Low-cost and straight forward rapid prototyping of flexible microfluidic devices using a desktop digital craft cutter is presented. This rapid prototyping method can consistently achieve microchannels as thin as 200 microm in width and can be used to fabricate three-dimensional (3D) microfluidic devices using only double-sided pressure sensitive adhesive (PSA) tape and laser printer transparency film. Various functional microfluidic devices are demonstrated with this rapid prototyping method. The complete fabrication process from device design concept to working device can be completed in minutes without the need of expensive equipment.

We describe a perfusion-based microfluidic device for three-dimensional (3D) dynamic primary human hepatocyte cell culture. The microfluidic device was used to promote and maintain 3D tissue-like cellular morphology and cell-specific functionality of primary human hepatocytes by restoring membrane polarity and hepatocyte transport function in vitro without the addition of biological or synthetic matrices or coagulants. A unique feature of our dynamic cell culture device is the creation of a microenvironment, without the addition of biological or synthetic matrices or coagulants, that promotes the 3D organization of hepatocytes into cord-like structures that exhibit functional membrane polarity as evidenced by the expression of gap junctions and the formation of an extended, functionally active, bile canalicular network.

The development of a microfluidic biosensor module with fluorescence detection for the identification of pathogenic organisms and viruses is presented in this article. The microfluidic biosensor consists of a network of microchannels fabricated in polydimethylsiloxane (PDMS) substrate. The microchannels are sealed with a glass substrate and packed in a Plexiglas housing to provide connection to the macro-world and ensure leakage-free flow operation. Reversible sealing permits easy disassembly for cleaning and replacing the microfluidic channels. The fluidic flow is generated by an applied positive pressure gradient, and the module can be operated under continuous solution flow of up to 80 microL min(-1). The biosensor recognition principle is based on DNA/RNA hybridization and liposome signal amplification. Superparamagnetic beads are incorporated into the system as a mobile solid support and are an essential part of the analysis scheme. In this study, the design, fabrication and the optimization of concentrations and amounts of the different biosensor components are carried out. The total time required for an assay is only 15 min including sample incubation time. The biosensor module is designed so that it can be easily integrated with a micro total analysis system, which will combine sample preparation and detection steps onto a single chip.

A microfluidic biosensor with electrochemical detection for the quantification of nucleic acid sequences was developed. In contrast to most microbiosensors that are based on fluorescence for signal generation, it takes advantage of the simplicity and high sensitivity provided by an amperometric and coulorimetric detection system. An interdigitated ultramicroelectrode array (IDUA) was fabricated in a glass chip and integrated directly with microchannels made of poly(dimethylsiloxane) (PDMS). The assembly was packaged into a Plexiglas housing providing fluid and electrical connections. IDUAs were characterized amperometrically and using cyclic voltammetry with respect to static and dynamic responses for the presence of a reversible redox couple-potassium hexacyanoferrate (ii)/hexacyanoferrate (iii) (ferri/ferrocyanide). A combined concentration of 0.5 microM of ferro/ferricyanide was determined as lower limit of detection with a dynamic range of 5 orders of magnitude. Background signals were negligible and the IDUA responded in a highly reversible manner to the injection of various volumes and various concentrations of the electrochemical marker. For the detection of nucleic acid sequences, liposomes entrapping the electrochemical marker were tagged with a DNA probe, and superparamagnetic beads were coated with a second DNA probe. A single stranded DNA target sequence hybridized with both probes. The sandwich was captured in the microfluidic channel just upstream of the IDUA via a magnet located in the outside housing. Liposomes were lysed using a detergent and the amount of released ferro/ferricyanide was quantified while passing by the IDUA. Optimal location of the magnet with respect to the IDUA was investigated, the effect of dextran sulfate on the hybridization reaction was studied and the amount of magnetic beads used in the assay was optimized. A dose response curve using varying concentrations of target DNA molecules was carried out demonstrating a limit of detection at 1 fmol assay(-1) and a dynamic range between 1 and 50 fmol. The overall assay took 6 min to complete, plus 15-20 min of pre-incubation and required only a simple potentiostat for signal recording and interpretation.

Dynamic combinatorial libraries are mixtures of compounds that exist in a dynamic equilibrium and can be driven to compositional self adaptation via selective binding of a specific assembly of certain components to a molecular target. We present here an extension of this initial concept to dynamic libraries that consists of two levels, the first formed by the coordination of terpyridine-based ligands to the transition metal template, and the second, by the imine formation with the aldehyde substituents on the terpyridine moieties. Dialdehyde 7 has been synthesized, converted into a variety of ligands, oxime ethers L 11-L33 and acyl hydrazones L44-L77, and subsequently into corresponding cobalt complexes. A typical complex, Co(L 22)2 2؉ is shown to engage in rapid exchange with a competing ligand L11 and with another complex, Co(L22) 2 2؉ in 30% acetonitrile͞water at pH 7.0 and 25°C. The exchange in the corresponding Co(III) complexes is shown to be much slower. Imine exchange in the acyl hydrazone complexes (L 44-L77) is strongly controlled by pH and temperature. The two types of exchange, ligand and imine, can thus be used as independent equilibrium processes controlled by different types of external intervention, i.e., via oxidation͞reduction of the metal template and͞or change in the pH͞temperature of the medium. The resulting double-level dynamic libraries are therefore named orthogonal, in similarity with the orthogonal protecting groups in organic synthesis. Sample libraries of this type have been synthesized and showed the complete expected set of components in electrospray ionization MS. R apid development of combinatorial chemistry and highthroughput experimentation in basic and applied research (1-4) generates increasing demand in new approaches that simplify and expedite synthesis and screening of diverse arrays of compounds and materials. Dynamic combinatorial chemistry (5-11) has attracted increasing interest over recent years as a new approach that combines in one system the library generation and screening processes. The dynamic libraries are designed as mixtures of components that can reversibly interconvert in a dynamic equilibrium that is driven by molecular recognition of a specific molecular target toward that assembly or a subset of components that form the library constituent best bound to the target.One of the key issues in designing dynamic libraries is the choice of the reversible chemical reaction that can interconvert the library components. A number of such reactions have been tested, which include transacylation (12-15), imine exchange (16-20), isomerization (21-23), thiol-disulfide exchange (24, 25), and ligand exchange in coordination complexes (17,18,26).A logical development of dynamic combinatorial chemistry would aim toward the combination of two or more reversible processes within one library. To extend the comparison with ''static'' chemical libraries, such multilevel organization in the dynamic library would be similar to advancing from a static library of components having ...