Micro Total Analysis Systems. Recent Developments Torsten Vilkner, † Dirk Janasek, ‡ and Andreas Manz* ,‡ Department of Chemistry, Imperial College London, Exhibition Road, SW7 2AZ London, U.K. and ISAS-Institute for Analytical Sciences, Bunsen-Kirchhoff-Strasse 11, D-44139 Dortmund, Germany Review Contents Technologies 3373 Microfabrication 3373 Bonding Techniques 3374 Surface Modification 3374 Design 3374 Interfaces and Interconnections 3375 Microvalves and Flow Control 3375 Micropumps 3375 Analytical Standard Operations 3376 Sample Preparation 3376 Injection 3376 Fluid and Particle Handling 3376 Reactors and Mixers 3377 Separation 3377 Detection 3378 Applications 3379 Cell Culture and Cell Handling 3379 Clinical Diagnostics 3380 Environmental Concerns 3380 Immunoassays 3380 Proteins 3380 DNA Separation and Analysis 3381 Polymerase Chain Reaction 3381 Sequencing 3381 Literature Cited 3382 The area of micro total analysis systems ( µTAS), also called “lab on a chip” or miniaturized analysis systems, is growing rapidly. This paper represents an update of the earlier reviews ( 1, 2) and covers the period from March 2002 to February 2004. The intention of this review paper is to provide help for a novice in the field to find the original papers. Publications in the area of µTAS are scattered over a larger number of journals, but most frequently articles can be found in Lab on a Chip, Analytical Chemistry, Electrophoresis, Sensors & Actuators , and others. Excel- lent sources of information are also conference proceedings from regular international meetings such as µTAS, Transducers, and HPCE. However, not all active groups participate in these conferences regularly. An on-line keyword search resulted in more than 3000 hits for the years 2002 and 2003. For this survey, we focused on about 1000 of these articles. Many publications about sensors, arrays (so-called “biochips”), chemical synthesis on-chip, and the more technical (engineering) papers have been omitted, as it is the scope of this paper to review microfluidic systems for analytical chemistry. We did not intend to cover 100%of the papers but rather tried to choose relevant examples for every distinct method or device. Interested readers may refer to citations in the original papers for additional references. In contrast to the earlier two reviews, we now focused on papers presented in peer-reviewed journals and dramatically reduced those presented at conferences as they have generally been published elsewhere or will be soon. We also recommend the text books by Madou ( 3) and Geschke et al. ( 4) for an extensive coverage of technological aspects in microengineering and the book by Oosterbroek and van den Berg ( 5) as well as Nguyen and Wereley ( 289) for further information about methods and applications in microfluidics. TECHNOLOGIES Microfabrication. Wolfe et al. described the use of a Ti: sapphire laser to create topographical structures in the flat surface of PDMS ( 6). Lee and co-workers investigated solvent compat- ibility of PDMS microfluidic devices ( 7). Camou et al. fabricated a two-dimensional lens of PDMS by SU-8 molding a channel with an arcuated end for the optical fiber ( 8). Different methods to remove highly cross-linked SU-8 photoresist from high aspect ratio structures after the development process were discussed by Dentinger et al. ( 9). Wu and co-workers reported on a technique called microlens array lithography where the design of a single photomask was projected via an array of microlenses onto a layer of photoresist ( 10). The same technique could also generate three- dimensional structures utilizing gray scale masks ( 11). Chen et al. proposed the use of microfluidic photomasks for certain applications in gray scale photolithography, where the transpar- ency level was determined by different concentrations of dye solutions that filled the channels in the photomask ( 12). Pan et al. reported the fabrication of calcium fluoride microfluidic devices that demonstrated the application of FT-IR spectroscopy for real- time observation of analytes in microchannels ( 13). Gray scale masks were also implemented in an excimer laser micromachining system to produce structures with a continuous profile, for example, in PET ( 14). A process described by Elsner and co- workers, that combines replica molding with UV-curing, can be used to form acrylate-based 3D microstructures ( 15). McDonald et al. presented the use of solid-object printing to manufacture 3D microfluidic devices larger than 250 µm( 16). Instead of using a spin-coater, a constant-volume injection was used by Lin and co-workers to create a planar SU-8 film of up to 1.5-mm thickness ( 17). A new technique, in which laser printer toner selectively deposited between two laminated polyester films formed channel walls, can be used to produce simple and low-cost microfluidic chips as shown by do Lago et al. ( 18). Hulme et al. fabricated a † Imperial College London. ‡ ISAS-Institute for Analytical Sciences. Anal. Chem. 2004, 76, 3373-3386 10.1021/ac040063q CCC: $27.50 © 2004 American Chemical Society Analytical Chemistry, Vol. 76, No. 12, June 15, 2004 3373 Published on Web 04/24/2004