Catechol

Dopamine and 2-aminophenol were purchased from Alfa Aesar (Ward Hill, MA, USA). Sodium phosphate monobasic was received from Fisher Scientific (Waltham, MA, USA) and catechol was obtained from Acros (Geel, Belgium). All chemicals were used as received. The background electrolyte (10 mM phosphate buffer) was prepared weekly by dissolving the desired amount of solid NaH₂PO₄. The pH of the solutions was adjusted, when necessary, using either 1 mol·L⁻¹ NaOH or 1 mol·L⁻¹ HCl (Fisher Scientific) and measured using a glass electrode and a digital pHmeter (Orion 420A+, Thermo; Waltham, MA). Stock solutions of Dopamine, 2-aminophenol and catechol (10 mM each) were prepared by dissolving the desired amount of each compound in ultrapure water (≥ 18 MΩ·cm, NANOpure Diamond, Barnstead; Dubuque, Iowa). Working solutions were prepared by diluting the stock solutions in 10 mM phosphate buffer. Standard-grade PMMA plates (150 × 70 × 1.5 mm) were purchased from Gravograph (Duluth, GA, USA) and used to produce the microdevices herein described. Sylgard 184 silicone elastomer and curing agent were obtained from Dow Corning. Sugar, used for the formation of the PDMS sponge (decoupler), was food-grade and acquired in a local grocery store.