Electrochemiluminescence immunosensor for tumor markers based on biological barcode mode with conductive nanospheres

• An ECL immunosensor based on biological barcode mode was proposed.
• Conductive nanospheres (CNSs) could extend the outer Helmholtz plane effectively.
• ABEI/Ab2-CNSs probes were constructed by immobilizing ABEI and Ab2 on CNSs.
• ABEI on CNSs give in-situ ECL signal as biological barcode without interfering Ab2.
• PSA could be detected in the concentration range from 0.04 to 10 fg/mL.

A novel sandwich-type electrochemiluminescence (ECL) immunosensor was developed for highly sensitive and selective determination of tumor markers based on biological barcode mode. N-(4-aminobutyl)-N-ethylisoluminol (ABEI) and the second antibody (Ab2) were simultaneously immobilized on conductive nanospheres to construct ABEI/Ab2-CNSs probes, which could form sandwich immunocomplex by Ab2 and emit ECL signals by ABEI. The gold layer coated on the surface of the conductive nanospheres could extend the outer Helmholtz plane (OHP) of the ECL immunosensor effectively. Benefited from it, all ABEI molecules immobilized on conductive nanospheres would act as biological barcode to give in-situ ECL signals without interfering with the activity of the second antibody. In such a case, the sensitivity of the ECL immunosensor would be greatly improved because an antigen molecule would correspond to ECL signals of thousands of ABEI molecules. Using prostate specific antigen (PSA) as a model tumor marker, the ECL intensity was found to increase with the logarithm of PSA concentration with a wide linear range from 0.04 to 10 fg/mL. In addition, specificity, stability, reproducibility, regeneration and application were satisfactory. Therefore, this developed ECL immunosensor has a potential for practical detection of disease-related proteins besides tumor markers in the clinical diagnostics.