Ratiometric detection of mitochondrial thiols with a two-photon fluorescent probe

A fluorescent probe based on novel fused four ring quinoxalinamine for palladium detection and bio-imaging

An “off–on” fluorescent probe was designed to detect palladium of all the typical oxidation states (0, +2, +4) without additional additives.

Design and Biosensing of a Ratiometric Electrochemiluminescence Resonance Energy Transfer Aptasensor between a g-C3N4 Nanosheet and Ru@MOF for Amyloid-β Protein

A dual-wavelength ratiometric electrochemiluminescence resonance energy transfer (ECL-RET) aptasensor based on the carbon nitride nanosheet (g-C₃N₄ NS) and metal-organic frameworks (Ru@MOFs) as energy donor-receptor pairs is first designed for the detection of the amyloid-β (Aβ) protein. The cathode ECL of g-C₃N₄ NS gradually decreased, whereas the anode ECL from Ru@MOF pyramidally enhanced along with the increasing concentration of Aβ in a 0.1 M phosphate-buffered saline solution containing 0.1 M S₂O₈^2-. Additionally, it is worth noting that 2-amino terephthalic acid from MOF not only can load abundant amounts of luminophor Ru(bpy)₃²⁺ but also promote the conversion of more amounts of S₂O₈^2- that served as a coreactant accelerator into SO₄^•-, further enhancing the ECL signal of Ru@MOF. Besides, the ECL intensity from the g-C₃N₄ NS had a tremendous spectrum overlap with the UV-vis spectrum of Ru@MOF, demonstrating the high-efficiency ECL-RET from g-C₃N₄ NS to Ru@MOF. According to the ratio of ECL_460nm/ECL_620nm, the constructed aptasensor for the detection of Aβ showed a wide linear range from 10^-5 to 500 ng/mL and a low detection limit of 3.9 fg/mL (S/N = 3) with a correction coefficient of 0.9965. The obtained results certified that the dual-wavelength ratiometric ECL sensor could provide a reliable direction and have the potential for application in biosensing and clinical diagnosis fields.

Direct Determination of Redox Statuses in Biological Thiols and Disulfides with Noncovalent Interactions of Poly(ionic liquid)s

The three most important redox couples, including cysteine (Cys)/cystine (Cyss), homocysteine (Hcys)/homocystine (Hcyss), and reduced glutathione (GSH)/glutathione disulfide (GSSG), are closely associated with human aging and many diseases. Thus, it is highly important to determine their redox statuses at the following two levels: (i) the redox identity in different thiols/disulfides and (ii) the redox ratio in a mixture of a specific couple. Herein, by using one single AIE-doped (AIE, aggregation-induced emission) photonic-structured poly(ionic liquid) (PIL) sphere as a virtual sensor array, we realize a direct determination of the redox status without a reducing pretreatment of disulfides, which will greatly promote the development of high-throughput and simple procedures. The pattern-recognition method uses the multiple noncovalent interactions of imidazolium-based PILs with these redox species to produce differential responses in both the photonic crystal and fluorescence dual channels. On the one hand, a single sphere enables the direct and simultaneous discrimination of the redox identities of Cys, Cyss, Hcys, Hcyss, GSH, and GSSG under the interference of other five commonly occurring thiols. On the other hand, this sphere also allows for not only a direct quantification of the GSH/GSSG ratios without previously determining the individual concentrations of GSH and GSSG but also the accurate prediction of the ratios in unknown redox samples. To further demonstrate applications of this method, redox mixtures in a biological sample are differentiated. Additionally, quantum calculations further support our assignments for interactions between the imidazolium-based PILs and these redox species.

A FRET-Based Near-Infrared Fluorescent Probe for Ratiometric Detection of Cysteine in Mitochondria

We report a near-infrared fluorescent probe A for the ratiometric detection of cysteine based on FRET from a coumarin donor to a near-infrared rhodamine acceptor. Upon addition of cysteine, the coumarin fluorescence increased dramatically up to 18-fold and the fluorescence of the rhodamine acceptor decreased moderately by 45 % under excitation of the coumarin unit. Probe A has been used to detect cysteine concentration changes in live cells ratiometrically and to visualize fluctuations in cysteine concentrations induced by oxidation stress through treatment with hydrogen peroxide or lipopolysaccharide (LPS). Finally, probe A was successfully applied for the in vivo imaging of Drosophila melanogaster larvae to measure cysteine concentration changes.

Chemically Responsive Photonic Crystal Hydrogels for Selective and Visual Sensing of Thiol-Containing Biomolecules

Intracellular thiols (e.g., cysteine, homocysteine, and glutathione) play critical roles in biological functions. Glutathione is the most abundant cellular thiol which is important for preserving redox homeostasis in biosystems. Herein, we demonstrated the fabrication of responsive photonic crystals (RPCs) for selective detection of thiol-containing biomolecules through the combination of self-assembly of monodisperse carbon-encapsulated Fe3O4 nanoparticles (NPs) and in situ photopolymerization. Typically, the polyacrylamide-based PCs were prepared by a cross-linking agent containing disulfide bonds. Interestingly, the specific chemical reaction between the disulfide bonds and thiol-containing biomolecules leads to the decrease of the cross-linking degree for the RPCs, triggering the swelling of the hydrogel and increase of the NP lattice spacing. The reduced glutathione (10-6 to 10-2 mol/L) can be determined by measuring the diffracted wavelength or visually observing the structural color change. Moreover, the RPCs can be used to detect different kinds of thiol-containing biomolecules by a simple color variation due to different reaction rates between disulfide bonds and different thiol-containing biomolecules. This study provides a facile yet effective strategy for visualized determination of the thiol-containing biomolecules.

Small-molecule fluorescent probes for specific detection and imaging of chemical species inside lysosomes

In the past few years, the preparation of novel small-molecule fluorescent probes for specific detection and imaging of chemical species inside lysosomes has attracted considerable attention because of their wide applications in chemistry, biology, and medical science. This feature article summarizes the recent advances in the design and preparation of small-molecule fluorescent probes for specific detection of chemical species inside lysosomes. In addition, their properties and applications for the detection and imaging of pH, H2O2, HOCl, O2˙-, lipid peroxidation, H2S, HSO3-, thiols, NO, ONOO-, HNO, Zn2+, Cu2+, enzymes, etc. in lysosomes are discussed as well.

Mitochondria-Targeted Two-Photon Fluorescent Photosensitizers for Cancer Cell Apoptosis via Spatial Selectability

Organelle-targeted photosensitizers have been reported to be effective cell apoptosis agents. Mitochondria is recognized as an ideal target for cancer treatment due to its central role in oxidative metabolism and apoptosis. Meanwhile, two-photon (TP) fluorescence microscopy has become a powerful tool for fluorescence imaging in biological events based on its minimizing photodamage/photobleaching and intrinsic 3D resolution in deep tissues and in vivo. In this study, a series of novel mitochondrial-targeted TP fluorescent photosensitizers (TP-tracers) are designed, synthesized, and systematically investigated. These TP-tracers exhibit extraordinary anti-interference capability among different cations, anions, and amino acids as well as the insensitivity to the changes of pH and complex biological environments. TP-tracers are further used in fluorescence living cells, Drosophila brains, and zebrafish imaging with low cytotoxicity, excellent mitochondria-targeting, and TP properties. The results demonstrate efficient mitochondria-targeting cell selective apoptosis based on TP-activated cancer cells with highly single cell selectivity, and the pharmacokinetic study reveals that MitoY2 does not have accumulation in rats. It is believed that these molecules hold great potential in TP-related smart phototherapy.

Two-photon imaging of the endoplasmic reticulum thiol flux in the brains of mice with depression phenotypes

Depression is a common mental illness with high morbidity and mortality. Mounting evidence suggests that an imbalance of the oxidant-antioxidant defence system is strongly correlated with depression and the dysfunction of the endoplasmic reticulum (ER) is strongly related to the oxidative stress. Therefore, as vital and abundant antioxidants in the ER, biothiols may contribute to the etiology of depression. However, ideal two-photon (TP) fluorescent probes for in vivo imaging of ER-associated thiols in the brains of mice with depression phenotypes are still lacking. Hence, we describe a fluorescent probe (ER-SH) to visualize thiols in living systems. ER-SH displays high sensitivity, excellent ER-targeting ability, outstanding TP properties and low cytotoxicity. Using this ER-SH probe, we succeeded in revealing an increase in the endogenous thiol levels under ER stress induced by DTT. Significantly, TP in vivo imaging showed for the first time that the thiol levels are reduced in brains of mice with depression phenotypes. Collectively, this work can assist in further understanding the molecular mechanism of depression and offers a crucial dimension for diagnosis and anti-depression treatments.

A novel mitochondrial-targeting near-infrared fluorescent probe for imaging γ-glutamyl transpeptidase activity in living cells

γ-Glutamyl transpeptidase (GGT) plays an essential role in regulating cellular glutathione and cysteine homeostasis, and its abnormal elevation is associated with different diseases including cancers. Here a novel mitochondrial-targeting near-infrared fluorescent probe was designed for GGT by conjugating glutamate acid to a newly synthesized amine hemicyanine fluorophore. The fluorescent probe was initially non-emissive due to the formation of an amide bond which destroyed the electronic-donating ability of the amine moiety and disrupted the push-pull structure. GGT-mediated cleavage of the γ-glutamyl bond regenerated the initial fluorophore with distinct intramolecular charge transfer (ICT) and activated the fluorescence signal. The fluorescent probe displayed a linear relationship to the concentration of GGT in the range of 1.0-90 U L-1, with an estimated limit of detection (LOD) of 0.4 U L-1. Its ability to target and image mitochondrial GGT activity was demonstrated in living cells with high specificity and fast response. We believe our near-infrared fluorescent probe could have great potential in imaging mitochondrial GGT activity and elucidating GGT-associated pathological consequences in living cells and even small animal models.

Immobilizable fluorescent probes for monitoring the mitochondria microenvironment: a next step from the classic

Immobilizable probes represent a valuable trend.

A NIR fluorescent sensor for biothiols based on a dicyanoisophorone derivative with a large Stokes shift and high quantum yield

Probe N-Bio exhibited rapid response, high sensitivity and strong NIR fluorescence in the detection of biothiols in living cells.

A long wavelength emission two-photon fluorescent probe for highly selective detection of cysteine in living cells and an inflamed mouse model

As a semi-essential proteinogenic amino acid and biothiol, cysteine (Cys) is highly important in many basic cellular processes.

Smart, chiral, and nonconjugated cyclohexane-based bis-salicylaldehyde hydrazides: multi-stimuli-responsive, turn-on, ratiometric, and thermochromic fluorescence, single-crystal structures via DFT calculations

Multidentate and environmentally sensitive dyes show turn-on, ratiometric, and thermochromic fluorescence.

A Ratiometric Two-Photon Fluorescent Cysteine Probe with Well-Resolved Dual Emissions Based on Intramolecular Charge Transfer-Mediated Two-Photon-FRET Integration Mechanism

The development of an efficient ratiometric two-photon fluorescence imaging probe is crucial for in situ monitoring of biothiol cysteine (Cys) in biosystems, but the current reported intramolecular charge transfer (ICT)-based one suffers from serious overlap between the shifted emission bands. To address this issue, we herein for the first time constructed an ICT-mediated two-photon excited fluorescence resonance energy transfer (TP-FRET) system consisting of a two-photon fluorogen benzo[ h]chromene and a Cys-responsive benzoxadiazole-analogue dye. Different from a previous mechanism that utilized single two-photon fluorogen to acquire a ratiometric signal, ICT was used to switch on the TP-FRET process of the energy transfer dyad by eliciting an absorption shift of benzoxadiazole with Cys to modulate the spectral overlap level between benzo[ h]chromene emission and benzoxadiazole absorption, resulting in two well-separated emission signal changes with large emission wavelength shift (120 nm), fixed two-photon excitation maximum (750 nm), and significant variation in fluorescence ratio (over 36-fold). Therefore, it can be successfully employed to ratiometrically visualize Cys in HeLa cells and liver tissues. Importantly, this new ICT-mediated TP-FRET integration mechanism would be convenient for designing ratiometric two-photon fluorescent probes with two well-resolved emission spectra suitable for high resolution two-photon fluorescence bioimaging.

A two-photon ratiometric fluorescent probe for highly selective sensing of mitochondrial cysteine in live cells

We report herein a two-photon ratiometric fluorescent probe (DNEPI) for mitochondrial cysteine (Cys) detection on the basis of a merocyanine (compound 1) as the two-photon fluorophore and a 2,4-dinitrobenzensulfonyl (DNBS) unit as the biothiol reaction site. Upon reaction with Cys in DMSO/PBS (1/1, v/v), DNEPI showed a distinct ratiometric fluorescence emission characteristic (F_{583 nm}/F_{485 nm}) linearly proportional to Cys concentrations over the range of 2-10 μM, which was attribute to the enhanced intramolecular charge transfer (ICT) effect by cleavage of the sulfonic acid ester bond of DNEPI to release compound 1. More importantly, the probe could detect Cys with a fast response time (within 2 min) and the detection limit was quantitatively calculated as 0.29 μM. Furthermore, DNEPI not only exhibited high selectivity toward Cys over other similar biothiols, including homocysteine (Hcy) and glutathione (GSH), but also displayed significant mitochondrial-targeting ability, which were favorable for mitochondrial Cys-selective imaging. Subsequently, application of DNEPI to Cys imaging in live cells was successfully achieved by two-photon fluorescence microscopy, suggesting that the probe proposed here could be used to monitor mitochondrial Cys concentration changes in live cells with negligible interference from other biological thiols.

Bimetallic Oxide MnMoOX Nanorods for in Vivo Photoacoustic Imaging of GSH and Tumor-Specific Photothermal Therapy

Accurate imaging of glutathione (GSH) in vivo is able to provide real-time visualization of physiological and pathological conditions. Herein, we successfully synthesize bimetallic oxide MnMoO_X nanorods as an intelligent nanoprobe for in vivo GSH detection via photoacoustic (PA) imaging. The obtained MnMoO_X nanoprobe with no near-infrared (NIR) absorption in the absence of GSH would exhibit strong GSH-responsive NIR absorbance, endowing PA imaging detection of GSH. Due to the up-regulated GSH concentration in the tumor microenvironment, our MnMoO_X nanoprobe could be utilized for in vivo tumor-specific PA imaging. Moreover, MnMoO_X nanorods with GSH-responsive NIR absorbance could also be employed to achieve tumor-specific photothermal therapy (PTT). Importantly, such MnMoO_X nanorods show inherent biodegradability and could be rapidly cleared out from the body, minimizing their long-term body retention and potential toxicity. Our work presents a new type of GSH-responsive nanoprobe based on bimetallic oxide nanostructures, promising for tumor-specific imaging and therapy.

Using Ultrafast Responsive Phosphorescent Nanoprobe to Visualize Elevated Peroxynitrite In Vitro and In Vivo via Ratiometric and Time-Resolved Photoluminescence Imaging

Peroxynitrite (ONOO^- ), a potent biological oxidant, which has a short half-life in physiological conditions, is related to many diseases. Accurate peroxynitrite determination with superior selectivity and sensitivity is important for understanding biological roles of peroxynitrite in different health and disease tissues. Autofluorescence is an inevitable interference in luminescence biodetection and bioimaging, which often reduces signal-to-noise ratio during detection. In this work, a phosphorescent peroxynitrite nanoprobe (MSN-ONOO) which displays two emission bands is prepared by immobilizing two long-lived phosphorescent iridium(III) complexes that are peroxynitrite-activable and -inert, respectively, into water-dispersible mesoporous silica nanoparticles. Owing to the fast response rate, excellent sensitivity and outstanding selectivity of the nanoprobe toward peroxynitrite, it is further used for peroxynitrite determination in vitro and in vivo via ratiometric photoluminescence imaging. More notably, taking advantage of the long-lived phosphorescence of MSN-ONOO, in vivo elevated peroxynitrite is imaged with diminished autofluorescence interference and improved signal-to-noise ratio via time-resolved photoluminescence imaging. As far as it is known, this is the first time for endogenous peroxynitrite detection in vivo via the time-resolved photoluminescence imaging. Furthermore, the production of peroxynitrite in inflamed tissues is visualized.

A low background D-A-D type fluorescent probe for imaging of biothiols in living cells

Two probes, structurally symmetric CBFB and asymmetric CBFM, constructed by a D-A-D (donor-acceptor-donor) type curcuminoid as the fluorophore and the DNBS (2,4-dinitrobenzenesulfonyl) group as the biothiol recognition site were designed and synthesized here. The DNBS group can quench the emission of the fluorophore by the PET (photoinduced electron transfer) process, and in the presence of biothiols, the emission of the probe was switched on as a result of the cleavage of the quencher by a nucleophilic aromatic substitution reaction. Experimental analyses and theoretical calculations revealed that two recognition moieties in the molecule can quench the fluorescence more efficiently, therefore, CBFB showed a much higher SNR (signal to noise ratio) than CBFM in biothiol detection with an emission maximum at 610 nm. This "low background" and "turn-on" fluorescent probe, CBFB, was successfully utilized to map endogenous biothiols in living cells.

A Zero Cross-Talk Ratiometric Two-Photon Probe for Imaging of Acid pH in Living Cells and Tissues and Early Detection of Tumor in Mouse Model

Acid-base disorders disrupt proper cellular functions, which are associated with diverse diseases. Development of highly sensitive pH probes being capable of detecting and monitoring the minor changes of pH environment in living systems is of considerable interest to diagnose disease as well as investigate biochemical processes in vivo. We report herein two novel high-resolution ratiometric two-photon (TP) fluorescent probes, namely, PSIOH and PSIBOH derived from carbazole-oxazolidine π-conjugated system for effective sensing and monitoring acid pH in a biological system. Remarkably, PSIOH exhibited the largest emission shift of ∼169 nm from 435 to 604 nm upon pH changing from basic to acidic with an ideal p K_a value of 6.6 within a linear pH variation range of 6.2-7.0, which is highly desirable for high-resolution tracking and imaging the minor fluctuation of pH in live cells and tissues. PSIOH also exhibits high pH sensitivity, excellent photostability, and reversibility as well as low cytotoxicity. More importantly, this probe was successfully applied to (i) sense and visualize the pH alteration in HeLa cells caused by various types of exogenous stimulation and (ii) detect and differentiate cancer and tumors in liver tissues and a mouse model, realizing its practical in vitro and in vivo applications.

Thiol Specific and Mitochondria Selective Fluorogenic Benzofurazan Sulfide for Live Cell Nonprotein Thiol Imaging and Quantification in Mitochondria

Cellular thiols are divided into two major categories: nonprotein thiols (NPSH) and protein thiols (PSH). Thiols are unevenly distributed inside the cell and compartmentalized in subcellular structures. Most of our knowledge on functions/dysfunctions of cellular/subcellular thiols is based on the quantification of cellular/subcellular thiols through homogenization of cellular/subcellular structures followed by a thiol quantification method. We would like to report a thiol-specific mitochondria-selective fluorogenic benzofurazan sulfide {7,7'-thiobis( N-rhodamine-benzo[c][1,2,5]oxadiazole-4-sulfonamide) (TBROS)} that can effectively image and quantify live cell NPSH in mitochondria through fluorescence intensity. Limited methods are available for imaging thiols in mitochondria in live cells especially in a quantitative manner. The thiol specificity of TBROS was demonstrated by its ability to react with thiols and inability to react with biologically relevant nucleophilic functional groups other than thiols. TBROS, with minimal fluorescence, formed strong fluorescent thiol adducts (λ_ex = 550 nm, λ_em = 580 nm) when reacting with NPSH confirming its fluorogenicity. TBROS failed to react with PSH from bovine serum albumin and cell homogenate proteins. The high mitochondrial thiol selectivity of TBROS was achieved by its mitochondria targeting structure and its higher reaction rate with NPSH at mitochondrial pH. Imaging of mitochondrial NPSH in live cells was confirmed by two colocalization methods and use of a thiol-depleting reagent. TBROS effectively imaged NPSH changes in a quantitative manner in mitochondria in live cells. The reagent will be a useful tool in exploring physiological and pathological roles of mitochondrial thiols.

Detection of analytes in mitochondria without interference from other sites based on an innovative ratiometric fluorophore

Mitochondria are vital organelles that not only produce cellular energy but also participate in many biological processes. Recently, various fluorescent probes have been developed for mitochondrial imaging. However, due to the lack of suitable dyes or strategies, it is difficult for most reported mitochondrial targeting probes to prove whether the analytes they detected are from mitochondria. In addition, positive charge on mitochondrial probes can seriously affect the mitochondrial environment. To address these issues, we herein put forward a novel strategy for probe design based on a smart NIR dye (HDFL) for mitochondrial targeting detection. Compared to general mitochondrial targeting probes that are modified with a target site and a reaction site, the new strategy is to combine the two sites together for a mitochondrial probe that would provide accurate detection of analytes in mitochondria without interference. As a proof of concept, we synthesized a mitochondrial-targetable probe HDFL-Cys for cysteine. Bioimaging studies have shown that the new type of probe HDFL-Cys can first accumulate in mitochondria and then react with the analyte (cysteine) accompanied by the departure of the targeting group (lipophilic cation moieties). Thus, it can specifically detect the analyte in mitochondria without interference from extra-mitochondrial analytes. We anticipate that the new strategy based on the novel NIR dye HDFL may be a potential platform for developing desirable ratiometric fluorescent probes for mitochondrial imaging.

Highly selective and ratiometric fluorescent nanoprobe for the detection of cysteine and its application in test strips

Cysteine (Cys) is a bithiol that plays a vital role in many physiological processes. However, it is difficult to discriminate Cys from homocysteine (Hcy) and glutathione (GSH), due to their similar chemical structures and reactivity. Herein, we have developed a polymeric nanoprobe, nanoHFA, for ratiometric, highly selective, and sensitive detection of Cys based on 7-hydroxycoumarin-3-carboxylic acid (HC) and fluorescein isothiocyanate (FITC)-acrylate (FITC-A) group-functionalized lipopolymer DSPE-PEG. The probe nanoHFA showed a strong fluorescence emission peak centered at 450 nm attributed to HC and a weak fluorescence emission peak centered at 520 nm due to the photoinduced electron transfer (PET) process of FITC induced by acrylate group. In the presence of Cys, the fluorescence signal at 520 nm could be lit up and the ratio of F_520nm/F_450nm showed a good linear relationship in the range of 5-60 μM with a low detection limit of 0.37 μM. The probe also displayed excellent water solubility and high selectivity to Cys over other biothiols such as Hcy and GSH. Moreover, we further used probe nanoHFA to detect Cu²⁺ ions in the range of 100-550 nM with a detection limit of 77 nM. The nanoprobe was successfully applied for the quantitative detection of Cys in fetal bovine serum, and fluorescent strips were developed for facile and visual detection of Cys and Cu²⁺ ions. Graphical abstract ᅟ.

A novel dicyanoisophorone based red-emitting fluorescent probe with a large Stokes shift for detection of hydrazine in solution and living cells

A novel dicyanoisophorone based fluorescent probe HP was developed to detect hydrazine. Upon the addition of hydrazine, probe HP displayed turn-on fluorescence in the red region with a large Stokes shift (180nm). This probe exhibited high selectivity and high sensitivity to hydrazine in solution. The detection limit of HP was found to be 3.26ppb, which was lower than the threshold limit value set by USEPA (10ppb). Moreover, the probe was successfully applied to detect hydrazine in different water samples and living cells.

Quinoline-derived fluorescent probes for the discrimination of Cys from Hcys/GSH and bioimaging in living cells

Development of thiol-specific fluorescent probes with selectivity in different thiol compounds is more practical and significant than those without that capacity. In this work, a new quinoline-derived fluorophore, hydroxyl-substituted quinoline-benzo[d]oxazole 6 with high fluorescence quantum yield is synthesized and esterified with acrylic acid to afford two fluorescent probes, BQA-1 and BQA-2 for selectively discriminating Cys from Hcys/GSH based on conjugate addition-cyclization mechanism. BQA-1 exhibits a large ratiometric fluorescence response toward Cys in aqueous pH 7.4 solution with big emission peak-shifting from 383 nm to 518 nm, over 130 nm. The detection limit is determined to be as low as 0.59 μM. In contrast to BQA-1, BQA-2 whose acrylic ester moiety is further modified with pyridine group, displays a turn-on fluorescence response to Cys with detection limit of 0.98 μM. Both BQA-1 and BQA-2 have relatively weak response to another two biothiols, Hcys and GSH and nearly no response to other nucleophiles. Furthermore, the potential application for the detection of biothiols in living cells has been demonstrated by cell imaging experiment.

Synthesis and characterisation of calix[4]arene based bis(triazole)-bis(hexahydroquinoline): Probing highly selective fluorescence quenching towards mercury (Hg2+) analyte

In the present study, we are reporting the synthesis of a triazoles incorporated fluorescent hexahydroquinoline appended calix[4]arene 7 and its highly selective optical recognition ability towards Hg²⁺. The optical sensor 7 was synthesized via two different synthetic pathways and unambiguously characterized by mass spectrometry and NMR spectroscopy. The stoichiometric ratio between 7 and Hg²⁺ was determined as 1:1 based on Job's plot and ESI-MS analysis. The chemosensor 7 selectively recognized Hg²⁺ in the presence of competitive cations such as Cu²⁺, Cu¹⁺, Co³⁺, Ni²⁺, Ag¹⁺, Fe²⁺, Fe³⁺, Cr³⁺, Pb²⁺, Cd²⁺, Zn²⁺, Sn²⁺, Ti⁴⁺, Sb³⁺, In³⁺, Ba²⁺, Ca²⁺, and K¹⁺. The limit of detection (LOD) was established as 0.5 μM on spectrofluorimetric analysis. According to world health organization (WHO) in guidelines for drinking-water quality, the mercury level in natural occurring ground and surface water is about ∼0.5 μM (μg/L). The supra molecule 7 with LOD (0.5 μM) could potentially serve effective receptors for Hg²⁺ cation. The probe 7 was applied effectively for detection of Hg²⁺ in real water samples (i.e. tap and deionized water), spiked with Hg²⁺ (10 μM) solution. Moreover, the compound 7 showed non-toxicity during cytotoxic assay against human B cells as they retain their morphology. The supramolecule 7 in living cells showed selectivity towards Hg²⁺ in cytotoxic assay with T lymphocytes, evident by morphological changes observed via AFM analysis.

TPZ, a bright centrosymmetric two-photon scaffold for bioimaging

The development of biocompatible two-photon fluorophores with a large absorption cross-section is challenging, despite the presence of theoretical guidelines. By rendering asymmetric PRODAN dye centrosymmetric, we designed and synthesized a novel class of two-photon fluorophores (TPZ). Their photophysical properties were investigated and their imaging potentials in cells, tissues and zebrafish were showcased.

An efficient two-photon fluorescent probe for monitoring mitochondrial singlet oxygen in tissues during photodynamic therapy

A promising two-photon fluorescent probe MNAH for detecting ¹O₂ during the PDT process in mitochondria was proposed for the first time. MNAH was successfully applied for two-photon imaging of ¹O₂ in living cells and tissues during the PDT process with deep-tissue imaging depth. MNAH can be a powerful molecular tool for studying ¹O₂ generation in mitochondria during the PDT process.

Two-photon fluorescent polysiloxane-based films with thermally responsive self switching properties achieved by a unique reversible spirocyclization mechanism

The first example of a two-photon fluorescent polysiloxane-based film with fantastic thermal-responsive properties was reported. A unique alkaline tuned reversible spirocyclization mechanism was proposed.

Responsiveness and reversibility are present in nature, and are ubiquitous in biological systems. The realization of reversibility and responsiveness is of great importance in the development of properties and the design of new materials. However, two-photon fluorescent thermal-responsive materials have not been reported to date. Herein, we engineered thermally responsive polysiloxane materials (Dns-non) that exhibited unique two-photon luminescence, and this is the first report about thermally responsive luminescent materials with two-photon fluorescence. The fluorescence of Dns-non could switch from the “on” to “off” state through a facile heating and cooling process, which could be observed by the naked eye. Monitoring the temperature of the CPU in situ was achieved by easily coating D1-non onto the CPU surface, which verified the potential application in devices of Dns-non. A unique alkaline tuned reversible transition mechanism of rhodamine-B from its spirocyclic to its ring-open state was proposed. Furthermore, Dns-non appeared to be a useful cell adhesive for the culture of cells on the surface. We believe that the constructed thermally responsive silicon films which have promising utilization as a new type of functional fluorescent material, may show broad applications in materials chemistry or bioscience.

Redox-Controlled Fluorescent Nanoswitch Based on Reversible Disulfide and Its Application in Butyrylcholinesterase Activity Assay

Butyrylcholinesterase (BChE) mainly contributing to plasma cholinesterase activity is an important indicator for routinely diagnosing liver function and organophosphorus poisoning in clinical diagnosis, but its current assays are scarce and frequently suffer from some significant interference and instability. Herein, we report a redox-controlled fluorescence nanoswtich based on reversible disulfide bonds, and further develop a fluorometric assay of BChE via thiol-triggered disaggregation-induced emission. Thiol-functionalized carbon quantum dots (thiol-CQDs) with intense fluorescence is found to be responsive to hydrogen peroxide, and their redox reaction transforms thiol-CQDs to nonfluorescent thiol-CQD assembly. The thiols inverse this process by a thiol-exchange reaction to turn on the fluorescence. The fluorescence can be reversibly switched by the formation and breaking of disulfide bonds caused by external redox stimuli. The specific thiol-triggered disaggregation-induced emission enables us to assay BChE activity in a fluorescence turn-on and real-time way using butyrylthiocholine iodide as the substrate. As-established BChE assay achieves sufficient sensitivity for practical determination in human serum, and is capable of avoiding the interference from micromolar glutathione and discriminatively quantifying BChE from its sister enzyme acetylcholinesterase. The first design of reversible redox-controlled nanosiwtch based on disulfide expands the application of disulfide chemistry in sensing and clinical diagnostics, and this novel BChE assay enriches the detection methods for cholinesterase activity.

A review: the trend of progress about pH probes in cell application in recent years

Intracellular pH values are some of the most important factors that govern biological processes and the acid-base homeostasis in cells, body fluids and organs sustains the normal operations of the body. Subcellular organelles including the acidic lysosomes and the alkalescent mitochondria undergo various processes such as intracellular digestion, ATP production and apoptosis. Due to their precise imaging capabilities, fluorescent probes have attracted great attention for the illustration of pH modulated processes. Furthermore, based on the unique acidic extracellular environment of acidic lysosomes, fluorescent probes can specifically be activated in cancer cells or tumors. In this review, recently reported lysosome and mitochondria specific pH imaging probes as well as pH-activatable cancer cell-targetable probes have been discussed.

A NBD-S-rhodamine dyad for dual-color discriminative imaging of biothiols and Cys/Hcy

A fluorescent probe based on fast thiolysis of NBD thioether is developed for dual-color discriminative imaging of Cys and GSH.

Rosamine with pyronine-pyridinium skeleton: unique mitochondrial targetable structure for fluorescent probes

Rosamine-based probes (1a–b) with pyronine-pyridinium skeleton served as mitochondrial targetable probes for detecting independent species (H₂O₂ and H₂S).

Specific and sensitive imaging of basal cysteine over homocysteine in living cells

Biological thiols play important roles in maintaining appropriate redox status of organisms. Accepting the challenge to differentiate structurally similar cysteine (Cys) and homocysteine (Hcy), we have successfully developed a miniature synthetic turn-on fluorescent probe based on 6-(2-benzothiazolyl)-2-naphthalenol for Cys. This probe is able to specifically react with Cys to yield its naphthalenol derivative, accompanied by remarkable green fluorescence enhancement with a detection limit of 14.8 nM. Besides, this probe displays much greater selectivity for Cys over other biological thiols, including homocysteine (Hcy) and glutathione (GSH). Practically, good cell permeability and low cytotoxicity make it suitable for monitoring basal Cys in living cells.

A turn-on fluorescent probe conjugating with a reactive acrylate for visualization of basal Cys specifically in living cells was developed.

A Michael addition–cyclization-based switch-on fluorescent chemodosimeter for cysteine and its application in live cell imaging

We designed and synthesized a fast response fluorescent probe, BTAC (benzothiazol-azacoumarin), for detection of cysteine (Cys).