Optimization of ELFSE DNA sequencing with EOF counterflow and microfluidics

A Review of Optical Imaging Technologies for Microfluidics

Microfluidics can precisely control and manipulate micro-scale fluids, and are also known as lab-on-a-chip or micro total analysis systems. Microfluidics have huge application potential in biology, chemistry, and medicine, among other fields. Coupled with a suitable detection system, the detection and analysis of small-volume and low-concentration samples can be completed. This paper reviews an optical imaging system combined with microfluidics, including bright-field microscopy, chemiluminescence imaging, spectrum-based microscopy imaging, and fluorescence-based microscopy imaging. At the end of the article, we summarize the advantages and disadvantages of each imaging technology.

Combining Affinity Selection and Specific Ion Mobility for Microchip Protein Sensing

The sensitive detection of proteins is a key objective in many areas of biomolecular science, ranging from biophysics to diagnostics. However, sensing in complex biological fluids is hindered by nonspecific interactions with off-target species. Here, we describe and demonstrate an assay that utilizes both the chemical and physical properties of the target species to achieve high selectivity in a manner not possible by chemical complementarity alone, in complex media. We achieve this objective through a combinatorial strategy, by simultaneously exploiting free-flow electrophoresis for target selection, on the basis of electrophoretic mobility, and conventional affinity-based selection. In addition, we demonstrate amplification of the resultant signal by a catalytic DNA nanocircuit. This approach brings together the inherent solution-phase advantages of microfluidic sample handling with isothermal, enzyme-free signal amplification. With this method, no surface immobilization or washing steps are required, and our assay is well suited to monoepitopic targets, presenting advantages over conventional ELISA techniques.

A 502-Base Free-Solution Electrophoretic DNA Sequencing Method Using End-Attached Wormlike Micelles

We demonstrate that the use of wormlike nonionic micelles as drag-tags in end-labeled free-solution electrophoresis ("micelle-ELFSE") provides single-base resolution of Sanger sequencing products up to 502 bases in length, a nearly 2-fold improvement over reported ELFSE separations. "CiEj" running buffers containing 48 mM C12E5, 6 mM C10E5, and 3 M urea (32.5 °C) form wormlike micelles that provide a drag equivalent to an uncharged DNA fragment with a length (α) of 509 bases (effective Rh = 27 nm). Runtime in a 40 cm capillary (30 kV) was 35 min for elution of all products down to the 26-base primer. We also show that smaller Triton X-100 micelles give a read length of 103 bases in a 4 min run, so that a combined analysis of the Sanger products using the two buffers in separate capillaries could be completed in 14 min for the full range of lengths. A van Deemter analysis shows that resolution is limited by diffusion-based peak broadening and wall adsorption. Effects of drag-tag polydispersity are not observed, despite the inherent polydispersity of the wormlike micelles. We ascribe this to a stochastic size-sampling process that occurs as micelle size fluctuates rapidly during the runtime. A theoretical model of the process suggests that fluctuations occur with a time scale less than 10 ms, consistent with the monomer exchange process in nonionic micelles. The CiEj buffer has a low viscosity (2.7 cP) and appears to be semidilute in micelle concentration. The large drag-tag size of the CiEj buffers leads to steric segregation of the DNA and tag for short fragments and attendant mobility shifts.

Capillary electrophoresis applied to DNA: determining and harnessing sequence and structure to advance bioanalyses (2009-2014)

This review of capillary electrophoresis methods for DNA analyses covers critical advances from 2009 to 2014, referencing 184 citations. Separation mechanisms based on free-zone capillary electrophoresis, Ogston sieving, and reptation are described. Two prevalent gel matrices for gel-facilitated sieving, which are linear polyacrylamide and polydimethylacrylamide, are compared in terms of performance, cost, viscosity, and passivation of electroosmotic flow. The role of capillary electrophoresis in the discovery, design, and characterization of DNA aptamers for molecular recognition is discussed. Expanding and emerging techniques in the field are also highlighted.