Vertical pipette puller

Voltammetric analysis of serotonin was performed as described previously (Hashemi et al., 2009 (link); Wood and Hashemi, 2013 (link); Wood et al., 2014 (link)). Briefly, CFMs were constructed by aspirating 7 μm carbon fibers (Goodfellow Corporation, Coraopolis, PA, United States) into glass capillaries (0.4 mm internal diameter, 0.6 mm outer diameter, AM Systems, Carlsborg, WA, United States). A vertical pipette puller (Narishige Group, Tokyo, Japan) was employed to create a carbon-glass seal. Subsequently, the exposed carbon fiber was cut to 150 μm and silver paint was used to forge an electrical connection to a connection pin. Finally, electrodes were electrodeposited with Nafion^TM as described previously (Hashemi et al., 2009 (link)).

Carbon fiber microelectrodes (CFMs) were made as previously described [25 (link)]. Briefly, a single carbon fiber (7 μm, Goodfellow, Corporation, Coraopolis, PA, USA) was aspirated into a glass capillary (0.6 mm OD, 0.4 mm ID, 10 cm length; A-M Systems, Sequim, WA, USA) and sealed under gravity and heat by vertical pipette puller (Narishige Group, Tokyo, JAP). Exposed fibers were trimmed to 150 µm under light microscope and silver paint was used to forge an electrical connection to a connection pin. Finally, electrodes were electrodeposited with Nafion™ (LQ-1105, Ion Power Solutions, New Castle DE, USA) as previously described [25 (link)].

All electrodes were made in house. A single carbon fiber was aspirated into a borosilicate capillary (0.6 mm × 0.4 mm × 10 cm; OD × ID × L) (A-M Systems, Sequim, WA, USA) and sealed under gravity and heat by a vertical pipette puller (Narishige, Amityville, NY, USA) to create two separate electrodes. The protruding fiber was trimmed under a light microscope to ~150 µm. An electrical connection was forged with the fiber through a stainless-steel connecting wire (Kauffman Engineering, Cornelius, OR, USA) and silver epoxy. Finally, a thin layer of Nafion (LQ-1105-MeOH), Ion Power, New Castle, DE, USA) was electrodeposited onto the fiber surface at 1 V for 30 s; the coated fiber was dried for 10 min at 70 °C [77 (link)].

carbon fiber microelectrodes were fabricated by aspirating a carbon fiber (Goodfellow Corporation, Coraopolis, PA, United States) into a glass capillary (0.4 mm internal diameter, 0.6 mm outer diameter, AM Systems, Carlsborg, WA, United States). Electrodes were pulled to a fine tip using a vertical pipette puller (Narishige Group, Tokyo, Japan), creating a carbon-glass seal. The exposed carbon fiber was then cut to 150 µm and Nafion (L-Q-1105, Ion Power, New Castle, DE, USA) was electroplated onto the electrode surface by applying a constant potential (~ 1 V) for 30 s.

This process has been previously described in detail (40 (link)), but, briefly, a T-650 carbon fiber (7 μm in diameter) was aspirated through a borosilicate glass capillary (Science Products GmbH, Hofheim, Germany). A carbon glass seal was made by melting and pulling the glass capillary with a vertical pipette puller (Narishige, Japan). The exposed fiber was cut to 150 μm under an optical microscope, and an electrical connection was forged from the open end of the capillary with a pinned stainless steel wire coated in silver paint. To maximize sensitivity to serotonin, the carbon surface was modified by (i) electropolymerizing a thin layer of NafionTM by applying 1 V for 30 s in a solution of NafionTM (Liquion-1105, Ion Power, New Castle, DE, USA) and then drying at 70°C for 10 min (40 (link)) and (ii) electropolymerizing polyglutamic acid by applying a waveform (−1.2 to 1.3 to −1.2 V at 400 V/s) at 60 Hz for 10 min in a solution of 1 μM glutamic acid in 1× tris buffer (pH 7.4) (41 (link)).