Elsevier

Analytical Biochemistry

Volume 341, Issue 2, 15 June 2005, Pages 344-351
Analytical Biochemistry

Noninvasive and continuous recordings of auxin fluxes in intact root apex with a carbon nanotube-modified and self-referencing microelectrode

https://doi.org/10.1016/j.ab.2005.03.054Get rights and content

Abstract

Auxin (also known as indole-3-acetic acid, IAA) represents an ancient signaling molecule of plants that also exerts bioactive actions on yeast and animal cells. Importantly, IAA emerges as a new anticancer agent due to the ability of oxidatively activated IAA to selectively kill tumor cells. IAA acts as a pheromone-like molecule in brown algae, whereas the hormone concept of IAA dominates current plant biology. However, recent advances also favor the morphogen- and transmitter-like nature of IAA in plants, making this small molecule one of the most unique molecules in the eukaryotic superkingdom. Here, we introduce new technology for the continuous measuring of IAA fluxes in living cells, tissues, and whole organs that is based on a carbon nanotube-modified and self-referencing microelectrode specific for IAA. This technique not only will advance our knowledge of how IAA regulates plant development but will also be applicable in medicine for its potential use in cancer therapy.

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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