Acousto-optic tunable filters (AOTF) and liquid crystal tunable filters (LCTF) are evaluated for their suitability as fluorescence microscopy imaging spectrometers. AOTFs are solid-state birefringent crystals that provide an electronically tunable spectral notch passband in response to an applied acoustic field. LCTFs also provide a notch passband that can be controlled by incorporating liquid crystal waveplate retarders within a Lyot birefringent filter. In this paper, spectroscopic performance and imaging quality are contrasted by evaluation of model systems. Studies include transmission imaging of standard resolution targets, multispectral fluorescence emission imaging of tagged polystyrene microspheres, and immunofluorescence imaging of neurotransmitters within rat-brainstem thin sections. In addition, the first use of LCTFs for Raman microscopy is demonstrated. Raman microscopy is a noninvasive spectral imaging technique that can provide chemically significant image contrast complementary to fluorescence microscopy without the use of stains or tags.

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A fast, simple procedure is described for obtaining an assembly of silver sulfide nanoparticles (Ag(2)S NPs) on a glass substrate through reaction of a template of an assembled layer of silver nanoparticles (Ag NPs) with hydrogen sulfide (H(2)S) gas. The Ag NP template was prepared by assembling a monolayer of spherical Ag NPs (mean diameter of 7.4 nm) on a polyethylenimine-treated glass substrate. Exposure to pure H(2)S for 10 min converted the Ag NPs of the template to Ag(2)S NPs. The resulting Ag(2)S NP assembly, which retains the template nanostructure and particle distribution, was characterized by optical absorption spectroscopy, atomic force microscopy, transmission electron microscopy (TEM), scanning high resolution TEM, energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy. The Ag(2)S NPs have a crystal structure of monoclinic acanthite, and while they retained the spherical shape of the original Ag NPs, their mean particle size increased to 8.4 nm due to changes to the crystal structure when the Ag NPs are converted into Ag(2)S NPs. The measured optical absorption edge of the Ag(2)S NP assembly indicated an indirect interband transition with a band gap energy of 1.71 eV. The Ag(2)S NP assembly absorbed light with wavelengths below 725 nm, and the absorbance increased monotonically toward the UV region.

A Lyot-type liquid crystal tunable filter (LCTF) suitable for high-definition Raman chemical imaging has been developed. The LCTF has been incorporated into an efficient Raman imaging system that provides significant performance advantages relative to any previous approach to Raman microscopy. The LCTF and associated optical path is physically compact, which accommodates integration of the LCTF within an infinity-corrected optical microscope. The LCTF simultaneously provides diffraction-limited spatial resolution and 7.6-cm-1 spectral bandpass across the full free spectral range of the imaging spectrometer. The LCTF Raman microscope successfully integrates, in a facile manner, the utility of optical microscopy and the analytical capabilities of Raman spectroscopy. In this paper the LCTF Raman imaging system is described in detail, as well as results of initial studies of polymer and corrosion product model systems.

Thermoplastic olefins (TPOs) are an important class of materials in the automotive industry. The surface properties of TPOs tend to prohibit adhesion of paints used to increase the longevity and enhance the cosmetic appearance of exterior TPO components. To increase adhesion, the TPO surface is coated with a chlorinated polypropylene (CPO) primer. The CPO thin film increases the TPO surface free energy and promotes paint adhesion. We have developed a generally applicable strategy for quantitative monitoring of CPO film uniformity, thickness, and adhesion based on the use of an environmentally sensitive fluorescence dye that is incorporated within the CPO adhesion promoter. The dye-tagged CPO thin film is analyzed in real time with a macroscopic imaging system employing novel liquid crystal tunable filter (LCTF) imaging spectrometers. The fluorescence chemical imaging approach is applicable to on-line monitoring of the TPO surface modification process. Controlled modification of the TPO surface is contingent on detailed understanding of the underlying TPO substrate. Raman chemical imaging is employed as a noninvasive approach to characterize TPO surface architecture. Specifically, we have developed a method for visualizing the surface to bulk distribution of CPO, polypropylene, and ethylene−propylene rubber phases in TPO without the use of dyes or stains. Blend components are visualized on the basis of their intrinsic vibrational spectrum. In general, Raman microscopy represents a powerful method for polymer characterization that is competitive with time-of-flight secondary ion mass spectrometry (TOF−SIMS) and transmission electron microscopy (TEM).