Holographic Interferometric Microscopy Research Articles

(Invited) In-Situ Observation of Dynamic Electrochemical Interfacial Phenomena

Electrochemical interfacial phenomena play important roles for developing advanced nano-materials such as actuators, MEMS and catalyst. For advanced control, metal nucleation by electrodeposition is one of key technology, while the research for high durability of the nanomaterials will be an important issue in the future. It is necessary to understand the corrosion in the fine region. These processes are electrochemical-deposition and dissolution reactions of metals. Thus, the reaction is too fast to observe in real time. In this presentation, I would like to introduce some recent research on dynamic electrochemical interface phenomena using a high-speed probe microscope [1, 2] and a holographic interferometric microscopy [3, 4].The Cu dissolution was investigated by HS-AFM (High-Speed Atomic Force Microscopy). The in-situ observation was conducted using an Au(111) single in 3 mM copper sulfate solution with 50 mM sulfuric acid. The HS-AFM operating in a dynamic mode can measure surfaces at frame rates up to 10 frame s−1. In the present experiment, the scan area range was in the range of 375–1000 nm2 and the scanning speed was 1 frame s−1. The dissolution process was observed at 0.05 V vs. Cu reference. The dissolution could be occurred as soon as the electrolysis was started. The dissolution rate was independent of the edge type. At 3 s, the effects of dissolution became clear and the step lines of the nuclei became uneven. Interestingly, as dissolution progressed beyond 5 s, some clusters [indicated by arrows in Fig.1] remained on the substrate briefly. This behavior had the appearance of small water droplets drying on a flat surface. The average size of the clusters was approximately 8 nm. After the large nuclei dissolved, these small clusters gradually dissolved. In the interferometric microscopy, the ionic mass transfer phenomenon of Al3+ in a sulfuric acid (pH 1) was investigated. The investigation revealed the refractive index profile corresponding to the Al3+ concentration profile in the electrolyte. The thickness of the diffusion layer was proportional to the square root of time, which supported the reaction dominated by the mass transportation. The Al3+ surface concentration started to decrease at 20 s after starting electrolysis, probably because the Al dissolution reaction was hindered and the Al oxide layer formation progressed. This in-situ research might be a steppingstone in order to understand the mechanism of anodization of Al.

In Situ Measurement of Al3+ Concentration Profile during Al Anodization using Digital Holographic Interferometric Microscope

In this study, the ionic mass transfer phenomenon of Al3+ in a sulfuric acid (pH 1) accompanying the anodization of an Al electrode was investigated using a digital holographic interferometric microscope. The anodization of an Al electrode is very popular technique to functionalize Al plates however, the anodization mechanism in the initial stage has not yet been understood, especially for the ionic mass transfer phenomenon. The investigation revealed the refractive index profile corresponding to the Al3+ concentration profile in the electrolyte. The Al3+ concentration on the electrode surface increased because of the Al dissolution in the initial stage of the anodization, and the thickness of the diffusion layer was proportional to the square root of time. The Al3+ surface concentration started to decrease after approximately 20 s probably because the Al dissolution reaction was hindered, and the Al oxide layer formation progressed. Additionally, ex situ scanning electron microscopy observation showed pores on the electrode surface at 80 s, which indicated that the pore formation was initiated from approximately 40 s with the progress of the oxide film formation. This research must be a steppingstone in order to understand the mechanism of anodization of Al.

Diagnosis of Malaria Using Wavelet Coefficients and Dynamic Time Warping

Malaria remains one of the world’s most deadly infectious disease and arguably, the greatest menace to modern society in terms of morbidity and mortality. Demand of time is to identify the methods, which can diagnose the disease and are economical and accurate. In this work, we have proposed a technique based on scientific computations. The aim is to provide a method which can do classification of Red Blood Cells (RBCs) into the malaria infected and healthy ones. The images of RBCs are captured using low cost digital holographic interferometric microscope (DHIM), these images are pre-processed for noise removal and then used for computing the discrete wavelet coefficients (DWC). The DWC are then used, as feature vectors, in dynamic time warping algorithm to find similarities or dissimilarities, between the RBCs. This allows the classification of RBCs into healthy or malaria infected. The proposed method shows excellent results for classification of RBCs for diagnosis of disease. Such automated detection methods, using low cost DHIM devices and minimal human intervene, will be good aid to medical area and are demand of time.

Holographic interferometric microscopy for measuring Cu2+ concentration profile during Cu electrodeposition in a magnetic field

We measured the concentration boundary layer during copper electrodeposition in a copper sulfate solution under an applied magnetic field. Using a holographic laser interference microscope, we demonstrated the formation of the diffusion layer near the cathode. In the initial stage of electrodeposition, the diffusion layer was distorted in a magnetic field. An analysis of the electrode surface concentration supported the following assertions: without a magnetic field, dendrites formed when the surface concentration of Cu2+ was depleted; with a magnetic field, the unique convection phenomena of the field gradient force and localized Lorentz force promoted Cu2+ mass transport in the diffusion layer, producing large crystal grains.

Entropy-based clustering of embryonic stem cells using digital holographic microscopy

Embryonic stem (ES) cells are an important factor in the development of cell-based therapeutic strategies. In this work, the use of digital holographic interferometric microscopy and statistical identification for automatic discrimination of ES cells and fibroblast (FB) cells is discussed in detail. The proposed algorithm first reduces the complex data structure to lower dimensions. Then, based on asymptotic normality, model-based clustering and linear discriminant analysis are applied to the transformed data to obtain the classification between ES and FB cells. The proposed algorithm is robust because it does not depend on parametric assumptions and can be extended to the classification of other cell image data. Experimental results are presented to demonstrate the performance of the system.

Automatic Identification of Malaria-Infected RBC With Digital Holographic Microscopy Using Correlation Algorithms

Diagnosis of malaria is important for its medication and treatment. An automatic compact diagnostic tool will be advantageous especially for healthcare personnel working in developing countries, which lack trained professionals and high-quality equipments. Digital holographic microscopy is one of the advanced techniques for quantitative evaluation of cells, providing cell thickness information directly. This information obtained by interferometric comparison can be used to identify as well as to compare cells. Here, we describe the use of digital holographic interferometric microscopy (DHIM) with numerical focusing for automatic identification of malaria-infected red blood cells (RBCs). Identification is done by comparing its shape profile with that of a healthy RBC. A correlation function was used to separate healthy and malaria-infected RBCs.

Imaging Embryonic Stem Cell Dynamics Using Quantitative 3-D Digital Holographic Microscopy

Embryonic stem cells are very important for the development of cell-based therapeutic strategies. Since stem cell colonies are nonpigmented and relatively transparent, they do not produce appreciable variation to the amplitude of probe electromagnetic radiation passing through them, necessitating the use of phase contrast imaging techniques for studying them. Here, we used digital holographic interferometric microscopy (DHIM) to observe temporal and spatial evolution of stem cell colonies. Three-dimensional or whole field imaging has yielded important quantitative information about their progression from single cell to colonies. Information on the time and spatial evolution of optical volume and path length change will be an important tool for biologists working in the area of stem cells and their development.

Holographic interferometric microscope with conjugate reconstruction for measurement of three-dimensional displacements

A holographic microscope with conjugate reconstruction for the interferometric determination of 3-D displacement vectors is described. Three double-exposed holograms of different illumination directions recorded on one hologram plate are reconstructed conjugately, and phase-stepping techniques are used to evaluate the interferograms. Only by conjugate reconstruction it is possible to obtain a perfectly optimized interferometer for the static evaluation method. Using both phase-step and filtering techniques, the evaluation of interferograms greatly disturbed by speckle noise can be performed successfully.

Application of Laser Holographic Interferometric Microscopy in Dental Investigation

Application of Laser Holographic Interferometric Microscopy in Dental Investigation