Prostate-specific antigen immunosensing based on mixed self-assembled monolayers, camel antibodies and colloidal gold enhanced sandwich assays

Biosens Bioelectron. 2005 Sep 15;21(3):483-90. doi: 10.1016/j.bios.2004.11.016. Epub 2004 Dec 25.


Prostate-specific antigen (PSA) is a valuable biomarker for prostate cancer screening. We developed a PSA immunoassay on a commercially available surface plasmon resonance biosensor. Our PSA receptor molecule consists of a single domain antigen-binding fragment, cAbPSA-N7, derived from dromedary heavy-chain antibodies and identified after phage display. It binds PSA with a high k(on) value of 1.9x10(6) M-1 s-1, and was covalently immobilised on a gold substrate via a mixed self-assembled monolayer (SAM) of alkanethiols by using carbodiimide-coupling chemistry in 10mM acetate buffer pH 5.5 to obtain an optimal pre-concentration. The best performing and optimised mixed SAM consisted of (10%) 16-mercapto-1-hexadecanoic acid (16-MHA) for covalent cAbPSA-N7 immobilisation and (90%) 11-mercapto-1-undecanol (11-MUOH) to minimise non-specific adsorption of the analyte. In this way, two advantages are incorporated in a single coupling layer. Up to 28 fmol/mm2 of cAbPSA-N7 could be immobilised and 30% of its binding sites participate actively in PSA interaction. In addition, the optimised layer showed also optimal performance to assess physiological samples. Although PSA concentrations as low as 10 ng/ml could be detected directly, this detection limit could be enhanced to PSA levels in the sub ng/ml range by introducing a sandwich assay involving a biotinylated secondary antibody and streptavidin modified gold nanoparticles. This approach realizes the PSA detection at clinical relevant concentrations.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adsorption
  • Animals
  • Antibodies / immunology*
  • Biosensing Techniques / instrumentation
  • Biosensing Techniques / methods*
  • Blood Chemical Analysis / instrumentation
  • Blood Chemical Analysis / methods
  • Camelus / immunology*
  • Coated Materials, Biocompatible / chemistry
  • Crystallization / methods
  • Gold Colloid / chemistry
  • Humans
  • Immunoassay / instrumentation
  • Immunoassay / methods*
  • Prostate-Specific Antigen / blood*
  • Prostate-Specific Antigen / chemistry
  • Prostate-Specific Antigen / immunology*
  • Protein Binding
  • Surface Plasmon Resonance / instrumentation
  • Surface Plasmon Resonance / methods*


  • Antibodies
  • Coated Materials, Biocompatible
  • Gold Colloid
  • Prostate-Specific Antigen