SERS biodetection using gold-silica nanoshells and nitrocellulose membranes.

We have developed a rapid, reproducible, easy to execute, surface enhanced Raman scattering (SERS) method for detection of low volumes and total amounts of biological antigens using an analyte capture system derived from methods commonly used in Western blotting. Our method is a "half-sandwich" assay with an antigen detection scheme that employs a nitrocellulose (NC) membrane with 200 nm pore size to capture subnanograms of analyte and concentrate them in a small area from applied volumes as low as one microliter. The SERS probes used for detection consist of gold-silica nanoshells modified with a two-component mixed monolayer system.

Experimental and theoretical spectroscopic study of 3(10)-helical peptides using isotopic labeling to evaluate vibrational coupling.

Coupling between the amide linkages in a peptide or protein is the key physical property that gives vibrational spectra and circular dichroism sensitivity to secondary structures. By use of (13)C isotopic labeling on individual and pairs of amide C═O groups, the amide I band for selected residues was effectively isolated in designed hexa- and octapeptides having dominant 3(10)-helical conformations. The resultant frequency and intensity responses were measured with IR absorption, vibrational circular dichroism (VCD), and Raman spectroscopies and simulated with density functional theory (DFT) based computations.

Inter-residue coupling and equilibrium unfolding of PPII helical peptides. Vibrational spectra enhanced with (13)C isotopic labeling.

Unordered proteins, unfolded peptides, and several "random coil" models have been shown to have local conformations similar to that of polyproline II (PPII). Inter-residue coupling of selected residues in a series of related peptides having predominantly PPII conformations were measured using IR, VCD, and Raman spectra of selected variants that were doubly C(1)-labeled with (13)C on the amide C═O. The characteristics of the (13)C═O component of the IR, VCD, and Raman amide I' bands and their sensitivity to the local structure of the peptide are compared to predictions based on DFT level calculations for related structures and used to estimate coupling interactions between pairs of C═O groups along the backbone of this helical structure.

The transition state transit time of WW domain folding is controlled by energy landscape roughness.

Protein folding barriers can be so low that a substantial protein population diffusing in the transition state region can be detected. The very fast kinetic phase contributed by transition state transit is the molecular phase. We detect the molecular phase of the beta-sheet protein FiP35 from 60 to 83 degrees C by T-jump relaxation experiments.