Studies of electroosmotic flow and the effects of protein adsorption in plasma‐polymerized microchannel surfaces

Abstract

This paper presents a study of EOF properties of plasma-polymerized microchannel surfaces and the effects of protein (fibrinogen and lysozyme) adsorption on the EOF behavior of the surface-modified microchannels. Three plasma polymer surfaces, i.e. tetraglyme, acrylic acid and allylamine, are tested. Results indicate EOF suppression in all plasma-coated channels compared with the uncoated glass microchannel surfaces. The EOF behaviors of the modified microchannels after exposure to protein solutions are also investigated and show that even low levels of protein adsorption can significantly influence EOF behavior, and in some cases, result in the reversal of flow. The results also highlight that EOF measurement can be used as a method for detecting the presence of proteins within microchannels at low surface coverage (<1 ng/cm(2) on glass). Critically, the results illustrate that the non-fouling tetraglyme plasma polymer is able to sustain EOF. Comparison of the plasma-polymerized surfaces with conventionally grafted polyelectrolyte surfaces demonstrates the stabilities of the plasma polymer films, enabling multiple EOF runs over 3 days without deterioration in performance. The results of this study clearly demonstrate that plasma polymers enable the surface chemistry of microfluidic devices to be tailored for specific applications. Critically, the deposition of the non-fouling tetraglyme coating enables stable EOF to be induced in the presence of protein.

Stable low-fouling plasma polymer coatings on polydimethylsiloxane

“…Figure 3 shows that uncoated PDMS avidly adsorbed fibrinogen, a material property characterized in previous studies. 22,42,44,57 The ppTTg coated silicon wafer again showed significant reductions in protein adsorption compared to uncoated PDMS, although not complete protein resistance. Double ppTTg clearly demonstrated very similar properties to those achieved on the positive control samples.…”

“…40 Lopez et al first showed that it was possible to produce protein resistant, ether carbon-rich films from glyme molecules using plasma polymerization. 41 The application of glyme, and a range of other plasma polymer inside glass and Teflon microfluidic devices, have been demonstrated to produce coatings with a range of specific surface charges, 42 spontaneous protein immobilization properties 43 and resistance to protein adsorption. 44 While a limited number of groups have access to dedicated plasma polymerization systems, it is possible that existing O 2 plasma units could be adapted for monomer handling or small chambers built from these systems at minimal cost.…”

“…44 The experimental setup has been explained in detail previously. 42 Briefly, the radio frequency power source (13.56 MHz, Coaxial Power Systems Ltd, UK) was coupled to the reactor via an impedance matching network. The substrates were placed in the reactor and the vessel was pumped down to a base pressure of 1 Â 10 À3 mbar.…”

Protein adsorption‐dependent electro‐kinetic pore flow: Modeling of ion‐exchange electrochromatography with an oscillatory transverse electric field

“…For the first case, Herr et al [27] have discovered that the velocity profile is a function of the average z potential in a capillary. More recently, Salim et al [28] studied EOF in micro-channels influenced by lysozyme adsorption. The results showed that the EOF decreased with increasing lysozyme adsorption.…”

Surface patterning of bonded microfluidic channels

“…Recently, plasma patterning of microfluidic channels has received significant attention. [28][29][30][31]46,71,72 In most cases, microchannel patterning was achieved prebonding using appropriate masks or directed jets; however, only a few examples of postbonding treatment have been reported. [28][29][30][31]72,73 Postbonding plasma modification of polystyrene microchannels has been demonstrated by Evju et al 28 Platinum electrodes were engineered in the microchannel to generate an electric field along the length of the channel, Fig.…”