February 9, 2009Aytug Gencoglu
| Aytug Gencoglu - Integration of Dialysis Membranes into a Poly(dimethylsiloxane) Microfluidic Chip for Isoelectric Focusing of Proteins Using Whole-Channel Imaging Detection
Junjie Ou, Tomasz Glawdel, Razim Samy, Shuwen Wang, Zhen Liu, Carolyn L. Ren, and Janusz Pawl | | | | Overview
A PDMS chip-based cartridge for isoelectric focusing (IEF) has been developed and its performance assessed. The main features are dialysis membranes, fused silica capillaries, whole-channel imaging detection (WCID) and preconditioning of the microchannel. The dialysis membranes reduce cross-contamination, simplify operation and reduce pressure-driven flow by separating electrolytes and sample. Use of fused silica capillaries for injection and discharge of solutions reduces pressure-driven flow and eliminates channel deformation problems. Use of WCID instead of detection at column exit shortens process duration and improves resolution by eliminating the mobilization step in IEF. Preconditioning of the microchannel suppresses the EOF and protein adsorption on microchannel walls. The device is reported to perform better than previous designs not featuring capillaries or dialysis membranes.
Introduction
Part of the background introduction on IEF is rather mundane and common, but the whole section builds the background, problem and related work very well.
Experimental Section
There is a good discussion on the problems that were addressed and the reasoning behind the choices that were made in solving them, although it is somewhat lengthy for the experimental section. The fabrication, especially the incorporation of the membranes is difficult to explain, and the authors were not completely able to overcome this difficulty. The written explanation is very good, but still a little difficult for the reader to understand. Figure 1 looks very nice, but contributes little to understand the procedure. A more utilitarian style could have worked better in this case. Also, it is not explained how the membranes improve the operation.
WCID and preconditioning have been carried out before, but the use of dialysis membranes to separate sample from electrolytes to improve performance is a novel concept, and the combination of fused silica capillaries with the microchannel contributed to the improvement of performance over earlier devices.
How the different parts (i.e. membrane-recess) were aligned is not explained at all.
The dialysis membranes and fused-silica channels could be used in future microdevices used in our lab, but the question of how to align the different components would have to be solved.
Results and discussion
This section is very clearly written and the results and the conclusions drawn from them are easily understood. However, the information presented in Figure 2a is inconclusive, since stationary peaks are not observed.
Findings:
-Using mortar on one side of the dialysis membranes results in leaks after a few runs. Using mortar on both sides extends lifetime greatly but significantly slows the process. On Fig. 2, when mortar was applied on one side, peaks were focused in 15 min, but when mortar was applied on both sides, they were not focused in 24 min.
-pH markers in a range of 4.65-8.18 have been separated successfully.
-Different channel dimensions have been tried successfully.
-Mixtures of hemoglobin isoforms have been separated.
-MC has been found to be problematic as a preconditioner, PVP has been found to be more effective at suppressing EOF and protein adsorption than PVA.
Conclusions
This section is a brief, concise summary that highlights the novel and important aspects of the presented work.
Recommendation
Accept with revisions to clarify some points that are not very clear.
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