Monitoring the lead-and-copper rule with a water-gated field effect transistor.

Nawal Alghamdi,Martin Grell,Zahrah Alqahtani

doi:10.2166/wh.2020.186

Nawal Alghamdi, Martin Grell + Show 1 more

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https://doi.org/10.2166/wh.2020.186

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Abstract

We use the natural zeolite clinoptilolite as the sensitive element in a plasticised PVC membrane. Separating a sample pool and a reference pool with such a membrane in water-gated SnO2 thin-film transistor (SnO2 WGTFT) leads to membrane potential, and thus transistor threshold shift in response to the common drinking water pollutants Pb2+ or Cu2+ in the sample pool. Threshold shift with ion concentration, c, follows a Langmuir-Freundlich (LF) characteristic. As the LF characteristic shows the steepest slope in the limit c → 0, this opens a window to limits-of-detection (LoDs) far below the 'action levels' of the 'lead-and-copper rule' for drinking water: Pb2+: LoD 0.9 nM vs 72 nM action level, Cu2+: LoD 14 nM vs 20.5 μM action level. LoDs are far lower than for membranes using organic macrocycles as their sensitive elements. Threshold shifts at the lead and copper action levels are more significant than shifts in response to variations in the concentration of non-toxic co-cations, and we discuss in detail how to moderate interference. The selective response to lead and copper qualifies clinoptilolite-sensitised WGTFTs as a low footprint sensor technology for monitoring the lead-and-copper rule, and to confirm the effectiveness of attempts to extract lead and copper from water.

Highlights

The report by Kergoat et al ( ) that thin-film transistors can be gated across water as electrolytic gate medium has paved the way for new potentiometric sensors: when a WGTFT is sensitised with a suitable receptor, a waterborne analyte binding to this receptor leads to a shift in the WGTFT’s threshold voltage, Vth
For the sensor calibration in ‘Lead and copper sensing results’, co-cation concentration in sample and reference were matched by calibrating sensors with sample solutions we prepared from the same tap water as we use for reference
When we embed powdered clinoptilolite into a plasticised Poly(vinyl chloride) (PVC) membrane that we use to separate a sample pool and a reference pool in water-gated SnO2 thin-film transistor, we find a membrane potential that leads to transistor threshold shift in response to the presence of either Pb2þ or Cu2þ in the sample pool

Summary

Introduction

The report by Kergoat et al ( ) that thin-film transistors can be gated across water as electrolytic gate medium (water-gated thin-film transistors, WGTFTs) has paved the way for new potentiometric sensors: when a WGTFT is sensitised with a suitable receptor, a waterborne analyte binding to this receptor leads to a shift in the WGTFT’s threshold voltage, Vth. The SnO2 transistor substrate was in contact with tap water held in an inner (reference) pool that is separated from an outer (sample) pool by the sensitised PVC membrane.

Results

Conclusion