Spectroscopic ultra-trace detection of nitroaromatic gas vapor on rationally designed two-dimensional nanoparticle cluster arrays.

Nanoparticle cluster arrays (NCAs) are engineered two-dimensional plasmonic arrays that provide high signal enhancements for critical sensing applications using surface enhanced Raman spectroscopy (SERS). In this work we demonstrate that rationally designed NCAs are capable of detecting ultra-traces of 2,4-dinitrotoluene (DNT) vapor. NCAs functionalized with a thin film of an aqueous NaOH solution facilitated the detection of DNT vapor at a concentration of at least 10 ppt, even in the presence of an excess of potential interferents, including Diesel fuel, fertilizers, and pesticides. Both in the presence and in the absence of this complex background the SERS signal intensity of the NO(2) stretching mode showed a continuous, concentration dependent response over the entire monitored concentration range (10 ppt-100 ppb). The small size, superb sensitivity, and selectivity, as well as the fast response time of <5 min, make NCAs a valuable photonic sensor platform for ultra-trace nitroaromatic gas vapor detection with potential applications in landmine removal and homeland security.

Optical sizing of immunolabel clusters through multispectral plasmon coupling microscopy.

The wavelength dependent scattering cross sections of self-assembled silver nanoparticle clusters of known size (n) were measured on five different wavelength channels between 427 and 510 nm through correlation of multispectral imaging and scanning electron microscopy. A multivariate statistical analysis of the spectral response of this training set provided a correlation between spectral response and cluster size and enabled a classification of new measurements into four distinct nanoparticle association levels (I1-I4) whose compositions were dominated by monomers (I1), dimers (I2), trimers and tetramers (I3), and larger clusters (I4), respectively. One potential application of the optical sizing approach is to map association levels of silver immunolabels on cellular surfaces. We demonstrate the feasibility of this approach using silver immunolabels targeted at the epidermal growth factor receptor on A431 cells in a proof of principle experiment. The ability to measure immunolabel association levels on subcellular length scales in an optical microscope provides new opportunities for experimentally assessing receptor density distributions on living cells in solution.

Calibration of Silver Plasmon Rulers in the 1-25 nm Separation Range: Experimental Indications of Distinct Plasmon Coupling Regimes.

In this manuscript pairs of flexibly linked silver nanoparticles, so called silver plasmon rulers, are synthesized using a rational DNA programmed self-assembly procedure. The plasmon resonance energy (E(res)) versus distance relationship is calibrated for dimers comprising sphere-like silver nanoparticles with diameters of 41.0 ± 4.6 nm and surface-to-surface separations between 1-25 nm. Single dimer Rayleigh scattering spectra are correlated with structural information of the same dimers obtained through transmission electron microscopy with 1 nm spatial resolution. The calibration reveals different plasmon coupling regimes. For larger separations the plasmon resonance energy red-shifts continuously with decreasing center-to-center distance (L) until the L to diameter (D) ratio reaches a value of L/D ≈ 1.05. For shorter interparticle separations E(res) does not further red-shift; instead the slope of E(res)(L/D) levels off, and the measured resonance energies become broadly distributed. Overall, the spectral response of nearly touching dimers indicates that the plasmon coupling does not continue to intensify with decreasing interparticle separation at very short separations. The performed characterization of the distance dependent plasmon coupling forms the quantitative foundation for applications of plasmon rulers in plasmon coupling microscopy and nanoplasmonic devices with defined near- and far-field properties.

Biomineralization nanolithography: combination of bottom-up and top-down fabrication to grow arrays of monodisperse gold nanoparticles along peptide lines.

From top to bottom: Peptide lines were formed in trenches in the self-assembled monolayer (SAM) on an Au substrate. Combination of the top-down (peptide nanolithography) and the bottom-up fabrications (biomineralization) yielded arrays of monodisperse Au nanoparticles assembled on the peptide lines (see picture). The number of nanoparticles on the lines was simply determined by the width of the peptide pattern.

Correlated Optical Spectroscopy and Transmission Electron Microscopy of Individual Hollow Nanoparticles and their Dimers.

The optical spectra of individual Ag-Au alloy hollow particles were correlated with the particles' structures obtained by transmission electron microscopy (TEM). The TEM provided direct experimental access to the dimension of the cavity, thickness of the metal shell, and the interparticle distance of hollow particle dimers with high spatial resolution. The analysis of correlated spectral and structural information enabled the quantification of the influence of the core-shell structure on the resonance energy, plasmon lifetime, and plasmon coupling efficiency. Electron beam exposure during TEM inspection was observed to affect plasmon wavelength and lifetime, making optical inspection prior to structural characterization mandatory.

Crossbar assembly of antibody-functionalized peptide nanotubes via biomimetic molecular recognition.

Previously, a large scale assembly of nanowires in a parallel array configuration has been demonstrated, and one type of nanowire could interconnect two electrodes in the high-wire density. However, to assemble nanowires into practical logic-gate configurations in integrated circuits, we need more than the parallel assembly of nanowires. For example, when the assembling nanowires are monopolar semiconductors, logic gates such as AND, OR and NOR are to be assembled necessarily from two types of semiconducting nanowires, n-type and p-type, and some of these nanowires must cross perpendicularly to form a crossbar geometry for the logical operation. In this paper, the crossbar assembly of antibody-functionalized peptide nanotubes was demonstrated by a new biomimetic bottom-up technique. Molecular recognition between antigens and antibodies enabled two types of the antibody-functionalized bionanotubes to place them onto targeted locations on substrates, where their complementary antigens were patterned. When two rectangular pads of antigens, human IgG and mouse IgG, were patterned perpendicularly on an Au substrate by nanolithography and then the antihuman IgG nanotubes and the antimouse IgG nanotubes were incubated on this substrate in solution, these bionanotubes were attached onto corresponding locations to form the crossbar configuration.

3D-ordered macroporous materials comprising DNA.

Macroporous materials comprising DNA were fabricated with the colloidal crystal template. First, DNA and diazoresin (DR) molecules are fully filled into the voids of a colloidal crystal template. After thermal treatment and removal of the colloids, DNA porous materials with highly ordered structure were obtained. In the process of thermal treatment the cross-linking reaction takes place between DR and DNA, which plays an important role for sustaining the porous framework. The DNA porous materials will turn into a fluorescent DNA/dye composite after staining with Hoechst 33258 (Hoe), a characteristic fluorescent dye for DNA. This kind of composite DNA porous material may have potential applications in optical devices.

Stable thin films and hollow spheres composing chiral polyaniline composites.

Chiral polyaniline composite (CPAC) thin films were fabricated by self-assembly using diazoresin (DR) and CPAC. The weak linkage between the DR and CPAC of the film will convert to covalent bonds under UV irradiation or heating, and the thin film becomes very stable toward polar solvents and electrolyte aqueous solutions. Core-shell particles with stable DR/CPAC shell and polystyrene (PS) core can be prepared by similar methods. After the PS core is removed by chemical etching, stable DR/CPAC hollow spheres were obtained. Circular dichroism spectra and cyclic voltammetry measurements show that the DR/CPAC thin films are chirally active and possess good electrochemical stability.

Luminescence 3D-ordered porous materials composed of CdSe and CdTe nanocrystals.

The luminescence porous materials of CdTe or CdSe nanocrystals (NCs) were prepared by filling the corresponding NCs into the voids of colloidal crystal by co-deposition of polymer beads and NCs. After removing the beads with tetrahydrofuran (THF), the 3D-ordered porous materials of CdTe (or CdSe) NCs were obtained. The wavelength of maximum photoluminescence of the NCs porous material shows obvious red shift compared with their aqueous dispersion. Under the excitation of high-energy electron the porous materials of CdTe and CdSe NCs will emit photons that can be collected to form a cathode luminescence (CL) image.