Magnetron sputtered diamond-like carbon microelectrodes for on-chip measurement of quantal catecholamine release from cells

Abstract

Carbon electrodes are widely used in electrochemistry due to their low cost, wide potential window, and low and stable background noise. Carbon-fiber electrodes (CFE) are commonly used to electrochemically measure "quantal" catecholamine release via exocytosis from individual cells, but it is difficult to integrate CFEs into lab-on-a-chip devices. Here we report the development of nitrogen doped diamond-like carbon (DLC:N) microelectrodes on a chip to monitor quantal release of catecholamines from cells. Advantages of DLC:N microelectrodes are that they are batch producible at low cost, and are harder and more durable than graphite films. The DLC:N microelectrodes were prepared by a magnetron sputtering process with nitrogen doping. The 30 μm by 40 μm DLC:N microelectrodes were patterned onto microscope glass slides by photolithography and lift-off technology. The properties of the DLC:N microelectrodes were characterized by AFM, Raman spectroscopy and cyclic voltammetry. Quantal catecholamine release was recorded amperometrically from bovine adrenal chromaffin cells on the DLC:N microelectrodes. Amperometric spikes due to quantal release of catecholamines were similar in amplitude and area as those recorded using CFEs and the background current and noise levels of microchip DLC:N electrodes were also comparable to CFEs. Therefore, DLC:N microelectrodes are suitable for microchip-based high-throughput measurement of quantal exocytosis with applications in basic research, drug discovery and cell-based biosensors.

Transparent Electrode Materials for Simultaneous Amperometric Detection of Exocytosis and Fluorescence Microscopy

“…A finished single DLC microwell/electrode is shown in Figure 1H. Mean DLC electrode roughness is 1.4 nm[11]. For comparison of DLC to ITO electrode responses, ITO electrodes were fabricated as above for the DLC devices in the configuration shown in Figure 1G, omitting the DLC deposition and etching steps.…”

“…Recently, planar transparent electrodes fabricated from either indium tin oxide (ITO)[9, 10], a transparent conductive material commonly used in flat screen displays, diamond-like carbon (DLC)[11], or thin transparent gold (Au) films[12] have been applied to record catecholamine release from chromaffin cells. ITO electrodes are capable of simultaneous amperometry and fluorescence imaging through the electrodes[10] and allow total internal reflection fluorescence (TIRF) excitation[13].…”

Fast deposition of diamond-like carbon films by radio frequency hollow cathode method

“…There are many ways to prepare DLC films [12][13][14][15]. The radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) process is widely used.…”

Automated Targeting of Cells to Electrochemical Electrodes Using a Surface Chemistry Approach for the Measurement of Quantal Exocytosis

“…We previously have shown that nitrogen-doped diamond-like carbon (DLC:N) is well suited as an electrochemical electrode material for amperometric measurement of quantal exocytosis(9) and also promotes adhesion of neuroendocrine cells(21) (also see (22)). In contrast, Teflon AF inhibits cell attachment(21) and is also an excellent electrical insulator.…”