Paper-based analytical devices for direct electrochemical detection of free IAA and SA in plant samples with the weight of several milligrams

It is not easy to directly obtain concentrations of auxin (mainly indole-3-acetic acid, or IAA) and other phytohormones in different locations of individual plants although such information is critical for the study of their functions. Here we developed a paper-based analytical device consisting of a disposable working electrode to provide a platform for direct and simultaneous detection of free IAA and salicylic acid (SA) in different parts of pea seedlings with the weights of several milligrams. The double sided conductive carbon tape modified with carbon nanotube was used as the disposable working electrodes after they were treated with oxygen plasma. Different parts of pea seedlings were applied on the surface of working electrodes for direct electrochemical detection of free IAA and SA in paper-based analytical devices. The requirement of solution volumes with only 10 microliters made it possible to quantify free IAA and SA at the level of ng. Our results suggested that large amounts of inherent IAA and SA could be lost because of complicated and time-consuming preparation of samples in traditional gas/liquid chromatography-mass spectrometry methods Our approach not only avoids such steps but also provides concentrations of IAA and SA in different zones of individual pea seedlings. The obtained results could be applied for the study of individual differences and interactions between IAA and SA in development of peas. This strategy not only paved the foundation for further investigation of regulating mechanisms of free IAA and its interaction with other phytohormones but also might provide an alternative approach for detection of free electroactive biomolecules in other living organs.