Iodide (I − ) is an essential micronutrient for thyroid function. Hence, rapid and portable sensing is important for I − quantification in food and biological samples. Herein, we report the first example of a halogen bonding (XB) tripodal ionophore (XB1) which is selective for the I − anion. NMR binding studies of XB1 and its H-triazole analog HB2 with I − demonstrated the dominant influence of XB interactions between the ionophore and the I − analyte. The phase boundary model was applied to formulate iodideselective electrodes with the ionophore XB1. The optimal electrode exhibited a near-Nernstian response of −51.9 mV per decade within a large dynamic range (10 −1 to 10 −6 M) and notably anti-Hofmeister selectivity for I − over thiocyanate (SCN − ), enabling the in situ determination of I − in complex samples. This work establishes XB as a viable supramolecular interaction in the potentiometric sensing of anions.
Poly(3,−polyethylene glycol (PEDOT:PEG) is a conductive material adopted in bioelectronics due to its biocompatibility and stability. While PEDOT has established its utility in cationic solid-contact ion-selective electrodes (sc-ISEs), its anionic counterpart remains less explored. Herein, we report the first example of PEDOT:PEG as a solution-printable solid-contact for all-solid-state nitrate-selective electrodes and a simple ion exchange treatment which can significantly enhance nitrate selectivity. Electrochemical impedance spectroscopy revealed that the sc-ISEs with perchlorate (ClO 4 − )-doped PEDOT:PEG suffered a large overall resistance. Removal of the ClO 4 − dopant via ion exchange reduced the resistance, resulting in significant improvement in sc-ISE performance. The optimal sc-ISE exhibited near-Nernstian response (−55.8 mV/ decade) across a wide dynamic range (0.1 M to 1.12 μM) and excellent Hofmeister selectivity, which was maintained after prolonged continuous usage. This simple drop-cast and ion-exchange protocol is amenable to the scalable preparation of flexible anion sc-ISEs.
Amino acids such as phenylalanine (Phe) are key building blocks of proteins and other biomolecules. Although recent advancements in electrochemical sensors have enabled the rapid detection of Phe, these sensors are often destructive as they irreversibly oxidise Phe. In addition, most of them rely on biorecognition elements, which suffer from limited stability at ambient conditions and sensitivity towards environmental fluctuations. Herein, we report the first example of ion transfer voltammetry of Phe using an all‐solid‐state ion‐selective electrode (ISE). The reversibility of this technique enables both the sensor and the Phe sample to be reused. The optimal voltammetric ISE (VISE) exhibits near Nernstian response (56.8 mV/decade) towards Phe and selectivity against amino acids of all classes (hydrophobic, hydrophilic and charged). Voltammetric interrogation of the ISE significantly enhances sensitivity, linear range, selectivity, and stability as compared to traditional open circuit potential measurements. Phe levels in a commercial nutritional supplement and drinking waters were determined to demonstrate the viability of our sensor in real life applications. This proof‐of‐concept can be applied to develop VISEs for other amino acids and biological ions for healthcare and nutrition sensing.
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