1EE C245Lab-on-a-ChipDr. Thara SrinivasanLecture 20Picture credit: Anderson et al.2U. Srinivasan ©EE C245Lecture Outline• Reading from reader• Auroux, P.-A., Manz, A. et al. , “Micro Total Analysis Systems,” (2002) pp. 2637-52.• Krishnan, M., et al., “Microfabricated Reaction and Separation Systems,” (2001) pp. 92-98.• Quake, S., R, and A. Scherer, “From Micro- to Nanofabrication Using Soft Materials,” (2001) pp. 1552-69.• Today’s Lecture• Lab-on-a-Chip Concept and Examples• Application to Proteomics• Lab-on-a-Chip Subunits• Sample handling• Reactors• Separation Methods• Detection23U. Srinivasan ©EE C245Lab-on-a-Chip• Micro total analysis system (µ-TAS)• Vision proposed by Manz, Widmer and Harrison in early ’90’s• Perform sample addition, pretreatment and transport, chemical reactions, separation, and detection on a microscope slide or credit card size chip • Annual conference, MicroTAS, had 700 attendees in ‘02• Applications• Genomics and proteomics • Environmental assays • Medical diagnostics • Drug discovery• Chemical production• Cellular analysis• Saves reagents and labor • Increases testing throughput• Creates portable systems4U. Srinivasan ©EE C245AffymetrixLab-on-a-Chip• Multiple operations performed• Cell lysis• Sample concentration• Enzymatic reactions such as reverse transcription, PCR, DNAse digestion and terminal transferase labeling• Dilution, hybridization, and washing• Dye stainingAnderson et al.35U. Srinivasan ©EE C245U of M Lab-on-a-Chip• Nanoliter liquid injector• Sample mixing and positioning system• Temperature-controlled PCR reaction chamber• Electrophoretic separation • Fluorescent photodetector• Mastrangelo and Burns groups’ integrated device6U. Srinivasan ©EE C245Microscope-on-a-Chip47U. Srinivasan ©EE C245Proteomics• A “proteome” is the set of proteins encoded by a gene• Proteomics• Identifying all the proteins made by a given cell, tissue or organism• Determining how the proteins network among themselves• Finding out precise 3D structures of the proteins• Proteins more complex than genes• DNA: 4 bases, proteins: 20 amino acids • Even with a protein’s sequence, its function and networks still unknown• 3D shape of folded protein difficult to predict• All human cells have same genome, but differ in which genes are active and which proteins are made• ~40,000 human genes, each gene can encode several proteins (typical cell makes 100,000’s proteins)8U. Srinivasan ©EE C245Scientific American April 200259U. Srinivasan ©EE C245Necessary Subunits for µ-TAS • Sample handling• Extraction• Mixers• Valves• Pumps• Reactors• Separation • Detection10U. Srinivasan ©EE C245Sample Extraction• Means for extracting samples from dilute solutions required• At macroscale, centrifugal force is used• For microfluidics, sample extraction is interface to macroscale• Most of the power consumption is spent at this step• Methods include• Filtration • Chromatography611U. Srinivasan ©EE C245Extraction Using Filters• Microfabricated filters• Mechanically robust to withstand high pressure drops for filtering µm-sized particles• Very uniform pore sizes determined by• Photolithography• Sacrificial layer thicknessC.-M. Ho group, UCLA Keller et al., UCB12U. Srinivasan ©EE C245Solid-Phase Extraction• As in chromatography,• Desired components bind reversibly to a coated porous solid and are later flushed out by a change in solvent• Hydrophobic coatings bind nonpolar compounds in aqueous flow• Bead chambers• Hydrophobic beads trapped in a flow chamberStemme group, SwedenHarrison group, Univ. of Alberta713U. Srinivasan ©EE C245Extraction Using Porous Polymers• Porous polymers increase available surface area for binding interactions • Fill channels with polymerization mixture ~ monomers, initiator, and porogenic solvent• Irradiate chip with UV light through photomask• Surface chemistry may be varied widelyFréchet group, UCB14U. Srinivasan ©EE C245Extraction by Diffusion• Mixing in low Re flows is nearly reversible• Two flows that have been stirred together may be “unstirred”—except for any mixing by diffusion—by reversing the driving force • Can we use irreversibility of diffusive mixing in reversibly stirred flows to separate chemical species based on size?815U. Srinivasan ©EE C245Extraction by Diffusion • As two parallel laminar flows contact, diffusion extracts certain components• Components with higher diffusivity extracted• Micronics H-filterpull elements out of sample into diluent16U. Srinivasan ©EE C245Necessary Subunits for µ-TAS • Sample handling• Preparation• Mixers• Pumps • Valves• Reactors• Separation • Detection917U. Srinivasan ©EE C245Mixing• Mixing of particles, cells and molecules often determines the system efficiency• PCR, DNA hybridization, cell lyses…• Diffusion, the mechanism of mixing at the microscale, still requires relatively long times for thorough mixing.• How to assist mixing?• Repeated lamination of flows increases contact area and decreases diffusion lengthC.-M. Ho Group, UCLA18U. Srinivasan ©EE C245• Chaotic flows can be very efficient mixers• Changing surface topography of microchannelfloor induces chaotic flows Stroock et al., Whitesides Group, Harvard1019U. Srinivasan ©EE C245Necessary Subunits for µ-TAS • Sample handling• Preparation• Mixers• Pumps • Valves• Reactors• Separation • Detection20U. Srinivasan ©EE C245Pumping Mechanisms• Pressure gradients• Electrokinetic forces• Surface tension forces• Electrowetting• Thermocapillary• Surface acoustic waves • Magnetohydrodynamic • DielectrophoresisC. M.Ho1121U. Srinivasan ©EE C245Centrifugal Forces• Gyros, Sweden• When CD spins, centrifugal force causes liquids on their surface to move outwards.• The force can drive liquids through microchannels…• …even breaking through hydrophobic barriers in the channels, releasing different chemicals selectively22U. Srinivasan ©EE C245Electrowetting• Electrical potential can control surface tension on a dielectric solid surface• Asymmetric contact angles generate internal pressure imbalance, leading to movement• Fluidic operations can be done on discrete droplets• Low voltages: 25 V DC for v = 30 mm/s; 100V AC for v = 200 mm/sCJ Kim group,
View Full Document
Unlocking...