Since Raman spectroscopy can measure sample composition, crystallinity, stress, etc. without contact, its application is expanding in various fields. Raman scattering was discovered by Dr. Raman of India in 1928. After improvement of the excitation source and optical system, the Raman microscope was developed by integrating with a microscope and commercially released for the first time in the 1970s. By combining with a microscope, Raman spectrum measurement with sub-μm order spatial resolution became possible. In recent years, there has been an increasing need for measurement of spatial resolution on a nanoscale that exceeds the diffraction limit. A high spatial resolution measurement technique that utilizes the Raman enhancement effect by near-field is developed. In this paper, we introduce the AFM-Raman which integrates a Raman microscope, and atomic force microscope (AFM), which enables spatial resolution of nanoscale by Tip-Enhanced Raman spectroscopy (TERS).
Biological tissues contain a wide variety of chemical components, and their amount and distribution change dynamically depending on health conditions. Mass spectrometry imaging has the potential for biomedical applications due to its unique ability to measure local chemical components as a mass spectrum and visualize the distribution of chemical compounds in a sample. In this article, we introduce the research and development of tapping-mode scanning probe electrospray ionization (t-SPESI). t-SPESI is a combination of atomic force microscopy and mass spectrometry, which uses a vibrating capillary probe to perform a rapid extraction and ionization as well as mass spectrometry imaging. Mass spectrometry imaging of biological tissues allowed us to visualize the distribution of disease-related components in the tissues. In addition, multimodal imaging by t-SPESI was achieved by applying the elemental technologies of atomic force microscopy, namely, probe vibration information measurement and feedback control.
In order to investigate the mechanical properties of nanomaterials (sizes of about 10 nm or less), we have developed an in-situ transmission electron microscope (TEM) holder equipped with a quartz length extension resonator (LER) as a force sensor. By using LER, the equivalent spring constant of the metal nanocontact can be measured from the shift of the resonance frequency, and the energy dissipation generated at the nanocontact can be estimated from the change of the excitation voltage applied so that the amplitude becomes constant. By evaluating LER, the measurement error was estimated to be about 1 N/m so that the equivalent spring constant of the metal atomic chain could be measured. Therefore, this method can measure elastic and plastic mechanical responses precisely by observing the atomic arrangement of nanoscale materials. In experiment, we found that the platinum atom chain took a quantized conductance of 2.0 G0, and its spring constant was measured to be 13.2 N/m. This method is expected to be effective in elucidating the mechanical properties peculiar to nanomaterials such as the size or orientation dependence of Young’s modulus of metal nanocontacts.
We recently developed (classical) scanning thermal noise microscopy (STNM) based on contact-mode atomic force microscopy (AFM) which enables us to investigate surface viscoelastic properties and to visualizing subsurface features. In the classical STNM, the thermal noise spectra of the cantilever were measured at every pixels during the raster scan, which requires quite a long measurement time. Here we developed the peak tracking (PT) method that enables us to track and measure the resonance frequency of the cantilever using the amplitude information rather than the phase information. By applying the PT method to the STNM, we developed PT-STNM that allows us to simultaneously measure the contact resonance frequency and Q-factor which correspond to the elasticity and viscosity, respectively, in real-time manner.
Viruses are infectious agents that have genomic information encapsulated within a protective shell and often enveloped with a lipid bilayer from the host cell. An infected cell is transformed into a viral factory and literally hijacked by the virus. As viruses are small, 5–300 nm in size and uniform they are ideal for visualisation using microscopy of all kinds including light microscopy, electron microscopy, cryo electron microscopy and atomic force microscopy. Our laboratory is interested in the cell biology of virus infections and virus-host interactions during viral entry into host cells at the molecular level. By deeply understanding virus cell biology, we can target essential virus-host interactions and formulate antiviral strategies that complement vaccines in the future. Here, I would like to introduce some of the microscopy techniques used in our work on influenza A virus and SARS-CoV-2.
Ptychography is a method of obtaining the transmission function of a sample from multiple diffraction patterns. Although it has received little attention, especially in electron beam ptychography, it has a long history, more than 50 years after its proposal. In recent years, with the advent of new detectors and improvements in computer performance, great progress has been made, and expectations are rising for practical methods. Ptychography, on the other hand, is a computer-aided method of obtaining phase from a set of diffraction patterns from multiple points, which is difficult to understand intuitively.
In this article, we will elaborate on the principles and phase reconstruction procedures using pixelated detectors, such as single-sideband method with focused probe and iterative methods with defocused probe, in order to encourage new researchers will join and contribute to this new and engaging area.
An aberration-corrected scanning transmission electron microscope (STEM) enables us to acquire images containing individual atoms in a crystallinity specimen. However, the evaluation value of such an atomic resolution is determined as a discrete value of the lattice spacing of the specimen. This paper proposes a new algorithm for evaluating atomic resolution on the basis of Rayleigh’s criterion, which enables a continuous value of atomic resolution. In the algorithm, hundreds of atomic dumbbells recorded in the STEM image are accumulated, and a very low noise dumbbell pattern is produced. The point spread function (PSF) is obtained by fitting the Gaussian distribution to the dumbbell pattern, and the Rayleigh resolution is calculated from the PSF. The algorithm also calculates the information entropy (bit/nm2) as a figure of merit for the image quality using the signal-to-noise ratio (SNR) and Rayleigh resolution of the image.
A new era of life science research has arrived in the use of electron cryo-microscopy. The combination of electron cryo-microscopy with single-particle analysis enables us to analyze structures of proteins and their complexes at the atomic resolution, which is becoming a key technology of structural biology. In addition, the combination of cryo-EM and electron tomography is revealing new and marvelous views of cells and tissues. However, cryo-EM images of living organisms and their components have a low signal-to-noise ratio, due to weakness against electron dosages, in terms of information technology, and thus automatic image acquisition system is necessary because a large number of images are required. In this paper, we will introduce the current efforts of automatic electron microscopy for this purpose, including the system we have been developing. From the standpoint of ‘System of Systems’, we will discuss open system and IoT as specifications for the automation of electron microscopy systems, and propose the necessity of a feedback system based on procedure logs.