Multilayer poly(vinyl alcohol)-adsorbed coating on poly(dimethylsiloxane) microfluidic chips for biopolymer separation

Abstract

A poly(dimethylsiloxane) (PDMS) microfluidic chip surface was modified by multilayer-adsorbed and heat-immobilized poly(vinyl alcohol) (PVA) after oxygen plasma treatment. The reflection absorption infrared spectrum (RAIRS) showed that 88% hydrolyzed PVA adsorbed more strongly than 100% hydrolyzed one on the oxygen plasma-pretreated PDMS surface, and they all had little adsorption on original PDMS surface. Repeating the coating procedure three times was found to produce the most robust and effective coating. PVA coating converted the original PDMS surface from a hydrophobic one into a hydrophilic surface, and suppressed electroosmotic flow (EOF) in the range of pH 3-11. More than 1,000,000 plates/m and baseline resolution were obtained for separation of fluorescently labeled basic proteins (lysozyme, ribonuclease B). Fluorescently labeled acidic proteins (bovine serum albumin, beta-lactoglobulin) and fragments of dsDNA phiX174 RF/HaeIII were also separated satisfactorily in the three-layer 88% PVA-coated PDMS microchip. Good separation of basic proteins was obtained for about 70 consecutive runs.

Hydrophilic surface modification of PDMS for droplet microfluidics using a simple, quick, and robust method via PVA deposition

“…This treatment generates radical species of surface silanol groups (Si-OH), alcoholic hydroxyls (C-OH), and carboxylic acids (COOH) 27,38,39 on the PDMS surface and these species can form covalent bonds with the PVA molecules. A series of contact angle measurements were taken to study the effect of PVA deposition on PDMS surface properties (Figure 1).…”

“…We evaluated the level of the surface hydrophilicity induced by two commercially available PVA solutions commonly used in PDMS surface modification [27][28][29][32][33][34] . We applied PVA solutions with 87-90% and 99+% hydrolysis degrees on PDMS surfaces that were plasma oxidized under the same conditions (50 W for 1 min) and concluded that the former had a more profound effect on the PDMS surface chemistry both in the short and the long term (Figure 1a).…”

“…Another strategy to achieve surface modification is to coat substrates with polyvinyl alcohol (PVA; a hydrophilic polymer). This strategy has primarily been used for non-PDMS surfaces, such as silica capillaries for biopolymer separation and DNA sizing applications [26][27][28] . PVA can also be irreversibly adsorbed onto hydrophobic polymer films 29 and gold substrates 30 .…”

“…PVA can also be irreversibly adsorbed onto hydrophobic polymer films 29 and gold substrates 30 . Others have demonstrated PVA adsorption onto PDMS via heat immobilization following plasma treatment 27 , via plasma oxidation and covalent attachment of an (3-aminopropyl) triethoxysilane (APTES) linker 31 , and via the synthesis of a PVA/PDMS copolymer microsuspension 32 . These procedures were developed to control the degree of biomolecule interaction with the PDMS substrate and not to modify the hydrophobicity of the surface with regards to droplet microfluidics.…”

Selective modification for polydimethylsiloxane chip by micro-plasma

“…However, the extremely hydrophobic property of PDMS surface limits the extent of its applications. As a result, many different methods for hydrophilization have been proposed to modify the surface of PDMS, such as rendering it hydrophilic by activating PDMS surface using oxygen plasma [9] and absorbed hydrophilic organic molecules coatings [8,12], nonetheless at the expense of its long-term stability [3]. Another conventional way of surface modification in polymer science is surface-attached polymerization, which provides chemically stable surfaces due to the covalent bonding of the polymer chains to the substrate [4][5][6]9].…”