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Structural characterization of biologically formed materials is essential for understanding biological phenomena and their enviro-nment, and for generating new bio-inspired engineering concepts. For example, nacre-the inner lining of some mollusk shells-encodes local environmental conditions throughout its formation and has exceptional strength due to its nanoscale brick-and-mortar structure. This layered structure, comprising alternating transparent aragonite (CaCO3) tablets and thinner organic polymer layers, also results in stunning interference colors. Existing methods of structural characterization of nacre rely on some form of cross-sectional analysis, such as scanning or transmission electron microscopy or polarization-dependent imaging contrast (PIC) mapping. However, these techniques are destructive and too time- and resource-intensive to analyze large sample areas. Here, we present an all-optical, rapid, and nondestructive imaging technique-hyperspectral interference tomography (HIT)-to spatially map the structural parameters of nacre and other disordered layered materials. We combined hyperspectral imaging with optical-interference modeling to infer the mean tablet thickness and its disorder in nacre across entire mollusk shells from red and rainbow abalone (Haliotis rufescens and Haliotis iris) at various stages of development. We observed that in red abalone, unexpectedly, nacre tablet thickness decreases with age of the mollusk, despite roughly similar appearance of nacre at all ages and positions in the shell. Our rapid, inexpensive, and nondestructive method can be readily applied to in-field studies.

The application of surface plasmon resonance (SPR) measurements to the study of ultrathin organic films adsorbed onto gold surfaces utilizing near-infrared (NIR) excitation from a Fourier transform (FT) spectrometer is described. The FT-SPR experiment measures the NIR reflectivity spectrum from a prism/gold film/water assembly at a fixed angle of incidence approximately 1-2 [degrees] greater than the critical angle. A strong reflectivity minimum is observed in the FT-SPR spectrum; this minimum can be shifted from 12 000 to 6000 [cm.sup.-1] by tuning the angle of incidence. Upon adsorption of a thin biopolymer film from solution, a shift in the minimum is observed that can be correlated to a film thickness using Fresnel calculations. From experiments on the adsorption of electrostatically bound poly(lysine)/poly(glutamic acid) multilayers, an [approximately]60-[cm.sup.-1] shift per 10-[Angstrom] change in film thickness was measured. Frequency shifts of 2 [cm.sup.-1] (corresponding to a thickness change of the polymer layer of [approximately]0.3 [Angstrom]) can be easily measured from the FT-SPR spectra, demonstrating that this technique has sensitivity equivalent to or better than other visible SPR angle shift or wavelength shift measurements. Furthermore, the ability to perform FT-SPR measurements over a wide range of NIR wavelengths allows one to avoid any absorption bands that might otherwise interfere with the analysis.

A novel carbon-on-metal thin film substrate is described, which has enabled surface plasmon resonance detection with photolithographically fabricated DNA arrays for the analysis of biomolecular interactions. The utility of the technology is shown in the analysis of specific DNA-DNA and DNA-protein binding interactions and this group has used new substrates to determine the secondary structure of RNA molecules.

Fourier transform (FT)-plasmon waveguide resonance (PWR) spectroscopy measures light reflectivity at a waveguide interface as the incident frequency and angle are scanned. Under conditions of total internal reflection, the reflected light intensity is attenuated when the incident frequency and angle satisfy conditions for exciting surface plasmon modes in the metal as well as guided modes within the waveguide. Expanding upon the concept of two-frequency surface plasmon resonance developed by Peterlinz and Georgiadis [Opt. Commun. 1996, 130, 260], the apparent index of refraction and the thickness of a waveguide can be measured precisely and simultaneously by FT-PWR with an average percent relative error of 0.4%. Measuring reflectivity for a range of frequencies extends the analysis to a wide variety of sample compositions and thicknesses since frequencies with the maximum attenuation can be selected to optimize the analysis. Additionally, the ability to measure reflectivity curves with both p- and s-polarized light provides anisotropic indices of refraction. FT-PWR is demonstrated using polystyrene waveguides of varying thickness, and the validity of FT-PWR measurements are verified by comparing the results to data from profilometry and atomic force microscopy (AFM). [ABSTRACT FROM AUTHOR]