Detection of organophosphate pesticides using a prototype liquid crystal monitor

Abstract

The precision and accuracy of a prototype wearable liquid crystal monitor (LCM) for the measurement of airborne organophosphate pesticide concentrations was explored in a series of laboratory experiments. LCM response to vapor-phase and aerosol diazinon was compared to concentrations obtained using a standard reference method (NIOSH 5600) at concentrations ranging from approximately 8 to 108 ppb (parts per billion) over durations of 2 to 80 hours. Temperature ( approximately 25, 30, and 35 degrees C) and relative humidity (15, 50, and 85%) were varied to estimate the effect of these factors on LCM performance. The LCM response to vapor phase pesticide exposure was linear for concentrations in the range of 8-20 ppb. At exposure concentrations above approximately 20 ppb, however, there was a decline in monitor response and measurement precision. Elevated temperatures improved diazinon vapor-only measurement precision, while increased relative humidity reduced LCM response at the extremes of tested temperatures. Compared to vapor-only exposures, the LCM was less sensitive to diazinon aerosol concentrations, but displayed reasonable precision over a relatively large range of exposures (29 to 1190 ppb-hr). Further efforts to characterize temperature and humidity effects and improve low-end sensitivity would likely provide a portable personal exposure monitor or environmental sensor for this widely used class of pesticides.

Seeing the Unseen: The Role of Liquid Crystals in Gas‐Sensing Technologies

“…Since then, especially over the last 10 years, an on‐going effort is being conducted by many research groups to understand and explore the potential applicability of different LC‐based systems (nematic, smectic, chiral, columnar phases) in the gas sensing field. [ 16,18,20,102,103 ]…”

“…Surface functionalization studies have extended to perchlorate salts of metal ions [ 125,126 ] such as, gallium, [ 102 ] lead, [ 127 ] or manganese. [ 128 ] Hunter and Abbott [ 129 ] have also explored the possibility of tuning the anion in perchlorate‐salt decorated surfaces in order to manipulate the LC anchoring to the binding surface, and hence increase the selectivity and sensitivity of surface‐induced LC transitions triggered by gas analytes.…”

Tunable Gas Sensing Gels by Cooperative Assembly

“…In the examples reported thus far, LCs are typically used as planar films deposited onto chemically treated glass surfaces. The surface-aligned LCs are then perturbed due to the interaction of VOCs with chemical groups on the anchoring surfaces,[24,25] on the LC films,[26] or with chemical dopants,[27] giving rise to changes in the optical pattern of the LCs visible under polarizing optical microscopy (POM). The encapsulation of LCs into droplets increases the available surface area, avoids extensive surface treatments to define the initial LC orientation, and takes advantage of self-assembled and phase-segregated LC structures.…”

Optical UV Dosimeters Based on Photoracemization of (R)‐(+)‐1,1′‐Bi(2‐Napthol) (BINOL) within a Chiral Nematic Liquid Crystalline Matrix

“…These sensors can broadly be divided into two groups: those based on changes to the interface between the liquid crystal (LC) and another substance, such as an alignment layer, and those that directly alter a property of the bulk LC. The former includes sensors for light, [10] gasses, [11,12] volatile organic compounds, [13] and larger biomolecules such as DNA, [14] and are described extensively in a review by Carlton et al [15] These sensors operate based on a change at an interface between the LC and another substance, which is amplified by the liquid crystal, resulting in a change in the alignment of the LC, which is monitored by viewing the sensor through crossed polarizers.…”