Discriminatory Detection of Cysteine and Homocysteine Based on Dialdehyde-Functionalized Aggregation-Induced Emission Fluorophores

A selective glutathione probe based on AIE fluorogen and its application in enzymatic activity assay

In this work, we design and synthesize a malonitrile-functionalized TPE derivative (TPE-DCV), which can react with thiol group through thiol-ene click reaction, leading to the fluorescence change of the system. Combined with the unique AIE property, TPE-DCV can selectively detect glutathione (GSH) but not cysteine or homocysteine. As the cleavage of GSSG with the aid of glutathione reductase produces GSH, which turns on the fluorescence of TPE-DCV, the ensemble of TPE-DCV and GSSG can thus serve as a label-free sensor for enzymatic activity assay of glutathione reductase. We also apply TPE-DCV for the detection of intracellular GSH in living cells.

Thiol-addition reactions and their applications in thiol recognition

Because of the biological importance of thiols, the development of probes for thiols has been an active research area in recent years. In this review, we summarize the results of recent exciting reports regarding thiol-addition reactions and their applications in thiol recognition. The examples reported can be classified into four reaction types including 1,1, 1,2, 1,3, 1,4 addition reactions, according to their addition mechanisms, based on different Michael acceptors. In all cases, the reactions are coupled to color and/or emission changes, although some examples dealing with electrochemical recognition have also been included. The use of thiol-addition reactions is a very simple and straightforward procedure for the preparation of thiol-sensing probes.

An aggregation-induced emission based “turn-on” fluorescent chemodosimeter for the selective detection of Pb2+ ions

An aggregation-induced emission (AIE) based “turn-on” fluorescent chemodosimeter for selective detection of Pb²⁺ ions has been developed. The probe is a phosphate functionalized tetraphenylethylene derivative and the resulting lead–TPE complex has very low solubility in working solvent and triggers AIE and shows a low detection limit of 10 ppb.

Extremely selective fluorescence detection of cysteine or superoxide with aliphatic ester hydrolysis

A novel fluorescence probe modality demonstrated with fluorescein affords a highly selective aqueous-based detection of cysteine over other biothiols,e.g.homocysteine, with a limit of detection of 11.3 μM.

Novel pyrazoline-based fluorescent probe for detecting glutathione and its application in cells

A novel compound, 2-(1,5-diphenyl-4,5-dihydro-1H-pyrazol-3-yl)phenyl acrylate (probe L), was designed and synthesized as a highly sensitive and selective fluorescent probe for recognizing and detecting glutathione among cysteine, homocysteine and other amino acids. The structures of related compounds were characterized using IR, NMR and HRMS spectroscopy analysis. The probe is a non-fluorescent compound. On being mixed with glutathione in buffered EtOH:PBS=3:7 solution at pH 7.4, the probe exhibited the blue emission of the pyrazoline at 474 nm and a 83-fold enhancement in fluorescence intensity. This probe is very sensitive and displayed a linear fluorescence off-on response to glutathione with fluorometric detection limit of 8.2 × 10(-8)M. The emission of the probe is pH independent in the physiological pH range. Live-cell imaging of HeLa cells confirmed the cell permeability of the probe and its ability to selectively discriminate GSH from Cys and Hcy in cells. The toxicity of the probe was low in cultured HeLa cells.

Lighting up cysteine and homocysteine in sequence based on the kinetic difference of the cyclization/addition reaction

A novel one- and two-photon fluorescent probe CB1 has been developed for discriminating Cys and Hcy in a successive manner with high selectivity. The discrete time-dependent fluorescent responses enable us to sequentially detect Cys and Hcy in different time windows. Two-step reaction and kinetic modes were used to explain the sensing mechanism. As a promising biosensor for cell imaging, CB1 has been confirmed to exhibit membrane permeability to intact cells, low cytotoxicity to viable cells and photostability to ultraviolet light excitation. Furthermore, the results from the control assay have shown that the one- and two-photon fluorescence of CB1 within cells is associated with intracellular mercapto biomolecules but yet there is little interference with physiological pH value, viscosity and common bioanalytes. Finally one- and two-photon fluorescent images of CB1 within living SiHa cells have been presented.

Novel fluorescent probes based on intramolecular charge- and proton-transfer compounds

Excited-state intramolecular proton-transfer (ESIPT) compounds and intramolecular charge-transfer (ICT) compounds have attracted attention due to their interesting and even unique emission properties. The intense and environment-sensitive emission showed by some members of the two families has been exploited in fluorescent probes for various forms of environmental sensing. In this paper, we summarize our recent study on the utilization of novel ESIPT and ICT compounds with intense emission as fluorescent probes after an introduction to the ESIPT and/or ICT processes and related photophysics mechanism.