Effects of peak anomalies with the hydrophilic or hydrophobic properties of reservoirs during serial injection on a capillary electrophoresis microchip

Robust and easy-to-use microchip electrophoresis within sub-millimeter channels for fast and highly efficient separation

Microchip capillary electrophoresis (MCE) is a powerful technique for rapid separation; however, its acceptance in routine laboratories is still limited. Compromises caused by the efforts for solving different problems, such as reducing its cost of fabrication and ensuring high separation efficiency, undermine the competitiveness of this technology compared to other separation techniques. Contrary to the conventional pursuit of narrow microchannels, this study investigated the suitability of microchips with channels at the sub-millimeter level, targeting the simplification of the overall operation, cost reduction, and robustness improvement. To this effect, we considered the influence of pressurized flow and Joule heating on the separation. The suppression of pressurized flow with viscous solutions was confirmed through a combination of simulations and experimental results, indicating that the buffer viscosity was enough for successful separation. We fabricated channels of 200 μm × 230 μm using computer numerical controlled (CNC) machining and obtained theoretical plate numbers of 4.8 × 10⁵ m^-1 and 5.3 × 10⁵ m^-1 for fluorescein isothiocyanate (FITC) labeled small molecules and DNA fragments, respectively, with a buffer viscosity of 168 mPa s (0.5 % hydroxypropyl methylcellulose, HPMC). These values are comparable with that of narrow-bore microchips. Furthermore, we did not observe any deleterious effects with low-conductivity buffers. We investigated the rapid and highly sensitive detection of mycoplasma contamination and the real samples of circulating cell-free DNA (cfDNA), which gave a limit of detection (LOD) as low as 2.3 ng mL^-1. Owing to the significant reduction in cost, ease of operation, and fast separation capabilities demonstrated in this work, MCE can be a viable alternative to the usual slab gel electrophoresis running in most biological laboratories.

Real time culture and analysis of embryo metabolism using a microfluidic device with deformation based actuation

We report a computerized microfluidic real time embryo culture and assay device that can perform automated periodic analyses of embryo metabolism. This automated program uses a modified "gated injection" scheme (sample injection, reagent mixing, enzyme reaction of 15 min incubation, and sample detection) to sequentially measure fluorescence from sample, reference, and background (without any analyte) every hour. Measurements assessed with reference solutions demonstrated the stability of these microfluidic measurements over a 24 h period. Furthermore, this system was able to measure time dependent nutrient consumption by single or multiple (10) live mouse blastocyst-stage embryos with pmol h(-1) sensitivity. Mechanical deformation-based microfluidic actuation created by computerized movement of Braille pins enables automated fluid pumping and valving sequences without unwanted gravity-driven backflow or exposure to electrical fields as would be required in electrokinetic schemes. The convenient, non-invasive, and automated nature of these assays open the way for the development of integrated microfluidic platforms for practical single embryo culture and real time biochemical analysis to assess embryo viability and select embryos with the greatest implantation potential, thus improving success in clinical assisted reproductive technology laboratories.

Study of injection bias in a simple hydrodynamic injection in microchip CE

The electrokinetically pinched method is the most commonly used mode for sample injection in microchip capillary electrophoresis (microCE) due to its simplicity and well-defined sample volume. However, the limited injection volume and the electrophoretic bias of the pinched injection may limit its universal usage to specific applications. Several hydrodynamic injection methods in microCE have been reported; however, almost all claimed that their methods are bias-free without considering the dispensing bias. To investigate the dispensing bias, a simple hydrodynamic injection was developed in single-T and double-T glass microchips. The sample flow was produced by hydrostatic pressure generated by the liquid level difference between the sample reservoir and the other reservoirs. The reproducibility of peak area and peak area ratio was improved to a significant extent using large-surface reservoirs for the buffer reservoir and the sample waste reservoir to reduce the Laplace pressure effect. Without a voltage applied on the sample solution, the voltage-related sample bias was eliminated. The dispensing bias was analyzed theoretically and studied experimentally. It was demonstrated that the dispensing bias existed and could be reduced significantly by appropriately setting up the voltage configuration and by controlling the appropriate liquid level difference.

Characterization and performance of injection molded poly(methylmethacrylate) microchips for capillary electrophoresis

Injection molded poly(methylmethacrylate) (IM-PMMA), chips were evaluated as potential candidates for capillary electrophoresis disposable chip applications. Mass production and usage of plastic microchips depends on chip-to-chip reproducibility and on analysis accuracy. Several important properties of IM-PMMA chips were considered: fabrication quality evaluated by environmental scanning electron microscope imaging, surface quality measurements, selected thermal/electrical properties as indicated by measurement of the current versus applied voltage (I-V) characteristic and the influence of channel surface treatments. Electroosmotic flow was also evaluated for untreated and O2 reactive ion etching (RIE) treated surface microchips. The performance characteristics of single lane plastic microchip capillary electrophoresis (MCE) separations were evaluated using a mixture of two dyes-fluorescein (FL) and fluorescein isothiocyanate (FITC). To overcome non-wettability of the native IM-PMMA surface, a modifier, polyethylene oxide was added to the buffer as a dynamic coating. Chip performance reproducibility was studied for chips with and without surface modification via the process of RIE with O2 and by varying the hole position for the reservoir in the cover plate or on the pattern side of the chip. Additionally, the importance of reconditioning steps to achieve optimal performance reproducibility was also examined. It was found that more reproducible quantitative results were obtained when normalized values of migration time, peak area and peak height of FL and FITC were used instead of actual measured parameters.

Surface Modification Effect of Wettability on the Performance of PDMS-Based Valveless Micropump

Experimental investigation and numerical simulation on the effect of surface wettability on the performance of a polydimethylsiloxane (PDMS) based diffuser micropump are presented. A valveless micro membrane pump with piezoelectric actuation has been examined. Using a replica molding technique, the valveless micropump was made of PDMS on a Pyrex glass substrate. A thin piezoelectric (PZT) disc was used as an actuator. Poly vinyl alcohol (PVA) and octadecyltrichlorosilane (OTS) coatings, which make the coated surface hydrophilic and hydrophobic, respectively, were used to modify the surface wettability inside the pump. In our experiments, the contact angle of the PDMS surface changed from 96.6 o to 29.1 o and 99.6 o by PVA and OTS coatings, respectively, and the contact angle of glass changed from 33.2 o to 17.5 o and 141.8 o. A self-priming process was numerically simulated in a diffuser element using a computational fluid dynamics program (CFD-ACE+). The results show that fewer gas bubbles were created in the hydrophilic coated pump than in the hydrophobic coated one as time progressed. This agrees well with experimental observations. Steady-state flow rates of the micropump were measured. Compared to the non-coated pump, the flow rate increased slightly with the hydrophobic coating but decreased with the hydrophilic coating. We determine that surface wettability significantly affects the performance of a PDMS-based micropump.