High fidelity optical detection and imaging of the bisulfate ion: Photophysical events, binding mechanisms and applications

Bisulfate is a common ingredient in several widely-used commodities such as toothpaste, shampoo and detergent. Whilst it has a number of positive effects on the efficacy of these materials, due to its widespread societal use, it also has an increasingly negative impact on the environment. This has resulted in growing interest in the development of operationally simple systems to detect and quantify this widely used anion. Given the large number of reports that have appeared on its detection to date, this systematic review article focuses on recent developments in such operationally simple colorimetric and fluorescent detection systems for the detection and estimation of bisulfate ions. The small molecule fluorophores utilized for its detection have been categorized according to the signaling moiety and are then discussed accordingly. The key features of recognition phenomena in such systems, including spectroscopic change, naked-eye detection, limit of detection, application in real-world samples and biocompatibility and toxicity in live cell imaging are discussed. The bisulfate ion has multiple features that have been used in its detection, including its high electron deficiency, low pKa, proton donor site, hydrogen bond donor and acceptor sites resulting in an array of chemosensors displaying a wide range of photophysical changes. Hence, a special focus is on the structure-photophysical property relationships and binding mechanisms in these systems. Finally, significant achievements and ongoing challenges in the field are highlighted. • Bisulfate is widely used in household commodities, resulting in increasingly negative environmental impacts. • Small molecule colorimetric and fluorescent sensors are increasingly popular for their detection, which is the focus of this review article. • The small molecule fluorophores reported have been categorized according to the signaling moiety utilized in the detection of bisulfate and are discussed chronologically. • Detection systems utilize their high electron deficiency, low p K a , proton donor site, hydrogen bond donor, and acceptor sites.