Solvatochromic coextraction‐based optical carbonate nanosensors.

Ionophore‐based carbonate‐selective sensors have become reliable analytical tools due to their high selectivity and versatility of applications. Nonetheless, successful examples of their implementation in nanoscale devices are yet to be found in the literature. Herein we describe the first attempt to develop carbonate sensors with ionophores using ion‐selective nanoemulsions. Classical chromoionophore‐based sensors were shown to perform poorly upon transfer to the nanoscale. We hypothesize that this is caused by the heightened surface activity of the ion‐ionophore complex. This challenge is overcome by the addition of a positively charged solvatochromic dye X3+ to the aqueous phase instead of the sensing particles. The presence of this dye facilitates transfer of carbonate from the particle surface into the sensor bulk, which is followed by an unexpected change of fluorescence with the emergence of a new peak at longer wavelengths, allowing for a ratiometric signal transduction. We have found that this spectral change originates from dye hyper‐polarization by the charged moiety of carbonate complex with the ionophore, in analogy to earlier work with protamine nanosensors. The dye‐coextraction‐based sensing protocol is shown to be reversible and selective with regard to both anionic and cationic interferences present in the sample and forms the foundation for further mechanistic advances for anion sensing with ionophores. [ABSTRACT FROM AUTHOR]