Purpose To investigate the use of photoacoustic (PA) spectrum analysis (PASA) to identify microstructural changes corresponding to fat accumulation in mouse livers ex vivo and in situ. Materials and Methods The laboratory animal protocol for this work was approved by the university committee on use and care of animals. Six mice with normal livers and six mice with fatty livers were examined ex vivo with a PA system at 1200 nm, and nine similar pairs of mice were examined at 532 nm. To explore the feasibility of this technique for future study in an in vivo mouse model, an additional pair of normal and fatty mouse livers was scanned in situ with an ultrasonographic (US) and PA dual-modality imaging system. The PA signals acquired were analyzed by using the proposed PASA method. Results of the groups were compared by using the Student t test. Results Prominent differences between the PASA parameters from the fatty and normal mouse livers were observed. The analysis of the PASA parameters from six normal and six fatty mouse livers indicates that there are differences of up to 5 standard deviations between the PASA parameters of the normal livers and those of the fatty livers at 1200 nm; for parameters from nine normal and nine fatty mouse livers at 532 nm, the differences were approximately 2 standard deviations (P < .05) for each PASA parameter. Conclusion The results supported our hypothesis that the PASA allows quantitative identification of the microstructural changes that differentiate normal from fatty livers. Compared with that at 532 nm, PASA at 1200 nm is more reliable for fatty liver diagnosis.

Low-energy-ion bombardment of semiconductors can lead to the development of complex and diverse nanostructures. Of particular interest in these structured surfaces is the formation of highly ordered patterns whose optical, electronic, and magnetic properties are different from those of bulk materials and might find technological uses. [1][2][3][4][5] Compared to the low efficiency of lithographic methods for mass production, this self-organized approach offers a new route for fabrication of ordered patterns over large areas in a short processing time on the nanometer scale, beyond the limits of lithography. [1,4] This technique is based on the morphological instability of a sputtered surface driven by a kinetic balance between roughening and smoothing. [6,7] Thus mechanisms that control the species concentration on the surface can make contributions to structure formation. [3,[7][8][9][10][11][12] It is now established that well-ordered quantum dots can be generated on the surface of semiconductors (Si, Ge, GaSb) under certain irradiation conditions. [1,13,14] For a long time it has been expected that the instability of a surface can also lead to well-ordered hole formation. However, to date experimental observation of such features has been lacking. In this Communication, we report that a hexagonally ordered, honeycomb-like structure of holes 35 nm across and 45 nm apart on the Ge surface can be formed under focused ion beam (FIB) bombardment at normal incidence. The structured Ge fabricated by FIB bombardment shows a high surface area and a considerably blue-shifted energy gap. We found that interplay between ion sputtering, redeposition, viscous flow, and surface diffusion is responsible for ordered pattern formation. Simulations of the evolution of the surface morphology on the basis of the damped Kuramoto-Sivashinsky (DKS) growth model have been performed to facilitate the interpretation of the experimental findings. [15][16][17][18][19] As an indirect energy-gap semiconductor, germanium is a poor light emitter, which makes it challenging to create efficient Ge-based light-emitting devices. Significant effort has been devoted to the development of the optical properties of Ge based on changing the surface morphology.[20] In the work reported here, we focused on the use of ion beam radiation to fabricate nanostructures on the Ge surface.The ion-induced nanostructures were fabricated on commercially available Ge with (100) orientation by FIB bombardment. Under normal bombardment with ion energy greater than 5 keV, worm-like structures were developed on Ge surface with large aspect ratio. When the energy was 5 keV, however, highly ordered hole arrays could be achieved. Figure 1 shows scanning electron microscopy (SEM) and atomic force microscopy (AFM) images of a typical nanohole pattern induced on a Ge(100) surface by 5 keV (Ga þ ) FIB bombardment for 5 min. A perfect hexagonal arrangement of holes is observed within domains of ca. 500 nm. Like polycrystalline structure, there are ''grain boundaries'' separati...

We propose a new design of optical nanoantennas and numerically study their optical properties. The nanoantennas are composed of two cylindrical metal nanorods stacked vertically with a circular dielectric disk spacer. Simulation results show that when the dielectric disk is less than 5nm in thickness, such nanoantennas exhibit two types of resonances: one corresponding to antenna resonance, the other corresponding to cavity resonances. The antenna resonance generates a peak in scattering spectra, while the cavity resonances lead to multiple dips in the scattering spectra. The cavity resonant frequency can be tuned by varying the size of the dielectric disk. The local field enhancement inside the cavity is maximized when the diameter of the dielectric disk is roughly half that of the rod and when the cavity and antenna resonant frequencies coincide with each other. This new nanoantenna promises applications in single molecule surface enhanced Raman spectroscopy (SERS) owing to its high local field enhancements and large scale manufacturability.

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Interactions of proteins with DNA play an important role in regulating the biological functions of DNA. Here we propose and demonstrate the detection of protein-DNA binding using surface-enhanced Raman scattering (SERS). In this method, double-stranded DNA molecules with potential protein-binding sites are labeled with dye molecules and immobilized on metal nanoparticles. The binding of proteins protects the DNA from complete digestion by exonuclease and can be detected by measuring the SERS signals before and after the exonuclease digestion. As a proof of concept, this SERS-based protein-DNA interaction assay is validated by studying the binding of a zinc finger transcription factor WT1 with DNA sequences derived from the promoter of the human vascular endothelial growth factor.

The authors fabricated two dimensional arrays of metal-dielectric-metal nanoantennas consisting of a thin layer of light-emitting polymers sandwiched between two Ag parallel cuboids and characterized them by measuring the optical transmission through the antenna arrays. The measured transmission spectra show two resonant dips. Numerical simulations reproduce the experimental results and show that the left dip is due to a cavity resonance mode and the right dip is due to the absorption of the polymer. With this vertical antenna design, the dielectric gap can be made much smaller with an extremely small mode volume, making it a potential candidate for single molecule studies using surface enhanced Raman scattering and for various other optoelectronic applications.

Surface enhanced Raman scattering, referring to enhanced Raman signals of molecules by plasmonic nanostructures, has been employed as a unique label-free detection scheme for various biological and chemical molecules. Here we present plasmonic patch nanoantennas as a platform for SERS applications. The patch antennas are made of metallic patches on the top of a metal film separated by a dielectric layer. This vertical metal-dielectric-metal design makes it possible to control the gap size in nanometers reproducibly by using thin film deposition techniques such as atomic layer deposition. We report numerical and experimental results on resonant cavity modes and measurements of the SERS enhancement factors for these plasmonic patch antennas.