Biosensor surface attachment of the ovarian cancer biomarker HSP10 via His-tag modification

Herein, we describe a new protocol for the silane-based surface modification of quartz substrates for the immobilization of hexa-histidine-tagged heat shock protein 10. This molecule is an attractive biomarker for the detection of ovarian cancer, particularly for possible early-stage diagnosis. The surface chemistry we have described is used for a study of the interaction between the protein and a novel DNA aptamer via an in-house built acoustic wave sensing platform. Quartz discs were modified with a mixed trichlorosilane adlayer and functionalized with a nickel-NTAL moiety to allow for immobilization of the protein in a correctly-oriented fashion. All layers were characterized by x-ray photoelectron spectroscopy to show successful layer modification. Detection of binding in phosphate buffered saline was determined using the EMPAS, operating at a fundamental frequency of 940 MHz. Results regarding the specific binding of the DNA aptamer to the surface-immobilized protein exhibited a significantly smaller signal compared to surfaces without protein, which comparatively yielded much larger frequency shifts. The smaller shift in frequency is attributed to the rigidification of the bulk layer upon interaction between probe and ligand as the overwhelming factor. This rigidification is counteracted by mass loading effects, in which a balance between these two factors is what contributes to the overall smaller frequency shift. Without the binding interaction, the bulk layer does not rigidify, resulting in mass loading being the main contributor to signal, and thus a large frequency shift is seen. Keywords: Ovarian cancer, Biomarker, Biosensor, HSP10, DNA aptamer, Acoustic wave sensor, EMPAS