Our fluorescent microscopy platform is directly attached to the existing camera unit of the cell-phone with a compact and light-weight interface, which mainly includes 3 LEDs, a simple lens, and a mechanical tray for holding a plastic colour filter as illustrated in . Note that the LEDs and the plastic filter can be easily changed for different excitation/emission colours, and therefore this platform is compatible with a wide range of fluorophores.
We initially demonstrated the fluorescent imaging capability of this platform by using fluorescent micro-beads (with a diameter of 10 μm) at two different emission wavelengths, i.e., 515 nm and 605 nm as shown in (bottom image) and , . To characterize the FOV of this platform, red fluorescent beads (between two microscope slides) were imaged as illustrated in over an area of 14.7 mm × 11 mm. Toward its edges, this large imaging area has aberrations (see e.g., ), and therefore only the central region spanning an area of ~9 mm × 9 mm exhibited a decent imaging performance, creating an FOV ~81 mm2 as indicated with the dashed square in . Due to its large FOV and low numerical aperture, this cellphone based fluorescent microscopy platform has the capability to screen large sample volumes (>0.1 mL) which could be especially important for rapid screening of e.g., blood, urine, saliva, water etc. We should also note that while the aberrated regions (e.g., ) look significantly distorted when compared to the central imaging area (e.g., ), for various cell counting or detection applications in resource-limited settings, such aberrated regions could still be useful, which would potentially further increase the imaging area beyond 81 mm2.
Fig. 2 Imaging performance of the cell-phone fluorescent microscope shown in is demonstrated using fluorescent beads (10 μm diameter; excitation/emission: 580 nm/605 nm). The central field-of-view of each cell-phone image is ~8l mm2, which exhibits (more ...)
Fig. 3 Spatial resolution of the cell-phone fluorescent microscope shown in is illustrated using green and red fluorescent beads. The top row shows raw cell-phone images of the particles which demonstrate ~20 μm resolution in both of the fluorescent (more ...)
Next we performed a series of experiments to characterize the spatial resolution of our platform using green and red fluorescent beads (10 μm diameter). top row () illustrates the imaging performance of the cell-phone microscope for several set of beads. The same samples were also imaged by a conventional fluorescent microscope using a 10x microscope-objective (numerical aperture 0.25) as shown in bottom row (). Based on these results, using the raw cell-phone images we can resolve 2 beads that are separated by ~20 μm (center-to-center). This resolving power can be further improved through digital signal processing of the captured fluorescent images based on compressive sampling theory,10-12
the details of which will be presented in the Experiment Methods section. Based on this numerical recipe, the decoded cell-phone images are shown in (Middle Row) which this time indicates that 2 beads having a center-to-center distance of ~10 μm (that could not be resolved in the raw cellphone images) are now digitally resolved as illustrated in and . We should emphasize that even though this resolving power (~10 μm) is fairly modest, because of the large FOV of this platform (~81 mm2
), it is still quite useful for various cell/pathogen detection and quantification applications, involving e.g
., bodily fluid analysis in remote locations.
Following these characterization experiments, we next investigated the feasibility of using our cell-phone based fluorescent microscopy platform to image labeled cells in whole blood samples. For this end, we imaged white-blood cells that were labeled with STYO®16 nucleic acid staining. These white-blood cells were excited with blue LEDs (470 nm peak wavelength) and were imaged using our cell-phone based microscope, the results of which are summarized in . In this , (A1-C1) are digitally cropped from the central FOV of the cell-phone fluorescent image, showing raw signatures of the labeled white-blood cells. For comparison purposes, the same zoomed regions of the sample were also imaged using a conventional fluorescent microscope (10x microscope objective) as shown in , which all provide a decent match to our cell-phone fluorescent images. To further improve our image quality, we have compressively decoded to digitally arrive at , which clearly demonstrate our improved resolving power similar to (see e.g., the closely spaced white-blood cells as pointed by white arrows in ).
Fig. 4 Imaging performance of our cell-phone fluorescent microscope is demonstrated using labeled white blood cells. Microscope objective (10×, NA = 0.25) images of the same samples, acquired with a conventional fluorescent microscope, are also provided (more ...)
We also explored the potential application of this cell-phone based fluorescent microscope for water quality monitoring. For this purpose, Giardia Lamblia was chosen as the model system in our study because it is one of the most widely found pathogen that exists in water sources. Since it only takes ingestion of as few as ten Giardia Lamblia cysts to cause an infection, it is highly desirable to have a detection method that can rapidly identify low concentration cysts in drinking water. To demonstrate its proof-of-concept, (Top Row) illustrates raw cell-phone fluorescent images of Giardia Lamblia cysts that were labeled using SYTO®16. These cell-phone images were digitally cropped from a large FOV (~81 mm2), and for comparison purposes, the same regions of interest were also imaged using a conventional fluorescent microscope (10x microscope-objective), which very well matched to our cell-phone imaging results. As discussed earlier, our cell-phone fluorescent microscopy platform has the capability to rapidly image large samples volumes of e.g., >0.1 mL. In addition to this, fluorescent labeling can also provide high specificity and sensitivity for detection of pathogenic parasites at low concentration levels, all of which make our cell-phone fluorescent microscope a promising tool for monitoring of water-quality in resource limited environments.
Fig. 5 (Top) Giardia Lamblia cysts that are imaged using the fluorescent cell-phone microscope of . (Bottom) Microscope objective (10×, NA = 0.25) images of the same samples are also provided for comparison purposes. Note that because the samples (more ...)
We would like to briefly point out an alternative sample handling method that involves the use of glass capillary tubes in our cell-phone microscopes. Rather than using planar substrates (as illustrated in - so far) our cell-phone based fluorescent microscope can also image samples that are loaded into capillary tubes through simple capillary action.
The excitation of the specimen within such capillary tubes shares the same approach that we used so far, such that the pump can be guided within the capillary tube which acts as a waveguide once loaded with a sample solution. This waveguide, even though has a lower refractive index at the core, permits efficient excitation of the labeled objects within its core as illustrated in and Supplementary Fig. 1
Such a simple capillary based sample preparation approach could be rather convenient to use especially in remote locations where even basic laboratory instruments might not be readily available.
Fig. 6 Fluorescent samples can also be imaged within micro-capillaries using our cell-phone based fluorescent microscope. In this case, simple capillary action is sufficient to load the specimen into a capillary tube. Each capillary, when loaded with the sample (more ...)
Finally, we would like to emphasize that the same compact and cost-effective cell-phone microscopy interface can also image non-fluorescent objects as demonstrated in . In this dark-field imaging mode, the scattered light from the objects is imaged using the cell-phone microscope without the use of any colour filters. In , a sample that contains both fluorescent and non-fluorescent beads (10 μm diameter) is imaged. In the top row of , darkfield images of two different zoomed regions of the sample are illustrated. Because the illumination was achieved using a white LED (without any colour filter in front of the sensor), the side-scattered light from non-fluorescent beads creates their darkfield images. The fluorescent beads within the mixture can still be excited using this white LED, and therefore their green fluorescent emission is also visible in this darkfield image. In the Second Row of fluorescent images of the same FOV are illustrated using our cell-phone microscope. The illumination was achieved using a blue LED which efficiently pumped the fluorescent beads as evident in their images. The non-fluorescent beads do not show up in this fluorescent image since a colour filter in front of the cell-phone sensor rejected the pump wavelength that is scattered toward the sensor. also presents conventional microscope comparison images (both fluorescent and brightfield) of the same samples.
Fig. 7 Darkfield imaging capability of our cell-phone microscope () is demonstrated using a mixture of fluorescent and non-fluorescent 10 μm beads. (Top row) Darkfield images of two different zoomed regions of the sample are illustrated. Because (more ...)