G. Ocvirk et al., Electrokinetic control of fluid flow in native poly(dimethylsiloxane) capillary electrophoresis devices, ELECTROPHOR, 21(1), 2000, pp. 107-115
Capillary zone electrophoresis (CZE) devices fabricated in poly(dimethylsil
oxane) (PDMS) require continuous voltage control of all intersecting channe
ls in the fluidic network in order to avoid catastrophic leakage at the int
ersections. This contrasts with the behavior of similar flow channel design
s fabricated in glass substrates. When the injection plugs are shaped by vo
ltage control and leakage from side channels is controlled by the applicati
on of pushback voltages during separation, fluorescein samples give 64 200
theoretical plates (7000 V separation voltage, E = 1340 V/cm). Native PDMS
devices exhibit stable retention times (+/- 8.6% RSD) over a period of five
days when filled with water. Contact angles were unchanged (+/- 1.9% RSD)
over a period of 16 weeks of dry storage, in contrast to the known behavior
of plasma-oxidized PDMS surfaces. Electroosmotic flow (EOF) was observed i
n the direction of the cathode for the buffer systems studied (phosphate, p
H 3-10.5), in the presence or absence of hydrophobic ions such as tetrabuty
lammonium or dodecyl sulfate. Electroosmotic mobilities of 1.49 x 10(-5) an
d 5.84 x 10(-4) cm(2)/Vs were observed on average at pH 3 and 10.5, respect
ively, the variation strongly suggesting that silica fillers in the polymer
dominate the zeta potential of the material. Hydrophobic compounds such as
dodecyl sulfate and BODIPY(R) 493/503 adsorbed strongly to the PDMS, indic
ating the hydrophobicity of the channel walls is clearly problematic for CZ
E analysis of hydrophobic analytes. A method to stack multiple channel laye
rs in PDMS is also described.