Preparation passivation oxide coatings

Silicon (100) wafers, passivated with silica, were employed as substrates. Prior to immobilization of PLL- -PEG onto the oxide surface, the wafers (0.5 cm 0.5 cm) were prepared by sonication in toluene (2 min) and in 2-propanol (10 min), extensively rinsed with ultrapure water (EM SCIENCE, Gibb-stown, NJ), dried under a gaseous nitrogen flow, and exposed for 2 min to an oxygen plasma (PDC-32G. Harrick Scientific Corp., Ossining, NY). The oxidized substrates were immediately transferred to a 1.0 mg/mL solution of PLL- -PEG in a 10 mM HEPES buffer and incubated there for 40 min. The polymer-coated substrates were then stored in a HEPES solution (in the absence of PLL- -PEG) until use in AFM experiments. Prior to AFM measurements, the polymer-coated substrates were withdrawn from solution, rinsed with a HEPES buffer and ultrapure water to remove free PLL- -PEG, and then dried under a nitrogen flow. 

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