Rational modulation of probe electrophilicity, hydrazine nucleophilicity and product fluorescence for accurate sensing of hydrazine.

BACKGROUND: Sensitive and specific detection of target analytes remains challenging but significant in the practical applications of hazardous chemical detection, biomarkers tracing, and environmental monitoring, etc. RESULTS: Here, a general strategy for boosting the sensitivity and specificity of the sensing system is proposed, which involves modulating the electrophilicity of the pyrimidine-based probes with different substituents (-Br, -H, -OMe), the nucleophilicity of the target analyte N2H4 , and the fluorescent properties of the product by adjusting the pH value. Remarkably, the bromine-substituted probe exhibited superior performance in a specific alkaline environment (pH = 7.5), achieving a theoretical limit of detection (LOD) of 5.77 nM (0.18 ppb) in solution, which is far below the 10 ppb occupational exposure limit reported by the U.S. Environmental Protection Agency. By embedding the BrPMtBu probe into a porous sponge substrate, specific recognition of trace hydrazine vapor was achieved, even in the presence of an 86-fold higher concentration of ethylenediamine (EDA) - a structural and property analog of hydrazine. Further validation of this strategy was performed using an optical sensing chip equipped with the BrPMtBu-loaded melamine sponge, which could precisely discriminate trace hydrazine in both liquid and gaseous phases at extremely low concentrations.

SIGNIFICANCE: This work provides a different viewpoint for the rational design of fluorescent probes by modulating the nature of the target, the probe and the product, as well as a versatile and reliable approach for ultra-sensitive detection of trace hazardous analytes.