Many sensing/catalytic applications in nanotechnology require a programmed assembly of nanospheres/nanorods onto surfaces. The gold nanorods, formed by a seed-mediated, surfactant-assisted synthesis protocol, are stabilized in solution due to surface modification by the surfactant cetyltrimethylammonium bromide. DNAtemplated self-assembly of gold nanorods with different aspect ratios at different DNA concentration values has been studied using transmission electron microscopy. Under appropriate conditions such as aspect ratio and DNA concentration, gold nanorods assemble into one-and two-dimensional structures. A stable phase of side-by-side supramolecular assemblies was formed, and some of the double-layer assemblies extend to superlattices of nanorods. The resulting guide for designing statistically patterned arrays of nanoparticles suggests the possibility of fabricating spontaneously organized nanoscale devices.

A unique, sensitive, and highly specific fluoroimmunoassay system for antigen detection using gold and magnetic nanoparticles has been developed. The assay is based on the fluorescence quenching of fluorescein isothiocyanate caused by gold nanoparticles coated with monoclonal antibody. To demonstrate its analytical capabilities, the magnetic nanoparticles were coated with anti-r-fetoprotein polyclonal antibodies, which specifically bound with r-fetoprotein. Gold nanoparticles coated with anti-r-fetoprotein monoclonal antibodies could sandwich the r-fetoprotein captured by the magnetic nanoparticle probes. The sandwich-type immunocomplex was formed on the surface of magnetic nanoparticles and could be separated by a magnetic field. The supernatant liquid, which contained the unbound gold nanoparticle probes, was used to quench the fluorescence, and the fluorescence intensity of fluorescein isothiocyanate at 516 nm was proportional to the r-fetoprotein concentration. The result showed that the limit of detection of r-fetoprotein was 0.17 nM. This new system can be extended to detect target molecules with matched antibodies and has broad potential applications in immunoassay and disease diagnosis.

We report molecular dynamics simulations showing that a DNA molecule could be spontaneously inserted into carbon nanotube (CNT) in a water solute environment. The van der Waals and hydrophobic forces were found to be important for the insertion process, with the former playing a more dominant role in the DNA-CNT interaction. Our study suggests that the encapsulated CNT-DNA molecular complex can be further exploited for applications such as DNA modulated molecular electronics, molecular sensors, electronic DNA sequencing, and nanotechnology of gene delivery systems.