Reactivity of a luminescent “off–on” pyrylium dye toward various classes of amines and its use in a fluorescence sensor microtiter plate for environmental samples

We report on a systematic study on the reactivity of the pyrylium dye Py-1 toward various classes of amines (primary aliphatic, primary aromatic, secondary, tertiary) and its use in environmental sensing of amines. While most primary aliphatic amines react almost quantitatively with Py-1 within 10 min, sterically hindered primary aliphatic amines and primary aromatic amines react more slowly. Secondary and tertiary amines just induce a decomposition of the chromophore of Py-1 but do not yield a fluorescent product. This makes Py-1 a suitable receptor and transducer in an optical sensing microplate for rapid screening of primary aliphatic amines in water and soil samples. Py-1 is embedded into a polymeric cocktail, which is deposited on the bottom of wells in microtiter plates to yield a high-throughput fluorescence sensing tool. On reaction with primary aliphatic amines, a significant fluorescence increase (λexc = 485 nm/λem = 620 nm) of the sensor spots is detected in a standard microplate reader after 10 min incubation at 25° C. The linear calibration plots of eight primary aliphatic amines are in the range of 0.350–70.0 μg mL−1. The limits of detection (LODs) are from 0.119 to 0.589 μg mL−1 and the limits of quantitation (LOQs) are from 0.399 to 1.965 μg mL−1. We further show that the sensing plate is suitable for sensing mixtures of primary amines and that the total content of amines (TAC) found is a good measure for the sum of the contents of the individual amines present. Finally, the sensing plate was successfully applied to the quantitative analysis of primary aliphatic amines in 3 samples of water and soil, respectively.