Noninvasive and continuous recordings of auxin fluxes in intact root apex with a carbon nanotube-modified and self-referencing microelectrode
Section snippets
Preparation of the platinum microsensor and of the CNT-modified electrode
The procedure for the fabrication of the platinum microsensor has been reported previously [24]. A platinum wire, 10 mm long and 0.2 mm in diameter, was soldered to a silver connecting wire of the same diameter. This assembly was then mounted in a glass capillary (2 mm o.d., 1.12 mm i.d., World Precision Instruments, Sarasota, FL, USA) such that approximately 3 mm of the platinum wire protruded from the capillary tip. The microwire was secured in position by melting the glass tip of the capillary
Electrochemical behavior of microelectrodes
The microelectrodes fabricated were initially tested in distilled water. Fig. 1 shows a polarogram graph obtained by a comparison of the current with the voltage. When the IAA microelectrode was polarized in a concentration of 5 μM IAA in pure water and with a voltage sweep from 0 to 1 V, it showed an oxidation peak in the range of 0.65–0.75 V with an output of approximately 40 pA (depending on the tip radius). During subsequent experiments, the microelectrode was polarized at a voltage of 700 mV,
Discussion
In the current work, we have provided results that demonstrate the effectiveness of an IAA-selective self-referencing microelectrode as a research tool to study IAA transport in biological systems. The CNT-modified electrode described in this article is inexpensive, is easy to prepare, and demonstrates high sensitivity in detecting IAA. Despite the fact that the technique did not show higher sensitivity than HPLC, the use of an IAA-selective microelectrode will allow one to monitor continuously
Acknowledgments
Financial support to AGRAVIS by the Deutsche Agentur für Raumfahrtangelegenheiten (DARA, Bonn, Germany) and the Ministerium für Wissenschaft und Forschung (MWF, Düsseldorf, Germany) is gratefully acknowledged. František Baluška receives partial support from the Slovak Academy of Sciences (grant agency VEGA, grant 2031, Bratislava, Slovakia).
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