Coupling antibody based recognition with DNA based signal amplification using an electrochemical probe modified with MnO 2 nanosheets and gold nanoclusters: Application to the sensitive voltammetric determination of the cancer biomarker alpha fetoprotein

The authors describe a sensitive electrochemical immunoassay for the cancer biomarker α-fetoprotein (AFP). It is based on a combination of an immunoassay with DNA-based signal amplification. Two-dimensional MnO2 nanosheets modified with gold nanoclusters (AuNC-MnO2) were synthesized through one-pot process and utilized as an electrochemical probe. Bovine serum albumin served as templating agent to guide the formation and assembly of the modified sheets. The detection antibody against AFP and a polycytosine DNA sequence (dC20) were immobilized onto the modified nanosheets. The electrochemical assay follows the usual sandwich protocol. The antibodies on the nanosheets then bind to AFP, while dC20 causes signal amplification. The reaction of the phosphate backbone of dC20 with molybdate leads to the formation of redox-active molybdophosphate which generates an electrochemical current, typically measured at 0.20 V (vs. Ag/AgCl). The method allows AFP to be determined in the 0.01 to 10 ng·mL−1 concentration range, and the detection limit is as low as 5 pg·mL−1. This strategy overcomes the drawbacks of conventional immunoassays whose sensitivity is often limited because many immunoassays are rather difficult to amplify. The method has a wide scope in that various other DNA signal amplification methods such as rolling circle amplification and hybridization chain reactions may also be applied.