A novel hydrazone-based fluorescent "off-on-off" probe for relay sensing of Ga3+ and PPi ions.

A novel hydrazone-based fluorescent probe (E)-3-((2-(benzo[d]thiazol-2-yl)hydrazono)methyl)-4H-chromen-4-one (BTC) has been rationally designed and synthesized. BTC can subsequently detect Ga3+ and PPi ions through the absorption and emission off-on-off response with high specificity. Importantly, fluorescent probe BTC can well discriminate Ga3+ from Al3+ and In3+. The association constant (K) was calculated as 2.06 × 104M-1, and the limit of detection (LOD) was calculated as 4.88 × 10-2µM. Competitive binding studies also illustrated good results of the probe BTC towards Ga3+. Job's plot and HRMS results substantiated the 1:1 stoichiometry between BTC and Ga3+ ion. The interaction binding mode of BTC with Ga3+ was proposed by HRMS, 1H NMR spectral titration, UV-vis absorption and fluorescence spectral measurements. The combination of the restraint of the photo-induced electron transfer (PET) process and the chelation enhanced fluorescence (CHEF) process is responsible for the fluorescence enhancement of this probe. The in situ chelated BTC-Ga3+ could further monitor pyrophosphate ion (PPi) by demetallization process with quenching fluorescence emission. Additionally, the BTC and BTC-Ga3+ showed good cell permeability and could detect Ga3+ and PPi ions in onioninner epidermal cells, respectively.

A hydrazone-based spectroscopic off-on probe for sensing of basic arginine and lysine.

A simple probe BHN based on naphthol and benzothiazole is reported for detecting of arginine (Arg) and lysine (Lys) with high selectivity and sensitivity. The BHN in aqueous solution upon reacting with Arg or Lys induced a visible color change from colorless to yellow. The probe BHN can also be employed for fluorescence turn-on sensing of Arg and Lys with the limits of detection (LOD) of 5.20 × 10-2 µM and 3.69 × 10-2 µM, respectively. The naked eye colorimetric and fluorimetric detecting is lack of sensitive to other common amino acids including Gly, Ala, Ser, Pro, Val, Thr, Cys, Leu, Ile, Asn, Asp, Glu, Gln, Met, His, and Phe. The sensing mechanism has been proposed by pH investigation and 1H NMR spectra.