The complete blood count (CBC) is a foundational diagnostic test, but its accessibility is limited due to the blood draw, expensive laboratory equipment, and trained personnel required. Here, we present a cell phone microscope design for achieving phase contrast in high resolution capillary imaging, which allows individual blood cells to be imaged for a non-invasive CBC. The cell phone microscope uses a reversed lens as an objective to maintain a high resolution. Relay lenses create space for incorporation of an offset LED that can be critically imaged to produce oblique back illumination, resulting in phase contrast.
The increasing performance and ubiquity of mobile phone cameras has led to several emerging opportunities for their use in global health and point-of-care diagnostics. High-resolution, low-cost microscopy can be achieved by pairing the cell phone lens with a second, identical lens in a reversed orientation, allowing 1x magnification over a large field of view. In previous work, we showed that reverse lens mobile phone capillaroscopy can visualize optical absorption gaps (OAGs) in nailfold capillaries. The frequency of these OAGs is known to be inversely correlated with degree of neutropenia. To extend this concept and enable the direct visualization of both red and white blood cells for more complete blood analysis, there is a need for improved resolution and phase contrast. Here, we present a design for a reverse lens mobile phone capillaroscope that pairs two different cell phone lenses to increase magnification for enhanced visualization. From an iPhone 12 Pro, the telephoto and wide cameras are combined with reversed wide and ultrawide lenses. The lens pairs provide magnification up to 4.02x and resolution up to approximately 1.49 μm, whereas the previous design only yielded a resolution of 3.75 μm. We use this system to image human blood in a microfluidic capillary phantom.
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