Flow-Induced Transport via Optical Heating of a Single Gold Nanoparticle

Optothermal trapping has gained increasing popularity in manipulation such as selecting, guiding, and positioning submicron objects because of a few mW laser power much lower than that required for optical trapping. The optotothermal trapping uses thermal gradient-induced phoretic motions, but the underlying physics of driving force has not been fully understood. In this study, we performed optotothermal trapping of 500-nm-diameter colloidal silica via a continuous laser illumination of a single gold nanoparticle from the bottom in a closed chamber. Under illumination, the tracer particles were attracted to the gold nanoparticle and trapped. Notably, the direction of migrating particles was always to hot gold nanoparticle regardless of the configuration of gold nanoparticle placed at two opposite sides of the chamber, on the bottom surface of an upper substrate (ceiling) or on the top surface of a lower substrate (floor). The previous interpretation based on thermal convective flow from the bottom to the top and circulating inside the chamber was only applicable to floor configuration and failed to explain our observation for ceiling. Instead, temperature-induced Marangoni effect at the water/superheated water interface is likely to play a role. This study promoted a better understanding of the driving mechanism in optothermal trapping. Moreover, as an application of the single-particle platform, we showed the photothermal phase separation-induced microdroplet formation of thermoresponsive polymers and the coating of non-thermoresponsive polymers on nanoparticles

Localized Phase Separation of Thermoresponsive Polymers Induced by Plasmonic Heating

Optical excitation-induced heating of a single gold nanoparticle potentially offers a high-temperature field confined to the immediate neighborhood of the particle. In this study, we applied darkfield microscopy imaging and Rayleigh scattering spectroscopy to pursue phase separation of aqueous thermoresponsive poly(N-isopropylacrylamide) and poly(vinyl methyl ether) adjacent to a gold nanoparticle that was heated by continuous wave laser illumination. Gold nanoparticles were supported on transparent substrates of glass or sapphire. From the imaging study, we observed that a 1−10-μm microdroplet covering the nanoparticle formed and grew in time scales of seconds to a few tens of seconds. The growth was triggered by the illumination and the droplet collapsed when the laser was blocked. At the same time, we observed scattering spectral changes characterized by a progressive redshift in the localized surface plasmon resonance (LSPR) band and an increasing scattering intensity in wavelengths region shorter than the LSPR band with increasing laser intensity. The scattering spectral changes were interpreted by the encapsulation of the nanoparticle by a polymer-rich droplet with increasing sizes. The present study revealed that thermoresponsive polymers were attracted to a hot gold nanoparticle and formed a microdroplet under illumination with a wavelength near the LSPR. Our findings demonstrate the potential of plasmonic heating to manipulate polymer migration and accumulation, which may find applications in protein crystallization

Purines. LXV. Preparatory study for the syntheses of the marine sponge purines agelasimines-A and -B: Synthesis and acetylation of their N(7)-benzyl analogues

Four-step synthetic routes from 3-methyladenine (10) to 7-benzyl-N6,3-dimethyladenine (1b) and 7-benzyl-1,2-dihydro-1,3-dimethyladenine (2b), selected as models for the marine sponge alkaloids agelasimine-A (1a) and agelasimine-B (2a), respectively, have been established. The key steps involved are regioselective methylations of 7-benzyl-3-methyladenine (8) and 7-benzyl-1,2-dihydro-3-methyladenine (11). The reaction of 1b with acetic anhydride in pyridine was found to give the monocyclic imidazole derivative 29b. A similar acetylation of 2b yielded the N6-acetyl derivative 20b. When treated with boiling H2O, 20b afforded 7-benzyl-2,3-dimethylhypoxanthine (21b) and a compound inferred to be the dihydrohypoxanthine derivative 30. Probable pathways to 29b from 1b and to 21b and 30 from 20b are proposed

The Quality Control Assessment of Commercially Available Coenzyme Q10-Containing Dietary and Health Supplements in Japan

Coenzyme Q10 (CoQ10) has been widely commercially available in Japan as a dietary and health supplement since 2001 and is used for the prevention of lifestyle-related diseases induced by free radicals and aging. We evaluated CoQ10 supplements to ensure that these supplements can be used effectively and safely. Commercially available products were selected and assessed by the quality control tests specified in the Japanese Pharmacopoeia XV. When the disintegration time of CoQ10 supplements was measured, a few tested supplements did not completely disintegrate even after incubation in water for an hour at 37°C. In the content test, many samples were well controlled. However, a few supplements showed low recovery rates of CoQ10 as compared to manufacturer’s indicated contents. Among soft capsule and liquid supplements, the reduced form of CoQ10 (H2CoQ10), as well as the oxidized form, was detected by HPLC with electrochemical detector. The results for experimental formulated CoQ10 supplements demonstrated that H2CoQ10 was produced by the interaction of CoQ10 with vitamins E and/or C. From these results, we concluded that quality varied considerably among the many supplement brands containing CoQ10. Additionally, we also demonstrated that H2CoQ10 can be detected in some foods as well as in CoQ10 supplements

Seismic exploration at Fuji volcano with active sources : The outline of the experiment and the arrival time data

Fuji volcano (altitude 3,776m) is the largest basaltic stratovolcano in Japan. In late August and early September 2003, seismic exploration was conducted around Fuji volcano by the detonation of 500 kg charges of dynamite to investigate the seismic structure of that area. Seismographs with an eigenfrequency of 2 Hz were used for observation, positioned along a WSW-ENE line passing through the summit of the mountain. A total of 469 seismic stations were installed at intervals of 250-500 m. The data were stored in memory on-site using data loggers. The sampling interval was 4 ms. Charges were detonated at 5 points, one at each end of the observation line and 3 along its length. The first arrival times and the later-phase arrival times at each station for each detonation were recorded as data. P-wave velocities in the surface layer were estimated from the travel time curves near the explosion points, with results of 2.5 km/s obtained for the vicinity of Fuji volcano and 4.0 km5/s elsewhere

Localized Phase Separation of Thermoresponsive Polymers Induced by Plasmonic Heating

Optical excitation-induced heating of a single gold nanoparticle potentially offers a high-temperature field confined to the immediate neighborhood of the particle. In this study, we applied darkfield microscopy imaging and Rayleigh scattering spectroscopy to pursue phase separation of aqueous thermoresponsive poly­(<i>N</i>-isopropylacrylamide) and poly­(vinyl methyl ether) adjacent to a gold nanoparticle that was heated by continuous wave laser illumination. Gold nanoparticles were supported on transparent substrates of glass or sapphire. From the imaging study, we observed that a 1–10 μm microdroplet covering the nanoparticle formed and grew in time scales of seconds to a few tens of seconds. The growth was triggered by the illumination, and the droplet collapsed when the laser was blocked. At the same time, we observed scattering spectral changes characterized by a progressive redshift in the localized surface plasmon resonance (LSPR) band and an increasing scattering intensity in the region of wavelengths shorter than the LSPR band with increasing laser intensity. The scattering spectral changes were interpreted by the encapsulation of the nanoparticle by a polymer-rich droplet with increasing sizes. The present study revealed that thermoresponsive polymers were attracted to a hot gold nanoparticle and formed a microdroplet under illumination with a wavelength near the LSPR. Our findings demonstrate the potential of plasmonic heating to manipulate polymer migration and accumulation, which may find applications in protein crystallization