Study of the peak broadening due to detection in the electrophoretic separation of DNA by CE and microchip CE and the application of image sensor for ultra-small detection cell length

Narrow peaks are important to high-resolution and high-speed separation of DNA fragments by capillary electrophoresis and microchip capillary electrophoresis. Detection cell length is one of the broadening factors, which is often ignored in experiments. However, is it always safe to neglect detection cell length under any condition? To answer this question, we investigated the influence of detection cell length by simulation and experiments. A parameter named as detection cell length ratio was proposed to directly compare the detection cell length and the spatial length of sample band. Electrophoretic peaks generated by various detection cell length ratios were analyzed. A simple rule to evaluate the peak broadening due to detection cell length was obtained. The current states of the detection cell length of detection system and their reliabilities in capillary electrophoresis and microchip capillary electrophoresis were analyzed. Microchip capillary electrophoresis detection with an ultra-small detection cell length of 0.36 μm was easily achieved by using an image sensor.

Capillary electrophoresis-based approaches for the study of affinity interactions combined with various sensitive and nontraditional detection techniques

Nearly all processes in living organisms are controlled and regulated by the synergy of many biomolecule interactions involving proteins, peptides, nucleic acids, nucleotides, saccharides, and small molecular weight ligands. There is growing interest in understanding them, not only for the purposes of interactomics as an essential part of system biology, but also in their further elucidation in disease pathology, diagnostics, and treatment. The necessity of detailed investigation of these interactions leads to the requirement of laboratory methods characterized by high efficiency and sensitivity. As a result, many instrumental approaches differing in their fundamental principles have been developed, including those based on capillary electrophoresis. Although capillary electrophoresis offers numerous advantages for such studies, it still has one serious limitation, its poor concentration sensitivity with the most commonly used detection method-ultraviolet-visible spectrometry. However, coupling capillary electrophoresis with a more sensitive detector fulfils the above-mentioned requirement. In this review, capillary electrophoresis combined with fluorescence, mass spectrometry, and several nontraditional detection techniques in affinity interaction studies are summarized and discussed, together with the possibility of conducting these measurements in microchip format.

Instrumentation design for hydrodynamic sample injection in microchip electrophoresis: a review

Reproducible and representative sample injection in microchip electrophoresis has been a bottleneck for quantitative analytical applications. Electrokinetic sample injection is the most used because it is easy to perform. However, this injection method is usually affected by sample composition and the bias effect. On the other hand, these drawbacks are overcome by the hydrodynamic (HD) sample injection, although this injection mode requires HD flow control. This review gives an overview of the basic principles, the instrumentation designs, and the performance of HD sample injection systems for microchip electrophoresis.

Rapid qualitative evaluation of DNA transcription factor NF-κB by microchip electrophoretic mobility shift assay in mammalian cells

We have developed a separation technique for DNA-protein complex based on electrophoretic mobility shift assay (EMSA) by microchip electrophoresis, which we call microchip electrophoretic mobility shift assay (μEMSA). To evaluate the μEMSA, we employed recombinant human nuclear factor-κB (rhNF-κB) and its consensus double-stranded oligonucleotide (dsOligo) fluorescently labeled with Cy5. We carried out the electrophoretic separation of the consensus dsOligo-rhNF-κB complex and the unbound dsOligo in methylcellulose solution and confirmed rapid (∼200  s) and reliable identification and semi-quantitation of the specific interaction between dsOligo and rhNF-κB. The binding specificity of rhNF-κB was confirmed by introducing non-fluorescently labeled consensus oligonucleotide as a competitor. The progression of the binding reaction under various incubation times was monitored, and it was found that the dsOligo and rhNF-κB complex formation reached equilibrium (ca. 90% of the dsOligo was bound to rhNF-κB) after 5  min. Furthermore, without any purification process, even crude NF-κB in nuclear extracts from HeLa cells was specifically detected within 120  s by the μEMSA.

Poly(dimethylsiloxane) photonic microbioreactors based on segmented waveguides for local absorbance measurement

We present the development of microbioreactors (MBRs) based on poly(dimethylsiloxane) (PDMS) segmented waveguides (SWG) for local absorbance measurements. Two different MBRs were studied, either using symmetric or asymmetric SWG (being defined as MBR-S and MBR-A, respectively). Their optical and fluidic performances were numerically analyzed, showing robustness from an optical point of view and distinct fluid flow profile. The optical characterization was done in two steps. Initially, the experimental limit of detection (LOD) and the sensitivity were determined for two different analytes (fluorescein and methylorange). With both systems, a similar limit of detection for both analytes was obtained, being in the micromolar level. Their sensitivities were 20.2±0.3 (×10⁻³) A.U./μM and 5.5±0.2 (×10⁻³) A.U./μM for fluorescein and methylorange, respectively. Once validated its applicability for local absorbance measurements, a continuous cultivation of Saccharomyces cerevisiae was done to test the viability of the proposed systems for photonic MBRs. Concretely, the cell growth was locally monitored inside the MBR during 33 h. Spectral analysis showed that the determination of the culture parameters were wavelength dependant, with a growth rate of 0.39±0.02 h⁻¹ and a doubling time of 1.65±0.09 h at an optimal wavelength of 469.9±0.3 nm. Besides the easy and monolithic integration of the SWG into poly(dimethylsiloxane) microfluidic systems, the results presented here are very promising for the application in any disposable photonic lab-on-a-chip systems used for online analysis or photonic MBRs.