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.

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.

Experiments on encapsulating Pt-labelled DNA molecules inside multiwalled carbon nanotubes (MWCNT) were performed under temperature and pressure conditions of 400K and 3 Bar. The DNA-CNT hybrids were purified via agarose gel electrophoresis and analyzed via high resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray spectroscopy (EDX). The results showed that the Pt-labelled DNA molecules attached to the outside walls of CNTs could be removed by electrophoresis. The HR-TEM and EDX results demonstrated that 2-3% of the Pt-labelled DNA molecules were successfully encapsulated inside the MWCNTs. The experimental study complements our previous molecular dynamics simulations on encapsulation of single stranded DNA oligonucleotides inside single wall carbon nanotubes under similar conditions in water. The van der Waals interaction between CNT and Pt-labelled DNA is believed to be the main driving force for this phenomenon. The DNA-CNT molecular complex could be further explored for potential applications in bio-nanotechnology.

The influence of single-walled carbon nanotubes (SWCNTs) on human HEK293 cells is investigated with the aim of exploring SWCNTs biocompatibility. Results showed that SWCNTs can inhibit HEK293 cell proliferation, decrease cell adhesive ability in a dose-and time-dependent manner. HEK293 cells exhibit active responses to SWCNTs such as secretion of some 20-30 kd proteins to wrap SWCNTs, aggregation of cells attached by SWCNTs and formation of nodular structures. Cell cycle analysis showed that 25g/ml SWCNTs in medium induced G1 arrest and cell apoptosis in HEK293 cells. Biochip analysis showed that SWCNTs can induce up-regulation expression of cell cycle-associated genes such as p16, bax, p57, hrk, cdc42 and cdc37, down-regulation expression of cell cycle genes such as cdk2, cdk4, cdk6 and cyclin D3, and down-regulation expression of signal transduction-associated genes such as mad2, jak1, ttk, pcdha9 and erk. Western blot analysis showed that SWCNTs can induce down-regulation expression of adhesion-associated proteins such as laminin, fibronectin, cadherin, FAK and collagen IV. These results suggest that down-regulation of G1-assoicated cdks and cyclins and upregulation of apoptosis-associated genes may contribute to SWCNTs induced G1 phase arrest and cell apoptosis. In conclusion, SWCNTs can inhibit HEK293 cells growth by inducing cell apoptosis and decreasing cellular adhesion ability.

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.