Abstract
Holographic microscopes are emerging as suitable tools for in situ diagnostics and environmental monitoring, providing high-throughput, label-free, quantitative imaging capabilities through small and compact devices. In-line holographic microscopes can be realized at contained costs, trading off complexity in the phase retrieval process and being limited to sparse samples. Here we present a 3D printed, cost effective and field portable off-axis holographic microscope based on the concept of holographic microfluidic slide. Our scheme removes complexity from the reconstruction process, as phase retrieval is non iterative and obtainable by hologram demodulation. The configuration we introduce ensures flexibility in the definition of the optical scheme, exploitable to realize modular devices with different features. We discuss trade-offs and design rules of thumb to follow for developing DH microscopes based on the proposed solution. Using our prototype, we image flowing marine microalgae, polystyrene beads, E.coli bacteria and microplastics. We detail the effect on the performance and costs of each parameter, design, and hardware choice, guiding readers toward the realization of optimized devices that can be employed out of the lab by non-expert users for point of care testing.
Highlights
The latest advances in the fields of Microscopy, Optical systems engineering, Materials science, Computer science, Physics, Chemistry and Bioinformatics have pushed the exponential growth in the last decade of the new paradigm of “point of care diagnostics” [1,2,3]
We maintain as the core element of our proposal the introduction of a grating inscribed on a commercial plastic chip that serves as a holographic slide
Portable Digital Holography (DH) offers label-free recording of the sample amplitude and quantitative phase information
Summary
The latest advances in the fields of Microscopy, Optical systems engineering, Materials science, Computer science, Physics, Chemistry and Bioinformatics have pushed the exponential growth in the last decade of the new paradigm of “point of care diagnostics” [1,2,3]. Ptychographic imaging, optical diffraction tomography and Spatial Light Interference Microscopy (SLIM) are good examples in this sense [4,5,6,7]. Introducing new methods and technologies to develop further field-portable analysis systems is undoubtedly a research topic of broad interest, connected to the trend of Lab-on-Chip (LoC) platforms. The latter are characterized by an outstanding compactness, resulting ideal for in situ analysis. They typically exploit microfluidic channels to handle extremely reduced volumes of liquid samples and reagents, which is a major advantage in terms of resources optimization
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