Optical Response Characteristics of Single-Walled Carbon Nanotube Chirality Exposed to Oxidants with Different Oxidizing Power.

Semiconductor single-walled carbon nanotubes (SWNTs) have unique characteristics owing to differences in the three-dimensional structure (chirality) expressed by the chiral index (n,m), and many studies on the redox characteristics of chirality have been reported. In this study, we investigated the relationship between the chirality of SWNTs and the oxidizing power of oxidants by measuring the near-infrared (NIR) absorption spectra of two double-stranded DNA-SWNT complexes with the addition of three oxidants with different oxidizing powers. A dispersion was prepared by mixing 0.5 mg of SWNT powder with 1 mg/mL of DNA solution. Different concentrations of hydrogen peroxide (H2O2), potassium hexachloroidylate (IV) (K2IrCl6), or potassium permanganate (KMnO4) were added to the dispersion to induce oxidation. Thereafter, a catechin solution was added to observe if the absorbance of the oxidized dispersion was restored by the reducing action of the catechin. We found that the difference in the oxidizing power had a significant effect on the detection sensitivity of the chiralities of the SWNTs. Furthermore, we revealed a detectable range of oxidants with different oxidizing powers for each chirality.

Label-free imaging and analysis of subcellular parts of a living diatom cylindrotheca sp. using optical diffraction tomography.

Optical diffraction tomography is an emerging label-free microscopic technique with its capability of label-free, quantitative, and rapid imaging of biological samples. In this work, we present the imaging and analysis of a living diatom Cylindrotheca sp. in seawater without using any pretreatment such as fluorescence staining. The 3D refractive index (RI) of a living diatom cell was measured, to which quantitative image analysis was perform to investigate subcellular parts of the diatom. Each part of the cell was well distinguished as RI values and distributions. From the analysis, RI values of frustules, protoplasm, vacuole, and chloroplast were estimated to be in the range of 1.352-1.388, 1.363-1.381, 1.388-1.395, and 1.403-1.436, respectively. Our results suggest that the present method will be a powerful tool not only for observing diatom cells but also for studying various cells and mesoscopic materials.•Subcellular parts of a living diatom cell was well visualized by digital holographic microscope.•Subcellular parts could be identified as differences of refractive indexes.•The observation was achieved without any pre-treatment of the living cell.

Corrigendum to "Label-free imaging and analysis of subcellular parts of a living diatom cylindrotheca sp. using optical diffraction tomography" [MethodsX: 7 (2020) 100889].

[This corrects the article DOI: 10.1016/j.mex.2020.100889.].

Effect on near-infrared absorption spectra of DNA/single-walled carbon nanotube (SWNT) complexes by adsorption of a blocking reagent.

In this study, we investigated whether the adsorption or coating of single-walled carbon nanotubes (SWNTs) with a blocking reagent would prevent the oxidation and reduction of SWNTs. Blocking reagents are widely used in life sciences to protect coated molecules from adsorption by other molecules. A complex of dsDNA-SWNT complex (Complex A) was prepared by mixing SWNTs powder with dsDNA solution of deoxyribonucleic acid and sodium salt from salmon testes. Blocking reagent (DB1130) was added to Complex A to a final concentration of 1% to prepare a dsDNA-SWNT-DB1130 complex (Complex B). Complex B was sonicated to prepare a dsDNA-SWNT-DB1130-s complex (Complex C). Each complex was oxidized with 0.03 % hydrogen peroxide (H2O2), after which the catechin solution, which has an anti-oxidative effect, was added to the sample. For Complex A, the height of the absorption spectra peak decreased with the addition of H2O2, and was recovered with the addition of catechin. In Complex B, the magnitude of change in the absorption peak height was smaller than that in Complex A, and no significant change was detected in Complex C. These results indicate that DB1130 blocks the redox action of SWNTs, and this effect becomes stronger with increasing DB1130 adsorption. We found that while the difference in the levels of DB1130 adsorption did not affect the absorbance significantly, it induces in a large change in photoluminescence intensity. Furthermore, ultrasonic treatment caused the replacement of dsDNA by DB1130 in Complex B, resulting in an increase in the amount of adsorption, and increasing the diameter of SWNTs. This was also confirmed by Atomic Force Microscopy (AFM) measurements.

Unique observation method of temperature dependence of diatom floating by direct microscope.

Diatoms are one of the earth's major oxygen producers. For that reason, studying the floating phenomena of living diatom cells in water is an important research subject. Efficiency of photosynthesis of diatom cells may be heavily affected by their floating behavior. In our previous research, we devised a 'tumbled' microscope, a device created by tilting an inverted microscope (CKX53, OLYMPUS) by 90 degrees, due to which allowed observation with a sample stage perpendicular to the ground. When we observed a Petri dish filled with diatom cell suspension, the floating behavior of diatom cells were well visualized. Cyclotella meneghiniana was isolated and subcultured in bold modified basal freshwater nutrient solution liquid medium (B5282-500ML, Sigma-Aldrich) at 18 °C. Before the microscopic observation, cell suspension was cultured for two weeks after the final subculture. Observation was performed at room temperature, 30 °C, and 40 °C with a temperature sensor in the center of the chamber (inside). Observations were started as soon as the sample was installed. In a typical image obtained using the tumbled microscope, the diatom cells were found to move from the top to the bottom. In order to analyze floating velocity and trajectory, observation was continued for 35 min at room temperature, 30 °C, and 40 °C. Tracking analysis was carried out using the two-dimensional motion image measurement software Move-tr/2D. The average speed of 100 cells was 7.0 ± 4.3 µm/s at room temperature, 85.6 ± 31.9 µm/s at 30 °C and 470.1 ± 279.8 µm/s at 40 °C. In this study, we devised the unique observation to visualize the temperature dependence of diatom cells.

Fabrication of Microscope Stage for Vertical Observation with Temperature Control Function.

Samples are usually placed onto a horizontal microscope stage for microscopic observation. However, to observe the influence of gravity on a sample or study afloat behavior, it is necessary to make the microscope stage vertical. To accomplish this, a sideways inverted microscope tilted by 90° has been devised. To observe samples with this microscope, sample containers such as Petri dishes or glass slides must be secured to the stage vertically. A device that can secure sample containers in place on a vertical microscope stage has been developed and is described here. Attachment of this device to the stage allows observation of sample dynamics in the vertical plane. The ability to regulate temperature using a silicone rubber heater also permits observation of temperature-dependent sample behaviors. Furthermore, the temperature data is transferred to an internet server. Temperature settings and log monitoring can be controlled remotely from a PC or smartphone.

Fabrication of an Optical Cell Dryer for the Spectroscopic Analysis Cells.

Optical cells, which are experimental instruments, are small, square tubes sealed on one side. A sample is placed in this tube, and a measurement is performed with a spectroscope. The materials used for optical cells generally include quartz glass or plastic, but expensive quartz glass is reused by removing substances, other than liquids, to be analyzed that adhere to the interior of the container. In such a case, the optical cells are washed with water or ethanol and dried. Then, the next sample is added and measured. Optical cells are dried naturally or with a manual hairdryer. However, drying takes time, which makes it one of the factors that increase the experiment time. In this study, the objective is to drastically reduce the drying time with a dedicated automatic dryer that can dry multiple optical cells at once. To realize this, a circuit was designed for a microcomputer, and the hardware using it was independently designed and manufactured.

Differences in the response of the near-infrared absorbance spectra of single-walled carbon nanotubes; Effects of chirality and wrapping polymers.

We detected antioxidant activity of catechin, one of the main components of tea, using SWNTs surface coated with two different biomolecules. Compared to coating with DNA already reported, it can hardly be detected when coated with carboxymethyl cellulose. For nanobiosensing using SWNTs, its sensitivity is not determined only by SWNTs, we found that biomolecules covering the surface are extremely important. In this experiment, we measured the near-infrared absorption spectra of SWNTs coated separately with two different water-soluble polymers; DNA (double-stranded DNA-SWNT complexes) and carboxymethyl cellulose (CMC, CMC-SWNT complexes), and uncovered the differences in their antioxidant properties against the flavonoid catechin. Each dispersion was oxidized with H2O2 at 0.03% (final concentration), following which catechin solutions were added to reduce the samples. Our results showed that the magnitude of the change in the absorbance spectra for dsDNA-SWNT complexes in response to oxidation and reduction was superior to that for CMC-SWNT complexes. The CMC-SWNT complexes exhibited almost no change in their spectra even though the same SWNT powder (produced by the high-pressure carbon monoxide (HiPco) method) was used. On the other hand, when (6, 5)-enriched SWNT powder produced by the ComoCat method was used, no significant change in the absorbance was observed, even though (6, 5)-enriched SWNTs are frequently used for nanobiosensing. Our results revealed that both the SWNT chirality and type of polymer for wrapping SWNTs are important factors for establishing nanobiosensing methods utilizing SWNTs.