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

Abstract

We introduce fluoride-selective anion exchange resin sorbents as sensitisers into membranes for water-gated field effect transistors (WGTFTs). Sorbents were prepared via metal (La or Al)-loading of a commercial macroporous aminophosphonic acid resin, PurometTM MTS9501, and were filled into a plasticised poly(vinyl chloride) (PVC) phase transfer membrane. We found a potentiometric response (membrane potential leading to WGTFT threshold shift) to fluoride following a Langmuir–Freundlich (LF) adsorption isotherm with saturated membrane potential up to ~480 mV, extremely low characteristic concentration c1/2 = 1/K, and picomolar limit of detection (LoD), even though ion exchange did not build up charge on the resin. La-loading gave a superior response compared to Al-loading. Membrane potential characteristics were distinctly different from charge accumulating sensitisers (e.g., organic macrocycles) but similar to the Cs+ (cation) selective ion-exchanging zeolite mineral ‘mordenite’. We propose a mechanism for the observed threshold shift and investigate interference from co-solutes. Strong interference from carbonate was brought under control by ‘diluting’ metal loading in the resin. This work sets a template for future studies using an entirely new ‘family’ of sensitisers in applications where very low limit of detection is essential such as for ions of arsenic, mercury, copper, palladium, and gold.

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

“…With the help of the analytic Equation (6a) with the model parameters fitted against measured data, as listed in table in Section 4.3 , we can determine a limit-of-detection (LoD). An appropriate procedure is described in [ 17 ] and is applied to our data in the Supplementary Materials Section S3 . As a result, we find an LoD of c LoD = 6.2 ng/mL RBD spike protein.…”

“…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 ]).…”

“…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 .…”

Combining Aqueous Solution Processing and Printing for Fabrication of Flexible and Sustainable Tin Dioxide Ion‐Gated Transistors

“…[ 20 ] Grell et al. used spray pyrolyzed SnO 2 films (processing temperature of 400 °C) as active layers in IGTs gated by aqueous electrolytes, which were used for the detection of Cs + , [ 21 ] Pb 2+ , [ 22 ] Cu 2+ , [ 22 ] F − , [ 23 ] and benzyl alcohol [ 24 ] in potable water, with limits of detection ranging from µ m to p m . Wei et al.…”

“…[19] The operating mechanism of IGTs relies on electrostatic (surface doping) and electrochemical doping (volumetric doping) and depends on the permeability of the semiconductor versus the mobile ions present in the gating medium. [20] Grell et al used spray pyrolyzed SnO 2 films (processing temperature of 400 °C) as active layers in IGTs gated by aqueous electrolytes, which were used for the detection of Cs + , [21] Pb 2+ , [22] Cu 2+ , [22] F − , [23] and benzyl alcohol [24] in potable water, with limits of detection ranging from µm to pm. Wei et al fabricated SnO 2 films by solution-processing method with a processing temperature of 150 °C and demonstrated a flexible synaptic transistor with 40% retention of its initial postsynaptic current value after 10 000 bending cycles.…”