Schematic of (a) Ray-tracing for virtual image formation in microsphere-assisted microscopy (MAM); MAM setup using a (b) low-index sphere working in air, (c) high-index sphere submerged in a liquid droplet, and (d) high-index sphere embedded in a solidified film; S: sample; MS: microsphere; VI: virtual image; MO: microscope objective. (e) Schematic representation of a microsphere-assisted interference microscope based on the Linnik configuration comprising two MO lenses and a beam splitter (BS). The illumination beam path, which corresponds to Kӧhler illumination is shown in blue, the imaging beam path in red. The illumination beam path appearing as a plane wave below the objective lens is omitted for better visibility. The figure is not drawn to scale to enhance comprehensibility. (f) Schematic setup for microsphere-assisted Mirau-DHM, in which a slight tilt (few degrees) is applied to the sample stage to achieve an off-axis digital holography configuration. (g) Schematic setup of the microsphere-assisted self-referencing DHM in transmission mode; S: sample; RI: real image; MO: microscope objective; GP: glass plate; TL: tube lens.
Newswise — Light microscopes, undoubtedly, are one of the most widely used devices for sample inspection in life and material sciences. Conventional microscopes translate the difference in intensity in an object to a brightness difference in the image. A phase microscope, on the other hand, converts the spatial differences in phase in the object to a difference in pixel brightness in the image. Interference microscopy, a phase-based approach, has found application in various disciplines. The spatial resolution in light microscopy is limited due to the wave nature of light. Enhancing the resolution in microscopy has been subject to intense investigation since the invention of the microscope. In the past decade, microsphere-assisted microscopy, the use of transparent microspheres to enhance the resolution, has emerged as a simple yet efficient approach to enhance microscopy resolution. Microsphere-assisted microscopy has been used in combination with several microscopic imaging techniques such as confocal, fluorescent, second harmonic generation, two-photon, dark-field, and interferometric and digital holographic microscopies to either improve their performance or provide new functionalities.
In a new paper (doi: https://www.light-am.com/en/article/doi/10.37188/lam.2024.006 ) published in Light: Advanced Manufacturing, international teams of authors, invited by Arash Darafsheh from Washington University School of Medicine in St. Louis, joined together to provide a comprehensive review on microsphere-assisted quantitative phase microscopy, the integration of microspheres with coherence scanning interference and digital holographic microscopies, while discussing the associated open questions, challenges, and opportunities.
Microsphere-assisted microscopy is a versatile technique that can be extended to coherence scanning interference and digital holographic microscopies to achieve 3D imaging with improved resolution. Microsphere-assisted interference microscopy offers a cost-effective and non-destructive high-speed single-shot imaging method for 3D surface metrology, and microsphere-assisted digital holographic microscopy provides a real-time method for high-contrast quantitative phase imaging in both transmission and reflection modes. Furthermore, quantitative phase microscopy arrangements improved by microspheres have the flexibility to be integrated with other methodologies, such as structured illumination and oblique illumination, to achieve further enhancements in resolution or other adjustments.
There is ample room for research in microsphere-assisted microscopy as discussed in this review. From the theoretical viewpoint, a comprehensive 3D model to describe the whole imaging system, including the illumination, microsphere, objective lens, 3D sample and its substrate, and imaging sensor would be of great interest to completely understand the resolution enhancement mechanism of microsphere-assisted microscopy. Besides a better understanding, full models help to further improve the resolution by optimizing system parameters. However, such models require an extremely large computational effort and hence cannot be implemented on current conventional computers. From the experimental point-of-view, implementation of microsphere-assisted microscopy in some scenarios may not be very straightforward; for example, the field-of-view is small and the speed for investigating larger areas may not be high. Overcoming these issues would bring new possibilities for the future of microsphere-assisted microscopy.
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DOI
Original Source URL
https://www.light-am.com/en/article/doi/10.37188/lam.2024.006
About Light: Advanced Manufacturing (LAM)
Light: Advanced Manufacturing (LAM) is a new, highly selective, open-access, and free of charge international sister journal of the Nature Journal Light: Science & Applications. The journal aims to publish innovative research in all modern areas of preferred light-based manufacturing, including fundamental and applied research as well as industrial innovations.
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