Design of controlled multi-probe coupled assay via bioinspired signal amplification approach for mercury detection

Abstract

We have designed and synthesized off–on fluorometric probes, 7-(but-3-yn-1-yloxy)-8-(difluoromethyl)-2H-chromen-2-one (AYF) and 7-((4-(tert-butyldiphenylsilyloxy)benzyl)oxy)-8-(difluoromethyl)coumarin (DPF₁), by incorporating the concept of biological signal transduction strategy into their molecular design and present their proof-of-concept demonstration for mercury (Hg²⁺) detection. AYF undergoes a cascade of self-immolative reactions in the presence of Hg²⁺ and unmasks fluorogenic coumarin 1 and releases two latent fluoride ions. These fluorides initiate the removal of silyl protecting trigger group on DPF₁ which directs another cascade of self-immolative reactions. The fluoride ions (amplifiers) are continuously activating the cascade reaction, and, as a result, coumarin 1 progressively accumulates in the reaction medium and the whole process accelerates an amplified signal for Hg²⁺. For detection of Hg²⁺, the limit of detection of the two-probe coupling assay (AYF and DPF₁) is 0.51 ppb which is more than 2000 times lower than that of AYF alone. Besides, 3-(benzothiazol-2-yl)-4-carbonitrile-7-((4-(tert-butyldiphenylsilyloxy)benzyl)oxy)coumarin (DCC), a long-wavelength probe, was coupled with AYF and DPF₁ in order to shift the emission to a higher wavelength region. Negative control studies revealed that the probes undergo controlled and organized sensing pathways as we designed.