A lysosome-targetable fluorescent probe for the simultaneous sensing of Cys/Hcy and GSH from different emission channels

Coumarin-based fluorescent probe with 4-phenylselenium as the active site for multi-channel discrimination of biothiols

Biological mercaptans, also known as biothiols, play their own roles in a number of important physiological processes, and the abnormal levels of biothiols are closely associated with a variety of...

Substitution-rearrangement-cyclization strategy to construct fluorescent probe for multicolor discriminative analysis biothiols in cells and zebrafish

Discriminative detection of biothiols (Cysteine, homocysteine and glutathione) is of great significance to clarificate their complex physiological processes, the occurrence and development of related diseases. However, similar structure and reactivity among such species pose huge challenges in developing fluorescent probes to distinguish among of them. In this work, a dual-site probe CTT reacted with the analytes to regulate molecular conjugation through substitution-rearrangement-cyclization strategy, utilizing a multi-channel signal combination mode to realize the distinguishing detection of the three biothiols. Cell and zebrafish imaging experiments sufficiently demonstrated that CTT could semiquantify biothiols, which will provide valuable chemical tool for elucidating the complex biological functions of biothiols.

A turn-on homodimer fluorescent probe based on homo-FRET for the sensing of biothiols in lysosome: a trial of a new turn-on strategy

Fluorescence resonance energy transfer (FRET) is often applied to construct fluorescent probes for acquiring high selectivity and sensitivity. According to the FRET theory, a homodimer composed of two identical fluorophores with a small Stokes shift has only weak fluorescence due to homo-FRET between fluorophores, and the fluorescence could be recovered after the destruction of the homodimer. In this study, we designed and synthesized a homodimer fluorescent probe, namely 1,3,5,7-tetramethyl-8-(4'-phenylthiophenol)-boron difluoride-dipyrrole methane dimer (D-TMSPB), based on this turn-on strategy. In D-TMSPB, the disulfide moiety was selected as the response moiety of biothiols, and BODIPY fluorophore was chosen as both donor and acceptor in FRET due to the ultra-small Stokes shifts and obvious overlap of its excitation/emission peak. D-TMSPB exhibited only weak fluorescence. After selective reaction with biothiols, FRET was destroyed and the derivative exhibited strong fluorescence at 514 nm with the limit of detection of about 0.15 μM for GSH. Notably, the derivative of biothiols shows remarkable fluorescence only in acidic conditions, which accords with the internal environment of lysosome. Thus, D-TMSPB was applied to image the biothiols of lysosome in living cells. The turn-on fluorescence of D-TMSPB indicated that homo-FRET is a practical strategy to design turn-on fluorescent probes, particularly for the sensing mechanism based on leaving groups.

A multifunctional fluorescent probe for visualizing H2S in wastewater with portable smartphone via fluorescent paper strip and sensing GSH in vivo

In this paper, a bifunctional tri-site fluorescent probe was designed for the first time not only for visualization and quantitative analysis of sensing H₂S in wastewater by coupling paper strip and smartphone (Color recognizer, Xiyi Technology) but also for sensitively monitoring GSH in living cells, which relied on different emission channels and the pH of solutions. The recognition properties of GH towards H₂S/GSH were satisfactorily demonstrated through fluorescence, UV-vis, ¹H NMR and DFT calculations. More importantly, integrated with the paper strip, portable smartphone-sensing platform with a color recognizer app would accomplish cost-effective and rapid assays for colorimetric water quality testing, which displayed huge application potential in fields of environmental monitoring.

A Pyrene-Based Fluorescent Probe for Specific Detection of Cysteine and its Application in Living Cell

Cysteine (Cys) is an essential amino acid in organism, which is transformed from methionine in vivo and participates in protein synthesis and cell redox process. Therefore, the detection of Cys is of great significance. In this work, a novel fluorescent probe, (E)-3-(2-chloroquinolin-3-yl)-1-(pyren-3-yl) prop-2-en-1-one (PAQ) was designed and synthesized to specifically detect Cys. The response mechanism of the reaction between PAQ and Cys was due to the addition reaction of Cys to α,β-unsaturated ketone of PAQ. Interestingly, the addition of Cys induced significant fluorescence intensity enhancement at 462 nm. PAQ exhibited favorable sensing properties towards Cys such as the low limit of detection (0.27 μM) and fast response speed (2 min). In addition, PAQ displayed high selectivity and anti-interference ability toward Cys among various analytes. Notably, PAQ has been successfully used to image exogenous and endogenous Cys in HeLa cells.

Fluorescent probes based on nucleophilic aromatic substitution reactions for reactive sulfur and selenium species: Recent progress, applications, and design strategies

Reactive sulfur species (RSS) and reactive selenium species (RSeS) are important substances for the maintenance of physiological balance. Imbalance of RSS and RSeS is closely related to a series of human diseases, so it is considered to be an important biomarker in early diagnosis, treatment, and stage monitoring. Fast and accurate quantitative analysis of different RSS and RSeS in complex biological systems may promote the development of personalized diagnosis and treatment in the future. One way to explore the physiological function of various types of RSS and RSeS in vivo is to detect them at the molecular level, and one of the most effective methods for this is to use fluorescent probes. Nucleophilic aromatic substitution (SNAr) reactions are commonly exploited as a detection mechanism for RSS and RSeS in fluorescent probes. In this review, we cover recent progress in fluorescent probes for RSS and RSeS based on SNAr reactions, and discuss their response mechanisms, properties, and applications. Benzenesulfonate, phenyl-O ether, phenyl-S ether, phenyl-Se ether, 7-nitro-2,1,3-benzoxadiazole (NBD), benzoate, and selenium-nitrogen bonds are all good detection groups. Moreover, based on an integration of different reports, we propose the design and synthesis of RSS- and RSeS-selective probes based on SNAr reactions, current challenges, and future research directions, considering the selection of active sites, the effect of substituents on the benzene ring, and the introduction of other functional groups.

Survival Mechanisms and Xenobiotic Susceptibility of Keratinocytes Exposed to Metal-Derived Nanoparticles

Metal-derived nanoparticles (Mt-NPs) are increasingly used in cosmetology due to their ultraviolet shielding (titanium dioxide [TiO₂]), antioxidant (cerium dioxide [CeO₂]), and biocidal (silver [Ag]) properties. In the absence of overt toxicity (i.e., cell death), Mt-NPs are considered safe for cosmetic applications. However, there is little understanding about the mechanisms involved in the survival of keratinocytes exposed to subtoxic levels of Mt-NPs. Human keratinocytes (HaCaT) were exposed subacutely to subtoxic concentrations (≤30 μg/mL, 48-72 h) of rutile (r) TiO₂ (cylindrical), CeO₂ (cubic) and Ag (spherical) with a core/hydrodynamic size of <50/<100 nm and >98% purity. Mt-NP uptake was indirectly quantified by changes in the light side scatter, where the kinetics (time/dose-response) suggested that the three types of Mt-NPs were similarly uptaken by keratinocytes. rTiO₂ and CeO₂, but not Ag-NPs, increased autophagy, whose inhibition prompted cell death. No increase in the steady-state levels of reactive oxygen species (ROS) was induced by exposure to any of the Mt-NPs tested. Interestingly, intracellular Ag-NP aggregates observed an increased far-red autofluorescence (≥740 nm em), which has been ascribed to their binding to thiol molecules such as glutathione (GSH). Accordingly, inhibition of GSH synthesis, but not the impairment of oxidized GSH recycling, sensitized keratinocytes to Ag-NPs suggesting that GSH homeostasis, and its direct scavenging of Ag-NPs, but not ROS, is essential for keratinocyte survival upon exposure to Ag-NP. rTiO₂ and Ag, but not CeO₂-NPs, compromised metabolic flux (glycolysis and respiration), but ATP levels were unaltered. Finally, we also observed that exposure to Mt-NPs sensitized keratinocytes to non-UV xenobiotic exposure (arsenite and paraquat). Our results demonstrate the differential contribution of autophagy and GSH homeostasis to the survival of human keratinocytes exposed to subtoxic concentrations of Mt-NPs and highlight the increased susceptibility of keratinocytes exposed to Mt-NPs to a second xenobiotic insult.