•A ratiometric sensor for Zn2+ detection was reported.•The fluorescent changes were attributed to ICT and FRET mechanisms.•The sensor is cell-permeable and can be used to detect Zn2+ within living cells.A ratiometric sensor (QA) for detecting Zn2+ with high sensitivity and selectivity was reported. The fluorescence changes of sensor upon the addition of Zn2+ were attributed to the conjugation of internal charge transfer and fluorescence resonance energy transfer mechanisms. There is a good linear relationship between the fluorescence ratio I497nm/I420nm and the concentrations of Zn2+ ranging from 0 μM to 40 μM, which makes an effective ratiometric detection of Zn2+ ion. The limit of detection (LOD) was evaluated to be 33.6 nM. The imaging experiments indicated that QA is cell-permeable and can be used to detect Zn2+ within living cells with good selectivity over Cd2+.

A fluorescein-based sensor was developed for the AChE activity assay and the inhibitor screening. The sensor provided the dual assay methods for the screening of AChE activity in the presence or absence of inhibitor. The colorimetric and fluorometric assays were based on the following processes: (1) owing to the hydrolysis of acetylthiocholine in the presence of AChE, the fluorescein-based probe can rapidly induce 1,4-addition of the hydrolysis product thiocholine to α,β-unsaturated ketone in the compound 1, resulting in strong fluorescence and absorption changes; (2) in the presence of the corresponding inhibitor, the fluorescence enhancement or the absorption change would be inhibited in that the formation of thiocholine was hindered.

Polydiacetylene supramolecules (PDAs) are unique sensing materials. Upon environmental stimulation, blue PDAs can undergo a colorimetric transition from blue to red accompanied by fluorescence enhancement. In this paper, we report a new PDA system polymerized from a mixed liposome comprising 2-(2-(2-hydroxyethoxy)ethoxy)ethyl pentacosa-10,12-diynoate and pentacosa-10,12-diynoic acid at a 3:7 ratio. The PDA system provided new colorimetric and fluorometric assay methods for screening acetylcholinesterase and its inhibitors through three processes. First, myristoylcholine reacted with PDAs, which then underwent colorimetric and fluorometric transition. Second, acetylcholinesterase catalyzed the hydrolysis of myristoylcholine into tetradecanoic acid, which reduced the myristoylcholine concentration and led to faded color and fluorescence. Third and last, acetylcholinesterase inhibitors retarded the activity of acetylcholinesterase, thereby inducing the recovery of color and fluorescence.Keywords: acetylcholinesterase; colorimetric and fluorometric assays; conjugated polymer; inhibitor; myristoylcholine; polydiacetylene;

A fluorescein-based sensor bearing nitroolefin moiety for the detection of thiols was prepared. Upon addition of thiols, such as cysteine (Cys), homocysteine (Hcy) and glutathione, the solution containing sensor showed an increase of absorption intensity at 497 nm with a slight blue-shift as well as the enhancement in fluorescence intensity at 520 nm. The fluorescence enhancement and absorption change are attributed to the Michael addition of thiols to the double bond of nitroolefin moiety in sensor. The probe displays a fast response to Cys with the rate constant (kobs) of 2.3 min−1 and the detection limit to Cys was evaluated to be 0.2 μM. The confocal microscopy experiments demonstrate that this sensor is potential for the imaging of thiols in living cells.Graphical abstractHighlights►A fluorescein-based sensor bearing nitroolefin moiety was prepared. ► The sensor showed fluorescence enhancement when thiols were added. ► The imaging experiments demonstrate that this sensor is potential.

A fluorescent probe based on fluorescein displays excellent selectivity and sensitivity for cysteine and its application for bio-imaging is described.

A fluorescent probe based on fluorescein displays excellent selectivity and sensitivity for cysteine and its application for bio-imaging is described.