Synthesis, optical properties, and application of novel chalcone skeleton as pH fluorescent probe: Based AIE + ESIPT strategy.

A series of "turn off" pH fluorescence probes with chalcone skeleton for basic system have been developed. The molecules emitted bright yellow fluorescence under acidic condition, resulting AIE coupled ESIPT characteristic and ICT process. What's more, the compounds exhibited excellent sensitivity and selectivity for detecting pH as a facile "On-Off" fluorescence probe, and the fluorescence of them were quenched with the ESIPT process interrupted under alkaline condition. Theoretical calculation for the related compounds also performed to verify the electron effect on photophysical properties and confirm the rational speculation on the mechanism.

Ratiometric fluorescent aptasensor for convenient detection of ochratoxin A in beer and orange juice.

Based on the principle of fluorescence resonance energy transfer (FRET), a simple ratiometric fluorescent aptasensor for convenient detection of ochratoxin A (OTA), a Group IIB carcinogen secreted by some fungi, was established. Initially, the anti-OTA aptamer with a quadruplex structure was flanked with FAM and BHQ1, and its partially complementary DNA (cDNA) was tagged with Cy3. In the absence of OTA, this aptamer hybridized with the cDNA strand forming a DNA duplex structure, in which BHQ1 was adjacent to Cy3 and distant from FAM. Due to the FRET principle, the fluorescence intensity emitted by Cy3 (FCy3) was quenched by BHQ1, and the fluorescence intensity emitted by FAM (FFAM) recovered. In the presence of OTA, the prepared aptamer preferred to bind with OTA instead of cDNA, forming an aptamer-OTA complex structure in which BHQ1 was adjacent to FAM and distant from Cy3. As a result, FFAM was quenched and FCy3 was restored. OTA can be accurately detected via the determination of the FCy3/FFAM ratio value. Under optimal conditions, this ratiometric fluorescent aptasensor offers excellent OTA detection in the range of 0.6 nmol L-1-5 µmol L-1, with a limit of detection (LOD) of 0.3 nmol L-1. This ratiometric aptasensor showed the advantages of easy operation, accuracy and sensitive analysis. Good specificity of this aptasensor was demonstrated. This ratiometric aptasensor could be used for the detection of OTA in real samples, e.g. beer and orange juice, showing its promising application potential.