Effects of recording media composition on the responses of Nafion-coated carbon fiber microelectrodes measured using high-speed chronoamperometry

The present study concerns methodological issues of electrochemical recordings using Nafion-coated 30 μm diameter single carbon fiber microelectrodes for high-speed chronoamperometric measurements of biogenic amines. First, the single carbon fiber microelectrodes were coated with Nafion and dried at 85 vs. 200 °C and their recording properties were determined. Second, the effects of shifts in solution pH, ionic strength, changes in recording solution levels of Ca²⁺ or Mg²⁺ and temperature on the recording characteristics and sensitivity of Nafion-coated high temperature dried (200 °C) single carbon fiber microelectrodes for measures of dopamine were studied. These studies showed that the high temperature drying of the Nafion produced a microelectrode with better recording properties: higher selectivity for cations versus anions, increased differences between the reduction and oxidation current ratios for the identification of dopamine versus serotonin, and more rapid response times. In addition, these studies demonstrated that the chronoamperometric recordings were insensitive to small changes in pH and divalent cations such as Ca²⁺ or Mg²⁺. However, increases in ionic strength decreased the sensitivity of the microelectrodes, while increases in temperature produced increases in the sensitivity of the microelectrodes for biogenic amines. These data support that Nafion-coated high temperature (200 °C) dried microelectrodes have enhanced recording properties as compared to microelectrodes, which are coated with Nafion and dried at 85 °C. In addition, high-speed chronoamperometric recordings of biogenic amines are not affected by solution changes in divalent cations (Ca²⁺ or Mg²⁺).