The authors describe an adapted rolling circle amplification (RCA) method for the determination of human epidermal growth factor receptor 2 (HER2). This method (which is termed immunoRCA) combines an immunoreaction with DNA based signal amplification. Gold nanoparticles (AuNPs) were loaded with antibodies against HER2 and DNA, and then fulfill the functions of recognizing HER2 and achieving signal amplification. The DNA serves as a primer to trigger RCA. This results in formation of a long DNA containing hundreds of copies of circular DNA sequence on the electrode surface. Then, molybdate is added which reacts with the phosphate group of the long DNA to generate the redox-active molybdophosphate. This, in turn, results in an increased current and, thus, in strongly increased sensitivity of the immunoassay. A linear response is linear relationship between the change of current intensity and the logarithm of the concentration in the range from 1 to 200 pg·mL-1 of HER2, and the detection limit is 90 fg·mL-1 (at an S/N ratio of 3). The method was applied to the determination of HER2 in breast cancer patients serum samples, and the results correlated well with those obtained by an ELISA. The method was further successfully applied to the determination of HER2 in HER2-expressed mouse breast cancer 4 T1 cells. Conceivably, this strategy may be adapted to other DNA amplification methods and also may be used for the determination of other proteins and biomarkers by using the appropriate antibodies. Graphical abstract Schematic presentation of an adapted rolling circle amplification (RCA) strategy for the electrochemical detection of human epidermal growth factor receptor 2 (HER2), termed "immunoRCA" utilizing gold nanoparticles (AuNPs). Ab stands for antibody, Phi29 is an E.coli DNA polymerase, dNTP represents deoxynucleotides, and SWV stands for square wave voltammetry.
Keywords: Human epidermal growth factor receptor 2; ImmunoRCA; Molybdate; Molybdophosphate; Rolling circle amplification.