Monolayer Sensitivity Enables a 2D IR Spectroscopic Immuno-biosensor for Studying Protein Structures: Application to Amyloid Polymorphs.

Immunosensors use antibodies to detect and quantify biomarkers of disease, though the sensors often lack structural information. We create a surface-sensitive two-dimensional infrared (2D IR) spectroscopic immunosensor for studying protein structures. We tether antibodies to a plasmonic surface, flow over a solution of amyloid proteins, and measure the 2D IR spectra.

Enhancing the signal strength of surface sensitive 2D IR spectroscopy.

Spectroscopic techniques that are capable of measuring surfaces and interfaces must overcome two technical challenges: one, the low coverage of molecules at the surface, and two, discerning between signals from the bulk and surface. We present surface enhanced attenuated reflection 2D infrared (SEAR 2D IR) spectroscopy, a method that combines localized surface plasmons with a reflection pump-probe geometry to achieve monolayer sensitivity. The method is demonstrated at 6 m with the amide I band of a model peptide, a cysteine terminated α-helical peptide tethered to a gold surface.

Site-specific detection of protein secondary structure using 2D IR dihedral indexing: a proposed assembly mechanism of oligomeric hIAPP.

Human islet amyloid polypeptide (hIAPP) aggregates into fibrils through oligomers that have been postulated to contain α-helices as well as β-sheets. We employ a site-specific isotope labeling strategy that is capable of detecting changes in dihedral angles when used in conjunction with 2D IR spectroscopy. The method is analogous to the chemical shift index used in NMR spectroscopy for assigning protein secondary structure.