Carbon electrode fabrication from pyrolyzed parylene C

Abstract

Carbon electrodes coupled with electrochemical detection have been used extensively for the investigation of biogenic amines. Herein we report the fabrication and characterization of carbonaceous electrodes prepared from pyrolyzed parylene C (PPC) films. High-aspect ratio carbonaceous microelectrodes have been prepared by masking PPC coated pipets with an insulating parylene C film. PPC thin film electrodes were characterized electrochemically, spectroscopically, and with electron microscopy. The procedures described here offer a route to fabrication of thin film carbon electrodes that can be patterned and produced in parallel. These electrodes are similar to carbon electrodes derived from pyrolyzed photoresist films but do not require spin-coating or lithography and can readily coat three-dimensional surfaces.

Figure 1

(a) Parylene reaction scheme. (b) A schematic of the microelectrode fabrication process from a bare pipette to a final pyrolyzed microelectrode. A bare quartz pipette (far left) is coated with a thin layer of parylene C and subsequently pyrolyzed under an inert atmosphere. The pipette is then masked and insulated with another layer of parylene C to form a carbon electrode (far right). (c) Optical micrographs of pipettes at different stages of this process. From left to right: a bare pipette, a pipette after initial parylene C deposition, after pyrolysis of parylene C and a final parylene-insulated carbonaceous pipette.

Figure 2

(a) Thermogravimetric analysis of parylene c in a nitrogen atmosphere. (b) UV-visible absorbance of 1.0 g of parylene c (-■-) and pyrolyzed parylene c () deposited on a quartz substrate. (c) Averaged Raman spectra (n = 10) of amorphous pyrolyzed parylene. Characteristic G and D modes are visible at 1308 cm⁻¹ and 1583 cm⁻¹ respectively in (d). λ_exc = 785 nm, 10 mW power average.

Figure 3

(a) Transmission electron micrograph of pyrolyzed parylene C thin film. (b) FFT of electron micrograph showing diffraction and film order. (c) Scanning electron micrograph of pyrolyzed parylene C electrode as prepared.

Figure 4

Voltammetric response in 5 mM Ru(NH₃)₆³⁺, with 0.1 M KCl as a supporting electrolyte, of 200 nm (a) and 1000 nm (b) thick films of pyrolyzed parylene C on a silicon surface (A = 0.25 cm²), at varying scan rates. Ag/AgCl reference and Pt counter electrodes were utilized for all cyclic voltammetry measurements. (c) Plot of uncorrected peak current as a function of scan rate for 200 nm and 1000 nm pyrolyzed parylene C films.

Figure 5

(a) Cyclic voltammetry of the electrode shown in Figure 3c in 5 mM Ru(NH₃)₆Cl₃ with 0.1 M KCl as a supporting electrolyte. Voltammetric response for slow and fast scan rates of a pyrolyzed parylene C electrode to (b) 5 mM Ru(NH₃)₆Cl₃ in 0.1 M KCl supporting electrolyte and to (c) 100 μM dopamine in 0.1 M phosphate buffered saline buffer (pH = 7.4). Ag/AgCl reference and Pt counter electrodes were utilized for all cyclic voltammetry measurements.