Methods of theoretical simulation of scanning probe microscopy, including scanning tunneling microscopy (STM), atomic force microscopy(AFM) and Kelvin prove force microscopy (KPFM) have been reviewed with recent topics as case studies. For the case of the STM simulation, the importance of the tip electronic states is emphasized and some advanced formalism is presented based on the non-equilibrium Green’s function theory beyond Bardeen’s perturbation theory. For the simulation of AFM, we show examples of 3D-force map for AFM in water, and theoretical analyses for a nano-mechanical experiment on a protein molecule. An attempt to simulate KPFM images based on the electrostatic multi-pole interaction between a tip and a sample is also introduced.
The two-dimensional polymerization and reaction at the solid/liquid interface has caused considerable attention in recent years because of its fundamental importance and many potential applications. Scanning tunneling microscopy (STM) provides the possibility for the observation and manipulation of polymerization and reaction occurring at the solid/liquid interface at the atomic level. Two-dimensional polymerization and reaction could be induced by external stimuli, such as electrochemistry-induced, STM tip-induced, or light-induced. The polymerization at the solid/liquid interface is the focus of this review, including the mechanism of polymerization and characterization of structural and electrical properties of the resulting polymers. Finally, the outlooks for developments in this field are described.
Near-field scanning optical microscope (NSOM or SNOM) is a form of scanning probe microscope (SPM), which is used to observe the optical properties of a sample surface with a nanometer-scale spatial resolution. Since the near-field light strongly interacts with the sample surface, or with nanometer-scale objects on the substrate’s surface, NSOM is advantageous to excite only the vicinity of a sample surface. From the view point of surface chemical analysis, a discussion about the light energy concentration within a nanometer-scale region, and an estimation of its efficiency are indispensable for accurate measurements of the optical properties in a nanometer-scale region. In this paper, we describe the concept, the cautions and the general guidelines of a method to measure the excitation efficiency of aperture-type NSOM instruments.
It is well known that the topography in atomic force microscopy (AFM) is a convolution of the tip’s shape and the sample’s geometry. The classical convolution model was established in contact mode assuming a static probe, but it is no longer valid in dynamic mode AFM. It is still not well understood whether or how the vibration of the probe in dynamic mode affects the convolution. Such ignorance complicates the interpretation of the topography. Here we propose a convolution model for dynamic mode by taking into account the typical design of the cantilever tilt in AFMs, which leads to a different convolution from that in contact mode. Our model indicates that the cantilever tilt results in a dynamic convolution affected by the absolute value of the amplitude, especially in the case that corresponding contact convolution has sharp edges beyond certain angle. The effect was experimentally demonstrated by a perpendicular SiO2/Si super-lattice structure. Our model is useful for quantitative characterizations in dynamic mode, especially in probe characterization and critical dimension measurements.
Time stability plays an important role in the applications of scanning probe microscopes (SPMs). Although SPMs integrated with a closed-loop control system could reduce the drift greatly, drift would still exist. The SPM drift in the lateral direction has been well studied, and several measurement methods have also been developed. However, due to coupling of the lateral drift, it is still difficult to determine the drift in the vertical direction. In this paper, we propose a method to measure the vertical drift of an SPM based on scanned topography images. This method considers the influence of the lateral drift. Experimental results show that the vertical drift of the SPM is non-negligible, and the vertical drift on each pixel of one scanned image is different from each other. By such a method, instability in the vertical direction of the SPM instrument could be revealed and evaluated.
Glitch artifacts appear in many scanning probe microscopy (SPM) images due to transient instabilities. Such artifacts can distort any quantitative analyses based on the measured images. A robust smoothing method has been adopted to eliminate the glitch artifacts. Results on different kinds of sample images demonstrate that this method is quite efficient. However, the smoothing operation will cause information loss in certain cases, especially on sharp structures. If these features are also crucial in analysis, the compromise between the elimination of glitches and the reservation of signal details should be settled. Post-restoration of image details from analyzing extracted glitch artifacts can meet this demand. Glitch elimination can help to improve the value of SPM in quantitative nanoscale measurements.
The establishment of more accurate imaging of surface microstructures is needed. The most significant distortion in atomic force microscopy (AFM) imaging is induced by the probe tip shape, whenever the sample surface contains features whose dimensions are comparable to the probe tip size. The acquired AFM image is the dilation between the tip shape and the sample topography. To restore the original topographical profile, a numerical erosion procedure using a precise probe shape function is required. Here, a new technique for reconstruction of probe shape function using a well-defined nanostructure is proposed. First, AFM topography images of the given-shape nanostructure dispersed on flat substrates are taken. Then, a probe shape function is determined by a numerical calculation procedure. By using the experimentally determined probe shape function, the most probable surface morphologies from the observed AFM topography images of unknown samples can be extracted.
The analysis of biological specimens is now expected to shift from multi-cell analysis to single cells to know about the molecular and cellular behavior precisely. Mass spectrometric approaches to clarify molecular profiles in a cell or very small region have been developed. Such techniques include matrix-assisted laser desorption ionization imaging mass spectrometry (MALDI-IMS), secondary-ion mass spectrometry (SIMS), single-cell MALDI and live single-cell mass spectrometry. In this paper, these methods are reviewed, and their characteristics are discussed concerning how these methods achieve our aim.
A simple and low-cost apparatus for continuous and efficient liquid–liquid extraction, which does not need continual mechanical forces (stirring, shaking, etc.) other than solution sending, has newly been developed. This apparatus, named “emulsion flow” extractor, is composed of a column part where an emulsified state fluid flow (emulsion flow) is generated by spraying micrometer-sized droplets of an aqueous phase into an organic phase and a phase-separating part where the emulsion flow is destabilized by means of a sudden decrease in its vertical liner velocity due to a drastic increase in cross-section area of the emulsion flow passing through. In the present study, the performance of a desktop emulsion flow extractor in the extraction of Yb(III) and U(VI) from aqueous HNO3 solutions into isooctane containing bis(2-ethylhexyl) phosphoric acid (D2EHPA) was evaluated. The mixing efficiency of the emulsion flow extractor was found to be comparable with that of a popular liquid–liquid extractor, mixer-settler. Moreover, the emulsion flow extractor proved to have an overwhelming advantage in terms of phase-separating ability.
Far-ultraviolet (FUV) spectra in the 190 – 300 nm region were measured for spring water in Awaji-Akashi area, Tamba area and Rokko-Arima area in Hyogo Prefecture, Japan, these areas have quite different geology features. The spectra of the spring water in the Awaji-Akashi area can be divided into two groups: the spring water samples containing large amounts of NO3− and/or Cl−, and those containing only small amounts of NO3− and Cl−. The former shows a saturated band below 190 nm due to NO3− and/or Cl−. These two types of spectra correspond to different lithological areas: sedimentary lithology near the sea shore containing many ions in the seawater and gravitic lithology far from the sea side, in the Awaji-Akashi area. The spring water from the Tamba area, which is far from the sea, contains relatively small amounts of NO3− and Cl−; it does not yield a strong band in the region observed. The FUV spectra of three of four kinds of spring water samples in the Arima Hotspring show characteristic spectral patterns. They are quite different from the spectra of the spring water samples of the Rokko area. Calibration models were developed for NO3−, Cl−, SO42−, Na+, and Mg2+ in the nine kinds of spring water collected in the Awaji-Akashi area, Tamba, and Rokko-Arima area by using univariate analysis of the first derivative spectra and the actual values obtained by ion chromatography. NO3− yields the best results: correlation coefficient of 0.999 and standard deviation of 0.09 ppm with the wavelength of 212 nm. Cl− also gives good results: correlation coefficient of 0.993 and standard deviation of 0.5 ppm with the wavelength of 192 nm.
A new chemiluminescence method is proposed for the determination of sulfide in seawater based on the chemiluminescence reaction between sulfide and an acidic permanganate solution. 3-Cyclohexylaminopropanesulfonic acid was used as a chemiluminescence enhancer. By use of this method, 1 – 150 μM of sulfide could be determined in artificial seawater. The limit of detection was 0.17 μM sulfide. We investigated the effects of salinity, water temperature, and interfering chemicals such as heavy-metal ions and organic matter. In addition, natural seawater spiked with sulfide was analyzed. The results showed that the CL method could be applied to a deep-sea sulfide analyzer.
A rapid method has been developed for the simultaneous determination of nitrite and nitrate. The separation of nitrite and nitrate was achieved using an octadecylsilane (ODS) short column (5 μm, 20 × 4.6 mm) with 10 mM of borate buffer–methanol (99.5:0.5, v/v; pH 10.0), containing 5 mM of lauryltrimethylammonium chloride and 50 mM of NaBr. These ions were detected by luminol chemiluminescence following online UV irradiation. The calibration curves of nitrite and nitrate were linear in the range of 1.0 × 10−7 to 2.0 × 10−5 M and 1.0 × 10−6 to 2.0 × 10−4 M, respectively. The detection limits for nitrite and nitrate were 0.05 and 0.4 μM, respectively (with a signal-to-noise ratio of 3). The precisions of peak heights for 7 identical injections of a standard mixture of 0.50 μM of nitrite and 5.0 μM of nitrate were 2.7 and 2.1%, respectively. Analysis time per sample was less than 2 min, and system pressure was low (2.1 MPa). The proposed method was successfully applied to water samples from various sources.
A novel mercury(II) ion (Hg2+) biosensor with electrogenerated chemiluminescence (ECL) detection using tris(2,2′-bipyridyl) ruthenium derivatives (ruthenium complex) as labeling was developed in the prescent work. One thymine (T)-rich single-strand DNA (ssDNA) labeled with a ruthenium complex was taken as an ECL probe. When the other T-rich capture ssDNA was self-assembled onto the surface of a gold electrode with a thiol group, and then hybridized with the ECL probe to form double-strand DNA (dsDNA) structures in the presence of Hg2+, a strong ECL response was electrochemically generated. The ECL intensity was linearly related to the concentration of Hg2+ in the range from 1.0 × 10−6 to 1 × 10−9 M with a detection limit of 3.0 × 10−10 M. The relative standard deviation was 4.1% at 1.0 × 10−7 M Hg2+ (n = 5). This work demonstrates that the combination of the strongly binding T-rich DNA to Hg2+ with the highly sensitive ECL technique to design an ECL Hg2+ biosensor is a great promising approach for the determination of metal ions.
An efficient and eco-friendly injection-port tert-butyldimethylsilylated (TBDMS) derivatization and gas chromatography–mass spectrometry (GC/MS) were developed to determine an antibacterial agent, triclosan (TCS), and its metabolite: methyltriclosan (MTCS), in wastewater and surface water samples. The effects of several parameters related to the TBDMS-derivatization process (i.e., injection-port temperature, residence time and volume of silylating agent) were investigated. This on-line derivatization-coupled large-volume (10 μL) sample introduction provides sensitive, fast and reproducible results for TCS residue analyses. Each water sample was extracted by reversed-phase C18 solid-phase extraction (SPE) cartridge, and then the recovery efficiency was evaluated using various eluting solutions. Limits of quantitation (LOQs) for MTCS and TCS were 3.0 and 1.0 ng/L in 100 mL of water samples, respectively. Intra- and inter-batch precision with their accuracy were also investigated. The precision for these analytes, as indicated by relative standard deviations (RSDs), proved to be less than 7 and 11%, respectively, for intra- and inter-batch. Accuracy, expressed as the mean recovery, was between 80 and 95%. The method was then applied to environmental water samples, showing the occurrence of TCS in both surface water and municipal wastewater treatment plant (MWTP) influent/effluent samples.
The effects of ionizing radiation generated by a beam of electrons, in that doses varied from 25 – 800 kGy, on the physico-chemical properties of sulfamethoxazole (SMX) in solid state have been studied at room temperature and in the air atmosphere. The changes appearing after the irradiation were detected and evaluated by the spectroscopic methods (UV, IR, MS, EPR), chromatography (TLC and HPLC) and SEM, XRD and DSC. Already the lowest dose of 25 kGy was found to change the color of SMX from white to pale cream; such change became more intense with our increasing the irradiation dose. Products of radiodegradation and decreases in the drug content were detected by TLC and HPLC only after irradiation with 400 kGy. Since the SMX radiolysis products (sulfanilamide and sulfanilic acid) are colorless compounds, it is supposed that the color results from trapping of free radicals in the crystal lattice; the concentration of free radicals was 1.04 × 1015 spin/g. Our results indicate that the radiolysis of SMX in the solid state caused by e-beams involves breaking of the S–N and N–C bonds. The mean radiolytic yield of this process is G(–SMX) = 1.89 × 10−7 mol/J, whereas the yield of formation of the two products of radiolysis is close and equal to 2.18 × 10−8 mol/J (sulfanilamide) and 2.13 × 10−8 mol/J (sulfanilic acid).
The absorption spectra of three kinds of medicines both before and after the expiration date: Amlodin OD® (5 mg), Basen OD® (0.2 mg) and Gaster D® (10 mg) have been measured by terahertz time domain spectroscopy (THz-TDS). All the medicines show some differences in the THz absorption spectra between medicines before and after the expiration dates. X-Ray powder diffraction (XRD) studies of all medicines suggest that the polymorph of the main effective compound is not changed before and after the expiration date. Therefore, the differences in the THz spectra between medicines before and after the expiration dates arise from aging variation of diluting agents and/or from modifications of intermolecular interaction between the effective compounds and diluting agents.
The removal of lipopolysaccharide (LPS) from a contaminated DNA solution was achieved using cross-linked cyclodextrin (CyD polymer) beads as LPS adsorbents. The LPS-removing activity of the β- and γ-CyD polymer beads was compared with that of common cationic LPS adsorbents. The γ-CyD polymer beads selectively removed LPS from a DNA solution (50 μg mL−1, pH 6, ionic strength μ = 0.2) containing natural LPS (15 EU mL−1), without the adsorption of DNA. The adsorptions of LPS and DNA were 85% and <1%, respectively.
We have developed a simple method to significantly improve the sensitivity in the LC/MS analysis of DNA adducts. A preconcentration tip for the selective recovery of DNA adducts was prepared. Using this tip, the total amount of DNA adducts in a treated DNA sample was injected in a one-shot manner into an LC/MS system. We were able to improve the sensitivity by more than one order of magnitude in concentration. This method will be a useful tool for the quantitative determination of trace DNA adducts.