Groove-spanning behavior of lipid membranes on microfabricated silicon substrates

We report on a spreading behavior of phospholipid membranes that arise from a lump of phospholipid (a lipid source) on topographically patterned substrates immersed in an aqueous solution. Microgrooves with well-defined shapes were prepared on Si111 surfaces by anisotropic etching in an alkaline solution. A spreading front that consists of membrane lobes and a single lipid bilayer was observed on the patterned silicon substrates by utilizing fluorescence interference contrast (FLIC) microscopy. FLIC images indicate that the membrane lobes span the microgrooves, while the underlying single lipid bilayer spread along the surface of the microgrooves. In fact, fluorescent polystyrene nanoparticles could be encapsulated in the microgrooves that were completely covered with the membrane lobes. The groove-spanning behavior of membrane lobes is discussed in terms of a balance between adhesion and bending energies of lipid bilayers.     

Fluorescence and Laser photolysis studies on 1,2,4,5-tetracy anobenzene CT complexes in micellar solutions

CT complexes of 1,2,4,5-tetracyanobenzene were formed in the inner part of neutral micelles and in the surface region of ionic ones. The excitation of the CT absorption band of these complexes gives broad and structureless CT fluorescence spectra, their lifetimes being relatively short (≈10 ns). Micellar effect upon ionic photodissociation was observed, and their quantum yeild is smaller than that obtained in acetonitrile. These results are quite different from those on another typical excited CT system of pyrene and N,N-dimethylaniline.     

Spatiotemporal Dynamics of Aggregation-Induced Emission Enhancement Controlled by Optical Manipulation

We present spatiotemporal control of aggregation-induced emission enhancement (AIEE) of a protonated tetraphenylethene derivative by optical manipulation. A single submicrometer-sized aggregate is initially confined by laser irradiation when its fluorescence is hardly detectable. The continuous irradiation of the formed aggregate leads to sudden and rapid growth, resulting in bright yellow fluorescence emission. The fluorescence intensity at the peak wavelength of 540 nm is tremendously enhanced with growth, meaning that AIEE is activated by optical manipulation. Amazingly, the switching on/off of the activation of AIEE is arbitrarily controlled by alternating the laser power. This result means that optical manipulation increases the local concentration, which overcomes the electrostatic repulsion between the protonated molecules, namely, optical manipulation changes the aggregate structure. The dynamics and mechanism in AIEE controlled by optical manipulation will be discussed from the viewpoint of molecular conformation and association depending on the laser power.     

Analysis of radiation pressure exerted on a metallic particle within an evanescent field

Radiation pressure induced by an evanescent field was experimentally analyzed for a single submicrometer-sized gold particle. The force measurement was based on a thermodynamic analysis of Brownian motion by use of a three-dimensional position-sensing technique. The lateral radiation pressure could be ascribed to a scattering force, which was oriented in the same direction as the propagation vector of the incident laser beam. The potential profile in the longitudinal direction indicated that the gold particle was attracted to the high-intensity region of the evanescent field by a gradient force.     

Confinement of photopolymerization and solidification with radiation pressure

Controlling chemical reactions within a small space is a significant issue in chemistry, and methods to induce reactions within a desired position have various potential applications. Here we demonstrate localized, efficient photopolymerization by radiation pressure. We induced a one-photon UV polymerization of liquid acrylate solutions in the optical-trapping potential of a focused near-IR (NIR) laser beam, leading to the confinement of solidification to a minute space with dimensions smaller or equal to one-fifth of the wavelength of the NIR laser. Our approach can produce solidification volumes smaller than those achievable with conventional one-photon polymerization, thus enabling the production of tiny polymeric structures that are smaller than the diffraction limit of the trapping light. This is the first demonstration of a radiation pressure effect on a photochemical reaction.     

Porphyrin-sensitized laser swelling and ablation of polymer films

Laser-induced morphological changes of poly(methyl methacrylate), poly(N-vinylcarbazole), and gelatin films doped with porphyrins have been studied by etch depth measurement and scanning electron microscopy. An irreversible swelling of the irradiated surface was observed for all films in the case of low laser fluence. The swelling was replaced by ablation when the fluence was increased. The etch depth depends on the irradiation fluence and the dye concentration in the polymer. The observation of the irradiated surfaces suggests that the thermal effect is predominant both for swelling and ablation. The surface temperature at which swelling or ablation is initiated was estimated, assuming that these morphological changes take place at a certain temperature for any dye concentration in each polymer film.     

Time-resolved total internal reflection fluorescence spectroscopy of polymer films

Using total internal reflection, the possibility of a subnanosecond fluorescence spectroscopy for elucidating photophysical and photochemical processes of polymer surface is demonstrated. The thickness which can be studied under the present experimental conditions is of the order of 0.01 μm.     

Grafting of methyl methacrylate and its derivatives onto blood

The grafting of vinyl monomers by tri-n-butylborane to blood has been investigated. The infrared spectra indicated that the monomers were grafted onto blood components. The grafting seems to occur onto blood proteins, mainly onto hemoglobin. The presence of water was essential to the grafting. The hydrolysis of the graft suggests that basic amino acids in the blood proteins, such as lysine and histidine, play an important role in the grafting.     

Energy transfer in the doped poly(N-Vinylcabazole)films

The energy transfer process to guest molecule5 m poly(N-vinylcarbJZole) films WJS directly nir.isurcd In (lie film con- taining pciylencihc sandwich excimer site opcralcs as an cncrEy donor, while the evciple't si-itc composed ofthccaiba2olc- dirnettiyl IcrcphtliaJate pair is fornied by trapping tlie migrating monomer fluorescent state.