Ion transfer voltammetry of amino acids with an all-solid-state ion-selective electrode for non-destructive phenylalanine sensing

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.