Fig. 2. Fluorescence-based chloride sensing. (A) Chloride quenches CA–cysteine fluorescence strictly under acidic conditions. (B) Stern–Volmer plots linearizing quenching rates over chloride concentration reveal that chloride sensitivity (K SV, or the slope) increases with acidity, R 2 > 0.997. Detection procedures for chloride sensing (shown in schematics) are simplified by standardizing at fixed sulfuric acid concentrations. (C) Comparison of quenching efficiency of common ions, each at 100 mM, in the presence of CA–cysteine at pH 1.3 (except for OH–).
