Yoriko Ando

Development of a Quantitative Bio/Chemiluminescence Spectrometer Determining Quantum Yields: Re-examination of the Aqueous Luminol Chemiluminescence Standard

We have developed a bio/chemiluminescence spectrometer with a cooled charge‐coupled‐device (CCD) detector to obtain a quantitative luminescence spectrum as the absolute number of all emitted photons at each wavelength. The integrated area of the spectrum divided by the number of reacted substrate molecules gives the quantum yield. Calibration of the absolute sensitivity of the CCD‐spectrometer system was performed by using lasers and a tungsten lamp with calibrated powers as primary light standards, and calibration of the light‐collection efficiency of the spectrometer with several kinds of cells for liquid samples was achieved by introducing a simple reference double‐plate cell. The reference cell is not convenient for final bio/chemiluminescence measurements but is useful for the calibration because it has well‐defined angular dependence of light emission, allowing accurate calculation of the light‐collection efficiency. Using this CCD‐spectrometer system, we re‐examined the quantum yield of aqueous luminol chemiluminescence with H2O2 catalyzed by horseradish peroxidase. The quantum yield was constant for a wide range of luminol concentrations, whereas it changed and had an optimum against H2O2 concentrations. The optimum quantum yield was 1.23(±0.20)%, which is in good agreement with previously reported values.

pH-Dependent Fluorescence Spectra, Lifetimes, and Quantum Yields of Firefly-Luciferin Aqueous Solutions Studied by Selective-Excitation Fluorescence Spectroscopy

We investigated the pH-dependent fluorescence spectra, quantum yields, and lifetimes of firefly luciferin in aqueous solutions by varying the pH and excitation wavelength. Green fluorescence peaking at 540 nm and red fluorescence peaking at about 620 nm were detectable in the pH range between 1 and 10. The lifetime of the green fluorescence decreased significantly from about 5 to 0.5 ns with decreasing pH from 10 to 1, while the red fluorescence lifetime was almost constant, about 0.4 ns, in the measurable pH range between 1 and 4. The pH dependence of the green-fluorescence lifetime had analogous pH-dependence with that of the fluorescence quantum yield. This reflects the contribution of the emission-efficiency variation of green fluorescence due to the pH-sensitivity of a non-radiative decay that competes with a pH-insensitive radiative decay.

Novel Electroluminescence Properties of Thin Films Using Soluble Metallophthalocyanine Salts

We have prepared organic thin films of soluble dicyano(phthalocyaninato)iron salt, [(n-C7H15)4N][FeIII(Pc)(CN)2], and fabricated the electroluminescence (EL) devices having the Metal-Insulator-Metal structure. The device exhibits emission for both positive and negative bias voltages. We observed two bands in the EL spectra. One band was assigned to the Q band of the phthalocyanine molecule. The other, which shifts with changing the applied voltage, could correspond to the metal-to-ligand charge transfer (MLCT) band and/or the ligand-to-metal charge transfer (LMCT) band.