4-(1H-benzimidazol-2-yl)benzaldehyde (1) has been developed as a new ratiometric fluorescent probe for bisulphite, based on the modulation of intramolecular charge transfer (ICT). Upon mixing with bisulphite in aqueous ethanol, an aldehyde–bisulphite adduct was formed and the ICT of the probe was switched off, which resulted in a ratiometric fluorescence response with an enhancement of the ratios of emission intensities at 368 and 498 nm. The detection range of the probe for bisulphite is in the 2.0–200 µmol/L concentration range and the detection limit is 0.4 µmol/L. Probe 1 produces a ratiometric fluorescent response to bisulphite with a marked emission wavelength shift (130 nm) and displays high selectivity for bisulphite over other anions. Copyright © 2012 John Wiley & Sons, Ltd.

A sensitive fluorogenic probe 1 for biothiols was developed based on the Michael addition reaction. The probe 1 was readily synthesized via the reaction of 2-(4′-hydroxyphenyl) benzimidazole (HPBI) with acryloyl chloride and shows weak fluorescence emission. Upon mixing with biothiols, the fluorescence of 1 is significantly enhanced due to the conjugate addition of thiols to the α,β-unsaturated carbonyl moiety, thus eliminating the photoinduced electron transfer (PET) quenching of the fluorophore by the intramolecular carbon–carbon double bond. Cysteine (Cys) was selected as the representative thiol in the spectral experiment. A good linear relationship was obtained from 1.0 to 30.0 µmol L⁻¹ for Cys and the detection limit was 0.17 µmol L⁻¹. Furthermore, probe 1 was highly selective for biothiols without the interference of some biologically relevant analytes and has been applied to detecting biothiols in human urine samples. Copyright © 2010 John Wiley & Sons, Ltd.

A new fluorogenic probe for sodium new houttuyfonate (SNH) was proposed. 4-Methylumbelliferyl-2,4-dinitrobenzenesulfonate (4-MUDNBS) was a nonfluorescent compound and was synthesized via the one-step reaction of 4-methylumbelliferone (4-MU) with 2,4-dinitrobenzenesulfonyl chloride. In basic media, SNH was decomposed to produce sodium sulfite, which then reacted with 4-MUDNBS to yield highly fluorescent 4-MU, hence leading to the fluorescence increase of the reaction solution. A linear correlation existed between the emission intensity and the concentration of SNH within the range from 0.5 to 15 μg·mL⁻¹ with a detection limit of 0.15 μg· mL⁻¹ (3δ). The effect of substituents on the benzenesulfonyl moiety of the probe is discussed, and the presence of electronegative groups is favorable for the proposed cleavage reaction.

A highly sensitive fluorogenic probe for tiopronin was proposed. 2,4-Dinitrobenzenesulfonyl-fluorescein (I) is an almost nonfluorescent compound. Upon mixing with tiopronin in aqueous solution, the 2,4-dinitrobenzenesulfonyl group of I was efficiently removed and its parent dye fluorescein was released, hence leading to dramatic increases in both fluorescence and absorbance of the reaction mixture. Under optimal conditions, the fluorescence increase is linear with tiopronin concentration in the range 5.0–600 ng mL⁻¹, with a detection limit of 1.5 ng mL⁻¹ (3σ). The proposed method has been successfully applied to tiopronin determination in pharmaceutical preparations and in spiked human urine samples. Copyright © 2009 John Wiley & Sons, Ltd.