Biotemplating rod-like viruses for the synthesis of copper nanorods and nanowires.

BACKGROUND: In the past decade spherical and rod-like viruses have been used for the design and synthesis of new kind of nanomaterials with unique chemical positioning, shape, and dimensions in the nanosize regime. Wild type and genetic engineered viruses have served as excellent templates and scaffolds for the synthesis of hybrid materials with unique properties imparted by the incorporation of biological and organic moieties and inorganic nanoparticles. Although great advances have been accomplished, still there is a broad interest in developing reaction conditions suitable for biological templates while not limiting the material property of the product. RESULTS: We demonstrate the controlled synthesis of copper nanorods and nanowires by electroless deposition of Cu on three types of Pd-activated rod-like viruses. Our aqueous solution-based method is scalable and versatile for biotemplating, resulting in Cu-nanorods 24-46 nm in diameter as measured by transmission electron microscopy. Cu2+ was chemically reduced onto Pd activated tobacco mosaic virus, fd and M13 bacteriophages to produce a complete and uniform Cu coverage. The Cu coating was a combination of Cu0 and Cu2O as determined by X- ray photoelectron spectroscopy analysis. A capping agent, synthesized in house, was used to disperse Cu-nanorods in aqueous and organic solvents. Likewise, reactions were developed to produce Cu-nanowires by metallization of polyaniline-coated tobacco mosaic virus. CONCLUSIONS: Synthesis conditions described in the current work are scalable and amenable for biological templates. The synthesized structures preserve the dimensions and shape of the rod-like viruses utilized during the study. The current work opens the possibility of generating a variety of nanorods and nanowires of different lengths ranging from 300 nm to micron sizes. Such biological-based materials may find ample use in nanoelectronics, sensing, and cancer therapy.

Spectral tuning of organic nanocolloids by controlled molecular interactions.

The controlled self-assembly of molecules and interactions between them remain a challenge in creating tunable and functional organic nanostructures. One class of molecular systems that has proven useful for incorporating tunable functionality at different length scales is liquid crystals (LCs) due to its ability to inherently self-organize. Here we present a novel approach to utilize the self-assembly of polymerizable liquid crystals to control the molecular aggregation of stable fluorescent chromophores and create a unique class of organic fluorescent nanocolloids. By adjusting the ratio between the dye and LC molecules inside the nanocolloids, we demonstrate the ability to control the molecular interactions and tune the fluorescent emission spectra of nanocolloid populations under single wavelength excitation. The single absorption spectrum and multiple emission spectra are highly desirable and reminiscent of the spectroscopic signature of quantum dots. These novel fluorescent nanocolloids have broad potential applications in fluorescent imaging and biological labeling.

Role of surfactant in the stability of liquid crystal-based nanocolloids.

We examine the dependence of liquid crystalline nanocolloid formation and stability on surfactant. Nanocolloids composed of polymerizable liquid crystal mesogens and cross-linking agents and capped with either ionic or nonionic surfactants are prepared via the miniemulsion technique. Colloids synthesized with anionic surfactant were stable and displayed 2D hexagonal packing when deposited via slow vertical pulling of the silicon substrate from an aqueous suspension. Liquid crystal nanocolloids stabilized with the nonionic, polar polymer polyvinyl alcohol (PVA) were stable in aqueous environments but coalesced upon drying to form relatively large, well-defined crystal-like structures with uniform birefringence. SEM images reveal that the coalesced structures have mesalike features. Polarized light, atomic force, and polarized Raman microscopy of these structures indicate that the liquid crystal molecules are arranged with their long molecular axis slightly tilted with respect to the surface normal. A mechanism is proposed to explain the formation of the mesalike structures from the nanocolloids. These studies provide fundamental insight into the incorporation and stabilization of polymerizable liquid crystal molecules into nanovolumes and open up opportunities for the incorporation of functionality and anisotropy into isotropically shaped nanocolloids.

Formation of aromatic siloxane self-assembled monolayers.

We describe reproducible protocols for the chemisorption of self-assembled monolayers (SAMs), useful as imaging layers for nanolithography applications, from p-chloromethylphenyltrichlorosilane (CMPS) and 1-(dimethylchlorosilyl)-2-(p,m-chloromethylphenyl)ethane on native oxide Si wafers. Film chemisorption was monitored and characterized using water contact angle, X-ray photoelectron spectroscopy, and ellipsometry measurements. Atomic force microscopy was used to monitor the onset of multilayer deposition for CMPS films, ultimately allowing film macroscopic properties to be correlated with their surface coverage and nanoscale morphologies. Although our results indicate the deposition of moderate coverage, disordered SAMs under our conditions, their quality is sufficient for the fabrication of sub-100-nm-resolution metal features. The significance of our observations on the design of future imaging layers capable of molecular scale resolution in nanolithography applications is briefly discussed.

Triarylphosphine-stabilized platinum nanoparticles in three-dimensional nanostructured films as active electrocatalysts.

Ligand-stabilized platinum nanoparticles (Pt NPs) can be used to build well-defined three-dimensional (3-D) nanostructured electrodes for better control of the catalyst architecture in proton exchange membrane fuel cells (PEMFCs). Platinum NPs of 1.7 +/- 0.5 nm diameter stabilized by the water-soluble phosphine ligand, tris(4-phosphonatophenyl)phosphine (TPPTP, P(4-C6H4PO3H2)3), were prepared by ethylene glycol reduction of chloroplatinic acid and subsequent treatment of the isolated nanoparticles with TPPTP. The isolated TPPTP-stabilized Pt NPs were characterized by multinuclear magnetic resonance spectroscopy (31P and 195Pt NMR), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS). The negatively charged TPPTP-Pt NPs were electrostatically deposited onto a glassy carbon electrode (GCE) modified with protonated 4-aminophenyl functional groups (APh). Multilayers were assembled via electrostatic layer-by-layer deposition with cationic poly(allylamine HCl) (PAH). These multilayer films are active for the key hydrogen fuel cell reactions, hydrogen oxidation (anode) and oxygen reduction (cathode). Using a rotating disk electrode configuration, fully mass-transport limited kinetics for hydrogen oxidation was obtained after 3 layers of TPPTP-Pt NPs with a total Pt loading of 4.2 microg/cm2. Complete reduction of oxygen by four electrons was achieved with 4 layers of TPPTP-Pt NPs and a total Pt loading of 5.6 microg/cm2. A maximum current density for oxygen reduction was reached with these films after 5 layers resulting in a mass-specific activity, i(m), of 0.11 A/mg(Pt) at 0.9 V. These films feature a high electrocatalytic activity and can be used to create systematic changes in the catalyst chemistry and architecture to provide insight for building better electrocatalysts.

Fabrication of biological nanostructures by scanning near-field photolithography of chloromethylphenylsiloxane monolayers.

We demonstrate the fabrication of sub-100-nm DNA surface patterns by scanning near-field optical lithography using a near-field scanning optical microscope coupled to a UV laser and a chloromethylphenylsiloxane (CMPS) self-assembled monolayer (SAM). The process involves 244-nm exposure of the CMPS SAM to create nanoscale patterns of surface carboxylic acid functional groups, followed by their conversion to the N-hydroxysuccinimidyl ester and reaction of the active ester with DNA to spatially control DNA grafting with high selectivity.

Fabrication and characterization of 3D hydrogel microarrays to measure antigenicity and antibody functionality for biosensor applications.

We report the fabrication, characterization and evaluation of three-dimensional (3D) hydrogel thin films used to measure protein binding (antigenicity) and antibody functionality in a microarray format. Protein antigenicity was evaluated using the protein toxin, staphylococcal enterotoxin B (SEB), as a model on highly crosslinked hydrogel thin films of polyacrylamide and on two-dimensional (2D) glass surfaces. Covalent crosslinking conditions were optimized and quantified. Interrogation of the modified 3D hydrogel was measured both by direct coupling of a Cy5-labeled SEB molecule and Cy5-anti-SEB antibody binding to immobilized unlabeled SEB. Antibody functionality experiments were conducted using three chemically modified surfaces (highly crosslinked polyacrylamide hydrogels, commercially available hydrogels and 2D glass surfaces). Cy3-labeled anti-mouse IgG (capture antibody) was microarrayed onto the hydrogel surfaces and interrogated with the corresponding Cy5-labeled mouse IgG (antigen). Five different concentrations of Cy5-labeled mouse IgG were applied to each microarrayed surface and the fluorescence quantified by scanning laser confocal microscopy. Experimental results showed fluorescence intensities 3-10-fold higher for the 3D films compared to analogous 2D surfaces with attomole level sensitivity measured in direct capture immunoassays. However, 2D surfaces reported equal or greater sensitivity on a per-molecule basis. Reported also are the immobilization efficiencies, inter-and intra-slide variability and detection limits.

Colored thin films for specific metal ion detection.

This paper describes the investigation of chitosan and poly(allylamine) (PAH) for the creation of a multi-film, color-based dipstick for the detection of metal ions in solution. Thin, colored films of chitosan and PAH cross-linked with hexamethylene 1,6-di(aminocarboxysulfonate) (HDACS) are created where color is due to film thickness and optical interference effects. The films are investigated for their ability to selectively detect aqueous metal ions via changes in thickness and/or color. Chitosan-HDACS films were selective for Cr(VI) over all other metal ions tested including Cr(acac)3 and Cr(NO3)3 x 9H2O, and PAH-HDACS films were selective for Cu(II) and Cu(I) salts over all other metal ions tested. The irreversible, selective changes due to metal ion solutions were not caused by varying the pH. Potomac River water was also tested using the two films, with results indicating the presence of Cu(II) in the aqueous sample.