Optical and dynamic properties of water-soluble highly luminescent CdTe quantum dots

CdTe quantum dots (QDs) were synthesized in aqueous solution using thioglycolic acid (HS-CH2COOH, TGA) as a stabilizer. The phenomenon of "on" and "off" luminescence intermittency (blinking) of CdTe QDs in PVA and trehalose was investigated by single-molecule optical microscopy, and we identified that the intermittencies of single QDs were correlated with the interaction of water molecules absorbed on the QD surface. The "off" times, the interval between adjacent "on" states, remained essentially unaffected with an increase in excitation intensity. Every QD showed a similar power law behavior for the "off" time distribution regardless of the excitation intensity and aqueous environment of the QDs. In the case of "on" time distribution, power law behavior with an exponential cutoff tail is observed at longer time scales. The time traces indicated that the "on" time was inversely proportional to the excitation intensity; the duration of "on" time became shorter with increasing excitation intensity. An increase in the duration of "on" time was observed in trehalose with respect to that in PVA. We obtained a clear decrease in the power law exponent when PVA was replaced with trehalose. These observations indicate that the luminescence blinking statistics of water-soluble single CdTe QDs is significantly dependent on the aqueous environment, which is interpreted in terms of passivation of the surface trap states of QDs.     

Solvent-driven multiply configurable on/off fluorescent indicator of the pH window: a diethylenetriamine bearing two end pyrene fragments

Fluorescence behaviors of a simple-structured molecule (L), a diethylenetriamine bearing two end pyrene fragments, have been investigated in water. Effects of adding a less-polar organic solvent (acetonitrile: MeCN) on the emission behaviors have been studied by means of steady-state and time-resolved fluorescence measurements. L dissolved in water shows dual-mode fluorescence consisting of monomer and excimer emissions. The monomer emission shows an "on-off" intensity profile against the pH window (pH 2-12), whereas the excimer emission shows an "off-on" profile. Upon MeCN addition, the monomer emission maintains the "on-off" profile. In contrast, the "off-on" profile of the excimer emission is drastically changed: L shows two more types of profiles, "off-on-off-on" and "off-on-off", along with the MeCN concentration increase, thus behaving as a multiply configurable fluorescent indicator of the pH window. The MeCN-driven excimer emission switching of L is triggered by (i) the decrease in stability of the intramolecular ground-state dimer (GSD) formed between the end pyrene fragments, which suppresses the direct photoexcitation of GSD (suppression of the "static" excimer formation), leading to a decrease in the excimer emission intensity at basic pH; and (ii) the decrease in polarity of solution, which allows formation of a "dynamic" excimer via a monomer-to-excimer transition, resulting in an enhancement of the excimer emission intensity at acidic-neutral pH.     

Intrinsic interaction mode of an inhalation anesthetic with globular proteins: a comparative study on ligand recognition

Interaction mode of an inhalation anesthetic halothane with water-soluble globular proteins, myoglobin (Mgb) and lysozyme (Lys), was studied by differential scanning calorimetry (DSC) and viscometry, and the results were compared with those of bovine serum albumin (BSA). The anesthetic sensitivity was markedly different among the proteins: Mgb was destabilized, Lys was slightly destabilized, and BSA was conversely stabilized. Further, the interaction mode was quite different from those of specific binders for the proteins. The anesthetic sensitivity was highly correlated with the hydrophilicity on the protein surface (Mgb?<?Lys?<?BSA) and the rigidity of the protein structure (BSA????Mgb?<?Lys). We showed that the anesthetic sensitivity among globular proteins can be roughly classified into four categories, and proteins with small hydrophilicity and soft structure are suitable as model proteins of anesthesia. By contrast, the binding of the specific binders was characterized by the lower effective concentrations. The molar ratio of the binder to the protein at the effective concentration was well consistent with the binding number determined from the X-ray structural analysis. Moreover, the interaction mode of the binder was not necessarily in accord with the mode expected from the change in the protein structure. Considering the above facts, we can systematically interpret the effect of an anesthetic on globular proteins by four factors: (1) hydrophobicity of an anesthetic, (2) hydrophilicity of a protein surface, (3) rigidity of a protein structure, and (4) molar ratio of an anesthetic to a protein at the effective concentration.     

Packing state in bilayer membranes of diacylphosphatidylcholines with varying acyl chain lengths under high pressures

The bilayer packing states of a series of diacylphosphatidylcholines (CnPC) containing linear saturated acyl chains were examined by a high-pressure fluorescence method. We revealed from the second derivatives of Prodan fluorescence spectra for all bilayer membranes that the Prodan molecules can be distributed into multiple sites in these bilayer membranes and move around the head-group region, depending on the phase state. The hydrophobicity of the PC molecules markedly affected the distribution quantities of the Prodan molecules between the gel and liquid crystalline phases. The distribution of the Prodan molecules into the gel phase decreased with the increasing acyl chain length while that into the liquid crystalline phase conversely increased. The present study suggests that Prodan can sensitively recognize the packing states and strengths in the bilayer membranes and becomes a good packing indicator.     

Femtosecond laser‐assisted formation of channels in sapphire using KOH solution

We report on wet etching of photomodified regions in crystalline sapphire using KOH solution. Tightly focused femtosecond laser pulses (150 fs at 800 nm wavelength) were used to create void structures enclosed in an amorphised sapphire shell inside the bulk of a crystalline host. The diameter of the amorphous regions can be controlled by pulse energy and was typically 0.5–1.5 µm. The etching rate depends on the distance between adjacent irradiation spots, pulse energy, concentration of etchant and ultrasonic agitation.

     

Reversible Carriers Tunnelling in Asymmetric Coupled InGaN/GaN Quantum Wells

Temperature-dependent photoluminescence （PL） and time resolved photoluminescence （TRPL） are performed to study the PL characteristics and carrier transfer mechanism in asymmetric coupled InGaN/GaN multiple quantum wells （AS-QWs）. Our results reveal that abnormal carrier tunnelling from the wide quantum well （WQW） to the narrow quantum well （NQW） is observed at temperature higher than about lOOK, while a normal carrier tunnelling from the NQW to the WQW is observed at temperature lower than 100 K. The reversible carrier tunnelling between the two Q Ws makes it possible to explore new types of temperature sensitive emission devices. It is shown that PL internal quantum efficiency （IQE） of the NQW is enhanced to about 46% due to the assistant of the abnormal carrier tunnelling.     

3D particle measurements by single beam two-views magnified digital in-line holography

Holography technique can be used for 3D measurement of particle positions. However, in general in-line holography, accurate determination of the object’s position in the optical axis direction is difficult. In order to overcome this defect, we proposed a two-views recording technique combined with a digital in-line holography. The two-views recording is executed by only one camera with the assistance of one mirror, capturing the real image of a particle and the mirror image of the same particle simultaneously. This method keeps simplicity of optical alignment and is free from a difficult calibration of multiple cameras. It was confirmed that the proposed technique can reduce the uncertainty in the depth direction to about 1 pixel. For application of this method to micro-PIV, magnified recording is desired. In this paper, magnified holograms were also taken through a lens. It was confirmed that the uncertainty in the optical-axis direction can be reduced to a few pixels by the proposed technique for the magnified holograms.