Plant Volatile Sensor: Enzymatic Transducer for Selective and Sensitive Determination of Methyl Salicyalte (2014)

Pathogen or herbivorous pest infested plants release organic volatile compounds. In the case of Aphis glycines (soybean aphid) invasion of Glycine max (soybean plant) results in stunted growth of the plant and methyl salicylate is released by Glycine max . In another example Nicotiana tabacum (tobacco) plants emit a high level of methyl salicylate when infested with tobacco mosaic virus. Early detection of plant disease infections is critical to minimize agricultural losses and increase crop productivity. Compared to robust instrument and detailed sampling procedures, amperometric electrochemical sensor is widely accepted due to the high accuracy, selectivity, rapid detection and field application. In this work, electrochemical sensing of methyl salicylate has been achieved using gold nanoparticle (AuNP) modified screen printed carbon electrode (SPCE). The reaction mechanism includes hydrolysis of methyl salicylate and the oxidation of negative species. The electrochemical responses were recorded using cyclic voltammetry and differential pulse voltammetry techniques, where the results showed characteristic signals for methyl salicylate oxidation. Among the examined electrodes, AuNP-SPCE possess three fold better sensitivity than planar gold and 35 times better than SPCE (at 0.5 V). The methyl salicylate sensing by AuNP-SPCE possessed <5% variation coefficient for repeatability, one week of stable performance with no more than 15% activity loss even if used multiple times (n=8). Even in the presence of high concentration of interfering compounds such as cis -3-hexenol, hexyl acetate and cis -hexenyl acetate, AuNP-SPCE retained >95% of its methyl salicylate response. The electroanalytical results of soybean extract show that AuNP-SPCE can be employed for the determination of methyl salicylate in real samples. To improve the sensitivity, selectivity and to decrease the limit of detection an enzyme based system has been developed for methyl salicylate determination. The methyl salicylate determination involves conversion of methyl salicylate in to methanol and salicylic acid and then the oxidation of methanol. Fig. 1: CVs of AuNP-SPCE in presence and absence of 1.7x10 -3 M methyl salicylate. The inset shows the current density measured at 0.5 V vs. methyl salicylate concentration, showing linear current density response for AuNP-SPCE electrode. Acknowledgements: We acknowledge the National Science Foundation (Award #CBET-1159540) and the American Chemical Society Herman Frasch Foundation for financial support. References: 1. Zhu, J.; Park, K. -C. (2005) Methyl salicylate, a soybean aphid-induced plant volatile attractive to the predator. J. Chem. Ecol. , 31, 1733-1746. 2. Mallinger, R. E.; Hogg, D. B.; Gratton, C. (2011) Methyl salicylate attracts natural enemies and reduces populations of soybean aphids (Hemiptera: Aphididae) in soybean agroecosystems. J. Econ. Entomol. , 104, 115-124. 3. Seskar, M.; Shulaev, V.; Raskin, I. (1998) Endogenous methyl salicylate in pathogen-inoculated tobacco plants. Plant Physiol. , 116, 387-392. 4. Umasankar, Y; Ramasamy, R. P. (2013) Highly sensitive electrochemical detection of methyl salicylate using electroactive gold nanoparticles. Analyst, 138, 6623-6631.