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Droplet-based Microfluidics

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Final edit on Droplet-based microfluidics page:

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Droplet-based microfluidics manipulate discrete volumes of fluids in immiscible phases with low Reynolds number and laminar flow regimes. Interest in droplet-based microfluidics systems has been growing substantially in past decades. Microdroplets offer the feasibility of handling miniature volumes (μl to fl) of fluids conveniently, provide better mixing, encapsulation, sorting, sensing and are suitable for high throughput experiments.

Two immiscible phases used for the droplet generation are termed as the continuous phase (medium in which droplets are generated) and dispersed phase (the droplet phase). The size of the generated droplets is mainly controlled by the flow rates of the continuous phase and dispersed phase, interfacial tension between two phases and the geometry used for the droplet generation. Generally, three types of microfluidic geometries are utilized for the droplet generation: (i) T-Junction, (ii) Flow Focusing, and (iii) Co-Flowing.

**Missing citations** I added them in the actual wikipedia page not my sandbox.

Original text from Microfluidics page:

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Droplet-based microfluidics as a subcategory of microfluidics in contrast with continuous microfluidics has the distinction of manipulating discrete volumes of fluids in immiscible phases with low Reynolds number and laminar flow regimes. Interest in droplet-based microfluidics systems has been growing substantially in past decades. Microdroplets offer the feasibility of handling miniature volumes (μl to fl) of fluids conveniently, provide better mixing, encapsulation, sorting, sensing and are suitable for high throughput experiments.[1] Exploiting the benefits of droplet-based microfluidics efficiently requires a deep understanding droplet generation [2] to perform various logical operations[3][4] such as droplet motion, droplet sorting, droplet merging, and droplet breakup.[5]

Two immiscible phases used for the droplet generation are termed as the continuous phase (medium in which droplets are generated) and dispersed phase (the droplet phase). The size of the generated droplets is mainly controlled by the flow rates of the continuous phase and dispersed phase, interfacial tension between two phases and the geometry used for the droplet generation.[6][3] Generally, three types of microfluidic geometries are utilised for the droplet generation : (i) T-Junction, (ii) Flow Focusing, and (iii) Co-Flowing. T-junction geometry follows a linear scaling law [7] for the droplet generation and hence, simple to use.

Micromagnetofluidic method,[8] which is the control of magnetic fluids by an applied magnetic field on a microfluidic platform,[9] offers wireless and programmable control of the magnetic droplets.[10][11] Hence, the magnetic force can also be used to perform various logical operations,[12][13] in addition to the hydrodynamic force and the surface tension force.[10][11] The magnetic field strength, type of the magnetic field (gradient, uniform or rotating), magnetic susceptibility, interfacial tension, flow rates, and flow rate ratios determine the control of the microdroplets on a micromagnetofluidic platform.[10]

One of the key advantages of droplet-based microfluidics is the ability to use droplets as incubators for single cells.[1][14]

Devices capable of generating thousands of droplets per second opens new ways characterise cell population, not only based on a specific marker measured at a specific time point but also based on cells kinetic behaviour such as protein secretion, enzyme activity or proliferation.[15] Recently, a method was found to generate a stationary array of microscopic droplets for single-cell incubation that does not require the use of a surfactant .[16]

Droplet based devices have also been used to investigate the conditions necessary for protein crystallization.[17][18][19]

Raman spectroscopy detection for microfluidics

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Raman spectroscopy is an optical technique that provides non-destructive analysis with chemical specificity without complex sample preparation, and is capable of detecting components within mixtures. Raman signal corresponds to vibrational excitation of specific molecules within the system based on the scattered visible light emitted from a molecule with a lower energy than the excitation light source. Raman spectroscopy, when coupled with microfluidic devices, can monitor fluid mixing and trapping[20] of liquids and can also detect solid and gas phases[21] within microfluidic platforms. Raman signal can be detected with integrated fiberoptics[22] within the microfluidic chip or by placing the device on Raman microscope[23].   

Raman signal is inherently weak; therefore for short detection times at small sample volumes in microfluidic devices, signal amplification is utilized. Some microfluidic systems utilize metallic colloids[24] or nanoparticles[25] within solution to capitalize on Surface-enhanced Raman spectroscopy (SERS) as a detection technique. Typical confocal Raman microscopy allows for spectroscopic information from small focal volumes less 1 micron cubed, and thus smaller than the microfluidic channel dimensions5. Multi-photon Raman spectroscopy, such as stimulated Raman scattering (SRS) or coherent anti-Stokes Raman scattering (CARS) also enhance signal from substances in microfluidic devices. 

For droplet based microfluidics, Raman detection provides online analysis of multiple analytes within droplets or carrier phase. Raman signal is sensitive to concentration changes, therefore solubility and mixing kinetics of a droplet-based microfluidic system can be detected using Raman[21][23].  Considerations include the refractive index difference at the interface of the droplet and carrier phase, as well as between fluid and channel connections.[20][23][26] 

Reflective Essay on wikiedu project

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1.     Droplet-based Microfluidics

a. I created a new page on droplet-based microfluidics

b.  I wrote the summary and formed the structure and outline for the page

              i.  I edited the “Droplet-based Microfluidics” section on the Microfluidics page to use as text for new page

             ii.  I deleted extraneous droplet based microfluidics text on microfluidics page

c.  I wrote the “Raman spectroscopy” part of detection methods

2.    Response to Peer reviewers

a. My assigned peer reviewers did not provide any structural or content-based edits, but only corrected a bit of grammar and word choice. I fixed those minor errors

b. Edits from other droplet-based microfluidics writers: Again, not much feedback, I was delivering more critique than receiving it.

3.    Reflection on the assignment:

I enjoyed working on this assignment. It’s pretty cool to work with wikiedu because I know my mom uses this assignment in her college level Psychology courses, so I heard about Wikipedia editing but haven’t actually done any until this class. I enjoy applying a concise writing style that I got to practice in my previous work in museum curating classes to science. To elaborate, I wrote lots of wall texts for an exhibition at my college and in my internship after my degree at an art museum, and the concise writing about a vastly studied subject is difficult but rewarding to me!

As far as the structure of the assignment. I appreciated all the steps that make this writing exercise more of a polished work. I also liked doing the research on a specific part of microfluidics that relates to my own research in Raman spectroscopy. Summarizing is always important when presenting scientific ideas so I thought this was a really good exercise!

  1. ^ a b Venkat Chokkalingam, Jurjen Tel, Florian Wimmers, Xin Liu, Sergey Semenov, Julian Thiele, Carl G. Figdor, Wilhelm T.S. Huck, Probing cellular heterogeneity in cytokine-secreting immune cells using droplet-based microfluidics, Lab on a Chip, 13, 4740-4744, 2013, DOI: 10.1039/C3LC50945A, http://pubs.rsc.org/en/content/articlelanding/2013/lc/c3lc50945a#!divAbstract
  2. ^ Chokkalingam, V.; Herminghaus, S.; Seemann, R. (2008). "Self-synchronizing Pairwise Production of Monodisperse Droplets by Microfluidic Step Emulsification". Applied Physics Letters. 93: 254101. doi:10.1063/1.3050461.
  3. ^ a b Teh, Shia-Yen and Lin, Robert and Hung, Lung-Hsin and Lee, Abraham P (2008). "Droplet microfluidics". Lab on a Chip. 8 (2). Royal Society of Chemistry: 198–220. doi:10.1039/B715524G.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  4. ^ Prakash, Manu; Gershenfeld, Neil (2007-02-09). "Microfluidic Bubble Logic". Science. 315 (5813): 832–835. doi:10.1126/science.1136907. ISSN 0036-8075. PMID 17289994.
  5. ^ Samie, Milad; Salari, Shafii (May 2013). "Breakup of microdroplets in asymmetric T junctions". Physical Review E. 87 (05). Bibcode:2013PhRvE..87e3003S. doi:10.1103/PhysRevE.87.053003.
  6. ^ Varma, Vijaykumar; Ray, Ayan; Wang, Z. M.; Wang, Z. P.; Ramanujan, R. V. (2016). "Droplet Merging on a Lab-on-a-Chip Platform by Uniform Magnetic Fields". Scientific Reports. 6: 37671 (In Press). doi:10.1038/srep37671. PMC 5124862. PMID 27892475 – via Nature Publishing Group.
  7. ^ Garstecki, Piotr and Fuerstman, Michael J and Stone, Howard A and Whitesides, George M (2006). "Formation of droplets and bubbles in a microfluidic T-junction—scaling and mechanism of break-up" (PDF). Lab on a Chip. 6 (3). Royal Society of Chemistry: 437–446. doi:10.1039/b510841a.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  8. ^ Wang, Zhaomeng; Varma, V. B.; Xia, Huan Ming; Wang, Z. P.; Ramanujan, R. V. (2015-05-01). "Spreading of a ferrofluid core in three-stream micromixer channels". Physics of Fluids (1994-present). 27 (5): 052004. doi:10.1063/1.4919927. ISSN 1070-6631.
  9. ^ Pamme,N. (2006). "Magnetism and microfluidics". Lab Chip. 6: 24–38. doi:10.1039/B513005K.
  10. ^ a b c Varma, V. B. and Ray, A. and Wang, Z. M. and Wang, Z. P. and Wu, R. G. and Jayaneel, P. J. and Sudharsan, N. M. and Ramanujan, R. V. (2016). "Control of Ferrofluid Droplets in Microchannels by Uniform Magnetic Fields". IEEE Magnetics Letters. 7. IEEE: 1–5. doi:10.1109/LMAG.2016.2594165.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  11. ^ a b Ray, A.; Varma, V. B.; Wang, Z.; Wang, Z.; Jayaneel, P. J.; Sudharsan, N. M.; Ramanujan, R. V. (2016-01-01). "Magnetic Droplet Merging by Hybrid Magnetic Fields". IEEE Magnetics Letters. PP (99): 1–1. doi:10.1109/LMAG.2016.2613065. ISSN 1949-307X.
  12. ^ Teh, Shia-Yen; Lin, Robert; Hung, Lung-Hsin; Lee, Abraham P. (2008-01-29). "Droplet microfluidics". Lab on a Chip. 8 (2): 198. doi:10.1039/B715524G. ISSN 1473-0189.
  13. ^ Katsikis, Georgios; Cybulski, James S.; Prakash, Manu (2015-07-01). "Synchronous universal droplet logic and control". Nature Physics. 11 (7): 588–596. doi:10.1038/nphys3341. ISSN 1745-2473.
  14. ^ Joensson, Haakan; Andersson Svahn, Helene (May 2012). "Droplet Microfluidics—A Tool for Single-Cell Analysis". Angewandte Reviews. 51 (1): 12176–12192. doi:10.1002/anie.201200460.
  15. ^ Shia Yen, Teh; Lin, Robert. "droplet microfluidics". Lab on a Chip. 8.
  16. ^ Shemesh, Jonathan; Ben Arye, Tom; Avesar, Jonathan; Kang, Joo; Fine, Amir; Super, Michael; Meller, Amit; Donald, Ingber; Levenberg, Shulamit. "Stationary nanoliter droplet array with a substrate of choice for single adherent nonadherent cell incubation and analysis". Proc Natl Acad Sci U S A. 111 (31): 11293–11298. doi:10.1073/pnas.1404472111. PMC 4128147. PMID 25053808.
  17. ^ Zheng, Bo; Gerdts, Cory J; Ismagilov, Rustem F. "Using nanoliter plugs in microfluidics to facilitate and understand protein crystallization". Current Opinion in Structural Biology. 15 (5): 548–555. doi:10.1016/j.sbi.2005.08.009.
  18. ^ Zheng, B.; Tice, J. D.; Roach, L. S.; Ismagilov, R. F. (2004). "A Droplet-Based, Composite PDMS/Glass Capillary Microfluidic System for Evaluating Protein Crystallization Conditions by Microbatch and Vapor-Diffusion Methods with On-Chip X-Ray Diffraction". Angewandte Chemie International Edition. 43: 2508–2511. doi:10.1002/anie.200453974.
  19. ^ Zheng, Bo; Roach, L. Spencer; Ismagilov, Rustem F. (2003). "Screening of Protein Crystallization Conditions on a Microfluidic Chip Using Nanoliter-Size Droplets". Journal of the American Chemical Society. 125 (37): 11170–11171. doi:10.1021/ja037166v.
  20. ^ a b Cristobal, Galder; Arbouet, Laurence; Sarrazin, Flavie; Talaga, David; Bruneel, Jean-Luc; Joanicot, Mathieu; Servant, Laurent (2006-08-23). "On-line laser Raman spectroscopic probing of droplets engineered in microfluidic devices". Lab on a Chip. 6 (9). doi:10.1039/b602702d. ISSN 1473-0189.
  21. ^ a b Liu, N.; Aymonier, C.; Lecoutre, C.; Garrabos, Y.; Marre, S. (2012-11-01). "Microfluidic approach for studying CO2 solubility in water and brine using confocal Raman spectroscopy". Chemical Physics Letters. 551: 139–143. doi:10.1016/j.cplett.2012.09.007.
  22. ^ Ashok, Praveen C.; Singh, Gajendra P.; Rendall, Helen A.; Krauss, Thomas F.; Dholakia, Kishan (2011-04-07). "Waveguide confined Raman spectroscopy for microfluidic interrogation". Lab on a Chip. 11 (7). doi:10.1039/c0lc00462f. ISSN 1473-0189.
  23. ^ a b c Chrimes, Adam F.; Khoshmanesh, Khashayar; Stoddart, Paul R.; Mitchell, Arnan; Kalantar-zadeh, Kourosh (2013-06-10). "Microfluidics and Raman microscopy: current applications and future challenges". Chemical Society Reviews. 42 (13). doi:10.1039/c3cs35515b. ISSN 1460-4744.
  24. ^ Park, Taehan; Lee, Sangyeop; Seong, Gi Hun; Choo, Jaebum; Lee, Eun Kyu; Kim, Yang S.; Ji, Won Ho; Hwang, Seung Yong; Gweon, Dae-Gab (2005-03-23). "Highly sensitive signal detection of duplex dye-labelled DNA oligonucleotides in a PDMS microfluidic chip: confocal surface-enhanced Raman spectroscopic study". Lab on a Chip. 5 (4). doi:10.1039/b414457k. ISSN 1473-0189.
  25. ^ Cecchini, Michael P.; Hong, Jongin; Lim, Chaesung; Choo, Jaebum; Albrecht, Tim; deMello, Andrew J.; Edel, Joshua B. (2011-04-15). "Ultrafast Surface Enhanced Resonance Raman Scattering Detection in Droplet-Based Microfluidic Systems". Analytical Chemistry. 83 (8): 3076–3081. doi:10.1021/ac103329b. ISSN 0003-2700.
  26. ^ Zhu, Ying; Fang, Qun (2013-07-17). "Analytical detection techniques for droplet microfluidics—A review". Analytica Chimica Acta. 787: 24–35. doi:10.1016/j.aca.2013.04.064.
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