A novel potentiometric immunosensor for the detection of adrenal cortical hormones (ACH) has been developed by means of self-assembling immobilization of adrenal cortical hormone antibody (anti-ACH) on a gold electrode-modified gold nanoparticle (Au) and a thiol-containing sol–gel network. A cleaned gold electrode was first immersed in a (3-mercaptopropyl)-trimethoxysilane (MPS) sol–gel solution to assemble a silica sol–gel monolayer, then the silane units were polymerized into a 2D sol–gel network (2D network) by dipping into aqueous NaOH. The second silane layer was formed by immersion back into the MPS solution overnight, and then the gold nanoparticles (nanogold) were chemisorbed onto the thiol groups of the second silane layer. Finally, anti-ACH was adsorbed onto the surface of the gold nanoparticles. The modified process was characterized by electrochemical impedance spectroscopy (EIS). The detection is based on the change in the potentiometric response before and after the antigen–antibody reaction. Using nanogold and 3-MPS as substrates, potentiometric detection at room temperature resulted in a pseudolinear detection range of about 22–1,000 ng mL⁻¹ with a detection limit of 5.2 ng mL⁻¹. Subsequently, several serum samples obtained from medical students with different anxiety extents were analyzed comparing with the ELISA method, and the results demonstrated that the immunoassay meets the demands of psychological analyses.