Biological network systems, such as inter- and intra-cellular signalling systems, are handled in a sophisticated manner by the transport of molecular information. Over the past few decades, there has been a growing interest in the development of synthetic molecular-transport systems. However, several key technologies have not been sufficiently realized to achieve optimum performance of transportation methods. Here we show that a new type of supramolecular system comprising of carbon nanotubes and liposomes enables the directional transport and controlled release of carrier molecules, and allows an enzymatic reaction at a desired area. The study highlights important progress that has been made towards the development of biomimetic molecular-transport systems and various lab-on-a-chip applications, such as medical diagnosis, sensors, bionic computers and artificial biological networks.

We report in situ observation of cluster growth of nanoparticles confined in an optical trapping potential by means of fluorescence correlation spectroscopy. When an optical trapping force caused by a highly focused laser beam acts on nanoparticle suspensions, the number of nanoparticles increases and an assembly can be formed at the focal spot. The decay times of fluorescence autocorrelation curves were investigated as a function of the irradiation time of the laser beam and the laser power. In the initial stage of the optical assembling, the decay time increases with the irradiation time of the laser beam. On the other hand, in the later stage, a decrease of the decay time was observed. This behavior is explained successfully by using two models of Brownian motion under weak and strong optical trapping. It was revealed that trapping and clustering of nanoparticles proceed simultaneously and clusters confined in the focal spot make larger aggregates spontaneously.

A method including surface silanization, phase transfer and self-assembly, and SiO₂ shell growth has been developed to incorporate multiple hydrophobic CdSe/ZnS nanocrystals into SiO₂ beads where they are well suited for bio-application due to their high brightness, less-cytotoxic, and non-blinking nature.

When a laser beam is focused into colloidal nanoparticle suspensions, a number of nanoparticles can be confined in the focal spot due to an optical gradient force. To reveal the assembling dynamics of polymer nanoparticles, the assembling process was investigated by analyzing the time evolution of the fluorescence intensity of the nanoparticles. In a dilute suspension of 100-nm-sized particles, a stepwise increase of the fluorescence intensity corresponding to a trapped single nanoparticle was observed. Statistical analysis revealed that the initial assembling rate of nanoparticles was proportional to the laser power and concentration of particle suspensions as expected from the diffusion equation. In 40-nm-sized particle suspensions, blinking profiles of fluorescence intensity were obtained, in which 2–3 particles were simultaneously trapped and then escaped from the focal point. It is considered from statistical analyses and two-dimensional Monte Carlo simulations that this assembling phenomenon is attributable to cluster formation assisted by optical trapping.