A dataset of digital holograms of normal and thalassemic cells.

Digital holographic microscopy (DHM) is an intriguing medical diagnostic tool due to its label-free and quantitative nature, providing high-contrast images of phase samples. By capturing both intensity and phase information, DHM enables the numerical reconstruction of quantitative phase images. However, the lateral resolution is limited by the diffraction limit, which prompted the recent suggestion of microsphere-assisted DHM to enhance the DHM resolution straightforwardly. The use of such a technique as a medical diagnostic tool requires testing and validation of the proposed assays to prove their feasibility and viability. This paper publishes 760 and 609 microsphere-assisted DHM images of normal and thalassemic red blood cells obtained from a normal and thalassemic male individual, respectively.

Simple high-resolution 3D microscopy by a dielectric microsphere: a proof of concept.

We present a simple high-resolution approach for 3D and quantitative phase imaging (QPI). Our method makes the most of a glass microsphere (MS) for microscopy and a glass plate for lateral shearing self-referencing interferometry. The single MS serves all the functions of a microscope objective (MO) in digital holographic microscopy (DHM) while offering the advantages of compactness, lightness, and affordability. A proof-of-concept experiment is performed on a standard diffraction grating, and various effective parameters on the imaging performance are investigated. The results are validated by atomic force microscopy and Mirau-DHM, and 3D morphometric information of the sample under inspection is obtained. The technique is then applied for 3D quantitative measurement and visualization of a human red blood cell, proving the principle of our easy-to-implement and vibration-immune arrangement for high-contrast label-free QPI of biological samples, and its utility in cell morphology, identification, and classification.

Evaluation of pitting corrosion by dynamic speckle pattern analysis.

There is an increasing interest in non-destructive and real-time high-resolution approaches for corrosion studies in metals. In this paper, we propose the dynamic speckle pattern method as a low-cost, easy-to-implement, and quasi in-situ optical technique for the quantitative evaluation of pitting corrosion. This type of corrosion occurs in a specific area of a metallic structure and causes holes formation leading to structural failure. A Custom 450 stainless steel sample, placed in 3.5 wt% NaCl solution and applied to a [Formula: see text] potential to initiate the corrosion, is used as the sample. The speckle patterns formed by the scattering of a He-Ne laser light is changed over time due to any corrosion in the sample. The analysis of the time-integrate speckle pattern suggests that the growth rate of pitting decreases with time.

Dielectric microspheres enhance microscopy resolution mainly due to increasing the effective numerical aperture.

Microsphere-assisted microscopy utilizing a microsphere in immediate proximity of the specimen boosts the imaging resolution mainly as a result of an increase in the effective numerical aperture of the system.

3D imaging using scanning diffractometry.

Imaging of cells is a challenging problem as they do not appreciably change the intensity of the illuminating light. Interferometry-based methods to do this task suffer from high sensitivity to environmental vibrations. We introduce scanning diffractometry as a simple non-contact and vibration-immune methodology for quantitative phase imaging. Fresnel diffractometry by a phase step has led to several applications such as high-precision measurements of displacement. Additional scanning may lead to 3D imaging straightforwardly. We apply the technique to acquire 3D images of holographic grating, red blood cell, neuron, and sperm cell. Either visibility of the diffraction fringes or the positions of extrema may be used for phase change detection. The theoretical analysis through the Fresnel diffraction from one-dimensional phase step is presented and the experimental results are validated with digital holographic microscopy. The presented technique can be suggested to serve as a robust device for 3D phase imaging and biomedical measurements.

Role of pH level on the morphology and growth rate of myelin figures.

The myelin figure (MF) is one of the basic structures of lipids, and the study of their formation and the effect of various parameters on their growth is useful in understanding several biological processes. In this paper, we address the influence of the pH degree of the surrounding medium on MF dynamics. We introduce a tunable shearing digital holographic microscopy arrangement to obtain quantitative and volumetric information about the complex growth of MFs. Our results show that (1) the time evolution of relative length and volume changes of MFs follows a power-law, (2) the acidity facilitates the growth rate, and (3) the acidic environment causes the formation of thicker MFs.

Microsphere-assisted super-resolved Mueller matrix microscopy.

Mueller matrix microscopy (MMM) is a powerful approach to probe microstructural and optical information of many important specimens (e.g., tissue and bacteria), which otherwise cannot be obtained directly from intensity or spectral images. Achieving high lateral resolution in MMM, similar to other microscopy approaches, remains a challenge. Here, we extend the idea of microsphere (MS) -assisted microscopy into MMM toward resolution-enhanced polarimetric imaging. The goal is achieved by insertion of a transparent MS in the working distance of the imaging microscope objective in the optical train of an MMM system. We experimentally show that an MS close to the sample in MMM may increase the resolution beyond the intrinsic diffraction limit of the system by redirecting the higher spatial frequencies of the sample into the acceptance cone. In order to be a case in point, the experiment is conducted on a standard holographic diffraction grating with 1 µm line-width, which is beyond the diffraction limit of a 10× objective. Two-dimensional images of the Mueller matrix and some of the widely used quantitative polarimetric parameters of the sample are calculated and compared in the two cases before and after insertion of MS. The proposed arrangement is easy to implement and has the potential to serve as a high-resolution polarimetric microscope for visualizing the polarization characteristics of the microscopic objects.

Erratum: Role of pH level on the morphology and growth rate of myelin figures: publisher's note.

[This corrects the article on p. 5565 in vol. 11, PMID: 33149971.].

Digital holographic microscopy for 3D surface characterization of polymeric nanocomposites.

The aim of this paper is to introduce digital holographic microscopy (DHM) as a non-contact, inexpensive, and non-abrasive method for 3D surface characterization of polymeric nanocomposites. A common-path and vibration-immune Mirau system with a microsphere-assisted arrangement is utilized to increase the lateral resolution of the images. The characterization is performed through the measurement of roughness parameters of the surfaces, which are derived from the recorded holograms. Pure poly(triazole-amide-imide) (PTAI) and PTAI nanocomposite reinforeced with surface modified TiO2 nanoparticles (MN-TiO2) are used and compared. The experimental results show the potential of the presented method to serve as an alternative for expensive surface measurement devices such as stylus profiler and atomic force microscope (AFM) for polymeric surface characterization.

Microsphere-assisted super-resolved Mirau digital holographic microscopy for cell identification.

In this paper, we use a glass microsphere incorporated into a digital holographic microscope to increase the effective resolution of the system, aiming at precise cell identification. A Mirau interferometric objective is employed in the experiments, which can be used for a common-path digital holographic microscopy (DHMicroscopy) arrangement. High-magnification Mirau objectives are expensive and suffer from low working distances, yet the commonly used low-magnification Mirau objectives do not have high lateral resolutions. We show that by placing a glass microsphere within the working distance of a low-magnification Mirau objective, its effective numerical aperture can be increased, leading to super-resolved three-dimensional images. The improvement in the lateral resolution depends on the size and vertical position of microsphere, and by varying these parameters, the lateral resolution and magnification may be adjusted. We used the information from the super-resolution DHMicroscopy to identify thalassemia minor red blood cells (tRBCs). Identification is done by comparing the volumetric measurements with those of healthy RBCs. Our results show that microsphere-assisted super-resolved Mirau DHMicroscopy, being common path and off-axis in nature, has the potential to serve as a benchtop device for cell identification and biomedical measurements.