Polyethylene Glycol Deposition Techniques for Antifouling Surfaces: Using Antistiction to Conserve Bioparticles for Reco
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0954-H03-03
Polyethylene Glycol Deposition Techniques for Antifouling Surfaces: Using Antistiction to Conserve Bioparticles for Recovery and Analysis Norine E. Chang, Meng H. Lean, and Scott J. Limb Hardware Systems Laboratory, Palo Alto Research Center, 3333 Coyote Hill Rd., Palo Alto, CA, 94304 ABSTRACT For bioparticle analysis within microfluidic devices, there is a risk of analytes adhering to surfaces, thereby compromising particle manipulation and recovery. To address this we have implemented polyethylene glycol (PEG)-type coatings by self-assembled monolayer (SAM) and plasma-polymerizing deposition techniques. Silane chemistry is used to deposit SAM films directly onto silicon dioxide surfaces, and in a special case for which a composite of metallic arrays and SiON within our MEMS device must be coated, an ultrathin layer of sputtered Si is added before the SAM protocol. We have also deposited PEG-like tetraglyme by plasmapolymerization onto substrates using an onsite-built reactor to provide antistiction treatment to all surfaces, including those that do not have chemical compatibility for the SAM technique. Three tests demonstrate the effectiveness of our surface treatments: static exposure to microbial suspensions, bioparticle transport across MEMS traveling-wave (TW) arrays, and bioparticle recovery from a circulating flow device. Our static microbial assays show significant reduction in B. thuringiensis adhesion to both the SAM and plasma-polymerized coatings and reduction in B. globigii adhesion to the plasma-polymerized coating. Our TW arrays, when coated with either the SAM or plasma-polymerized PEG film, are effective at reducing adhesion to polystyrene beads as well as both Bacillus species. Lastly, our bioparticle recovery, as gauged by spectrophotometry, improves by as much as one order of magnitude when we coat flow chambers with our plasma-polymerized film.
INTRODUCTION In microfluidic devices that process dilute particle concentrations, there is a need to address adhesion of analyte particles to the device surfaces that could present substantial losses affecting analysis. We have investigated two approaches for solving this problem: self-assembled monolayer (SAM) and plasma-polymerization of antistiction coatings. Applications of these techniques have been effective for bioparticulate-transporting TW devices under development at Palo Alto Research Center1, 2. In addition to antistiction properties, our choice of coating also requires compatibility with a microfluidic, electrochemical environment. It is necessary to determine the thermal, mechanical, and chemical conditions the coating can withstand while allowing the protected TW surface to electrically conduct through the coating layer for particle movement. Processing conditions affecting coating morphology, thickness, and coverage are important. Polyethylene glycol (PEG) has had an extensive history of antifouling applications3 where a nontoxic coating is preferred, and exists in a variety of commercially available functionalized forms. Ph
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