This study demonstrates that spectral fingerprint patterns for a weakly scattering biological sample can be obtained reproducibly and reliably with tip-enhanced Raman spectroscopy (TERS) that correspond well with the conventional confocal Raman spectra collected for the bulk substance. These provided the basis for obtaining TERS images of individual self-assembled peptide nanotapes using an automated, objective procedure that correlate with the simultaneously obtained scanning tunneling microscopy (STM) images. TERS and STM images (64 × 64 pixels, 3 × 3 μm²) of peptide nanotapes are presented that rely on marker bands in the Raman fingerprint region. Full spectroscopic information in every pixel was obtained, allowing post-processing of data and identification of species of interest. Experimentally, the "gap-mode" TERS configuration was used with a solid metal (Ag) tip in feedback with a metal substrate (Au). Confocal Raman data of bulk nanotapes, TERS point measurements with longer acquisition time, atomic force microscopy images, and an infrared absorption spectrum of bulk nanotapes were recorded for comparison. It is shown that the unique combination of topographic and spectroscopic data that TERS imaging provides reveals differences between the STM and TERS images, for example, nanotapes that are only weakly visible in the STM images, a coverage of the surface with an unknown substance, and the identification of a patch as a protein assembly that could not be unambiguously assigned based on the STM image alone.

Core/thick-shell giant quantum dots (gQDs) possessing type II electronic structures exhibit suppressed blinking and diminished nonradiative Auger recombination. We investigate CdSe/ZnSe and ZnSe/CdS as potential new gQDs. We show theoretically and experimentally that both can exhibit partial or complete spatial separation of an excited-state electron-hole pair (i.e., type II behavior). However, we reveal that thick-shell growth is challenged by competing processes: alloying and cation exchange. We demonstrate that these can be largely avoided by choice of shelling conditions (e.g., time, temperature, and QD core identity). The resulting CdSe/ZnSe gQDs exhibit unusual single-QD properties, principally emitting from dim gray states but having high two-exciton (biexciton) emission efficiencies, whereas ZnSe/CdS gQDs show characteristic gQD blinking suppression, though only if shelling is accompanied by partial cation exchange.

Amyloid fibril diseases are characterized by the abnormal production of aggregated proteins and are associated with many types of neuro- and physically degenerative diseases. X-ray diffraction techniques, solid-state magic-angle spinning NMR spectroscopy, circular dichroism (CD) spectroscopy, and transmission electron microscopy studies have been utilized to detect and examine the chemical, electronic, material, and structural properties of amyloid fibrils at up to angstrom spatial resolution. However, X-ray diffraction studies require crystals of the fibril to be analyzed, while other techniques can only probe the bulk solution or solid samples. In the work reported here, apertureless near-field scanning infrared microscopy (ANSIM) was used to probe the secondary structure of individual amyloid fibrils made from an in vitro solution. Simultaneous topographic and infrared images of individual amyloid fibrils synthesized from the #21-31 peptide fragment of β(2)-microglobulin were acquired. Using this technique, IR spectra of the amyloid fibrils were obtained with a spatial resolution of less than 30 nm. It is observed that the experimental scattered field spectrum correlates strongly with that calculated using the far-field absorption spectrum. The near-field images of the amyloid fibrils exhibit much lower scattering of the IR radiation at approximately 1630 cm(-1). In addition, the near-field images also indicate that composition and/or structural variations among individual amyloid fibrils were present.

The nanoscale chemical composition variations of the surfaces of thin films of polystyrene- b-poly(methyl methacrylate) (PS- b-PMMA) diblock copolymers are investigated using apertureless near-field IR microscopy. The scattering of the incident infrared beam from a modulated atomic force microscopy (AFM) tip is probed using homodyne detection and demodulation at the tip oscillation frequency. An increase in the IR attenuation is observed in the PMMA-rich domains with a wavenumber dependence that is consistent with the bulk absorption spectrum. The results indicate that even though a small topography-induced artifact can be observed in the near-field images, the chemical signature of the sample is detected clearly.