An "OR-AND" logic gate based multifunctional colorimetric sensor for the discrimination of Pb and Cd.

Pb and Cd are the most ubiquitous heavy metal ion pollutants, and they have aroused much attention due to their irreversible and significant damage to human organ. In this work, a new fluorescein-based "OR-AND" logic gate colorimetric probe 3',6'-bis((tert-butyldiphenylsilyl)oxy)-2-(2-((2-hydroxyphenyl)imino)ethylidene)aminspiro[isoindoline-1,9'-xanthen]-3-one (FP) was designed and synthesized via attaching 2-(2-((2-hydroxyphenyl)imino)ethylidene)amino and tert-butyldiphenylsilyl to fluorescein as the specific identification groups. This sensor can rapidly and sensitively discriminate Pb and Cd by utilizing F as an auxiliary reagent. When Pb or Cd was added into the FP solution, the absorption band at 533 nm increased and the peak at 374 nm decreased, the color changed from colorless to pale-purple, resulting in a ratiometric spectral change. However, adding fluoride ion to the FP solution containing Pb or Cd resulted in a distinct phenomenon in which the pale purple color fades out to colorless for a Pb-containing solution and deepen to dark purple for a Cd-containing solution, which is attributable to the different coordination mechanisms. In aqueous solution, the detection limits of FP can reach 0.42 μM for Pb and 0.53 μM for Cd. The probe exhibited rapid responses for these analytes. Moreover, FP was successfully used to rapidly detect trace amounts of hazardous Pb and Cd in tap water with good relative recovery and the relative standard deviations (RSD) were 1.8% for Pb and 0.3% for Cd, providing a novel approach for detecting Pb and Cd in practical application.