This investigation utilizes surface plasmon resonance (SPR) spectroscopy to detect and quantify human epidermal growth factor receptor 2 (HER-2), an oncogene product that is over-expressed in some aggressive forms of breast cancer. Specifically, the HER-2 trans-membrane protein p185 and its extra cellular fragment p105 are analytes targeted in this work by using a gold-based biosensor slide on which an anti-HER-2 antibody has been immobilized by attachment to Protein G that is fixed to the gold film. A detection limit of ≥11 ng/mL for p185 resulted when trastuzumab was used as the anti-HER-2 antibody on the biosensor slide. Experiments with semi-purified p105 revealed that it binds weakly and reversibly to trastuzumab, therefore complicating its detection and quantification. Results of studies that reacted a 13-amino-acid peptide (PP13) from the HER-2 kinase domain with its specific antibody were critically different than p185 and p105 studies. Spectral analysis of the reflectivity at constant bulk buffer refractive index revealed a progressive negative SPR shift over time. A negative shift suggests that a loss of protein mass from the anti-PP13 antibody–Protein G biosensor is occurring. Several possibilities that may explain these negative SPR shifts are discussed.

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