Fabrication of enclosed SU-8 tips for electrospray ionization-mass spectrometry

We describe a novel electrospray tip design for MS which is fabricated completely out of SU-8 photoepoxy. A three-layer SU-8 fabrication process provides fully enclosed channels and tips. The tip shape and alignment of all SU-8 layers is done lithographically and is therefore very accurate. Fabrication process enables easy integration of additional fluidic functions on the same chip. Separation channels can be made with exactly the same process. Fluidic inlets are made in SU-8 during the fabrication process and no drilling or other postprocessing is needed. Channels have been fabricated and tested in the size range of 10 microm x 10 microm-50 microm x 200 microm. Mass spectrometric performance of the tips has been demonstrated with both pressure-driven flow and EOF. SU-8 microtips have been shown to produce stable electrospray with EOF in a timescale of tens of minutes. With pressure driven flow stable spray is maintained for hours. Taylor cone was shown to be small in volume and well defined even with the largest channel cross section. The spray was also shown to be well directed with our tip design.     

Electrospray interfacing of polymer microfluidics to MALDI-MS

The off-line coupling of polymer microfluidics to MALDI-MS is presented using electrospray deposition. Using polycarbonate microfluidic chips with integrated hydrophobic membrane electrospray tips, peptides and proteins are deposited onto a stainless steel target followed by MALDI-MS analysis. Microchip electrospray deposition is found to yield excellent spatial control and homogeneity of deposited peptide spots, and significantly improved MALDI-MS spectral reproducibility compared to traditional target preparation methods. A detection limit of 3.5 fmol is demonstrated for angiotensin. Furthermore, multiple electrospray tips on a single chip provide the ability to simultaneously elute parallel sample streams onto a MALDI target for high-throughput multiplexed analysis. Using a three-element electrospray tip array with 150 microm spacing, the simultaneous deposition of bradykinin, fibrinopeptide, and angiotensin is achieved with no cross talk between deposited samples. In addition, in-line proteolytic digestion of intact proteins is successfully achieved during the electrospray process by binding trypsin within the electrospray membrane, eliminating the need for on-probe digestion prior to MALDI-MS. The technology offers promise for a range of microfluidic platforms designed for high-throughput multiplexed proteomic analyses in which simultaneous on-chip separations require an effective interface to MS.     

Deformation,Stretching, and Relaxation of Single‐Polymer Chains: Fundamentals and Examples#

Abstract

We review the basic theory for the static and dynamic properties of ideal and real chains. We describe the stretching of single ideal chains in both the strain and the stress ensembles, give scaling arguments for the deformation of real chains, and also consider the impact of chain rigidity by discussing the stretching of worm-like chains. We complement this theoretical outlook with specific examples that highlight the relevance of the single-molecule deformation in a practical perspective: the translocation of a macromolecule over a potential barrier, the collision of a single chain with fixed obstacles or other chains, the dynamics of a thethered chain in a strong shear flow, and some remarkable predictions concerning the deformation of composite chain molecules during free-solution electrophoresis.     

Utility of lab-on-a-chip technology for high-throughput nucleic acid and protein analysis

On-chip electrophoresis can provide size separations of nucleic acids and proteins similar to more traditional slab gel electrophoresis. Lab-on-a-chip (LoaC) systems utilize on-chip electrophoresis in conjunction with sizing calibration, sensitive detection schemes, and sophisticated data analysis to achieve rapid analysis times (<120 s). This work describes the utility of LoaC systems to enable and augment systems biology investigations. RNA quality, as assessed by an RNA integrity number score, is compared to existing quality control (QC) measurements. High-throughput DNA analysis of multiplex PCR samples is used to stratify gene sets for disease discovery. Finally, the applicability of a high-throughput LoaC system for assessing protein purification is demonstrated. The improvements in workflow processes, speed of analysis, data accuracy and reproducibility, and automated data analysis are illustrated.     

Comparison of a pump-around, a diffusion-driven, and a shear-driven system for the hybridization of mouse lung and testis total RNA on microarrays

In the present study, we demonstrate the benefits of a shear-driven rotating microchamber system for the enhancement of microarray hybridizations, by comparing the system with two commonly used hybridization techniques: purely diffusion-driven hybridization under coverslip and hybridization using a fully automated hybridization station, in which the sample is pumped in an oscillating manner. Starting from the same amount of DNA for the three different methods, a series of hybridization experiments using mouse lung and testis DNA is presented to demonstrate these benefits. The gain observed using the rotating microchamber is large: both in terms of analysis speed (up to tenfold increase) and in final spot intensity (up to sixfold increase). The gain is due to the combined effect of the hybridization chamber miniaturization (leading to a sample concentration increase if comparing iso-mass conditions) and the transport enhancement originating from the rotational shear-driven flow induced by the rotation of the chamber bottom wall.     

玻璃微流控芯片廉价快速制作方法的研究

研究了一种玻璃微流控芯片的快速、低成本制作工艺和方法. 该方法采用商品化的显微载玻片(soda-lime玻璃)作为芯片基质材料, 利用AZ 4620光刻胶代替传统工艺中的溅射金属层或多晶硅/氮化硅层作为玻璃刻蚀的掩膜层, 同时利用一种紫外光学胶键合方法代替传统熔融键合方法实现芯片的键合, 整个工艺对玻璃基质材料要求低, 普通微流控芯片(深度小于50 μm)制作流程仅需约3.5 h, 可降低制作成本, 缩短制作周期. 还系统地研究了光刻胶厚度、光刻胶硬烘时间和玻璃腐蚀液配比对玻璃微流控芯片制作的影响, 获得了优化的工艺参数.     

Development of a passive micromixer based on repeated fluid twisting and flattening,and its application to DNA purification

We have developed a three-dimensional passive micromixer based on new mixing principles, fluid twisting and flattening. This micromixer is constructed by repeating two microchannel segments, a “main channel” and a “flattened channel”, which are very different in size and are arranged perpendicularly. At the intersection of these segments the fluid inside the micromixer is twisted and then, in the flattened channel, the diffusion length is greatly reduced, achieving high mixing efficiency. Several types of micromixer were fabricated and the effect of microchannel geometry on mixing performance was evaluated. We also integrated this micromixer with a miniaturized DNA purification device, in which the concentration of the buffer solution could be rapidly changed, to perform DNA purification based on solid-phase extraction.     

Spectroscopic ellipsometry of SU‐8 photoresist from 190 to 1680 nm (0.740–6.50 eV)

SU‐8 is an important, epoxy‐based, negative photoresist that can create high aspect ratio features. Spectroscopic ellipsometry (SE) is a nondestructive analytical technique that can be performed in the open air. In this study, reflection and transmission SE measurement data were combined to model the optical function of SU‐8 photoresist. The data were fit using three different models: (i) a B‐spline model, (ii) a four‐Gaussian oscillator model with an ultraviolet (UV) and an infrared (IR) pole, and (iii) a Cody–Lorentz model with three additional Gaussian oscillators. All three models successfully fit the data, where the B‐spline model showed the lowest mean squared error. In situ SE data were also collected and fitted to follow possible changes in the optical properties of the SU‐8 during its development. Time‐dependent density functional theory (TD‐DFT) modeling of a complete SU‐8 monomer is qualitatively and quantitatively consistent with the measured optical function.     

The good,the bad,and the tiny: a review of microflow cytometry

Recent developments in microflow cytometry have concentrated on advancing technology in four main areas: (1) focusing the particles to be analyzed in the microfluidic channel, (2) miniaturization of the fluid-handling components, (3) miniaturization of the optics, and (4) integration and applications development. Strategies for focusing particles in a narrow path as they pass through the detection region include the use of focusing fluids, nozzles, and dielectrophoresis. Strategies for optics range from the use of microscope objectives to polymer waveguides or optical fibers embedded on-chip. While most investigators use off-chip fluidic control, there are a few examples of integrated valves and pumps. To date, demonstrations of applications are primarily used to establish that the microflow systems provide data of the same quality as laboratory systems, but new capabilities-such as automated sample staining-are beginning to emerge. Each of these four areas is discussed in detail in terms of the progress of development, the continuing limitations, and potential future directions for microflow cytometers.     

Adhesion of nylon particles to a quartz plate in an aqueous solution and their removal by electro-osmosis

Particle removal by electro-osmotic flow was investigated by comparison with the removal by ordinary flow of water without electrokmetic effect. The relationship between adhesion and removal of particles in terms of force acting on the particle was also discussed. Experiments were carried out in an aqueous solution using nylon particles and a quartz plate. The adhesive force,F _T, for the particles which adhered to the quartz plate in secondary minima in the total potential energy of interaction versus separation distance curves was calculated. Particle removal experiments were carried out applying electro-osmotic and Poiseuille flows. The hydrodynamic force,F _d, which was required to remove particles from the plate was estimated using flow velocities. The effectiveness of electro-osmotic flow on particle removal was larger than that of Poiseuille flow. In the particle removal by electro-osmotic flow, the minimum of the ratioF _d/F _t for particle removal was found to be 50 and the ratio for removal efficiency of 0.5 was about 140.     

Investigation of solution‐grown,chain‐folded lamellar crystals of the even‐even nylons: 6 6, 8 6, 8 8, 10 6, 10 8, 10 10, 12 6, 12 8, 12 10, and 12 12

Chain‐folded lamellar crystals of the ten even‐even nylons: 6 6, 8 6, 8 8, 10 6, 10 8, 10 10, 12 6, 12 8, 12 10, and 12 12 have been grown from solution and their morphologies and structures studied using transmission electron microscopy, both imaging and diffraction. Sedimented mats were examined using X‐ray diffraction. The solution‐grown crystals are lath‐shaped lamellae and diffraction from these crystals, at room temperature, reveals that three crystalline forms are present in differing ratios. The crystals are composed of chain‐folded, hydrogen‐bonded sheets, the linear hydrogen bonds within which generate a progressive shear of the chains (p‐sheets). The sheets are found to stack in two different ways. Some p‐sheets stack with a progressive shear, to form the “α_p structure”; others sheets stack with an alternate stagger, to form the “β_p structure”. Both the α_p and β_p structures give two strong diffraction signals at spacings of 0.44 nm and 0.37 nm; these signals represent a projected intrasheet interchain distance (actual value 0.48 nm) and the intersheet spacing, respectively. Preparations of nylons 6 6, 8 6, 8 8, 12 6, and 12 8 consisted almost entirely of α_p‐structure material, with only a trace of β_p‐structure material being present. In contrast, nylons 10 6, 10 8, 10 10, 12 10, and 12 12 contained substantial quantities of both α_p‐ and β_p‐structure material, with α_p‐structure material always being in the majority. Preparations of nylons 10 8, 12 10, and 12 12 also showed an additional diffraction signal at 0.42 nm; this signal is characteristic of the pseudohexagonal (high temperature) structure. The melting temperature of solution‐grown lamellae of these even‐even nylons decreases with decreasing linear amide density. On heating, the strong diffraction signals (0.44 nm and 0.37 nm) gradually moved together and merge at the Brill temperature to form a single diffraction signal (0.42 nm), characteristic of the pseudohexagonal structure. This single diffraction signal remained until melting. For nylons 6 6, 8 6, 8 8, 10 6, and 12 6, the Brill temperatures were substantially below the respective melting temperatures and the single 0.42 nm diffraction signal was stable over temperature ranges of 14 °C to 56 °C, depending on the nylon. Conversely, nylons 10 8, 10 10, 12 8, 12 10, and 12 12 had coincident melting and extrapolated Brill temperatures. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1209–1221, 2000     

A microfluidic chip with a staircase pH gradient generator,a packed column and a fraction collector for chromatofocusing of proteins

A microfluidic device for pH gradient chromatofocusing is presented, which performs creation of a micro‐column, pH gradient generation, and fraction collection in a single device. Using a sieve micro‐valve, anion exchange particles were packed into a microchannel in order to realize a solid‐phase absorption column. To fractionate proteins according to their isoelectric points, elution buffer solutions with a stepwise pH gradient were prepared in 16 parallel mixing reactors and flowed through the micro‐column, wherein a protein mixture was previously loaded. The volume of the column is only 20 nL, hence it allows extremely low sample consumption and fast analysis compared with a conventional system. We demonstrated separation of two proteins, albumin–fluorescein isothiocyanate conjugate (FITC‐BSA) and R‐Phycoerythrin (R‐PE), by using a microcolumn of commercial charged polymeric particles (Source 15Q). The microfluidic device can be used as a rapid diagnostic tool to analyse crude mixtures of proteins or nucleic acids and determine adsorption/desorption characteristics of various biochemical products, which can be helpful for scientific fundamental understanding as well as instrumental in various industrial applications, especially in early stage screening and process development.     

Binding of Ionic Pyrene Derivatives to Polyelectrolytes. A Uv Absorption and Fluorescence Study

Abstract

The binding of pyrenesulfonic acid and pyrenebutyric acid to poly(vinyl benzyl trimethylammonium) chloride was investigated by UV and fluorescence spectroscopy. It was found that the binding constant was 7.5 × 10⁴ and 3.5 × 10⁴M^?1, respectively. The addition of the polyelectrolyte quenches the fluorescence of the pyrene group, and at the same time the typical excimer emission appears. This emission originates in pre-formed ground state aggregates of the pyrene derivatives incorporated into the polyion domain. Similar effects were observed when anionic polyelectrolytes, poly(styrene sulfonic), and poly(vinyl sulfonic) acids were added to cationic pyrene derivatives. The binding constants depend on the length of the aliphatic sidechain of the derivatives.     

高分子结构与性能研究的密度泛函理论方法

随着高分子科学的发展,高分子的性质需要更多的理论给予解释。本文介绍了目前正在形成的密度泛函理论方法及其在高分子结构和性能研究中的应用。由于该理论处于初始阶段,有许多问题尚待研究。     

Ba2[Ni3N2]: a low-valent nitridonickelate-synthesis, crystal structure, and physical properties

The ternary alkaline-earth nitridonickelate Ba2[Ni3N2] (Ba2[NiI2Ni0N2]) was prepared by the reaction of mixtures of Ba2N and Ni in nitrogen gas of ambient back-pressure at 1173 K. The crystal structure determined by X-ray single-crystal and powder diffraction methods as well as from neutron diffraction data at various temperatures between 2 and 298 K is orthorhombic (Cmca (no. 64), 298 K: a=715.27(18) pm, b=1032.99(21) pm, c=740.12(20) pm) and provides the first example of a nitridonickelate with a two-dimensional complex anion. The Ni2 atom is described with a split position and the corresponding superstructure variants are investigated by theoretical full-potential nonorthogonal local-orbital calculations (FPLO). The average oxidation state of Ni in Ba2[Ni3N2] is +0.67, the lowest average value observed in nitridonickelates so far. Investigations of the physical properties demonstrate that Ba2[Ni3N2] acts as a "poor" metal with a large resistivity of approximately 2.7 mOmega cm at 300 K and exhibits low-dimensional magnetism with antiferromagnetic ordering at T approximately 90 K. XAS spectra correspond with low-valent Ni states.     

Experimental and Theoretical Approaches to the Influence of the Addition of Pyrene to a Series of Pd and Ni NHC‐Based Complexes: Catalytic Consequences

A series of Ni and Pd complexes with three different N‐heterocyclic carbene (NHC)‐based ligands (imidazolylidene, benzimidazolylidene and pyrene–imidazolylidene) has been prepared and fully characterized. The influence of the addition of pyrene to solutions containing these complexes is studied by means of NMR and UV/Vis spectroscopies and by cyclic voltammetry. The addition of pyrene to the pyrene–NHC‐containing Pd and Ni complexes gives rise to the formation of adducts by π–π stacking interactions between pyrene and the pyrene group of the NHC ligand. This interaction causes a modification of the electronic properties of the metal, as demonstrated by cyclic voltammetric studies of the Ni–NHC complexes. Theoretical calculations support this type of π‐interactions, and justify the higher interactions observed with the pyrene–NHC containing complexes. The catalytic activities of the complexes were tested in the Suzuki–Miyaura C?C coupling and in the α‐arylation of ketones. The addition of pyrene as an external π‐stacking additive does not affect the activities of the complexes in the Suzuki–Miyaura coupling, but this observation may be justified due to the fact that the process is heterogeneously catalyzed, as indicated by the mercury‐drop test. The addition of pyrene to the catalytic α‐arylation of ketones results in a decrease in the activity of the reactions catalyzed by the pyrene–imidazolylidene palladium complex, whereas the other two catalysts do not modify their activity in the presence of this π‐stacking additive.