A lateral field excited acoustic wave pesticide sensor

Abstract

Excessive use of pesticides such as organophosphates (OPs) on fruits and vegetables can have adverse effects on the environment and jeopardize the health of the consumer. As a result a need exists for an accurate, low cost, portable sensor to detect harmful pesticide levels. In the present work a lateral field excited (LFE) sensor (1), which has a bare sensing surface that allows the measurement of mechanical and electrical property changes in a target analyte selective film, has been used to detect phosmet, a commonly used OP. The acoustic energy distribution of this LFE sensor has been found to exhibit a circular pattern with maximum sensitivity at the center of the sensor. The LFE pesticide sensor is shown to be more sensitive than the standard QCM. Also, it is shown that the response time of the sensor can be drastically shortened by using the derivative of the frequency response. I. INTRODUCTION Organophosphates (OPs) are widely used in agriculture for pest control in fruits and vegetables, with about 25,000 brands of pesticides sold in the United States (2). Categorized as neurotoxins or cholinesterase inhibitors, they can affect neuromuscular transmission (2). This is especially critical for young children who consume large amounts of fruits and vegetables and have a lower tolerance than adults (3). In order to guard against the adverse effects of OPs, the Environmental Protection Agency (EPA) has determined the allowable concentration of pesticides. Depending on the crop and pesticide used, tolerances are normally restricted to the 0.1 - 100 ppm range (4). Since many countries do not have such regulations, a need exists to detect pesticides on imported fruits and vegetables. Currently, the two standard methods of testing for the presence of pesticides are gas chromatography/mass spectroscopy (GC/MS) and immunoassay. GC/MS is the testing procedure approved by the EPA. Although very precise and accurate, these tests are expensive to run, time consuming and have to be performed in a laboratory environment. Also significant training is required to operate the GC/MS machine. Recently, immunoassay tests have been introduced as a cheaper, quicker, and portable alternative to GC/MS. This test method is however not reusable and is qualitative in that it indicates only whether the measurand is above or below a particular level. Also, cross reactivity and reaction to broken down pesticides in these tests may lead to false positive tests (5). Therefore a need exists for a sensor that would combine the quantative and reusable properties of the GC/MS with the low cost, quick, and portable properties of the immunoassay tests.