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Adrenergic signaling that controls the contraction of cardiac myocyte cells and the beating of the mammalian heart is initiated by ligand binding to adrenergic receptors contained in nanoscale multiprotein complexes at the cellular membrane. Here we demonstrate that the surface-enhanced Raman scattering (SERS) of functionalized silver nanoparticles can be used to report on the receptor aggregation state of specifically label beta(2)-adrenergic receptors on mouse cardiac myocyte cells. Furthermore, multimodal imaging including Raman, Rayleigh scattering, scanning electron microscopy, and luminescence imaging was combined to fully characterize the beta(2)-adrenergic receptor-mediated aggregation of silver nanoparticles on the membrane of cardiac myocytes. Scanning electron microscopy analysis reveals distinct SERS active clusters of between 10 and 70 nanoparticles per signaling domain from ultra-high-resolution images of beta(2)-adrenergic receptor clusters on the cellular membrane. These techniques can be generally applied to study the aggregation of other cell surface receptors and explore their distribution on cell surfaces.
ACS Nano 2009 Aug 25
PMID:Nanoscale aggregation of cellular beta2-adrenergic receptors measured by plasmonic interactions of functionalized nanoparticles. 1970 24

We have demonstrated that mixed-base PNA oligomers are effective coagulants of citrate ion-coated gold and silver nanoparticles (AuNPs and AgNPs), and PNA-induced particle aggregation can be disrupted by hybridization of PNA with a specific DNA. Using particles' aggregation/dispersion as a measure, we have investigated how PNA and PNA-DNA complexes bind to AuNPs and AgNPs and modulate particles' stability differently relative to their DNA counterparts. We have made the following original discoveries: (1) mix-base PNA oligomers can induce immediate particle aggregation in a concentration- and chain-length-dependent manner; (2) PNA oligomers have a higher affinity to AuNPs and AgNPs than its ssDNA counterpart; (3) PNA-DNA complexes, although having a stable double helix structure similar to dsDNA, can effectively protect the particles from salt induced aggregation, and the protection effect of different nucleic acids are in the order of PNA-DNA complex > ssDNA > dsDNA; (4) all the characteristics are identical for AuNPs and AgNPs; and (5) AgNPs is more sensitive in response to destabilization effect and is proven a more sensitive platform for colorimetric assays. The control of particle aggregation and dispersion by PNA and PNA-DNA complexes has been used to detect a specific DNA sequence with single-base-mismatch resolution. zeta potential measurements have been conducted to reveal how distinct backbone properties of PNA and PNA-DNA complexes relative to their DNA counterparts contribute to the distinct binding characteristics.
ACS Nano 2009 Sep 22
PMID:Control of metal nanoparticles aggregation and dispersion by PNA and PNA-DNA complexes, and its application for colorimetric DNA detection. 1970 41

Cathodoluminescence spectroscopy has been performed on silver nanoparticles in a scanning electron microscopy setup. Peaks appearing in the visible range for particles fabricated on silicon substrate are shown to arrive from excitation of out-of-plane eigenmodes by the electron beam. Monochromatic emission maps have been shown to resolve spatial field variation of resonant plasmon mode on length scale smaller than 25 nm. Finite-difference time-domain numerical simulations are performed for both the cases of light excitation and electron excitation. The results of radiative emission under electron excitation show an excellent agreement with experiments. A complete vectorial description of induced field is given, which complements the information obtained from experiments.
ACS Nano 2009 Oct 27
PMID:Imaging of plasmonic modes of silver nanoparticles using high-resolution cathodoluminescence spectroscopy. 1973 3

We demonstrated that by properly coupling to silver nanoprisms, single CdSe/ZnS semiconductor quantum dots (QDs) exhibited suppressed blinking behavior, an enhanced fluorescence intensity ( approximately 2.5 fold), increased radiative decay rates ( approximately 12.5 fold), and antibunching single-photon emission. All these modifications significantly promote the overall performance of the proposed single-photon sources based on colloidal semiconductor QDs.
ACS Nano 2009 Oct 27
PMID:Antibunching single-photon emission and blinking suppression of CdSe/ZnS quantum dots. 1985 80

The development of new and better substrates is a major focus of research aimed at improving the analytical capabilities of surface-enhanced Raman spectroscopy (SERS). Perhaps the most common type of SERS substrate, one consistently exhibiting large enhancements, is simple colloidal gold or silver nanoparticles in the 10-150 nm size range. The colloidal systems that are used most for ultrasensitive detection are generally aggregated clusters that possess "hot spot(s)" within some of the aggregates. A significant limitation of these synthetic substrates is that the "hot" aggregates are extremely difficult to create consistently or predict. Electron beam lithography (EBL) along with combinatorial spectral mapping can be used to overcome this limitation. Our previous work, and that of other researchers, invokes the special capabilities of EBL to design and fabricate periodic, highly ordered nanoparticle arrays for SERS. Building on this work, EBL, in conjunction with ancillary fabrication steps, can be used to create complex patterns that mimic random aggregates. These aggregates, unlike those created by colloidal deposition methods, can be uniquely reproduced within the resolution limits of EBL. In the work reported herein, we use a unique approach to create substrates containing a large number of randomly generated cells with different morphologies that are arrayed on silicon wafers. Instead of isolated metal nanoparticles, these structures resemble the aggregates of colloid. By spectral mapping, we investigate the SERS activity of the combinatorial arrays of cells using probe analytes. Two general categories of shapes are randomly designed in different sizes and densities into several hundred different 5 mum square cells. Following fabrication, it is shown that a SERS performance contrast of more than a factor of 44 is achieved among these cells and that the best performing cells can be cloned into uniformly high performing macropatterns of lithographically defined nanoaggregates (LDNAs). In this manner, extended LDNA surfaces with uniform 5 x 10(8) enhancement factors are created. Furthermore, the LDNAs can be further dissected and studied in an effort to increase the SERS enhancement per unit geometric substrate area.
ACS Nano 2009 Dec 22
PMID:Controllable nanofabrication of aggregate-like nanoparticle substrates and evaluation for surface-enhanced Raman spectroscopy. 1991 35

We report here a concept for utilization of the "coffee ring effect" and inkjet printing to obtain transparent conductive patterns, which can replace the widely used transparent conductive oxides, such as ITO. The transparent conductive coating is achieved by forming a 2-D array of interconnected metallic rings. The rim of the individual rings is less than 10 microm in width and less than 300 nm in height, surrounding a "hole" with a diameter of about 150 microm; therefore the whole array of the interconnected rings is almost invisible to the naked eye. The rims of the rings are composed of self-assembled, closely packed silver nanoparticles, which make the individual rings and the resulting array electrically conductive. The resulting arrays of rings have a transparency of 95%; resistivity of 0.5 cm(2) was 4 +/- 0.5 Omega/, which is better than conventional ITO transparent thin films. The silver rings and arrays are fabricated by a very simple, low cost process, based on inkjet printing of a dispersion of 0.5 wt % silver nanoparticles (approximately 20 nm diameter) on plastic substrates. The performance of this transparent conductive coating was demonstrated by using it as an electrode for a plastic electroluminescent device, demonstrating the applicability of this concept in plastics electronics. It is expected that such transparent conductive coatings can be used in a wide range of applications such as displays (LCD, plasma, touch screens, e-paper), lighting devices (electroluminescence, OLED), and solar cells.
ACS Nano 2009 Nov 24
PMID:Transparent conductive coatings by printing coffee ring arrays obtained at room temperature. 1992 33

We report on the fabrication and optical characterization of dense and ordered arrays of metal nanoparticles. The metal arrays are produced by reducing metal salts in block copolymer (BCP) templates made by solvent annealing of poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) or poly(styrene-b-ethylene oxide) (PS-b-PEO) diblock copolymer thin films in mixed solvents. The gold and gold/silver composite nanoparticle arrays show characteristic surface plasmon resonances in the visible wavelength range. The patterning can be applied over large areas onto various substrates. We demonstrate that these metal nanoparticle arrays on metal thin films interact with surface plasmon polaritons (SPPs) that propagate at the film/nanoparticle interface and, therefore, modify the dispersion relation of the SPPs.
ACS Nano 2009 Dec 22
PMID:Block-copolymer-based plasmonic nanostructures. 1994 82

Metal-assisted chemical etching (MaCE) of silicon in conjunction with shaped catalysts was used to fabricate 3D nanostructures such as sloping channels, cycloids, and spirals along with traditional vertical channels. The investigation used silver nanorods, nanodonuts along with electron beam lithography (EBL)-patterned gold nanodiscs, nanolines, squares, grids, and star-shaped catalysts to show how catalyst shape and line width directly influence etching direction. Feature sizes ranging from micrometers down to 25 nm were achieved with aspect ratios of at least 10:1 and wall roughness of 10 nm or less. This research demonstrates the potential of MaCE as a new, maskless nanofabrication technology.
ACS Nano 2009 Dec 22
PMID:Effect of catalyst shape and etchant composition on etching direction in metal-assisted chemical etching of silicon to fabricate 3D nanostructures. 1995 71

We demonstrate organic photovoltaic cells in which every layer is deposited by solution processing on opaque metal substrates, with efficiencies similar to those obtained in conventional device structures on transparent substrates. The device architecture is enabled by solution-processed, laminated silver nanowire films serving as the top transparent anode. The cells are based on the regioregular poly(3-hexylthiophene) and C(61) butyric acid methyl ester bulk heterojunction and reach an efficiency of 2.5% under 100 mW/cm(2) of AM 1.5G illumination. The metal substrates are adequate barriers to moisture and oxygen, in contrast to transparent plastics that have previously been used, giving rise to the possibility of roll-to-roll solution-processed solar cells that are packaged by lamination to glass substrates, combining the cost advantage of roll-to-roll processing with the barrier properties of glass and metal foil.
ACS Nano 2010 Jan 26
PMID:Fully solution-processed inverted polymer solar cells with laminated nanowire electrodes. 2002 90

Solution phase triangular silver nanoplates (TSNP) with versatile tunability throughout the visible-NIR wavelengths are presented as highly sensitive localized surface plasmon refractive index sensors. A range of 20 TSNP solutions with edge lengths ranging from 11 to 200 nm and aspect ratios from 2 to 13 have been studied comprehensively using AFM, TEM, and UV-vis-NIR spectroscopy. Studies of the localized surface plasmon resonance (LSPR) peak's sensitivity to refractive index changes are performed using a simple sucrose concentration method whereby the surrounding refractive index can solely be changed without variation in any other parameter. The dependence of the TSNP localized surface plasmon resonance (LSPR) peak wavelength lambda(max) and its bulk refractive index sensitivity on the nanoplate's structure is determined. LSPR sensitivities are observed to increase linearly with lambda(max) up to 800 nm, with the values lying within the upper limit theoretically predicted for optimal sensitivity, notwithstanding any diminution due to ensemble averaging. A nonlinear increase in sensitivity is apparent at wavelengths within the NIR region with values reaching 1096 nm.RIU(-1) at lambda(max) 1093 nm. Theoretical studies performed using a simple aspect ratio dependent approximation method and discrete dipole approximation methods confirm the dependence of the LSPR bulk refractive index sensitivity upon the TSNP aspect ratio measured experimentally. These studies highlight the importance of this key parameter in acquiring such high sensitivities and promote these TSNP sols for sensing applications at appropriate wavelengths for biological samples.
ACS Nano 2010 Jan 26
PMID:Versatile solution phase triangular silver nanoplates for highly sensitive plasmon resonance sensing. 2003 Mar 62


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