An integrated microfluidic device for large-scale in situ click chemistry screening

Biomaterials meet microfluidics: building the next generation of artificial niches

Biomaterials are increasingly being developed as in vitro microenvironments mimicking in vivo stem cell niches. However, current macroscale methodologies to produce these niche models fail to recapitulate the spatial and temporal characteristics of the complex native stem cell regulatory systems. Microfluidic technology offers unprecedented control over the spatial and temporal display of biological signals and therefore promises new avenues for stem cell niche engineering. Here we discuss how the two approaches can be combined to generate more physiological models of stem cell niches that could facilitate the identification of new mechanisms of stem cell regulation, profoundly impacting drug discovery and ultimately therapeutic applications of stem cells.

Molecular Imaging Probe Development using Microfluidics

In this manuscript, we review the latest advancement of microfluidics in molecular imaging probe development. Due to increasing needs for medical imaging, high demand for many types of molecular imaging probes will have to be met by exploiting novel chemistry/radiochemistry and engineering technologies to improve the production and development of suitable probes. The microfluidic-based probe synthesis is currently attracting a great deal of interest because of their potential to deliver many advantages over conventional systems. Numerous chemical reactions have been successfully performed in micro-reactors and the results convincingly demonstrate with great benefits to aid synthetic procedures, such as purer products, higher yields, shorter reaction times compared to the corresponding batch/macroscale reactions, and more benign reaction conditions. Several 'proof-of-principle' examples of molecular imaging probe syntheses using microfluidics, along with basics of device architecture and operation, and their potential limitations are discussed here.

Screening of protein-protein interaction modulators via sulfo-click kinetic target-guided synthesis

Kinetic target-guided synthesis (TGS) and in situ click chemistry are among unconventional discovery strategies having the potential to streamline the development of protein-protein interaction modulators (PPIMs). In kinetic TGS and in situ click chemistry, the target is directly involved in the assembly of its own potent, bidentate ligand from a pool of reactive fragments. Herein, we report the use and validation of kinetic TGS based on the sulfo-click reaction between thio acids and sulfonyl azides as a screening and synthesis platform for the identification of high-quality PPIMs. Starting from a randomly designed library consisting of 9 thio acids and 9 sulfonyl azides leading to 81 potential acylsulfonamides, the target protein, Bcl-X(L), selectively assembled four PPIMs, acylsulfonamides SZ4TA2, SZ7TA2, SZ9TA1, and SZ9TA5, which have been shown to modulate Bcl-X(L)/BH3 interactions. To further investigate the Bcl-X(L) templation effect, control experiments were carried out using two mutants of Bcl-X(L). In one mutant, phenylalanine Phe131 and aspartic acid Asp133, which are critical for the BH3 domain binding, were substituted by alanines, while arginine Arg139, a residue identified to play a crucial role in the binding of ABT-737, a BH3 mimetic, was replaced by an alanine in the other mutant. Incubation of these mutants with the reactive fragments and subsequent LC/MS-SIM analysis confirmed that these building block combinations yield the corresponding acylsulfonamides at the BH3 binding site, the actual "hot spot" of Bcl-X(L). These results validate kinetic TGS using the sulfo-click reaction as a valuable tool for the straightforward identification of high-quality PPIMs.

Three-dimensional large-scale microfluidic integration by laser ablation of interlayer connections

Multilayer Soft Lithography (MSL) is a robust and mature fabrication technique for the rapid prototyping of microfluidic circuits having thousands of integrated valves. Despite the success and wide application of this method, it is fundamentally a planar fabrication technique which imposes serious design constraints on channel routing, feature density, and fluid handling complexity. We present here methods and related instrumentation to remove these limitations by combining the advantages of MSL processing with laser micromachining using a CO(2) laser ablation system. This system is applied to both the dense integration of layer-layer interconnects and the direct writing of microchannels. Real-time image recognition and computer control allow for robust wafer-scale registration of laser ablation features with moulded channel structures. Ablation rates of up to 8 Hz are achieved with positional accuracy of approximately 20 microm independent of mechanical distortions in the elastomer substrate. We demonstrate these capabilities in the design and fabrication of a production scale multi-laminate micromixer that achieves sub-millisecond mixing of two streams at flow rates up to 1 mL min(-1). The marriage of laser micromachining with MSL-based valve integration allows for high-yield fabrication of topologically complex microfluidic circuits having thousands of layer-layer interconnects and integrated valves.

Integrated microfluidic and imaging platform for a kinase activity radioassay to analyze minute patient cancer samples

Oncogenic kinase activity and the resulting aberrant growth and survival signaling are a common driving force of cancer. Accordingly, many successful molecularly targeted anticancer therapeutics are directed at inhibiting kinase activity. To assess kinase activity in minute patient samples, we have developed an immunocapture-based in vitro kinase assay on an integrated polydimethylsiloxane microfluidics platform that can reproducibly measure kinase activity from as few as 3,000 cells. For this platform, we adopted the standard radiometric (32)P-ATP-labeled phosphate transfer assay. Implementation on a microfluidic device required us to develop methods for repeated trapping and mixing of solid-phase affinity microbeads. We also developed a solid-state beta-particle camera imbedded directly below the microfluidic device for real-time quantitative detection of the signal from this and other microfluidic radiobioassays. We show that the resulting integrated device can measure ABL kinase activity from BCR-ABL-positive leukemia patient samples. The low sample input requirement of the device creates new potential for direct kinase activity experimentation and diagnostics on patient blood, bone marrow, and needle biopsy samples.

Microfluidics for positron emission tomography probe development

Owing to increased needs for positron emission tomography (PET), high demands for a wide variety of radiolabeled compounds will have to be met by exploiting novel radiochemistry and engineering technologies to improve the production and development of PET probes. The application of microfluidic reactors to perform radiosyntheses is currently attracting a great deal of interest because of their potential to deliver many advantages over conventional labeling systems. Microfluidics-based radiochemistry can lead to the use of smaller quantities of precursors, accelerated reaction rates, and easier purification processes with greater yield and higher specific activity of desired probes. Several proof-of-principle examples along with the basics of device architecture and operation and the potential limitations of each design are discussed. Along with the concept of radioisotope distribution from centralized cyclotron facilities to individual imaging centers and laboratories ("decentralized model"), an easy-to-use, stand-alone, flexible, fully automated, radiochemical microfluidic platform can provide simpler and more cost-effective procedures for molecular imaging using PET.

Multi-channel microfluidic devices combined with electrospray ionization quadrupole time-of-flight mass spectrometry applied to the monitoring of glutamate release from neuronal cells

This paper describes an integrated system combining microfluidic devices with electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-Q-TOF-MS) for monitoring cellular chemical release. To demonstrate the feasibility of this new system, the reported carnosine-protection process against Abeta42-induced glutamate released from PC12 cells, was monitored. Poly-L-lysine coated microchannels were used to culture cells. A multi-channel miniature extraction chip (MEC) was integrated into the design to remove salts and protein interference effects. ESI-Q-TOF-MS was employed to realize semi-quantitative and highly sensitive qualitative analysis. The protective effect of carnosine against Abeta42-induced neurotoxicity was evaluated under different conditions in microchannels in parallel. The secretion product analysis, carried out by ESI-Q-TOF-MS, was accomplished in 5 min using only 2.5 microL of solvent. Furthermore, we show that integrated microfluidic devices have significant potential for the analysis of cellular secretions, as well as for medical screening tests and for the diagnosis of specific diseases.

In situ click chemistry: probing the binding landscapes of biological molecules

Combinatorial approaches to the discovery of new functional molecules are well established among chemists and biologists, inspired in large measure by the modular composition of many systems and molecules in Nature. Many approaches rely on the synthesis and testing of individual members of a candidate combinatorial library, but attention has also been paid to techniques that allow the target to self-assemble its own binding agents. These fragment-based methods, grouped under the general heading of target-guided synthesis (TGS), show great promise in lead discovery applications. In this tutorial review, we review the use of the 1,3-dipolar cycloaddition reaction of organic azides and alkynes in a kinetically-controlled TGS approach, termed in situ click chemistry. The azide-alkyne reaction has several distinct advantages, most notably high chemoselectivity, very low background ligation rates, facile synthetic accessibility, and the stability and properties of the 1,2,3-triazole products. Examples of the discovery of potent inhibitors of acetylcholinesterases, carbonic anhydrase, HIV-protease, and chitinase are described, as are methods for the templated assembly of agents that bind DNA and proteins.

A small library of DNA-encapsulated supramolecular nanoparticles for targeted gene delivery

We demonstrated a convenient, flexible and modular synthetic approach for preparation of a small library of DNA-encapsulated supramolecular nanoparticles SNPs superset DNA and RGD-SNPs superset DNA with different sizes and RGD target ligand coverage for targeted gene delivery.

Integrated microreactors for reaction automation: new approaches to reaction development

Applications of microsystems (microreactors) in continuous-flow chemistry have expanded rapidly over the past two decades, with numerous reports of higher conversions and yields compared to conventional batch benchtop equipment. Synthesis applications are enhanced by chemical information gained from integrating microreactor components with sensors, actuators, and automated fluid handling. Moreover, miniaturized systems allow experiments on well-defined samples at conditions not easily accessed by conventional means, such as reactions at high pressure and temperatures. The wealth of synthesis information that could potentially be acquired through use of microreactors integrated with physical sensors and analytical chemistry techniques for online reaction monitoring has not yet been well explored. The increased efficiency resulting from use of continuous-flow microreactor platforms to automate reaction screening and optimization encourages a shift from current batchwise chemical reaction development to this new approach. We review advances in this new area and provide application examples of online monitoring and automation.

Integrated Microfluidic Reactors

Microfluidic reactors exhibit intrinsic advantages of reduced chemical consumption, safety, high surface-area-to-volume ratios, and improved control over mass and heat transfer superior to the macroscopic reaction setting. In contract to a continuous-flow microfluidic system composed of only a microchannel network, an integrated microfluidic system represents a scalable integration of a microchannel network with functional microfluidic modules, thus enabling the execution and automation of complicated chemical reactions in a single device. In this review, we summarize recent progresses on the development of integrated microfluidics-based chemical reactors for (i) parallel screening of in situ click chemistry libraries, (ii) multistep synthesis of radiolabeled imaging probes for positron emission tomography (PET), (iii) sequential preparation of individually addressable conducting polymer nanowire (CPNW), and (iv) solid-phase synthesis of DNA oligonucleotides. These proof-of-principle demonstrations validate the feasibility and set a solid foundation for exploring a broad application of the integrated microfluidic system.