures　including　positively　charged　polyethyleneimine-poly(styrene.　co-acrylic　acid)　(PEI-PSAA)　nanospheres　and　negatively　charged　gold　nanoparticles　conjugated　with　anti-PSA　antibody　(Ab-AuNP)　were　first　synthesized　by　using　mulsifier-free　emulsion　copolymerization　and　wet　chemistry　method,　respectively.　Thereafter,　the　as-prepared　PEI-PSAA　was　used　as　a　pseudo　hapten　for　the　construction　of　immunosensing　probe　based　on　an　electrostatic　interaction　between　PEI-PSAA　and　Ab-AuNP.　Upon　target　introduction,　the　added　PSA　competed　with　PEI-PASS　for　Ab-AuNP　based　on　a　specific　antigen-antibody　interaction,　and　displaced　Ab-AuNP　from　PEI-PASS.　The　dissociated　PEI-PASS　was　captured　through　the　negatively　charged　Nafion-　modified　electrode,　thereby　resulting　in　the　change　of　membrane　potential.　The　fabrication　process　was　characterized　by　using　high-resolution　transmission　electron　microscope　(HRTEM),　scanning　electron　microscope　with　energy-dispersive　X-ray　spectroscopy　(SEM-EDX),　surface　plasmon　resonance　(SPR)　and　dynamic　laser　scattering　(DLS)　technique.　Under　optimal　conditions,　the　output　signal　was　indirectly　proportional　to　the　concentration　of　target　PSA　in　the　sample　and　exhibited　a　dynamic　range　from　0.1　to　50.　ng/mL　with　a　detection　limit　(LOD)　of　0.04.　ng/mL.　Intra-　and　inter-assay　coefficients　of　variation　(CVs)　were　6.8　and　7.5%,　respectively.　In　addition,　the　methodology　was　evaluated　for　analysis　of　12　clinical　serum　samples　and　showed　good　accordance　between　the　results　obtained　by　the　developed　immunosensing　protocol　and　a　commercialized　enzyme-linked　immunosorbent　assay　(ELISA)　method.　©　2013　Elsevier　B.V.