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BITS Embryo Chemical Engineering Lecture Microfluidics – A Primer Ketan “Kittu” Bhatt (97 A1) Post Doc, Material Science & Engineering University of Illinois at Urbana-Champaign Ph. D., Chemical & Biomolecular Engineering North Carolina State University Outline • What are microfluidics & lab-on-a-chip systems? • Why microfluidics? • Some concepts • Applications Wikipedia: (www.wikipedia.org) • Microfluidics deals with the behavior, precise control and manipulation of microliter and nanoliter volumes of fluids • Lab on Chip - Devices that integrate (multiple) laboratory functions on a single chip of only millimeters to a few square centimeters in size that are capable of handling extremely small fluid volumes down to less than picoliters mFluidics & Lab-on-chip systems Advantages: - Low cost - High throughput - Faster analysis - Compact design - Ease-of-use - Reduced sample & reagent consumption - Extensive parallel architectures - Reliability Entirely new techniques might become available opening up possibilities for new experiments and innovations not possible by traditional methods Photolithography: Fabrication of mfluidic channels Photoresist Glass UV Light Mask Glass is coated with a layer of photoresist The channel pattern is transferred via a mask and radiation source eg. UV light The exposed photoresist is removed An appropriate etchant, eg. HF/NH4F, is used to etch the channel pattern After the remaining photoresist surface have been removed, the top plate can be attached eg. by thermal bonding Soft lithography: Stamp Fabrication Schematics of the procedure for fabricating PDMS stamps from a master having relief structures on its surface Press on a surface, connect tubing (Slide courtesy: Orlin Velev) Xia & Whitesides, Annu. Rev. Mater. Sci. 28, 153 (1998) Liquid transport: Pressure driven Laminar flow Re LVavg m L = Length scale, Diameter Vavg = Average fluid velocity = Density m = viscosity Typical values: Channel width, L = 1 mm Average fluid velocity = 1 mm/s Density = 1000 kg/m3 Viscosity = 0.001Ns/m2 Re = 1 (strc.herts.ac.uk/mm/) Liquid transport: Electroosmotic pumping The counterions next to the wall move with the field: plug flow (Slide courtesy: Orlin Velev) mFluidics: What principles are used to make liquids and particles move? Comparison of fluid- and particle-propulsion methods in microfluidics Huang et al., Anal. Bioanal. Chem. 372, 49 (2002) (Slide courtesy: Orlin Velev) Microfluidic chips & devices: examples Uses include: Separations Chemical analysis Chemical sensing Microscale synthesis Combinatorial synthesis Drug screening Genetic fingerprinting Genetic research Cell screening Clinical diagnostics Materials research Catalysis research Microfabrication Photonics Electronics (Slide courtesy: Orlin Velev) DNA Arrays DNA pairing basics (Slide courtesy: Orlin Velev) DNA array chips – Basic principles Human genome contains ~ 30000 genes which encode more than 90000 RNA species and basic proteins. The possible mutations increase this number multiple fold. Many genes work in combination with others, so understanding and using their function requires characterization of multiple genes. Massively parallel detection and analysis is required. The amount of reagents and samples is small and they are very expensive so it all needs to be done on a miniature scale. Fluorophore Immobilized fragments (Slide courtesy: Orlin Velev) Hybridization Match DNA array chips – Basics Basics of what’s on the surface of a DNA chip (Slide courtesy: Orlin Velev) Bioarrays: Future of bioresearch and medicine Thousands of genes checked on chip Clinical diagnostics Genetic fingerprinting Drug screening Genetic research Cell research (Slide courtesy: Orlin Velev) Droplet – Based Microfluidics Dielectrophoretic chips with suspended microdroplets: Principle of operation Liquid – liquid chip system without walls or channels Velev, Prevo and Bhatt, Nature 426, 515 (2003) Droplet equilibrium positions High intensity regions Droplet-chip geometry to scale. Finite element electrostatic calculations using conformal triangles (Femlab) Controlled parallel transport of multiple droplets 300 V, 300 Hz - 500 V DC gold nanoparticles 2% white polystyrene latex 2% pink fluorescent latex 0.2% white latex 0.2% white polystyrene latex 0.2% pink fluorescent latex On-chip microdroplet engineering Mixing Reaction Synthesis of supraparticles Separation at the top Separation at the bottom Microbioassays Mixing of droplets of aqueous suspension and encapsulation inside oil droplet latex in water gold nanoparticles dodecane Foil /Water Dodecane/Water Foil / Dodecane Chemical reactions and precipitations 3 CaCl2 + 2 K2HPO4 Ca3(PO4)2 + 4 KCl + 2 HCl FeSO4 + 2 NaOH Fe(OH)2 + Na2SO4 Simultaneous “eyeballs” syntheses in multiple on-chip droplet microreactors Massive parallelization possible Gold – latex anisotropic assemblies 1 min 7 min 11 min 18 min 50 min Time Acknowledgements Orlin Velev Jennifer Lewis BITS Embryo Team Nitish Korula Velev Group members Lewis Group members Contact information [email protected]