Sensing aromatic pollutants in water with catalyst-sensitized water-gated transistor

Abstract

Some materials that are active heterogeneous catalysts for the breakdown of non-ionic aromatic solutes in water are found to act as potentiometric sensitizers for same solutes.As an example, here the aromatic water pollutant, benzyl alcohol, was sensed with a limitof-detection (LoD) below its potability limit of 19 M. Our findings are rationalized on the grounds that both catalysis and sensing rely on adhesion of analyte/substrate on the sensitizer / catalyst. Specifically, a set of powdered transition metal doped zeolites and related frameworks that catalyze the oxidation of waterborne aromatic pollutants were dispersed in phase transfer matrices. Matrices were introduced into water-gated thin film transistors (WGTFTs) that act as potentiometric transducers. Potentiometric sensing of non-ionic waterborne pollutants is limited to molecules with a 'free' molecular dipole, i.e. a dipole that is not locked in the molecular plane. The present work establishes an application for catalysts beyond catalysis itself. The use of catalysts as sensitizers is recommended for wider uptake and in reverse, to screen candidate catalysts.

Parallel Potentiometric and Capacitive Response in a Water-Gate Thin Film Transistor Biosensor at High Ionic Strength

“…In the absence of inhomogeneity, β = 1 retrieves the classic Langmuir surface adsorption isotherm. The Langmuir and LF models have been employed previously to describe the potentiometric response of some WGTFT sensors based on either the adsorption of small organic molecules on a sensitiser surface [ 8 ], or ion-exchanging sensitisers [ 12 , 13 , 17 ]. The LF model is mathematically equivalent to the equation introduced by Hill in 1910 [ 28 ], which has ever since been routinely used for the quantitative description of biochemical interactions (e.g., [ 29 ]).…”

“…Within the WGTFT platform, researchers introduced a range of sensitisers for the detection of waterborne analytes, including ions, as well as organic pollutants, hormones, and viruses. Sensitisers may be immobilised onto the WGTFT’s gate electrode [ 6 , 7 , 8 ] or semiconducting channel [ 9 , 10 ], introduced via a plasticised PVC membrane that separates the electrolyte into two compartments [ 11 , 12 , 13 ], or even dispersed into an organic semiconducting film itself [ 14 ]. Sometimes, the semiconductor itself may be sensitive, e.g., to pH [ 15 ].…”

“…In principle, this opens a second, capacitive sensing window in addition to the potentiometric mode to which ISFET and EGFET are limited. Characteristics of WGTFT sensors for inorganic ions and small organic molecules are accounted for by a solely potentiometric response, e.g., [ 6 , 8 , 11 , 12 ], and often can be fitted well to established potentiometric response laws. However, when the sensitiser is a large protein, e.g., an antibody that sensitises for a virus, a dominantly or almost exclusively capacitive response mode was claimed for WGTFTs using an organic semiconductor, e.g., [ 7 , 9 , 16 ].…”

“…Instead of the more common organic WGTFT [ 6 , 7 , 9 , 11 , 14 , 16 ], we use the precursor-route metal oxide SnO 2 as a WGTFT semiconductor. SnO 2 is far cheaper than organic semiconductors, avoids aromatic or chlorinated processing solvents, and is known for its good stability and low threshold in the WGTFT sensor platform [ 8 , 12 , 13 , 17 ]. SnO 2 is immune to electrochemical doping that is undesirable in WGTFT sensors, but sometimes occurs with organic semiconductors in strong electrolytes [ 18 ], and may show less dependency of mobility on V G .…”

Water-Gated Transistor Using Ion Exchange Resin for Potentiometric Fluoride Sensing

“…The different response characteristics allow a much lower limit of detection. Moreover, the response characteristics of a catalyst-sensitised WGTFT for the non-ionic water pollutant benzyl alcohol also followed a Langmuir isotherm [ 7 ]. The origin of the membrane potential remained unclear, however: ion exchange does not accumulate a net charge on the membrane.…”