Advancements in Solid-State Metal pH Sensors: A Comprehensive Review of Metal Oxides and Nitrides for Enhanced Chemical Sensing: A Review

Solid-state pH sensors have emerged as vital tools across various scientific and industrial applications, from agriculture and environmental monitoring to biotechnology and the pharmaceutical industry. Among pH sensing devices, conventional glass electrodes have long been the standard due to their Nernstian sensitivity, wide operating range, and excellent ion selectivity. However, glass electrodes present significant drawbacks, including fragility, storage limitations, and difficulty in miniaturization for applications like capsule endoscopy and in vivo pH monitoring. To overcome these challenges, researchers have explored alternative materials for solid-state pH sensing, particularly focusing on metal oxides and nitrides. This article presents a comprehensive review of solid-state metal pH sensors, with an emphasis on the potential of metal nitrides to address the limitations of glass electrodes and metal oxides. Metal oxides, despite their robustness and ability to be miniaturized, often face interference in redox environments, reducing their sensitivity. In contrast, metal nitrides, known for their superior chemical inertness, thermal stability, and mechanical strength, offer promising characteristics for pH sensing, particularly in challenging sample matrices. By reviewing the latest developments in the field, this article explores the structure-property relationships that make metal nitrides excellent candidates for next-generation pH sensors. Moreover, this review outlines the key principles behind potentiometric and amperometric sensing techniques, highlighting the various fabrication methods used for solid-state electrodes. Special attention is given to different sensing materials, including liquid-hydrophobic membranes, carbon-based materials, conducting polymers, and the role of functional groups in optimizing the sensing performance of each material. In addition, this article addresses the limitations of metal oxides in redox environments and provides a comparative analysis of their sensitivity to pH changes while discussing potential improvements in electrode performance through innovative material selection and design.