Poly(N,N-dimethylacrylamide)-grafted polyacrylamide: a self-coating copolymer for sieving separation of native proteins by CE

The potential of a series of newly synthesized poly(N,N-dimethylacrylamide) (PDMA) grafted polyacrylamide (PAM) copolymers (P(AM-PDMA)) as a replaceable separation medium for protein analysis was studied. A comparative study with and without copolymers was performed; the separation efficiency, analysis reproducibility and protein recovery proved that the P(AM-PDMA) copolymers were efficient in suppressing the adsorption of basic proteins onto the silica capillary wall. Furthermore, the size-dependent retardation of native proteins in a representative P(AM-PDMA) copolymer was demonstrated by Ferguson analysis. The results showed that the P(AM-PDMA) copolymers combine the good coating property of PDMA and the sieving property of PAM and could be applied as a sieving matrix for the analysis of native proteins.     

Fabrication of thermoplastics chips through lamination based techniques

In this work, we propose a novel strategy for the fabrication of flexible thermoplastic microdevices entirely based on lamination processes. The same low-cost laminator apparatus can be used from master fabrication to microchannel sealing. This process is appropriate for rapid prototyping at laboratory scale, but it can also be easily upscaled to industrial manufacturing. For demonstration, we used here Cycloolefin Copolymer (COC), a thermoplastic polymer that is extensively used for microfluidic applications. COC is a thermoplastic polymer with good chemical resistance to common chemicals used in microfluidics such as acids, bases and most polar solvents. Its optical quality and mechanical resistance make this material suitable for a large range of applications in chemistry or biology. As an example, the electrokinetic separation of pollutants is proposed in the present study.     

Tube relaxation: A quantitative molecular model for the viscoelastic plateau of entangled polymeric media

The relaxation of an entangled polymeric medium in the viscoelastic plateau is investigated theoretically by using the slip-link representation of topological constraints. In addition to the chain retraction process introduced by Daoudi and investigated theoretically by Doi, we show that two processes contribute significantly to the relaxation: The first, “equilibration across slip-links,” is a longitudinal reequilibration between parts of the chain which have been differently extended or compressed, depending on their initial orientation relatively to the strain tensor. The second, “tube relaxation,” is a mean-field representation of the loss of topological constraints on one chain due to the retraction of the others. Closed analytical expressions for the stress accounting for these three processes are derived and compared with previous theories: the relaxation should be much more progressive than previously predicted, and the terminal time for retraction is reduced significantly by tube relaxation.     

Injection and flow control system for microchannels

In spite of considerable efforts, flow control in micro-channels remains a challenge owing to the very small ratio of channel/supply-system volumes, as well as the induction of spurious flows by extremely small pressure or geometry changes. We present here an inexpensive and robust system for flow control in a microchannel system, based on a dynamic control of reservoir pressures at the end of each channel. This system allows flow equilibration with a time constant smaller than one second, and is also able to maintain stable flux from stopped flow to many microl min(-1) range over several hours. It is robust to changes in ambient pressure and temperature. This system further includes a feature for sub-microliter sample injection during the experiment. We quantify flow control in elastomer and thermoplastic channels, and demonstrate the impact on one application of the system, namely the reproducible, automated separation of large DNA by electrophoresis in a self-organized magnetic bead matrix in a microchannel.     

Instability of a Nematic Lyophase

We have observed that a ternary nematic solution from sodium decyl sulphate, decanol and heavy water separated into layers of different phases during storage. The separation was favoured when the sample had been previously heated above room temperature up to 50°C. The time needed for the demixing to occur varied from several hours to weeks. The solution ended up as a three-phase system: lamellar at the top, nematic in the middle, and isotropic at the bottom. The initial homogeneous nematic solution was restored when the layers were stirred. The nematic solution prepared with ordinary water was far more resistant to demixing. The similarity to emulsions is discussed.     

Improving sensitivity of electrophoretic heteroduplex analysis using nucleosides as additives: Application to the breast cancer predisposition gene BRCA2

A new method for the detection of unknown mutations, enhanced mismatch mutation analysis (EMMA), is proposed. It is based on electrophoretic heteroduplex analysis (HDA). The resolution is considerably improved, thanks to the combination of high-resolution block-copolymer sieving matrix, and nucleosides as additives in the electrophoretic medium. The EMMA method is compared to denaturing HPLC (DHPLC) in a large-scale study of mutations in the breast cancer-associated gene BRCA2, involving 4655 DNA amplicons from 94 patients. The rate of false positives was 0.09%. The raw success rate, without optimization of the amplicons tiling, was 94%, a value much higher than that achieved earlier with HDA, and comparable with that obtained with DHPLC. An analysis of the missed mutations suggest that the success rate could be improved up to about 97%, simply by redesigning the amplicons, while retaining the speed, cost effectiveness, and simplicity of the method.     

Systematic study of field and concentration effects in capillary electrophoresis of DNA in polymer solutions

A systematic study of the separation of double-stranded DNA in hydroxypropylcellulose (HPC) with a molecular mass of 10⁶ was undertaken, using a variety of concentrations (from 0.1 to 1%) and different electric fields (from 6 to 540 V/cm). The data show that a high polymer concentrations (0.4%) and low fields, the separation mechanism is similar to that occurring in gels. The results are in good agreement with theoretical models, and in particular with a recently proposed theory for gels with a pore size smaller than the persistence length of DNA. For more dilute solutions and high fields, however, the separation pattern cannot be explained by existing theories. The existence of an original mechanism was confirmed by the direct observation of the conformation of double-stranded DNA molecules in the polymer solution by fluorescence videomicroscopy. Practical conclusions for the capillary electrophoretic separation of duplex DNA are drawn.     

Synthesis and Diels-Alder Reactions of a New Kind of Chiral Dienophiles: Cyclic Vinyl-p-tolylsulfilimines

A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group.