Optimization of on-chip elongation for fabricating double-stranded DNA microarrays

The sequence-specific recognitions between DNA and proteins are playing important roles in many biological functions. The double-stranded DNA microarrays (dsDNA microarrays) can be used to study the sequence-specific recognitions between DNAs and proteins in highly parallel way. In this paper, two different elongation processes in forming dsDNA from the immobilized oligonucleotides have been compared in order to optimize the fabrication of dsDNA microarrays: (1) elongation from the hairpins formed by the self-hybridized oligonucleatides spotted on a glass; (2) elongation from the complementary primers hybridized on the spotted oligonucleatides. The results suggested that the dsDNA probes density produced by the hybridized-primer extension was about four times lower than those by the self-hybridized hairpins. Meanwhile, in order to reduce the cost of dsDNA microarrays, we have replaced the Klenow DNA polymerase with Taq DNA polymerase, and optimized the reaction conditions of on-chip elongation. Our experiements showed that the elongation temperature of 50 °C and the Mg²⁺ concentration of 2.5 mM are the optimized conditions in elongation with Taq DNA polymerase. A dsDNA microarray has been successfully constructed with the above method to detect NF-kB protein.     

Macromodeling of high-speed interconnects by positive interpolation of vertical segments

In this paper a novel macromodeling scheme is presented to model the per unit of length (p.u.l.) parameters of uniform transmission lines. In particular, it is focused on single on-chip interconnects, because their p.u.l. parameters are influenced by the presence of semiconductor (s) and as such exhibit a strong frequency-dependency, making the modeling process harder. Starting from a set of very accurate tabulated data samples, obtained by two-dimensional electromagnetic modeling, rational models for the four p.u.l. parameters are constructed. The novelty of the approach lies in the fact that the rational models are positive by construction and that a controllable accuracy is obtained. These models can then further be used to construct multivariate models, e.g., for variability analysis. Here, the novel scheme is applied to an on-chip inverted embedded microstrip line, of which the signal integrity behavior is assessed in both the frequency and the time domain, demonstrating the applicability of the macromodels.     

An integrated plastic microchip for enhancing electrophoretic separation using tunable pressure-driven backflows

Microfluidic CE (MCE) is an effective solution for rapid and sensitive determination of multiple analytes. Herein, a dynamic coated cyclic olefin copolymer microchip was developed having an on-chip micropump for fluid velocity adjusting in electrophoretic separations. This micropump was fabricated by constructing a polyacrylamide gel membrane at one channel terminal. Once applying electric field across the membrane, a pressure-driven flow generated automatically to balance the electroosmotic flow (EOF) mismatch at the channel-membrane interface. The influence of gel precursor concentration and operating voltages on the fluid velocity was carefully evaluated. Moreover, the highly integration of injection, separation, and pumping units of the MCE system minimized the dead volume and provides satisfied column efficiency. Experiments showed that by adjusting of pumping voltage reduced the fluid velocity by a factor of 6, resulting six- and threefold resolving power enhancements of rhodamine dye mixture and amino acid mixture, respectively. Furthermore, the developed MCE method was applied for rhodamines and amino acids quantitation in food and cosmetics, with standard addition recoveries of 87.3–106.9% and 89.9–117.4%, respectively. These results were also confirmed by standard HPLC method, revealing the application potential in fast and onsite analysis of complex samples.     

Experimental study of the depth influence on the band broadening effect in a cyclo-olefin polymer column containing an array of ordered pillars

An experimental study of a micromachined non-porous pillar array column performance under non-retentive conditions is presented. The same pillar structure has been fabricated in cyclo-olefin polymer (COP) chips with three different depths via hot embossing and pressure-assisted thermal bonding. The influence of the depth on the band broadening along with the already known contribution arising from the top and bottom cover plates has been studied. The experimental results exhibit reduced plate heights as low as 0.2, which are in agreement with the previous experimental work. Moreover, the constant values of the reduced Van Deemter expression are also in accordance with the previous studies. A more exhaustive study of the C-term band broadening is also presented, showing that comparing the space between the pillars with different open tubular rectangular channels offers a good estimation of the C-term band broadening that is obtained experimentally. These experimental results, hence, confirm that micromachined pillar array columns fabricated in COP can achieve the same performance as the ones fabricated in silicon for the presently studied pillar channel design.     

Integration of continuous-flow sampling with microchip electrophoresis using poly(dimethylsiloxane)-based valves in a reversibly sealed device

Here we describe a reversibly sealed microchip device that incorporates poly(dimethylsiloxane) (PDMS)-based valves for the rapid injection of analytes from a continuously flowing stream into a channel network for analysis with microchip electrophoresis. The microchip was reversibly sealed to a PDMS-coated glass substrate and microbore tubing was used for the introduction of gas and fluids to the microchip device. Two pneumatic valves were incorporated into the design and actuated on the order of hundreds of milliseconds, allowing analyte from a continuously flowing sampling stream to be injected into an electrophoresis separation channel. The device was characterized in terms of the valve actuation time and pushback voltage. It was also found that the addition of sodium dodecyl sulfate (SDS) to the buffer system greatly increased the reproducibility of the injection scheme and enabled the analysis of amino acids derivatized with naphthalene-2,3-dicarboxaldehyde/cyanide. Results from continuous injections of a 0.39 nL fluorescein plug into the optimized system showed that the injection process was reproducible (RSD of 0.7%, n = 10). Studies also showed that the device was capable of monitoring off-chip changes in concentration with a device lag time of 90 s. Finally, the ability of the device to rapidly monitor on-chip concentration changes was demonstrated by continually sampling from an analyte plug that was derivatized upstream from the electrophoresis/continuous flow interface. A reversibly sealed device of this type will be useful for the continuous monitoring and analysis of processes that occur either off-chip (such as microdialysis sampling) or on-chip from other integrated functions.     

Portable microfluidic system for determination of urinary creatinine

A simple, low cost and portable microfluidic system based on a two-point alkaline picrate kinetic reaction has been developed for the determination of urinary creatinine. The creatinine reacts with picric acid under alkaline conditions, forming an orange-red colour, which is monitored on PDMS microchip using a portable miniature fibre optic spectrometer at 510 nm. A linear range was displayed from 0 to 40 mg L⁻¹ creatinine (r² = 0.997) with a detection limit of 3.3 mg L⁻¹ (S/N = 3). On-chip absorbance signals are reproducible, with relative standard deviations (RSDs) of 7.1%, when evaluated with 20 mg L⁻¹ creatinine (n = 10). The standard curves in which the intra-run CVs (4.7-6.8%) and inter-run CVs (7.9%) obtained were performed on three different days and exhibited good reproducibility. The method was highly correlated with the conventional spectrophotometric method when real urine samples were evaluated (r² = 0.948; n = 15).     

微流控芯片NDA在线衍生测定单细胞中谷胱甘肽

单细胞分析对研究细胞内信号传递和重大疾病的早期诊断等具有重要意义,荧光标记是检测细胞内物质的常用技术,为防止衍生时的过度稀释,大多采用柱前细胞内衍生法,衍生后再用微流控芯片分析,此法操作复杂,需多次离心分离,且能透过细胞膜标记胞内组分的荧光试剂较少。     

在线衍生微流控芯片电泳和激光诱导荧光法测定单细胞中谷胱甘肽

微流控分析芯片的网络结构和微米通道尺寸适合于单细胞进样、控制和分离分析^[1~4].在测定细胞内容物时,大多采用柱前细胞内衍生法^[1,2,4],但操作复杂,需多次离心分离,且能透过细胞膜标记胞内组分的荧光试剂较少.     

Preparation of hybrid soda-lime/quartz glass chips with wettability-patterned channels for manipulation of flow profiles in droplet-based analytical systems

Profile switching of two-phase flows is often required in microfluidic systems. Manipulation of flow profiles can be realized by control of local surface energy of micro channel through wettability-patterning of channel surface. This article presents a facile approach for wettability-patterning of the micro channels of glass chips. Commercially available octadecyltrichlorosilane (OTS) was used to hydrophobilize the channels via the formation of OTS self-assembly monolayer (SAM), and a UV-source that mainly emits deep UV-light of 254 and 185 nm was employed to degrade the in-channel formed OTS-SAM. The architecture of soda-lime glass/quartz glass hybrid chip was designed to facilitate the deep UV-light effective degrading the OTS-SAM. The established approach, together with the side-by-side laminar-flow patterning technique, was applied to prepare various finely patterned channel networks for different tasks of flow profile switching. The micro device capable of conducting the profile switch from W/O droplets to two separated continuous phases was demonstrated to perform on-chip quick liquid–liquid extraction for the determination of partition coefficients of pharmaceuticals.