Biomedical subjects

Fumitaka Mafuné

Publications and source records attributed to Fumitaka Mafuné.

6 recordsLinked to original sources

PubMed2006

Mechanism of laser-induced size-reduction of gold nanoparticles as studied by nanosecond transient absorption spectroscopy.

Gold nanoparticles with an average diameter of approximately 8 nm (Au approximately 15,000) were irradiated with a tightly focused pulse laser at 355 nm in an aqueous solution of sodium dodecyl sulfate (SDS). Transient absorption spectra of the solution were measured at 25-100 ns after the laser irradiation. The observed transient absorption around 720 nm is assignable to the 2p <-- 1s transition of solvated electrons produced via multiple ionization of the gold nanoparticles. The nascent charge state of the gold nanoparticles was estimated from the transient absorbance. The dependence of the charge state on the SDS concentration shows a gradual increase from approximately +60 to approximately +70 in the 2 x 10(-4) to 3 x 10(-4) M range and an abrupt increase up to approximately +710 at the critical micelle concentration (CMC) of SDS, 8 x 10(-3) M. TEM measurements after laser irradiation reveal that the gold nanoparticles fragment into Au(approximately 1000) at a SDS concentration of 3 x 10(-4) M, whereas they are significantly dissociated into Au(approximately 100) above the CMC. The observed correlation between the nascent charge states and the extent of size reduction of the gold nanoparticles after the laser treatment indicates that the size reduction is caused by the Coulomb explosion of the highly charged gold nanoparticles. The mechanism of laser-induced size reduction is quantitatively discussed based on the liquid drop model.

Journal Article↗

PubMed2006

Degradation of protein in nanoplasma generated around gold nanoparticles in solution by laser irradiation.

We developed a method of protein degradation in an aqueous solution containing gold nanoparticles by irradiation of a pulse laser. In the present study, lysozyme was used as an example. Lysozyme degradation proceeded most efficiently when a pH of the solution was adjusted so that it was at the isoelectric point. The scheme of the lysozyme degradation is as follows: (1) Lysozyme molecules in the solution are neutralized and adsorbed on the gold nanoparticles with its pH value adjusted at the isoelectric point, (2) nanoplasma is generated in the close vicinity of a gold nanoparticle which is excited by an intense 532-nm laser, (3) lysozyme molecules in the nanoplasma are degraded into small fragments. Lysozyme degradation does not proceed efficiently at a pH value deviated from the isoelectric point because the lysozyme molecules are dissolved uniformly so that only a small portion of the lysozyme molecules are located in the vicinity of gold nanoparticles which create the nanoplasma.

Gold↗

PubMed2005

Formation of Au(III)-DNA coordinate complex by laser ablation of Au nanoparticles in solution.

We discovered that an Au(III)-DNA coordinate complex, Au(III)(DNA-base)2(amine)L, are formed by laser ablation of Au nanoparticles in an aqueous solution containing DNA molecules in the presence of amines and multi-valent cations, where L represents an unknown ligand (either amine or water). Optical absorption spectrum of the solution after laser ablation exhibited a 360 nm absorption peak assined to ligand-->Au(III) charge transfer (LMCT) band of the coordinate complex. The complex is considered to be formed as follows: (1) the DNA molecules are neutralized by binding the multi-valent cations to their negatively charged phosphate groups, and adsorbed on the surface of the Au nanoparticles by a hydrophobic interaction, (2) Au(III) ions are liberated from the Au nanoparticles by laser ablation, and (3) an Au(III) ion reacts with amine and two DNA bases of a DNA molecule into an Au(III)(DNA-base)2(amine)L.

Amines↗

PubMed2004

Entropy production mapping on stretched DNA interacted with proteins.

This paper presents an entropy production mapping (EPM) method for detecting a higher-order structure change of a stretched and immobilized DNA molecule on a cover slip through measuring and mapping an increment of the orientational entropy (defined as "entropy production") of the Watson-Crick base pairs by the interaction of biological factors such as proteins; the stretched DNA molecule undergoes a higher-order structure change by the interaction, so that the orientational entropy at the interaction regions increases because the alignment of the base pairs is reduced at the regions. We demonstrated the utility of this "EPM method" by using a histone-lambda DNA system. It is revealed that the histone interaction region is clearly distinguished from no interaction regions on a stretched lambda DNA molecule immobilized on a cover slip.

Algorithms↗

PubMed2003

Nanoscale soldering of metal nanoparticles for construction of higher-order structures.

We demonstrated that platinum nanoparticles dispersed in pure water were "soldered" by gold into higher-order structures such as "nanowebs". In practice, gold nanoparticles in water containing the platinum nanoparticles were melted by irradiation of a pulsed 532-nm laser, which excites selectively the surface plasmon band of the gold nanoparticles, and the melted gold nanoparticles solder the platinum nanoparticles together into the nanowebs. Optical absorption spectroscopy and electron microscopy together with electron probe microanalysis were employed to observe the structure of the nanowebs and to elucidate their formation dynamics.

Journal Article↗

PubMed2003

Cleavage of stretched DNA on glass by histones observed with fluorescence microscopy.

A stretched single lambda DNA molecule labeled with TOTO-1 dye molecules was immobilized on a cover slip by casting a solution of DNA-lipid polyion complex containing TOTO-1 dye, and were loaded with an aqueous solution of histone. Fluorescence microscopy applied to the single DNA showed that (1) the TOTO-1 dye molecules intercalated in the stretched DNA molecule were vertically aligned almost completely with respect to the DNA axis, and (2) the stretched DNA was cleaved by interaction with histone molecules.

DNA↗