A polymer-based microfluidic device for immunosensing biochips

This paper describes the design, fabrication, and test of a PDMS/PMMA-laminated microfluidic device for an immunosensing biochip. A poly(dimethyl siloxane)(PDMS) top substrate molded by polymer casting and a poly(methyl methacrylate)(PMMA) bottom substrate fabricated by hot embossing are bonded with pressure and hermetically sealed. Two inlet ports and an air vent are opened through the PDMS top substrate, while gold electrodes for electrochemical biosensing are patterned onto the PMMA bottom substrate. The analyte sample is loaded from the sample inlet port to the detection chamber by capillary force, without any external intervening forces. For this and to control the time duration of sample fluid in each compartment of the device, including the inlet port, diffusion barrier, reaction chamber, flow-delay neck, and detection chamber, the fluid conduit has been designed with various geometries of channel width, depth, and shape. Especially, the fluid path has been designed so that the sample flow naturally stops after filling the detection chamber to allow sufficient time for biochemical reaction and subsequent washing steps. As model immunosensing tests for the microfluidic device, functionalizations of ferritin and biotin to the sensing surfaces on gold electrodes and their biospecific interactions with antiferritin antiserum and streptavidin have been investigated. An electrochemical detection method for immunosensing by biocatalyzed precipitation has been developed and applied for signal registration. With the biochip, the whole immunosensing processes could be completed within 30 min.     

Strength of fibers from wholly aromatic polyesters

A theory of the strength (or the tenacity) of highly oriented Liquid Crystal Polymer (LCP) fibers was developed, and its results were compared with existing tensile strength data of fibers of a copolymer of 1,4-oxybenzoate and 6,2-oxynaphthoate. A basic premise of the theory is that the mechanical load transfer between polymer chains is through intermolecular interaction which acts in a manner similar to that of shear stress, and that the fiber strength is primarily governed by the intermolecular adhesion strength. The theory also incorporates the effects of MW, MW distribution, and the chain orientation distribution. Analysis of the experimental tenacity data demonstrates that the present theory can quantitatively describe the variation of the tenacity of LCP fibers with MW both in the as-spun and in the heat-treated states. The theory further predicts that the predominant factor governing the tenacity of LCP fibers is primarily due to MW increase due to solid-state polymerization. It is also demonstrated that the intermolecular adhesion between LCP chains is relatively weak and does not improve with heat treatment. The absence of factors that limit the MW increase (i.e, imbalanced end-groups and side reactions of end groups) is a prerequisite for fast heat treatment of a LCP fiber to a high tenacity.Symbols A _f the cross-sectional area of a single polymer chain - E _f the theoretical modulus of a polymer chain - G _m the shear modulus of fiber - h(l) the chain length distribution function - l the chain length - l the number average chain length - l _c the length of chain units that are bonded to adjacent polymer chains - n ² 4G _m/CE_f - N _c the number of polymer chains per unit area perpendicular to the fiber axis - P _b the probability that a chain does not have a chain end in the fracture zone - P _e the probability that a chain has, at least, a chain end in the fracture zone - q _e,q _b the probability of finding an ending and a bridging polymer chain, respectively, in the fracture zone - l the length of fracture zone - the elongation of a polymer chain - the chain orientation angle - _f the normal stress that acts on a polymer chain - _fu the fiber tenacity - _e the shear stress that acts on a polymer chain surface Dedicated to Prof. Dr. rer. nat. Wolfgang Hilger, Chairman of Hoechst A.G. in honor of his 60th birthday     

Excitation-energy migration in self-assembled cyclic zinc(II)-porphyrin arrays: a close mimicry of a natural light-harvesting system

The excitation-energy-hopping (EEH) times within two-dimensional cyclic zinc(II)-porphyrin arrays 5 and 6, which were prepared by intermolecular coordination and ring-closing metathesis reaction of olefins, were deduced by modeling the EEH process based on the anisotropy depolarization as well as the exciton-exciton annihilation dynamics. Assuming the number of energy-hopping sites N = 5 and 6, the two different experimental observables, that is, anisotropy depolarization and exciton-excition annihilation times, consistently give the EEH times of 8.0 +/- 0.5 and 5.3 +/- 0.6 ps through the 1,3-phenylene linkages of 5 and 6, respectively. Accordingly, the self-assembled cyclic porphyrin arrays have proven to be well-defined two-dimensional models for natural light-harvesting complexes.     

Pressure-driven sample injection with quantitative liquid dispensing for on-chip electrophoresis.

A novel pressure-driven sample injection method was developed as an alternative to electrokinetic injection, and electrophoretic separation was carried out on a microfabricated device employing this method. This method enables a defined volume of liquid dispensing, followed by instantaneous injection driven by pneumatic pressure, greatly simplifying the injection procedure. A particular microstructure, called a "metering chamber", has been designed for the quantitative dispensing of an ultra-low volume of sample liquid; a "hydrophobic passive valve" equipped with an air vent channel is employed for injecting a dispensed sample into the separation channel. The reproducibility of dispensing was 3.3% (n = 15), expressed by the variation of dispensed volumes. The electrophoretic separation of DNA fragments was performed using this injection method, varying the injection volumes from 0.45 to 4.0 nL, and the separation efficiencies were compared. This precise injection method, easily variable in injection volumes, is highly suitable for quantitative as well as qualitative electrophoretic analyses.     

Native agarose gel electrophoresis and electroelution: A fast and cost‐effective method to separate the small and large hepatitis B capsids

Hepatitis B core antigen (HBcAg) expressed in Escherichia coli is able to self‐assemble into large and small capsids comprising 240 (triangulation number T = 4) and 180 (triangulation number T = 3) subunits, respectively. Conventionally, sucrose density gradient ultracentrifugation and SEC have been used to separate these capsids. However, good separation of the large and small particles with these methods is never achieved. In the present study, we employed a simple, fast, and cost‐effective method to separate the T = 3 and T = 4 HBcAg capsids by using native agarose gel electrophoresis followed by an electroelution method (NAGE‐EE). This is a direct, fast, and economic method for isolating the large and small HBcAg particles homogenously based on the hydrodynamic radius of the spherical particles. Dynamic light scattering analysis demonstrated that the T = 3 and T = 4 HBcAg capsids prepared using the NAGE‐EE method are monodisperse with polydispersity values of ～15% and ～13%, respectively. ELISA proved that the antigenicity of the capsids was not affected in the purification process. Overall, NAGE‐EE produced T = 3 and T = 4 capsids with a purity above 90%, and the recovery was 34% and 50%, respectively (total recovery of HBcAg is ～84%), and the operation time is 15 and 4 times lesser than that of the sucrose density gradient ultracentrifugation and SEC, respectively.