Construction of a new supramolecular probe with turn-on mechanism for tricyclazole detection

A new supramolecular fluorescence “turn-on” probe ( QL 2 @Q[8]) based on quinolinium derivative ( QL ) and cucurbit[8]uril (Q[8]) was constructed by host-guest interaction to detect tricyclazole ( TC ). The probe was formed with a 1:2 interaction ratio between host and guest and confirmed by 1 H NMR, UV–vis spectroscopy, and fluorescent spectroscopy. QL 2 @Q[8] inclusion complex exhibited quenching fluorescence, while an enhanced fluorescence signal was observed obviously when gradually adding TC into the aqueous solution of QL 2 @Q[8]. It was noted that other pesticides tested in the probe system didn't cause any fluorescence enhancement, showing the probe could selectively respond to TC with no effects and afford a lower limit of detection of 1.5 × 10 −8  mol/L. The investigation on the fluorescence “turn-on” mechanism demonstrated that a QL molecule was squeezed out from the cavity of Q[8] and was replaced by a TC molecule to form a 1:1:1 ternary complex between TC , QL and Q[8], confirmed by UV–vis, 1 H NMR and isothermal titration calorimetry (ITC) experiments. The formation of ternary complex restricted intramolecular rotation of QL and promoted intramolecular charge transfer (ICT), hence, an obvious fluorescence enhancement was observed. The fluorescence “turn-on” probe system could be made into a smartphone model by which TC residue level was obtained by just reading the blue-red channel ratio values, and could also be utilized to detect the TC residues in real agricultural products, with clear fluorescence signals observed.