title: A smartphone-readable barcode assay for the detection and quantitation of pesticide residues.
abstract: In this paper, we present a smartphone-readable barcode assay for the qualitative detection of methyl parathion residues, a toxic organophosphorus pesticide that is popularly used in agriculture worldwide. The detection principle is based on the irreversible inhibition of the enzymatic activity of acetylcholinesterase (AchE) by methyl parathion; AchE catalytically hydrolyzes acetylthiocholine iodine to thiocholine that in turn dissociates dithiobis-nitrobenzoate to produce a yellow product (deprotonated thio-nitrobenzoate). The yellow intensity of the product was confirmed to be inversely dependent on the concentration of the pesticide. We have designed a barcode-formatted assay chip by using a PDMS (polydimethylsiloxane) channel plate (as the reaction reservoir), situated under a printed partial barcode, to complete the whole barcode such that it can be directly read by a barcode scanning app installed on a smartphone. The app is able to qualitatively present the result of the pesticide test; the absence or a low concentration of methyl parathion results in the barcode reading as "-", identifying the test as negative for pesticides. Upon obtaining a positive result (the app reads a "+" character), the captured image can be further analyzed to quantitate the methyl parathion concentration in the sample. Besides the portability and simplicity, this mobile-app based colorimetric barcode assay compares favorably with the standard spectrophotometric method.
authors.affiliation: Key Laboratory of Advanced Transducers and Intelligent Control Systems (Ministry of Education and Shanxi Province), College of Physics and Optoelectronic Engineering, Taiyuan University of Technology, Shanxi 030024, P.R. China. hogan_yu@sfu.ca lixiaochun@tyut.edu.cn.
authors.forename: Juan
authors.initials: J
authors.lastname: Guo
authors.forename: Jessica X H
authors.initials: JX
authors.lastname: Wong
authors.forename: Caie
authors.initials: C
authors.lastname: Cui
authors.forename: Xiaochun
authors.initials: X
authors.lastname: Li
authors.forename: Hua-Zhong
authors.initials: HZ
authors.lastname: Yu
mesh_terms: D000110:Acetylcholinesterase / Q000737:chemistry / Q000378:metabolism; D015374:Biosensing Techniques / Q000379:methods*; D003124:Colorimetry / Q000379:methods*; D004800:Enzymes, Immobilized / Q000737:chemistry / Q000378:metabolism; D027845:Malus / Q000737:chemistry*; D008743:Methyl Parathion / Q000032:analysis*; D010573:Pesticide Residues / Q000032:analysis*; D000068997:Smartphone / Q000706:statistics & numerical data*; D013053:Spectrophotometry / Q000379:methods
chemical_list: D004800:Enzymes, Immobilized; D010573:Pesticide Residues; D008743:Methyl Parathion; D000110:Acetylcholinesterase