Background: Prostate-specific antigen (PSA), a serine protease, is a biomarker for preoperative diagnosis and screening of prostate cancer and monitoring of its posttreatment.
Methods: In this work, we reported a colorimetric method for clinical detection of PSA using gold nanoparticles (AuNPs) as the reporters. The method is based on ascorbic acid (AA)-induced in situ formation of AuNPs and Cu²⁺-catalyzed oxidation of AA. Specifically, HAuCl₄ can be reduced into AuNPs by AA; Cu²⁺ ion can catalyze the oxidation of AA by O₂ to inhibit the formation of AuNPs. In the presence of the PSA-specific peptide (DAH SSKLQLAPP)-modified gold-coated magnetic microbeads (MMBs; denoted as DAH SSKLQLAPP-MMBs), complexation of Cu²⁺ by the MMBs through the DAH–Cu²⁺ interaction depressed the catalyzed oxidation of AA and thus allowed for the formation of red AuNPs. However, once the peptide immobilized on the MMB surface was cleaved by PSA, the DAH SSKLQ segment would be released. The resultant LAPP fragment remaining on the MMB surface could not sequestrate Cu²⁺ to depress its catalytic activity toward AA oxidation. Consequently, no or less AuNPs were generated.
Results: The linear range for PSA detection was found to be 0~0.8 ng/mL with a detection limit of 0.02 ng/mL. Because of the separation of cleavage step and measurement step, the interference of matrix components in biological samples was avoided.
Conclusion: The high extinction coefficient of AuNPs facilitates the colorimetric analysis of PSA in serum samples. This work is helpful for designing of other protease biosensors by matching specific peptide substrates.
Keywords: colorimetric assay, gold nanoparticles, prostate-specific antigen, ascorbic acid, Cu²⁺ ion