Sample transport and electrokinetic injection in a microchip device for chemical cytometry.
Sample transport and electrokinetic injection bias are well characterized in capillary electrophoresis and simple microchips, but a thorough understanding of sample transport on devices combining electroosmosis, electrophoresis, and pressure-driven flow is lacking. In this work, we evaluate the effects of electric fields from 0 to 300  V/cm, electrophoretic mobilities from 10(-4) to 10(-6)  cm(2)/Vs, and pressure-driven fluid velocities from 50 to 250  μm/s on sample injection in a microfluidic chemical cytometry device. By studying a continuous sample stream, we find that increasing electric field strength and electrophoretic mobility result in improved injection and that COMSOL simulations accurately predict sample transport. The effects of pressure-driven fluid velocity on injection are complex, and relative concentration values lie on a surface defined by pressure-driven flow rates. For high-mobility analytes, this surface is flat, and sample injection is robust despite fluctuations in flow rate. For lower mobility analytes, the surface becomes steeper, and injection depends strongly on pressure-driven flow. These results indicate generally that device design must account for analyte characteristics and specifically that this device is suited to high-mobility analytes. We demonstrate that for a suitable pair of peptides fluctuations in injection volume are correlated; electrokinetic injection bias is minimized; and electrophoretic separation is achieved.
Department of Chemistry, University of North Carolina, Chapel Hill, NC, USA.
Michelle L
ML
Kovarik
Hsuan-Hong
HH
Lai
Jessie C
JC
Xiong
Nancy L
NL
Allbritton
D003198:Computer Simulation; D004867:Equipment Design; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation*; D008956:Models, Chemical; D010455:Peptides / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry; D010715:Phosphatidylglycerols / Q000737:chemistry; D011312:Pressure; D015203:Reproducibility of Results; D059010:Single-Cell Analysis / Q000295:instrumentation* / Q000379:methods
D010455:Peptides; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols