The photothermal effect of an ultratrace amount of nonfluorescent molecules in liquid was determined by optimizing the optical arrangement for a thermal lens microscope. The optimized experimental setup could be determined from the evaluation of probing volume and the concentration of the sample solutions even when the expectation of the molecule number in the probing region was less than a single molecule. The minimum expectation, which is explained as being the time average, was 0.4 molecule of Pb(II) octaethylporphyrin (OEP) in benzene. The concentrations in the 9.7 x 10(-11)-7.8 x 10(-10) M region used in this work corresponded to the expected number of 0.4-3.4 molecules, and the calibration curve in this region showed good linearity. Taking into account the enhancement factor of solvent, the molar absorption coefficient of solute, and the optimization of the optical arrangement, the present result, which was the determination limit of 0.34, was consistent with that previously reported. The relation between molecular behavior in the probing volume and the signal was discussed. The average temperature rise in the probing volume by the photothermal effect for the single OEP molecule was estimated as 3.1 muK, and this value was detectable, based on conventional thermal lens measurements for bulk scale sample.

We developed a novel laser microscope based on the thermal lens effect induced by a coaxial beam comprised of excitation and probe beams. The signal generation mechanism was confirmed to be an authentic thermal lens effect from the measurement of signal and phase dependences on optical configurations between the sample and the probe beam focus, and therefore, the thermal lens effect theory could be applied. Two-point spatial resolution was determined by the spot size of the excitation beam, not by the thermal diffusion length. Sensitivity was quite high, and the detection ability, evaluated using a submicron microparticle containing dye molecules, was 0.8 zmol/µm 2 , hence a distribution image of trace chemical species could be obtained quantitatively. In addition, analytes are not restricted to fluorescent species, therefore, the thermal lens microscope is a promising analytical microscope. A two-dimensional image of a histamine molecule distribution, which was produced in mast cells at the femtomole level in a human nasal mucous polyp, was obtained.

Membrane composition serves to identify intracellular compartments, signal cell death, as well as to alter a cell's electrical and physical properties. Here we use amperometry to show that supplementation with the phospholipids phosphatidylcholine (PC), phosphatidylethanolamine (PE), sphingomyelin (SM), and phosphatidylserine (PS) can alter several aspects of exocytosis. Changes in the amperometric peak shape derived from individual exocytosing vesicles reveal that PC slows expulsion of neurotransmitter while PE accelerates expulsion of neurotransmitter. Amperometry data reveal a reduced amount of catecholamine released per event from PC-treated cells while electron micrographs indicate the vesicles in these cells are 50% larger than controls, thus providing evidence of pharmacological changes in vesicle concentration. Addition of SM appears to affect the rate of fusion pore expansion, indicated by slower peak rise times, but does not affect decay times or quantal size. Addition of PS results in a 1.7-fold increase in the number of events elicited by high-K + depolarization. Electron micrographs of PS-treated cells suggest that increased vesicle recruitment underlies enhanced secretion. We did not observe any effect of phosphatidylinositol (PI) treatment. Together these data suggest that differences in membrane composition affect exocytosis and might be involved in mechanisms of cell function controlling the dynamics of communication via exocytosis.

We considered the trans → cis photoisomerization dynamics of the S2-excited azobenzene derivatives in terms of the potential energy gap between the n-π* (S1) and the π-π* (S2) state. The photoisomerization dynamics of trans-4-aminoazobenzene (trans-4-AAB) which has an energy gap (3000−4000 cm-1) rather smaller than that of trans-azobenzene (∼10000 cm-1) due to an amino-substitution was investigated using UV−vis transient absorption spectroscopy. The recorded transient absorption spectra of the π-π* (S2) excited trans-4-AAB in ethanol and heptanol indicated that the π-π* state of the trans-4-AAB decays to the n-π* state with a time constant of 0.2 ps. Following this process, the n-π* state decays to the ground state via two reaction pathways with time constants of 0.6 and 1.9 ps, and finally vibrational cooling of the ground state occurs with ∼15 ps. The π-π* state decay dynamics of the π-π* excited trans-4-AAB showed good agreement with that of the π-π* excited trans-azobenzene. On the other hand, the n-π* state decay dynamics of the π-π* excited trans-4-AAB was apparently different from that of the π-π* excited trans-azobenzene, and it corresponds well to that of the trans-azobenzene directly excited to the n- π * state. In addition, in the photoisomerization of the π-π* excited trans-4-AAB, we could not observe the solvent dependence of the n-π* state lifetime which has been reported in the photoisomerization of the π-π* excited trans-azobenzene. On the basis of the potential energy diagram of azobenzene, we considered that the similarity of the n-π* state decay dynamics observed for the π-π* excited trans-4-AAB and the n-π* excited trans-azobenzene originated from the small potential energy gap between the π-π* and the n-π* states of 4-AAB. These results indicated that not only the photoexcitation condition (π-π* excitation or n-π* excitation), but also the potential energy gap between the π-π* and the n-π* states is an important factor which determines the trans → cis photoisomerization dynamics of azobenzene derivatives.

The ultrafast relaxation dynamics of a widely used viscosity probe molecule, auramine O (AuO), was investigated in water and a water/aerosol-OT (AOT)/n-heptane reversed micelle. We discussed the contribution of specific interactions between AuO and the local environment to the relaxation dynamics. The transient absorption spectra of AuO showed that the nonradiative relaxation process of the photoexcited AuO in the AOT-reversed micelle was approximately 1 order slower than that in bulk water and the relaxation rate decreased with a decrease of the size of the reversed micelle. The slowing down of the relaxation was attributed to a depletion of the ultrafast solvation dynamics of water molecules in the interfacial area of the reversed micelle as well as an increase of viscosity, which strongly suggested that the viscosity of the reversed micelle determined from the fluorescence yield of AuO was somewhat overestimated. In addition, it was observed that the absorption coefficient of the twisted intramolecular charge transfer-like (TICT-like) intermediate state of the AuO in the reversed micelle was about half as large as that in bulk water. A decrease of the refractive index of the TICT-like state was also observed in the reversed micelle by the ultrafast transient lens measurements. The reduction of both the absorption coefficient and the refractive index of the TICTlike state indicated a considerable change of the molecular structure or the charge distribution of the TICTlike state. Such a change of the TICT-like state suggested the existence of strong interactions between AuO and AOT. These interactions would also affect the relaxation dynamics and the fluorescence yield of the AuO in the reversed micelle.

We monitored the change in the number density of cetyltrimethylammonium bromide (CTAB) molecules at a water/nitrobenzene (W/NB) liquid/liquid interface by a newly developed time-resolved quasi-elastic laser scattering (QELS) method. The results are used to discuss the molecular collective behavior there. From the time-courses after the injection of a CTAB solution beyond its critical micelle concentration (cmc), we found an anomalous temporary increase of the number density of CTAB molecules at the interface, which cannot be explained by a simple diffusion model. This suggests that the transfer of CTAB micelles across the interface occurs in the following process: the collapse of micelles at the interface region; the oriented adsorption of CTAB molecules onto the interface, forming a monolayer; and the desorption from the interface. Thermodynamic evaluation results also support this model; that is, the equilibrium number density of CTAB molecules at the interface follows the Langmuir adsorption isotherm obtained from our measurement, and the adsorption energy calculated from the isotherm agrees well with the theoretical value of the micelles.

We investigated the local environment of water confined inside the hollow cylinder of lipid nanotubes (LNTs) by time-resolved fluorescent measurements and attenuated-total-reflectance infrared (ATR-IR) spectroscopy. The LNT was obtained by self-assembly of cardanyl glucosides in water at room temperature and had an open-ended cylindrical nanospace with a diameter of 10-15 nm, a length of 10-100 microm, and hydrophilic inner and outer surfaces. We introduced a fluorescent probe of 8-anilinonaphthalene-1-sulfonate into the confined water and observed an extremely slow dynamic Stokes shift with a correlation time of 1.26 ns, which was 2-3 orders of magnitude longer than that of bulk-phase water. From the peak shift of the fluorescent spectrum, the local solvent polarity (ET(30)) of the confined water was estimated as 50 kcal/mol, which is 20% lower than that in bulk water. ATR-IR measurements showed that the hydrogen-bond network of water inside the LNT was more developed than that in bulk water at room temperature, which is in contrast to the water in other self-assembled confined geometries, such as Aerosol-OT (AOT) reversed micelles.

Ultrafast measurements of photoexcited carrier dynamics within a 60 nm subsurface of a crystalline silicon wafer were carried out using subpicosecond transient reflectivity. A uv pump light was employed to restrict carrier generation to occur within the subsurface by direct interband transitions. Carrier diffusion was found to be suppressed in the subsurface region of the intrinsic silicon wafer. For ion-implanted silicon wafers, heat was generated within a few picoseconds after the laser irradiation. By scanning a partially ion-implanted silicon wafer, the two-dimensional image was obtained, which showed that time-resolved imaging can separately map photoexcited carrier density and transient temperature rise. The possibility of three-dimensional process monitoring was considered as well.