Ultrasensitive SEIRA detection using gold nanobipyramids: Toward efficient multimodal immunosensor.

• FT-IR technique confirmed the successful formation of the AuBPs-based immunosensor. • Theoretical calculations were performed to sustain the experimental results. • The SEIRA LOD of the immunosensor was determined to reach pM values. Surface enhanced spectroscopies are proven to be highly efficient in biosensing applications. Their implementation as analytical tools in the detection of medically relevant target analytes demonstrated their ability to considerably decrease the minimum detected analyte concentration, thus showing improved sensitivity compared to commercially available detection kits. In this work, we propose the employment of Surface Enhanced Infrared Absorption (SEIRA), a less exploited analysis tool, for the efficient, specific, and ultrasensitive detection of the biotin-streptavidin recognition interaction using a gold nano-bipyramid-based (AuBPs) immunosensor. The unique optical properties of the AuBPs, such as tunability of the LSPR band ranging from the visible to NIR regions of the spectrum, great absorption capabilities and locally enhanced electromagnetic field at their tips and edges, enable an improved efficiency of the IR absorption of the target analytes. To the as-synthesized AuBPs, a chemically formed p-ATP@biotin recognition element was grafted due to the strong Au-S interaction, followed by the exposure of the obtained biotinylated nanosystem to the streptavidin target analyte. FT-IR experimental measurements as well as theoretical simulations confirm both the successful grafting of the p-ATP@biotin onto the Au surface and successful capture of the target streptavidin protein. A limit of detection of 10−12 M streptavidin concentration was determined, thus standing as a "proof-of-concept" for the development of efficient ultrasensitive SEIRA biosensing devices for more complex biologically relevant applications. [Display omitted] [ABSTRACT FROM AUTHOR]