| Summary: | Prostate specific antigen (PSA) is considered as an important biomarker in prostate cancer diagnosis. Herein, an ultrasensitive ratiometric electrochemical aptasensor was constructed for analyzing PSA. The ferrocene (Fc)-labeled thiolated hairpin probe 2 (Fc-HP2) was conjugated to the gold nanoparticles (AuNPs)-modified gold electrode (AuE) surface by Au-S bonds. With the introduction of PSA, the aptamer region of hairpin probe 1 (HP1) preferred to bind with PSA, and the rest of HP1 could hybridize with Fc-HP2 to form Fc-HP2/HP1/PSA complex with a blunt 3′ terminus, which triggered the exonuclease III (Exo III) cleavage process accompanied by Fc leaving from the electrode and recycling of HP1/PSA. The remaining Fc-HP2 fragments left on the electrode surface were then hybridized with methylene blue-labeled DNA (MB-DNA). This resulted in an enhancement of MB signal (IMB) and a decrement of Fc signal (IFc). Under the optimal conditions, the proposed aptasensor showed good analytical performance for sensitive detection of PSA with a linear range from 100 fg·mL−1 to 10 ng·mL−1 and a detection limit of 34.7 fg·mL−1. The fabricated aptasensor had been applied to detect PSA in diluted human serum samples and obtained satisfied results, suggesting it had great potential in clinical diagnosis.
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