Specific Picomolar Detection of a Breast Cancer Biomarker HER‐2/neu Protein in Serum: Electrocatalytically Amplified Electroanalysis by the Aptamer/PEG‐Modified Electrode

Abstract

AbstractSpecific and sensitive electroanalysis of blood‐circulating protein cancer biomarkers is often complicated by interference from serum proteins nonspecifically adsorbing at the biosensing interface and masking specific reactions of interest. Here, we have developed an electrocatalytically amplified assay for specific and sensitive analysis of human epidermal growth factor receptor‐2 (HER‐2/neu, a protein cancer biomarker over‐expressed in breast cancers) that allows us to avoid both the interference from bovine serum albumin (BSA) and electrocatalytic amplification of the signal stemming from the specific aptamer−HER‐2/neu binding. A HER‐2/neu‐specific thiolated aptamer sequence was co‐adsorbed on gold together with a C11 alkanethiol bearing two ethylene glycol (EG)2 head groups that prevented non‐specific adsorption of BSA. On such layers, electrochemical reduction of a ferricyanide redox indicator is inhibited and is shown to be electrocatalyzed by methylene blue electrostatically interacting with negatively charged HER‐2/neu. The electrocatalytic signal increased upon HER‐2/neu binding to the aptamer, which allowed 10−12–10−8 M HER‐2/neu detection in 1 % serum, being practically applicable for clinical testing. The developed strategy can be considered as general and applicable for the electroanalysis of other blood‐circulating proteins once the electrostatic compatibility between the protein and redox probe is established.