Field-portable reflection and transmission microscopy based on lensless holography

Abstract

We demonstrate a lensfree dual-mode holographic microscope that can image specimens in both transmission and reflection geometries using in-line transmission and off-axis reflection holography, respectively. This field-portable dual-mode holographic microscope has a weight of ~200 g with dimensions of 15 x 5.5 x 5cm, where a laser source is powered by two batteries. Based on digital in-line holography, our transmission microscope achieves a sub-pixel lateral resolution of ≤2 µm over a wide field-of-view (FOV) of ~24 mm2 due to its unit fringe magnification geometry. Despite its simplicity and ease of operation, in-line transmission geometry is not suitable to image dense or connected objects such as tissue slides since the reference beam gets distorted causing severe aberrations in reconstruction of such objects. To mitigate this challenge, on the same cost-effective and field-portable assembly we built a lensless reflection mode microscope based on digital off-axis holography where a beam-splitter is used to interfere a tilted reference wave with the reflected light from the object surface, creating an off-axis hologram of the specimens on a CMOS sensor-chip. As a result of the reduced space-bandwidth product of the off-axis geometry compared to its in-line counterpart, the imaging FOV of our reflection mode is reduced to ~9 mm2, while still achieving a similar sub-pixel resolution of ≤2 µm. We tested the performance of this compact dual-mode microscopy unit by imaging a US-air force resolution test target, various micro-particles as well as a histopathology slide corresponding to skin tissue. Due to its compact, cost-effective, and lightweight design, this dual-mode lensless holographic microscope might especially be useful for field-use or for conducting microscopic analysis in resource-poor settings.

05 gigapixel microscopy using a flatbed scanner

“…In addition, there have been exciting research efforts into wide FOV imaging systems, including contact-imaging microscopy [5,6], digital in-line holography [7][8][9], focus-grid scanning illumination [10][11][12], and off-axis holography microscopy [13,14]. All these methods try to break the tie between resolution and FOV by abandoning the conventional microscopy design and shifting away from the use of optics schemes that perform optical image magnification.…”

A semi-automated, field-portable microscopy platform for clinical diagnostic applications

“…5,7 The second approach is based on reconstruction of holographic diffraction signature of the microscopic specimen obtained using a lens-free CCD/CMOS camera. 9,[16][17][18] Amongst the two methods, the first one is computationally less intensive. We have chosen the first approach wherein, the device can function with no additional computational hardware.…”

“…In the recent past, there have been many reports of field portable digital microscope designs. [5][6][7][8][9][10] Although portable, compact and efficient, these microscopes require manpower with expertise to manually prepare the slides for examination. The process of sample preparation can potentially be automated with the application of recent techniques developed in the field of microfluidics.…”

Reflective lens-free imaging on high-density silicon microelectrode arrays for monitoring and evaluation of in vitro cardiac contractility

“…However, this approach was only applied to optically dense or spatially connected specimens (e.g. tissue slices) on transparent glass slides [43]. Additionally, the low temporal resolution, limited FOV and long analysis times impede contractility monitoring.…”