Abstract
There is a growing demand for developing wearable sensors that can non-invasively detect the signs of chronic diseases early on to possibly enable self-health management. Among these the flexible and stretchable electrochemical pH sensors are particularly important as the pH levels influence most chemical and biological reactions in materials, life and environmental sciences. In this review, we discuss the most recent developments in wearable electrochemical potentiometric pH sensors, covering the key topics such as (i) suitability of potentiometric pH sensors in wearable systems; (ii) designs of flexible potentiometric pH sensors, which may vary with target applications; (iii) materials for various components of the sensor such as substrates, reference and sensitive electrode; (iv) applications of flexible potentiometric pH sensors, and (v) the challenges relating to flexible potentiometric pH sensors.
Highlights
Chronic diseases, including diabetes, cancer, cardiovascular disease and mental health disorders are the leading cause of death and disability worldwide.[1,2,3] The early and real-time detection of the physicochemical and biological representations of these diseases could ensure rapid and efficient patient treatment, leading to positive health impacts
We discuss the most recent developments in wearable electrochemical potentiometric pH sensors, covering the key topics such as (i) suitability of potentiometric pH sensors in wearable systems; (ii) designs of flexible potentiometric pH sensors, which may vary with target applications; (iii) materials for various components of the sensor such as substrates, reference and sensitive electrode; (iv) applications of flexible potentiometric pH sensors, and (v) the challenges relating to flexible potentiometric pH sensors
This study suggests that a proper calibration algorithm and a number of additional sensors can overcome issues related to the in uence of other parameters[184] The recent investigation in metal oxides (MOx) based pH sensors for biomedical and clinical applications is concentrated towards ion sensitive eld effect transistors (ISFET), extended-gate eld effect transistor (EGFET)[199] based pH sensors, both of which work on the principle of potentiometry
Summary
Electrodes are large in size, are difficult to be miniaturized, and require regular topping up of the reference buffer solution.[33,34,35] As a result, alternative technologies such as solid-state pH sensors are being explored.[8] Besides the possibility of miniaturization and exibility, they offer several attractive features such as faster response, wider pH sensing range, excellent sensitivity, simple electronics, biocompatibility, low cost of fabrication, and the possibility of integration on different substrates (polymer, plastic, textiles, paper, etc.). A substantial part of the discussion focuses on the design of exible potentiometric pH sensors, with emphasis on exible substrates, the materials for the reference and sensitive electrodes, sensitivity and biocompatibility – which is paramount to the success of wearable pH sensors for health applications
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