A novel selective probe for detecting glutathione from other biothiols based on the concept of Fluorescence Fusion

Glutathione detection in water and milk using a new probe DCYP based on benzopyranonitrile

Glutathione (GSH) is a potent antioxidant, fragrance, and anti-browning agent in the field of food chemistry. The accurate GSH evaluation in food and vegetables is critical for instructing the right supplementation of GSH in body. However, most reported GSH fluorescent probes were utilized for the biological imaging. In this study, a new probe DCYP-GSH was developed by coupling of benzopyranonitrile as signal reporter to N-methylpyridine through C = C bond as binding site. Notably, a significant increase in fluorescence intensity and a λmax red-shift of DCYP-GSH in electron spectra were found as a result of the response to GSH. Quantitative detection of GSH in water and milk samples were achieved using probe DCYP-GSH. The development of DCYP-GSH was anticipated to provide an effective toolkit for food safe evaluation.

A novel 2-(2-aminophenyl) imidazo [1,5-a] pyridine-based fluorescent probe for rapid detection of phosgene

Phosgene is a highly concealed and highly toxic gas that seriously threatens human health and public security. Therefore, the detection of phosgene is of great significance to world security. Herein, a new type of fluorescent probe based on 2-(2-aminophenyl) imidazo [1,5-a] pyridine is reported for the rapid detection of phosgene. The probe itself only emits a faint green fluorescence, while phosgene allows it to produce a strong blue fluorescence. During the recognition process, phosgene interacts simultaneously with both amino site and imidazole moiety in the probe molecule, resulting in a four-ring-fused rigid structure with high fluorescence quantum yield. The probe not only has the characteristics of high efficiency, high sensitivity (detection limit 2.68 nM), and high selectivity, but also has remarkable spectral changes. Finally, a portable test strip is used to detect phosgene in the gas phase, and the fluorescent color change of the test strip can be easily observed. The most exciting thing is that the portable test strip with the probe PMPY-NH2 can produce a strong fluorescence response to 1 ppm of phosgene, which is far lower than the level of phosgene that seriously threatens to human health.

A resorufin-based fluorescent probe for hydrazine detection and its application in environmental analysis and bioimaging

Hydrazine (N2H4) is an important industrial raw material that has been widely used in industrial production and agricultural interventions, but its widespread application also inevitably causes environmental pollution. In this study, based on resorufin, we constructed a novel "turn-on" fluorescent probe RFT for the selective detection of hydrazine under complex environmental conditions and in vivo. The probe RFT exhibited excellent stability and selectivity towards the detection of hydrazine with a low detection limit of 260 nM. In addition, RFT was successfully applied to the detection of hydrazine in environmental water samples and living cells. Most importantly, RFT could not only detect the exogenous hydrazine in zebrafish and mice, but also image and visualize the up-regulation of endogenous hydrazine induced by isoniazid in zebrafish.

Multiple organelle-targeted 1,8-naphthyridine derivatives for detecting the polarity of organelles

Four 1,8-naphthyridine derivatives (1a-1d) with different organelle targeting abilities were obtained using the Knoevenagel condensation reaction of 1,8-naphthyridine with 4-(N,N-diethylamino)benzaldehyde (2a), 4-(N,N-diphenylamino)benzaldehyde (2b), 4-(piperazin-1-yl)benzaldehyde (2c) and 4-(ethyl(4-formylphenyl)amino)-N-(2-((4-methylphenyl)sulfonamido)ethyl)butanamide (2d), respectively. The maximal absorption bands of dyes 1a-1d were observed at 375-447 nm, while their maximum emission peaks were situated at 495-605 nm. The optical properties showed that the fluorescence emission of dyes 1a-1d is shifted toward greater wavelengths as the system polarity (Δf) increased. Meanwhile, with increasing polarity of the mixed 1,4-dioxane/H₂O system, the fluorescence intensity of dyes 1a-1d gradually decreased. Furthermore, the fluorescence intensity of 1a-1d enhanced by 12-239 fold as the polarity of 1,4-dioxane/H₂O mixtures declined. 1a-1d had a large Stokes shift (up to 229 nm) in polar solvents in comparison to nonpolar solvents. The colocalization imaging experiments demonstrated that dyes 1a-1d (3-10 μM) were located in mitochondria, lipid droplets, lysosomes and the endoplasmic reticulum in living HeLa cells, respectively; and they could monitor the polarity fluctuation of the corresponding organelles. Consequently, this work proposes a molecular design idea with different organelle targeting capabilities based on the same new fluorophore, and this molecular design idea may provide more alternatives for polarity-sensitive fluorescent probes with organelle targeting.

Recent Progress in the Rational Design of Biothiol-Responsive Fluorescent Probes

Biothiols such as cysteine, homocysteine, and glutathione play significant roles in important biological activities, and their abnormal concentrations have been found to be closely associated with certain diseases, making their detection a critical task. To this end, fluorescent probes have become increasingly popular due to their numerous advantages, including easy handling, desirable spatiotemporal resolution, high sensitivity, fast response, and favorable biocompatibility. As a result, intensive research has been conducted to create fluorescent probes for the detection and imaging of biothiols. This brief review summarizes recent advances in the field of biothiol-responsive fluorescent probes, with an emphasis on rational probe design, including the reaction mechanism, discriminating detection, reversible detection, and specific detection. Furthermore, the challenges and prospects of fluorescence probes for biothiols are also outlined.

TDDFT study on the simultaneous sensing mechanism for peroxynitrite and glutathione by a bifunctional fluorescent probe

Using time-dependent density functional theory (TDDFT) method, the response mechanism of a reported bifunctional fluorescent probe for simultaneous recognition of peroxynitrite and glutathione (Chem. Commun. 2018, 54, 11336) was theoretically studied. Calculated vertical excitation energies based on the ground-state and excited-state geometries were consistent with the corresponding experimental ultraviolet-visible and fluorescence spectra. In the ground state, electron delocalization in the probe was limited because its geometry was restrained by steric hindrance. Frontier molecular orbital analysis has shown that the probe should undergo photoinduced electron transfer (PET) from the benzothiazole moiety to the maleimide moiety after excitation. The nonplanar structure together with PET led to fluorescence quenching of the probe. The probe could be dealkylated by peroxynitrite anion. The resulting intramolecular hydrogen bond increasesd the planarity of the molecule, while also gave rise to an excited-state proton-transfer process. Moreover, the addition reaction between the probe and glutathione inhibited the PET process. These two analytes together contributed to the fluorescence enhancement of the final product. This theoretical sensing mechanism for peroxynitrite and glutathione may potentially be important for the design and enhancement of novel probes.

A flavonol-derived fluorescent probe for highly specific and sensitive detection of hydrazine in actual environmental samples and living zebrafish

Hydrazine (N₂H₄) is a significant chemical reagent and widely applied in industrial field, which can bring potential risk to environmental safety and human health due to its high toxicity and potential carcinogenicity. In this paper, a flavonol-derived fluorescent probe named TB-N₂H₄ was rationally developed for detecting N₂H₄ based on the excited intramolecular proton transfer (ESIPT) principle. TB-N₂H₄ exhibited a remarkable fluorescence turn-on response toward N₂H₄ with a large Stokes shift of 191 nm. Moreover, TB-N₂H₄ could selectively recognize N₂H₄ over other competitive analytes, and displayed high sensitivity toward N₂H₄ with a low detection limit of 0.117 μM. The sensing mechanism of the probe TB-N₂H₄ for N₂H₄ was confirmed by theoretical calculation and HRMS analysis. This probe was able to quantitatively determine N₂H₄ in environmental water and soil samples. Additionally, TB-N₂H₄ was also successfully utilized for real-time tracking of the distribution of N₂H₄ in living zebrafish.