Highly organized supercrystals of Au nanorods with plasmonic antennae enhancement of electrical field have made possible fast direct detection of prions in complex biological media such as serum and blood. The nearly perfect three-dimensional organization of nanorods render these systems excellent surface enhanced Raman scattering spectroscopy substrates with uniform electric field enhancement, leading to reproducibly high enhancement factor in the desirable spectral range.S urface enhanced Raman scattering (SERS) spectroscopy is not only one of the most sensitive analytical techniques but also can be used under biological conditions. Additionally, SERS signals are strongly dependent on conformational changes in macromolecules such as proteins (1). Unfortunately, although SERS of proteins has been consistently investigated during the last decade (2-6), enhancement factors (EFs) obtained for most conventional (nonfluorescent) proteins are still insufficient for their direct detection in complex biological media (7). There are two additional very serious challenges as well. Both quantitative detection by SERS and reproducible geometry of the "hot spots" necessary for SERS are difficult to achieve. The way to solve these challenges is to design and fabricate a highly organized photonic structure (8) that provides a high electromagnetic field enhancement in a reproducible geometry (9, 10). Recent demonstration of near-field focalization by nanoantennas (11,12) has paved the way for development of ultrasensitive SERS substrates that can concentrate the near field within certain confined regions, allowing one to obtain extremely high EFs (13-15). Such a nanoantenna effect was predicted and found for nanorod (NR) dimers, where the maximum focalization is present at the NR tips (16,17). One can hypothesize, therefore, that a highly organized system of NRs (18-21) acting as an extended nanoantenna may provide resolution for the SERS challenges of proteins or their segments. In turn, this hypothesis can lead to significant technological development for relevant biomedical problems. One example of those problems is the presymptomatic detection of scrambled prions directly in biological fluids.Prions are hard-to-detect infectious agents that cause a number of fatal neurodegenerative diseases in mammalians such as bovine spongiform encephalopathy (BSE), scrapie of sheep, and Creutzfeldt-Jakob disease (CJD) of humans (22), and recently traced as well to other neurodegenerative syndromes as Alzheimer's (23) and Parkinson (24). Invariably, all of these diseases involve the modification of the endogenous and functional prion protein (PrP C ) into a nonfunctional but much more stable form (PrP SC ) giving rise to the so-called amyloid plaques in the brain and other nervous tissues (25). Detection of its presence for contention in cattle or diagnosis in humans or blood transfusion banks (26) is very difficult even by state-of-the-art immunological methods such as fluorescence immunoassay, RIA, or ELISA (27) or protein misfolding c...

Polymerase chain reaction (PCR) was realized on the surface of gold nanoparticles (NPs) as a tool for self-organization at nanoscale and as a step toward programmable production of sufficient quantities of functional metallic superstructures. The assembly is controlled by varying the density of the primer on the surface of gold NPs and the number of PCR cycles generating a mixture of dimers, trimers, tetramers, etc., with gradually increasing complexity. This process leads to strong chirality of the assemblies arising from the three-dimensional positioning of NPs in space which had never been observed before. A circular dichroism band of the superstructures coincides with the plasmon oscillations of the multi-NP systems of Au colloids. This new collective optical property of NPs embracing the diversity of shapes and diameters in the starting dispersions opens unique opportunities for the development of negative index materials.

A targeted gold nanoparticle has been developed as a contrast agent for photoacoustic medical imaging. We have studied cancer cell targeting by antibody conjugated gold nanorods for high contrast photoacoustic imaging. By changing the aspect ratio of the elongated "rod" shape of the gold nanoparticle, its plasmon peak absorption wavelength can be tuned to the near IR ͑700-900 nm͒ for an increased penetration depth into biological tissue. Effective cell targeting and sensitive photoacoustic detection of a single layer of cells are demonstrated. Combining ultrasound with contrast agent based photoacoustic imaging is proposed as a visual tool to compound molecular and structural information for early stage prostate cancer detection.

Conductive organic and composite films represent the critical component of many areas of technology. This study demonstrates that highly conductive coatings can be made by layer-by-layer (LBL) assembly of single-walled carbon nanotubes (SWNTs). These films reveal electrical conductivities of 10 2 to ∼10 3 S/m at room temperature without doping with nanotube loading as low as ∼10%. This is indicative of efficient utilization of SWNT in percolation pathways. Low SWNT loading also makes the coatings quite transparent with transmission as high as 97% for visible light. Thicker delaminated LBL films displayed conductivities of 4.15 × 10 4 S/m. The free-standing films were highly flexible and possessed 160 MPa of tensile strength, which makes them the strongest organic conductor. The high strength and conductivities are attributed to the unique homogeneity of the LBL assembled composites, which opens the way to future optimization of electrical, mechanical, and optical properties and to fit the needs of specific applications, which may be exemplified by transparent flexible electronics, light emitting diodes, smart windows, solar cells, sensors, structural materials, and biomedical devices.

Parallel or angle parked: Gold nanorods (see picture) were selectively modified either on the sides or ends using complementary microcystin (MC‐LR) antibody and antigen (blue). Fast detection of MC‐LR (green) was successfully achieved with these assemblies, and both sensitivity and detection ranges were markedly better for the end‐to‐end motif (right) than the side‐to‐side variant (left).

The preparation of a high-strength and highly transparent nacre-like nanocomposite via layer-by-layer assembly technique from poly(vinyl alcohol) (PVA) and Na+-montmorillonite clay nanosheets is reported in this article. We show that a high density of weak bonding interactions between the polymer and the clay particles: hydrogen, dipole-induced dipole, and van der Waals undergoing break-reform deformations, can lead to high strength nanocomposites: sigmaUTS approximately 150 MPa and E' approximately 13 GPa. Further introduction of ionic bonds into the polymeric matrix creates a double network of sacrificial bonds which dramatically increases the mechanical properties: sigmaUTS approximately 320 MPa and E' approximately 60 GPa.

Gold nanorods have unusually strong absorption in near infrared, which can be utilized for an optical imaging with nanocolloids. The feasibility of photoacoustic imaging of inflammatory responses using bioconjugated gold nanorods is demonstrated. To target the stimulated cells, gold nanorods were conjugated to anti-intercellular adhesion molecule-1 (ICAM-1) which binds to cell surfaces over expressing ICAM-1. A monolayer of stimulated endothelial cells labeled with bioconjugated gold nanorods was scanned using a high frequency transducer. Photoacoustic images differentiated inflamed cells from control cells and matched well with fluorescence images. This technology may permit identification of critical inflammation sites such as blood vessels.

Layer-by-layer (LBL) assembly is one of the most ubiquitous coating techniques today. It also offers a pathway for multifunctional/multicomponent materials with molecular-scale control of stratified structures. However, technological applications of LBL are impeded by laborious and fluid-demanding nature of the process. While vertical organization of LBL films is natural for this technique, the control of lateral organization of the films is fairly difficult. Using the deposition of carbon nanotubes (SWNTs) and other nanoscale colloids, we introduce here a new approach to LBL based on dewetting phenomena, d-LBL. Its strengths include: (1) elimination of rinsing steps, (2) significant acceleration of the process, (3) improvement of lateral organization of LBL films, and (4) ability to produce nanostructured coatings from colloids when classical LBL fails. The generality of d-LBL can compete with traditional LBL and is demonstrated for cellulose nanowires, polyelectrolyte pairs, and semiconductor nanoparticles, metal oxides, and Au nanorods.