Sodium phosphate dibasic

A commercial silver plating solution (1025 RTU @ Troy/gallon, Technic Inc.) was used for all electro-depositions. Riboflavin (≥98%) and sodium hydroxide (NaOH) (99.99%) were purchased from Sigma-Aldrich. Ultrapure water (18.2 MΩ cm) was obtained from a Barnstead Nanopure filtration system. Buffers were made using sodium phosphate monobasic dihydrate (>99.9%, Sigma-Aldrich) and sodium phosphate dibasic (Electron Microscopy Sciences). The pH was adjusted by adding NaOH or H₂SO₄ while monitoring with an Accumet Basic AB15+ pH Meter. Polydimethyslsiloxane (PDMS) devices were made using Sylgard 184 elastomer base (Ellsworth Adhesives, Germantown, WI, USA) from masters fabricated with SU-8 50 photoresist and Nano SU-8 developer (Microchem, Newton, MA, USA). All other chemicals were analytical grade and used without any further purification. Polystyrene bases were made with polystyrene powder (250 μm particle size, Goodfellow, Huntingdon, England) and a gold array made from 3 mm 200 mesh regular grid (SPI supplies, West Chester, PA, USA).

Dopamine hydrochloride, norepinephrine (≥98%), catechol (≥99%), epinephrine, serotonin, sodium phosphate monobasic dihydrate (>99%), and sodium hydroxide (NaOH, 99.99%) were purchased from Sigma-Aldrich. Sodium phosphate dibasic was purchased from Electron Microscopy Sciences. Phosphate buffer was made using sodium phosphate monobasic dihydrate and Sodium phosphate dibasic. The pH was adjusted by adding NaOH while monitoring with an Accumet Basic AB15+ pH Meter. Ultrapure water (18.2 MΩ cm) was obtained from a Barnstead Nanopure filtration system. Polydimethyslsiloxane (PDMS) devices were made using Sylgard 184 elastomer base (Ellsworth Adhesives, Germantown, WI, USA) from masters fabricated with SU-8 50 photoresist and Nano SU-8 developer (Microchem, Newton, MA, USA). Polystyrene bases were made with polystyrene powder (250 μm particle size, Goodfellow, Huntingdon, England), fused silica capillary (360 μm o.d., 150 μm i.d., Molex), and a gold wire electrode (25 μm diameter, Alfa Aesar, Ward Hill, MA, USA). The electrode was connected to a copper wire with colloidal silver (Ted Pella, Redding, CA, USA). A commercial gold plating solution (OROTEMP® 24 RTU RACK, Technic Inc.) was used for all electrodeposition. All other chemicals were analytical grade and used without any further purification.