Non-Destructive Measurement of Acetic Acid and Its Distribution in a Photovoltaic Module during Damp Heat Testing Using pH-Sensitive Fluorescent Dye Sensors.

An optical pH sensor that enables the non-destructive measurement of acetic acid and its distribution in a photovoltaic module during damp heat (DH) testing is reported. The sensor was fabricated by impregnating a solution of a pH-sensitive fluorescent dye into a fluororesin membrane filter, which was then dried. While conducting the DH test, fluorescence spectra from 20 pH sensors were periodically recorded and converted into pH values using a predetermined calibration curve. As a result, we succeeded in measuring changes in pH with a DH test time of up to 2000 h, and it was possible to obtain information on the pH distribution in the module. We also confirmed no change in pH in a module with a silicone encapsulant free from acetic acid, and revealed that the sensor that we developed does not respond to moisture and heat, but only to acetic acid.

Highly-efficient and angle-independent zero-order half waveplate at broad visible wavelength based on Au nanofin array embedded in dielectric.

A Au nanofin array embedded in SiO2 was designed and fabricated to achieve an achromatic half waveplate with high transmittance at visible wavelengths. On the basis of the waveguide theory of nanogaps and the Fresnel reflection theory, nanofin array is calculated to have ideal properties for an achromatic half-waveplate in the visible band from 560 to 660 nm with the transmittance of around 50%. A Au nanofin array with a height of 830 nm and a period of 400 nm was fabricated through a sidewall-deposition process and overcoating with spin on glass. The polarization microscopy results showed that both transmittance greater than 50% and retardation of 165° at broadband wavelengths ranging from 600 to 800 nm were simultaneously achieved. It was also demonstrated that retardation had little dependence on the incident angle.

Analysis of mitochondrial mechanical dynamics using a confocal fluorescence microscope with a bent optical fibre.

The cells in the cardiovascular system are constantly subjected to mechanical forces created by blood flow and the beating heart. The effect of forces on cells has been extensively investigated, but their effect on cellular organelles such as mitochondria remains unclear. We examined the impact of nano-Newton forces on mitochondria using a bent optical fibre (BOF) with a flat-ended tip (diameter exceeding 2 µm) and a confocal fluorescence microscope. By indenting a single mitochondrion with the BOF tip, we found that the mitochondrial elastic modulus was proportional to the (-1/2) power of the mitochondrial radius in the 9.6-115 kPa range. We stained the mitochondria with a potential-metric dye (TMRE) and measured the changes in TMRE fluorescence intensity. We confirmed that more active mitochondria exhibit a higher frequency of repetitive transient depolarization. The same trend was observed at forces lower than 50 nN. We further showed that the depolarization frequency of mitochondria decreases under an extremely large force (nearly 100 nN). We conclude that mitochondrial function is affected by physical environmental factors, such as external forces at the nano-Newton level.

Significant correlation between refractive index and activity of mitochondria: single mitochondrion study.

Measurements of refractive indices (RIs) of intracellular components can provide useful information on the structure and function of cells. The present study reports, for the first time, determination of the RI of an isolated mitochondrion in isotonic solution using retardation-modulated differential interference contrast microscopy. The value was 1.41 ± 0.01, indicating that mitochondria are densely packed with molecules having high RIs. Further, the RIs of each mitochondrion were significantly correlated with the mitochondrial membrane potential, an index of mitochondrial activity. These results will provide useful information on the structures and functions of cells based on the intracellular distribution of RIs.

Detection of swelling of single isolated mitochondrion with optical microscopy.

Volume regulation under osmotic loading is one of the most fundamental functions in cells and organelles. However, the effective method to detect volume changes of a single organelle has not been developed. Here, we present a novel technique for detecting volume changes of a single isolated mitochondrion in aqueous solution based on the transmittance of the light through the mitochondrion. We found that 70% and 21% of mitochondria swelled upon addition of a hypotonic solution and Ca(2+), respectively. These results show the potential of the present technique to detect the physiological volume changes of individual small organelles such as mitochondria.

Measurement of nanoparticle sizes by conventional optical microscopy with standing evanescent field illumination.

The size of a particle smaller than the diffraction limit is measured using a conventional optical microscope by adopting a standing evanescent field illumination. The scattering intensity from a nanoparticle is periodically modulated by shifting the intensity fringes of the standing evanescent field. By measuring contrast of scattering intensity variation during one cycle of modulation, particle sizes can be estimated easily. Furthermore, material dependence can be canceled using contrast as an evaluation factor. From the experimental results, particle sizes ranging from 20 to 250 nm are successfully determined. This technique offers a low-cost size measurement for nanoparticles.