Design and fabrication of a passive droplet dispenser for portable high resolution imaging system

Tahseen Kamal, Rachel Watkins, Zijian Cen, Jaden Rubinstein, Gary Kong, Woei Ming Lee, Tahseen Kamal, Rachel Watkins, Zijian Cen, Jaden Rubinstein, Gary Kong, Woei Ming Lee

Abstract

Moldless lens manufacturing techniques using standard droplet dispensing technology often require precise control over pressure to initiate fluid flow and control droplet formation. We have determined a series of interfacial fluid parameters optimised using standard 3D printed tools to extract, dispense and capture a single silicone droplet that is then cured to obtain high quality lenses. The dispensing process relies on the recapitulation of liquid dripping action (Rayleigh-Plateau instability) and the capturing method uses the interplay of gravitational force, capillary forces and liquid pinning to control the droplet shape. The key advantage of the passive lens fabrication approach is rapid scale-up using 3D printing by avoiding complex dispensing tools. We characterise the quality of the lenses fabricated using the passive approach by measuring wavefront aberration and high resolution imaging. The fabricated lenses are then integrated into a portable imaging system; a wearable thimble imaging device with a detachable camera housing, that is constructed for field imaging. This paper provides the full exposition of steps, from lens fabrication to imaging platform, necessary to construct a standalone high resolution imaging system. The simplicity of our methodology can be implemented using a regular desktop 3D printer and commercially available digital imaging systems.

Conflict of interest statement

The authors declare no competing financial interests.

Figures

Figure 1. Immersion/extract, dispensing, capturing single silicone…
Figure 1. Immersion/extract, dispensing, capturing single silicone droplet using the proposed 3D substrates.
(a1–a2) Shows the immersion process for extracting fixed fluid volume using the conic substrate and a reservoir of fluid. (b1–d1) Shows three different conic-droppers of angle 16.9°, 31.9° (Supplementary Video 1) and 58.3° (Supplementary Video 2) respectively. (b2) A dropper with slope 16.9° extracting a small amount of PDMS at the tip. (c2) and (d2) are droppers with slope 31.9° and 58.3° respectively that extracts a fixed volume of PDMS, a droplet hangs over the tip of each of cone dropper. (b3) A holder (1 mm thick) captures no droplet as cone dropper in (b2) did not dispense any droplets. (c3) and (d3) both collects a droplet from by the cone-droppers in (c2) and (d2). However, the droplet held in (d2) fails to capture the first droplet (supplementary video 3). Red dotted line indicates the angle, white dotted lines shows the position of the holder. All the images are on a scale bar of 1 mm.
Figure 2. Reduced droplet wetting via pinning…
Figure 2. Reduced droplet wetting via pinning on the holder using 3D printed barrier.
(a1) A droplet first deposited onto a holder without a barrier (inset (a1)). (a2) Droplet with reduced curvatures as it spread across the substrate. (b1) Shows a droplet first deposited onto a holder with a fixed barrier (height of 1.04 mm) (Supplementary Video 4). (b2) Shows droplet holding its shape in the presence of the barrier showing the effect of liquid pinning. (Supplementary Video 5). The holder images are on a scale bar of 1 mm.
Figure 3. A flowchart depicting the passive…
Figure 3. A flowchart depicting the passive droplet dispenser lens-making process supported by schematics.
The lens making protocol has been elaborately in Supplementary Information S1 and S2.
Figure 4. Optical aberrations and focal lengths…
Figure 4. Optical aberrations and focal lengths of silicone lenses.
(a) The optical bench setup using a SHWS that has been used for optical characterization of the lenses. (b) Optical characteristics of the lenses are summarized using Zernike modes of various orders. Comparison among the silicone lenses and a commercial aspheric lens has been shown in a chart. Zernike modes 1, 2, 3 and 5 which are piston, tilt and tip, were not included as they do not represent true aberrations from the lenses. Higher Zernike modes with negligible values were also ignored. (c) Plot of magnitude (unit wavelengths) of spherical aberrations (Zernike mode 13) with lenses of various focal lengths. (d) Relationship between the dip numbers and the corresponding focal lengths of the lenses.
Figure 5. Optical profiling of surface roughness…
Figure 5. Optical profiling of surface roughness of a silicone lens and a commercial lens.
(a) 3D map of curvature of front surface of a silicone lens. (b) A cross-section (line plot) of the surface, measuring the surface roughness of the silicone lens. (c) 3D map of the curvature of the front surface of a commercial aspheric lens. (d) Corresponding line plot of cross section of the surface.
Figure 6. Lens curvature profiling and imaging.
Figure 6. Lens curvature profiling and imaging.
(a) Curve tracing of the front surface of three silicone lenses fabricated using the passive dispenser. (b) Gaussian fitting of the corresponding profiles and the calculated radii of curvatures. (c) Measured and calculated focal lengths plotted as a function of the volume of the harvested lenses. (d1–d4) Magnified images of the USAF target card of magnifications 30X, 50X, 80X and 25X respectively. (e1–e4) Images of an onion root tip at different magnifications.
Figure 7. Overview of a portable imaging…
Figure 7. Overview of a portable imaging system.
(a) Schematic representing the components required for a compact microscopic imaging system. (b) A Raspberry Pi -2, the Pi camera and a 2.8″ LCD display is another option for designing a small imaging system.
Figure 8. Portable thimble imaging system.
Figure 8. Portable thimble imaging system.
(a) Chart showing average of length of index fingers (n = 5). (b) (top) 3D designs of the thimble mount (bottom) thimble mounted on the index finger. (c) Thimble design. (i) Completed 3D printed thimble mount. (ii) Back section of the finger brace. (iii) Front section of the finger brace. (iv) Back connector of camera holder. (v) 3D schematic of Raspberry Pi camera. (vi) Front part of the camera holder. (vii) DIP switch to control illumination. (viii) Coin cell battery to supply power for the light emitting diodes. (ix–x) Two neopixel white LEDs. (xi) A silicone lens, designed using the passive dispenser, aligned with the Raspberry Pi camera.
Figure 9. Thimble imaging device with macroscopic…
Figure 9. Thimble imaging device with macroscopic and microscopic imaging.
(a) Handheld imaging device used with standard laptop for imaging outdoors. (b) Thimble imaging system with miniature LCD display in an outdoor environment. (c) A macroscopic image of a section of the back of a Latrodectus hasseltii (male redback spider of around 3 mm body length) has been captured using the thimble imaging device. (d) Macroscopic image of section of a wing of a regular Musca domestica (house fly) has been captured using the thimble imaging device. Microscopic imaging of histology slides of (e) Human colon and (f) Liver tissue.

References

    1. Ozcan A. Mobile phones democratize and cultivate next-generation imaging, diagnostics and measurement tools. Lab on a Chip 14, 3187–3194, doi: 10.1039/c4lc00010b (2014).
    1. Boppart S. A. & Richards-Kortum R. Point-of-care and point-of-procedure optical imaging technologies for primary care and global health. Science Translational Medicine 6, 253rv252–253rv252, doi: 10.1126/scitranslmed.3009725 (2014).
    1. Graham E. A., Henderson S. & Schloss A. Using mobile phones to engage citizen scientists in research. Eos, Transactions American Geophysical Union 92, 313–315, doi: 10.1029/2011eo380002 (2011).
    1. Overeem A. et al.. Crowdsourcing urban air temperatures from smartphone battery temperatures. Geophysical Research Letters 40, 4081–4085, doi: 10.1002/grl.50786 (2013).
    1. Price S. et al.. Fostering geospatial thinking in science education through a customisable smartphone application. British Journal of Educational Technology 45, 160–170, doi: 10.1111/bjet.12000 (2014).
    1. Devictor V., Whittaker R. J. & Beltrame C. Beyond scarcity: citizen science programmes as useful tools for conservation biogeography. Diversity and Distributions 16, 354–362, doi: 10.1111/j.1472-4642.2009.00615.x (2010).
    1. Deville P. et al.. Dynamic population mapping using mobile phone data. Proceedings of the National Academy of Sciences 111, 15888–15893, doi: 10.1073/pnas.1408439111 (2014).
    1. Steinhubl S. R., Muse E. D. & Topol E. J. The emerging field of mobile health. Science Translational Medicine 7, 283rv283–283rv283, doi: 10.1126/scitranslmed.aaa3487 (2015).
    1. Greenbaum A. et al.. Wide-field computational imaging of pathology slides using lens-free on-chip microscopy. Science Translational Medicine 6, 267ra175–267ra175, doi: 10.1126/scitranslmed.3009850 (2014).
    1. D’Ambrosio M. V. et al.. Point-of-care quantification of blood-borne filarial parasites with a mobile phone microscope. Science Translational Medicine 7, 286re284–286re284, doi: 10.1126/scitranslmed.aaa3480 (2015).
    1. Lipson H. & Kurman M. Fabricated: The new world of 3D printing. (John Wiley & Sons, 2013).
    1. Bogoch I. I. et al.. Mobile Phone Microscopy for the Diagnosis of Soil-Transmitted Helminth Infections: A Proof-of-Concept Study. The American Journal of Tropical Medicine and Hygiene, doi: 10.4269/ajtmh.12-0742 (2013).
    1. Contreras-Naranjo J. C., Wei Q. & Ozcan A. Mobile Phone-Based Microscopy, Sensing, and Diagnostics. IEEE Journal of Selected Topics in Quantum Electronics 22, 1–14, doi: 10.1109/jstqe.2015.2478657 (2016).
    1. Vashist S. K., Luppa P. B., Yeo L. Y., Ozcan A. & Luong J. H. T. Emerging Technologies for Next-Generation Point-of-Care Testing. Trends in Biotechnology 33, 692–705, doi: 10.1016/j.tibtech.2015.09.001.
    1. Lee W. M., Upadhya A., Reece P. J. & Phan T. G. Fabricating low cost and high performance elastomer lenses using hanging droplets. Biomed. Opt. Express 5, 1626–1635, doi: 10.1364/boe.5.001626 (2014).
    1. McDonald C. & McGloin D. Low-cost optical manipulation using hanging droplets of PDMS. RSC Advances 5, 55561–55565, doi: 10.1039/c5ra11431d (2015).
    1. Roy A. C., Yadav M., Arul E. P., Khanna A. & Ghatak A. Generation of Aspherical Optical Lenses via Arrested Spreading and Pinching of a Cross-Linkable Liquid. Langmuir 32, 5356–5364, doi: 10.1021/acs.langmuir.5b04631 (2016).
    1. Sung Y.-L., Jeang J., Lee C.-H. & Shih W.-C. Fabricating optical lenses by inkjet printing and heat-assisted in situ curing of polydimethylsiloxane for smartphone microscopy. BIOMEDO 20, 047005–047005, doi: 10.1117/1.jbo.20.4.047005 (2015).
    1. Henderson D. M., Pritchard W. G. & Smolka L. B. On the pinch-off of a pendant drop of viscous fluid. Physics of Fluids 9, 3188–3200, doi: 10.1063/1.869435 (1997).
    1. Rayleigh L. On the Capillary Phenomenon of Jets. Proceedings of the Royal Society of London A, 71–97 (1879).
    1. Driessen T., Jeurissen R., Wijshoff H., Toschi F. & Lohse D. Stability of viscous long liquid filaments. Physics of Fluids 25, 062109, doi: 10.1063/1.4811849 (2013).
    1. Grilli S. et al.. 3D lithography by rapid curing of the liquid instabilities at nanoscale. Proceedings of the National Academy of Sciences 108, 15106–15111, doi: 10.1073/pnas.1110676108 (2011).
    1. Kaufman J. J. et al.. Structured spheres generated by an in-fibre fluid instability. Nature 487, 463–467, doi: 10.1038/nature11215 (2012).
    1. Wilson S. D. R. The slow dripping of a viscous fluid. Journal of Fluid Mechanics 190, 561–570, doi: doi: 10.1017/S0022112088001454 (1988).
    1. Zhu Z.-Q., Wang Y., Liu Q.-S. & Xie J.-C. Influence of Bond Number on Behaviors of Liquid Drops Deposited onto Solid Substrates. Microgravity Science and Technology 24, 181–188, doi: 10.1007/s12217-011-9294-1 (2012).
    1. van Hoeve W. et al.. Breakup of diminutive Rayleigh jets. Physics of Fluids 22, 122003, doi: 10.1063/1.3524533 (2010).
    1. Zhang X. & Basaran O. A. An experimental study of dynamics of drop formation. Physics of Fluids 7, 1184–1203, doi: 10.1063/1.868577 (1995).
    1. Yuan Y. & Lee T. R. In Surface Science Techniques (eds Bracco Gianangelo & Holst Bodil) 3–34 (Springer Berlin Heidelberg, 2013).
    1. Chang B., Shah A., Routa I., Lipsanen H. & Zhou Q. Low-height sharp edged patterns for capillary self-alignment assisted hybrid microassembly. Journal of Micro-Bio Robotics 9, 1–10, doi: 10.1007/s12213-014-0073-0 (2014).
    1. Lock J. A., Walker J. D. & Andrews J. H. Using refraction caustics to monitor evaporation of liquid drop lenses. Appl. Opt. 29, 4599–4607, doi: 10.1364/ao.29.004599 (1990).
    1. Hamblen D. P. Optical Activities in Industry Miniature aspheric lenses with spherical index gradients. Appl. Opt. 33, 561–564, doi: 10.1364/AO.33.000561 (1994).
    1. Yang X.-D., Grossman T., Wigdor D. & Fitzmaurice G. In Proceedings of the 25th annual ACM symposium on User interface software and technology 147–156 (ACM, Cambridge, Massachusetts, USA, 2012).
    1. Cybulski J. S., Clements J. & Prakash M. Foldscope: Origami-based paper microscope. Plos One 9, e98781 (2014).
    1. Zheng G., Horstmeyer R. & Yang C. Wide-field, high-resolution Fourier ptychographic microscopy. Nat Photon 7, 739–745, doi: 10.1038/nphoton.2013.187 (2013).

Source: PubMed

Sponsorit ja yhteistyökumppanit

Sairaudet

Huumeiden interventiot

3
Tilaa