A Dual Colorimetric/Fluorescence System for Determining pH Based on the Nucleophilic Addition Reaction of an o‐Hydroxymerocyanine Dye

Abstract

Owing to their ability to monitor pH in a precise and rapid manner, optical probes have widely been developed for biological and nonbiological applications. The strategies thus far employed to determine pH rely on two types of processes including reversible protonation of amine nitrogen atoms and deprotonation of phenols. We have developed a novel dual, colorimetric/fluorescence system for determining the pH of a solution. This system utilizes an o-hydroxymerocyanine dye that undergoes a nucleophilic addition reaction that subsequently causes reversible structural changes interconverting a merocyanine to a spirocyanine and a spirocyanine to a spiropyran. It was demonstrated that the dye can be employed to measure the pH of solutions in the 2.5-5.75 and 9.6-11.8 ranges with color changes from yellow to dark blue and then to lavender. Moreover, the fluorescence response associated with the spirocyanine-spiropyran transformation of the dye occurring in alkaline solutions provides a precise method.

Tuning the Interfacial Chemistry of Redox‐Active Polymer for Bifunctional Probing

“…The sensing architecture consists of a polyaniline (PANI) conducting polymer probe (with and without a cation selective upper layer) in combination with a non‐polarizable interface such as Ag/AgCl (3 M KCl) housed in double junction Luggin capillary. The scanning electron micrographs – of as‐deposited PANI (see experimental section) show a near granular morphology, Figure S1a (Supporting Information) and the energy dispersive spectroscopy (EDS), Figure S1b (Supporting Information), shows the presence of chloride dopant along with carbon and nitrogen indicating as‐synthesized PANI is in the conducting form . The cyclic voltammogram of PANI without a cation selective upper layer in protic acids (for example in HClO 4 ), Figure a, shows mainly two pairs of redox peaks corresponding to the redox trans formation of lucoemeraldine (EB) to emeraldine (ES) and ES to pernigraniline (PG) during the positive going scan and their reversal during the negative going scan .…”

“…The response of the state of the art pH meter is generally independent of the nature of the anion and hence it is an ideal candidate for pH measurement . Though this aspect is usually considered as an advantage as the sensing architecture probes only the H+ ion concentration, its obvious disadvantage is the inability to identify different types of acids or more specifically the nature of the conjugate base.…”

A Colorimetric and Fluorescent pH Probe for Extremely Acidic Conditions and its Application in pH Test Paper

“…As a result, a number of fluorescent pH probes have been reported in the literature, functioning mainly at three pH regions: (1) cytosolic pH at 6.8–7.4, (2) lysosomal and endosomal pH at 4.5–6.0, and (3) mitochondrial pH at ~8.0 . However, fluorescent pH probes operating in extremely acidic conditions (pH < 4.0) are still rare . Although the most living species could not survive in extremely acidic conditions, there are still some microbes which prefer an extreme environment, e.g.…”

An unexpected dual-response pH probe based on acridine

“…17,18 Among them, uorescent probes have attracted much attention because of their quick response, excellent sensitivity, good selectivity, non-invasive detection and low cost. 19 Till now, the improvements in synthetic methods have directed the development of uorescent probes with many skeletons, including carbazole, [20][21][22] BODIPY, [23][24][25] rhodamine, [26][27][28] cyanine, 29 etc.…”