On-Line Monitoring1H-Indole-3-Acetic Acid in Plant Tissues Using Molecular Imprinting Monolayer Techniques on a Surface Plasmon Resonance Sensor

A surface plasmon resonance (SPR)-based detection methodology, which allows the identification and quantification of the plant hormone, 1H-indole-3-acetic acid (IAA) in Peach, Rosa flower, and Crape myrtle bud is described. To achieve high selectivity, a molecularly imprinted monolayer (MIM) was prepared from alkanethiols self-assembled on an SPR sensor chip with preadsorbed template (IAA). The association constant of the MIM to IAA was calculated to be 2.8 × 1011 M−1 by analysis of the SPR wavenumber changes induced by different concentrations of IAA. A good calibration curve was obtained in a low concentration range of IAA. Moreover, the MIM revealed impressive selectivity with the selectivity factors of 1.0, 0.12, and 0.20 for IAA and other related analogues. Compared to the MIM sensor chip, the affinity of the self-assembled monolayer (SAM) control sensor chip for IAA was significantly low. The single SPR sensor decorated with the MIM was used to determine IAA concentrations in peach, Rosa flower, and Crape myrtle bud, and satisfactory results were obtained. Based on a signal to noise ratio of 3, the detection limits were 0.23 pM for Crape myrtle, 0.20 pM for Peach, and 0.32 pM for Rosa. The method showed good recoveries and precision, 95.7% (RSD 0.54%) for Peach, 98.1% (RSD 3.4%) for Rosa, and 98.1% (RSD 2.5%) for Crape myrtle, spiked with 0.4171 µg, respectively. These results indicate that a combination of SPR sensing and the MIM provides a simple, promising alternative method for determining endogenous IAA in plant tissue in a real-time manner.