A novel electrochemical immunosensor for sensitive detection of cancer biomarker prostate-specific antigen (PSA) has been reported based on nanoporous gold (NPG) and hollow mesoporous silica microspheres (HSMs). The immunoassay was conducted by following the typical procedure for sandwich-type immunoreaction. Nanoporous gold (NPG) foils were immobilized onto a glassy carbon electrode (GCE) for primary anti-PSA (Ab₁) anchoring. Making use of the unique properties of NPG, antibodies could be self-assembled onto the support-free NPGviaamine-Au affinity with a high loading amount and reserve high immunological activity. HSMs were used as a secondary anti-PSA antibody (Ab₂) label. For the preparation of the label, mediator thionine (TH) was first conjugated onto amino-functionalized HSMs (NH₂-HSMs) via crosslinking with glutaraldehyde, and then the amino group of TH was used to immobilize horseradish peroxidase (HRP) and Ab₂. Due to the large specific surface area of NH₂-HSMs, the loading of antibodies as well as mediator and enzyme onto HSMs was substantially increased, which increased the sensitivity of the immunosensor. The immunosensor exhibited a high sensitivity and showed a linear response within the range of 0.01–10 ng mL⁻¹ PSA, low detection limit (6.00 pg mL⁻¹), good reproducibility and stability. Significantly, the new method may be quite promising, with potential broad applications for clinical immunoassays.