Recent developments in ionophore-based potentiometric electrochemical sensors for oceanic carbonate detection

The increasing level of atmospheric carbon dioxide (CO2) driven by human activities contributes to the global concern of climate change. A consequence of these circumstances is ocean acidification, which reduces seawater pH. The increasing absorption of atmospheric CO2 into the ocean decreases the concentration of carbonate ions and causes the sea to become more acidic, severely harming marine species. This harm to marine life has created the need for in situ carbonate sensing and monitoring to understand how marine ecosystems respond to pH reduction. Over the past few decades, many sensors with different compositions and structures have been developed to detect carbonate in seawater and other aquatic environments to simulate oceanic conditions. This review summarizes the recent developments in carbonate ionophores, a key component in carbonate electrochemical sensors, and compares the reported performance of these sensors through various parameters (e.g., sensitivity, response time, lifetime, testing media, and measuring range). Current challenges within the development of carbonate ionophores and sensors and possibilities for future research are also discussed. The increasing oceanic absorption of atmospheric CO2 decreases the ocean's carbonate and pH levels, harming marine life. This review covers carbonate electrochemical sensors based on ionophores for the advancement of ocean acidification research.