Indirect Electrochemical Sensing of the L-abrine Biomarker of Abrin Toxin Via Enzymatic Oxidation of N-methyl-L-tryptophan

Abstract

The biotoxin abrin, if inhaled or ingested, can be fatal to humans within several days. Because of the initial flu-like symptoms and the lack of analytical technologies for determining abrin poisoning, the high possibility of misdiagnosis makes this biochemical weapon particularly threatening. This urged us to develop a sensing device for real time monitoring of abrin poisoning. We introduce an enzyme-linked electrochemical sensor for the detection of the chemical marker of abrin poisoning, known as N-methyl-L-tryptophan (MT) or more commonly referred to as L-abrine. Indium tin oxide (ITO) was employed as the electrode substrate for immobilization of the enzyme methyl tryptophan oxidase (MTOX), which is selective for the MT substrate. The MTOX-immobilized ITO electrode obtained via the amino-glutaraldehyde cross-linking chemistry exhibited a sensitivity of 23.3 ± 1.28 µA per decade concentration of MT in a linear detection range from 98.1 pM to 1.17 µM (pH 7 in phosphate-buffered saline), and the detection limit was 22.7 pM. Each of the electrode modification steps were verified by electrochemical impedance spectroscopy, cyclic voltammetry, and Fourier transform-infrared spectroscopy. The approximate amount of MTOX immobilized on a 1 cm² ITO substrate was determined by cyclic voltammetry in a phosphate buffered saline solution at neutral conditions, revealing 3.3 ± 0.46 µC which is equivalent to 11.4 pmole of MTOX. With this MT detection strategy in hand, we look to further optimize our approach toward a rapid clinical diagnostic tool.