High-performance electrochemical immunomagnetic assay for breast cancer analysis

Despite the evolution of targeted therapies in oncology, some challenges such as screening and early diagnosis of cancer-related biomarkers still remain. The analysis of the Human Epidermal growth factor Receptor 2 (HER2) in biological fluids provides essential information for effective treatments. In this work we report the development of an electrochemical immunomagnetic bioassay for the analysis of the extracellular domain of HER2 (HER2-ECD) in human serum and cancer cells. Biomodified carboxylic acid functionalized magnetic beads (COOH-MBs) were used as the capture probe and an antibody labelled with alkaline phosphatase (AP) as the signalling probe. In the presence of HER2-ECD a sandwich complex was formed on the MBs, which were magnetically attracted to the surface of a screen-printed carbon electrode (SPCE). After the addition of 3-indoxyl phosphate and silver ions, used as the enzymatic substrate, the immunological interaction was detected by linear sweep voltammetry. Two linear concentration ranges were established: one between 5.0 and 50 ng/mL and another between 50 and 100 ng/mL. The developed assay provided a clinically useful detection limit (2.8 ng/mL) and has an adequate precision (Vx0 < 5%). The assay provided accurate results and was selective towards the target biomarker. Additionally, CTCs were analysed in human serum and a detection limit of 3 cells/mL was achieved for the HER+ breast cancer cell line SK-BR-3.The authors are grateful for the financial support from the Fundação para a Ciência e a Tecnologia (FCT) / the Ministério da Ciência, Tecnologia e Ensino Superior (MCTES) through national funds (Portugal) (LAQV - UID/QUI/50006/2019 and CINTESIS - UID/IC/4255/2019). Maria Freitas is grateful to FCT for her PhD grant (SFRH/BD/111942/2015), financed by POPH- QREN-Tipologia 4.1-Formação Avançada, subsidized by Fundo Social Europeu and the MCTES. The authors are also thankful to Rui Rocha and CEMUP “Centro de Materiais da Universidade do Porto” for the SEM work