Volatile organic compounds released by pathogen-infected and pest-infested plants can be used as fingerprints for plant disease and infestation detection via electronic nose technologies ^1,2. p-ethylphenol (EP) and methyl salicylate (MeSA) were discovered as two most important volatile organic compounds. In this work, enzymatic based electrochemical biosensors were developed for the detection of EP and MeSA. For EP detection, a tyrosinase (TYR)-immobilized amperometric biosensor was developed. Cyclic voltammetry (CV) was used to study the electrochemical reaction. CV indicated that the sensitivity reached to 8.528 µA·cm^-2·µM while limit of detection (LOD) reached to 0.210 µM. Steady state constant potential amperometry displayed lower sensitivity (4.052 µA·cm^-2·µM), but better LOD (0.095 µM) than CV. For MeSA detection, alcohol oxidase and horseradish peroxidase were applied for detection of methanol that produced after hydrolysis of MeSA. CV and constant potential amperometry techniques were used to determine sensitivity of 0.112 and 0.283 µA·cm^-2·µM, and LOD of 23 and 1 µM for the CV and DPV respectively. In order to obtain better sensitivity and higher specificity for MeSA detection, salicylate hydroxylase (SH) and TYR were immobilized on the multiwalled carbon nanotube modified glassy-carbon electrode. After hydrolysis of MeSA, salicylate reacts with SH and TYR to generate amperometric signal. The sensitivity and LOD generated from CV were reported to be 21.29 µA·cm^-2·µM and 0.137 µM respectively. Constant potential amperometry was also applied for MeSA detection. The results display that sensitivity of 30.61 µA·cm^-2·µM and LOD of 0.013 µM can be achieved. Interference and simulated analyte based studies indicate that the biosensor is suitable for application in agricultural sensing.

Reference:

1. T. Baldwin, A. Kessler and R. Halitschke, Curr. Opin. Plant Biol., 2002, 5, 351.
2. P. W. Par´e and J. H. Tumlinson, Plant Physiol., 1999, 121, 325.