Ratiometric Change Research Articles

A Piperazine Linked Rhodamine-BODIPY FRET-based Fluorescent Sensor for Highly Selective Pd2+ and Biothiol Detection.

A class of rhodamine-based fluorescent sensors for the selective and sensitive detection of Pd2+ metal ions in aqueous media has been developed. A rhodamine-based sensor PMS and a rhodamine-BODIPY Förster resonance energy transfer (FRET)-pair sensor PRS have been incorporated with a piperazine linker and an O-N-S-N podand ligand for specific recognition of Pd2+ ion. Both probes displayed colorimetric and fluorescent ratiometric changes when exposed to Pd2+, due to their spirolactam rings opening and restoring rhodamine conjugation. PRS is highly selective to Pd2+ over 22 other metal ions, showing a 0.6-fold ratiometric difference at I600nm/I515nm. Additionally, the lactam ring in Pd2+ coordinated PRS-Pd could be switched back to the closed form in the presence of various thiols, providing a "red-green traffic light" detection mechanism between red and green emission. Furthermore, PRS showed excellent cell viability and was successfully employed to image Pd2+ and the PRS-Pd complex ensemble could interchangeably detect biothiols including glutathione (GSH) in A549 human lung cancer cells.

Intelligent Colorimetric Sensor for Discriminative Detection of Pd2+/Pd0 and PPh3 at Different Wavelength Readouts

AbstractIn this report, we presented our results on a recognition of multiple analytes using trisubstituted PDI‐based chemosensor DNP in 50 % HEPES buffered‐CH3CN solution. Upon addition of Pd2+ or Pd0, DNP showed near IR ratiometric changes (A759nm/A560nm) with detection limit of 283 nM and 190 nM, respectively. These spectroscopic changes are associated with color change from violet to light yellow (de‐propargylation). The de‐propargylation reaction of DNP is faster in the presence of Pd2+ than Pd0. Upon addition of PPh3, DNP resulted in appearance of new bands at 615 and 698 nm with decrease of absorbance intensity at 560 nm with detection limit of 349 nM. Two isosbestic points at 504 nm and 600 nm was observed. This change is associated with color changes from violet to blue. DNP coated TLC‐strips can be used for the detection of 4×10−4 M Pd0 and PPh3. We have demonstrated the practical application of DNP (i) for the detection of Pd0 in live A549 cells and (ii) for detection of Pd2+/Pd0 in simulated urine (10 %) samples with recovery of (>98±5 %).

A terpyridyl-rhodamine hybrid fluorescent probe for discriminative sensing of Hg (II) and Cu (II) in water and applications for molecular logic gate and cell imaging

Sensitive and discriminative sensing of more than one analyte with a single fluorescent probe is significant and challenging. Herein a new terpyridyl-rhodamine hybrid, namely TRH, has been rationally designed and prepared with two responsive groups in the molecular structure, which facilitate the discriminative detection of Hg2+ and Cu2+ ions in water with detection limits of 4.9 and 53.3 nM by ratiometric fluorescence change (F595/F485) and fluorescence quenching, respectively. Investigations show that the selectivity to Hg2+ ions can be attributed to Hg2+-promoted spirolactam ring opening and further hydrolysis, followed by a through-bond energy transfer (TBET) process. The selective fluorescence quenching to Cu2+ ions probably can be ascribed to the binding Cu2+ to terpyridyl that triggers a ligand-to-metal charge transfer (LMCT) process, which can also efficiently inhibit the TBET process induced by Hg2+ ions and promotes the discriminative sensing of Cu (II) and Hg (II). In addition, the fluorescent responses to Hg2+ and Cu2+ ions cover a wide pH range. Moreover, a combinatorial logic gate with the functions of NOR and INHIBIT has been fabricated by using Hg2+ and Cu2+ ions as chemical input signals, and fluorescence at 485 and 595 nm as output signals. Besides, TRH also exhibits sensitive and discriminative sensing ability to Hg2+ and Cu2+ ions by the fluorescence of rhodamine fluorophore. Significantly, based on the fluorescence signal output of rhodamine moiety, TRH can be used as a tracer for the discriminative sensing of Hg2+ and Cu2+ ions by using living cells.

Sensitive dual-mode sensing platform for Amyloid β detection: Combining dual Z-scheme heterojunction enhanced photoelectrochemistry analysis and dual-wavelength ratiometric electrochemiluminescence strategy

As a tumor biomarker, the accumulation of amyloid β oligomers (Aβo) in the brain has been suggested as a key feature in the pathogenesis and progression of Alzheimer's disease (AD). In this work, we designed a novel photoelectrochemical (PEC) and electrochemiluminescence resonance energy transfer (ECL-RET) dual-mode biosensor to achieve ultra-sensitive detection of Aβo. Specifically, the electrode surface modified Carbon Dots (C Dots) and the electrodeposited polyaniline (PANI) film formed a Z-scheme heterojunction reversing the photocurrent signal, and then the Aβo specific recognition peptide was attached to the surface via amide bonding between the amino group of PANI and carbonyl group of peptide. After that, in the presence of CdTe labeled specific recognition aptamer for Aβ (CdTe-Apt), Aβo was captured to construct a sandwich-type biosensor and exhibited a significantly enhanced cathodic photocurrent response because the formed dual Z-scheme heterojunction promoted charge separation efficiency. Interestingly, the proposed biosensor also caused a ratiometric change in the ECL intensity at 555 nm and 640 nm. Therefore, the developed biosensor achieved dual-mode detection of Aβo, where the PEC detection range of Aβo was from 10 fM to 0.1 μM (with a detection limit of 4.27 fM) and the ECL method provided a linear detection range of 10 fM to 10 nM (with a detection limit of 6.41 fM). The stability and reliability of the experimental results indicate that this has been a promising biosensing pattern and could be extended to the analysis of other biomarkers.

Cell-Membrane-Localizing Fluorescence Probes for Aminopeptidase N.

Aminopeptidase N (APN), a transmembrane ectoenzyme, plays multifunctional roles in cell survival and migration, angiogenesis, blood pressure regulation, and viral uptake. Abnormally high levels of the enzyme can be found in some tumors and injured liver and kidney. Therefore, noninvasive detection methods for APN are in demand for diagnosing and studying the associated diseases, leading to two dozen activatable small-molecule probes reported up to date. All of the known probes, however, analyze the enzyme activity by monitoring fluorescent molecules inside cells, despite the enzymatic reaction taking place on the outer cell membrane. In this case, different cell permeability and enzyme kinetics can cause false signal data. To address this critical issue, we have developed two cell-membrane-localizing APN probes whose enzymatic products also localize the outer cell membrane. The probes selectively respond to APN with ratiometric fluorescence signal changes. A selected probe, which has two-photon imaging capability, allowed us to determine the relative APN levels in various organ tissues for the first time: 4.3 (intestine), 2.1 (kidney), 2.7 (liver), 3.2 (lung), and 1.0 (stomach). Also, a higher APN level was observed from a HepG2-xenograft mouse tissue in comparison with the normal tissue. Furthermore, we observed a significant APN level increase in the mouse liver of a drug (acetaminophen)-induced liver injury model. The probe thus offers a reliable means for studying APN-associated biology including drug-induced hepatotoxicity simply by ratiometric imaging.

Single-benzene-based ratiometric fluorescent probe for hydrazine visualization

Hydrazine (N2H4) is a crucial chemical being widely used in various industrial fields. However, hydrazine exposure can cause severe harm to humans, animals, and the natural environment due to its high reactivity and toxicity. In this work, we disclosed a new fluorescent probe for hydrazine detection, utilizing a single benzene-based fluorophore (SBBF). The new hydrazine probe, named HP, reacted explicitly with hydrazine in a short time (<1 min) and had ratiometric emission changes with a large Stokes shift (172 nm). HP also showed high physicochemical stability, which is the most critical characteristic for practical application in environmental conditions. Furthermore, we conducted hydrazine detection experiments across multiple applications, encompassing paper strips, soils, and liquid samples. This study presents a new hydrazine fluorescent probe based on SBBF that holds immense potential for widespread application across various fields.

A highly selective NIR ratiometric fluorescent probe for in situ detection of metabolized hydrazine in living cells

Hydrazine (N2H4) is a great concern to human health and its detection in living cells is of growing importance. In this report, we employed a hydrogen bonding-anchored sensing strategy to develop a near-infrared (NIR) fluorescent probe CDM-1, which is capable of detecting N2H4 with ratiometric and colorimetric responses. The introduction of a chloro-substitution to the dicyanoisophorone scaffold improved the stability of the probe through Cl…CO n→π * interactions. Meanwhile, this substitution also provided a lower pKa value of the phenol CDM, allowing the generation of ratiometric changes after CDM-1 reacted with N2H4 under physiological conditions (pH = 7.4). Notably, we took advantage of utilizing both the hydrogen-bonding interaction and the 6-exo addition to target two anchors on N2H4 through “N” and “H” atoms, which enabled high selectivity and reactivity with a low limit of detection value at 0.3 ppb. CDM-1 has been successfully loaded onto paper strips to detect N2H4 vapor. Furthermore, the probe demonstrated its potential biological value in monitoring both the exogenous and endogenous N2H4, particularly as a metabolite of the anti-tuberculosis drug, Isoniazid (INH), in living cells.

Ratiometric detection of Zn(II) and Cd(II) ions by a benzobisimidazole based probe in aqueous systems and theoretical calculations

The probe 2,6-di(2-pyridyl)-1,5-dihydroimidazo[4,5-f]benzimidazole (LH2) was investigated for its sensing application towards metal ions. This probe can detect Zn2+ and Cd2+ ions in three different aqueous systems viz., water, DMSO/HEPES buffer (1:1, pH = 7.34, rt), and DMSO/water (1:1, rt). In water a “turn-on” response was observed for both metal ions, whereas in the later two solvent systems, a ratiometric change in fluorescence maximum was observed. The detection limit of this probe is as low as 0.3 μM and 0.62 μM (in water) for Zn2+ and Cd2+ ions, respectively. In both DMSO/HEPES buffer and DMSO/water (1:1), LOD values were identically 1.67 μM (for Zn2+) and 1.93 μM (for Cd2+). This probe has a good pH tolerance range which is 4–8 (for Zn2+) and 4–11 (for Cd2+). Lehrer and Chipman plot and Job’s plot suggested a 2:1 binding ratio between metal ion and LH2. The high binding constants obtained from the Lehrer and Chipman method are suggestive of the formation of a very stable complex in the solution. The binding of Zn2+ and Cd2+ ions to the probe was further confirmed by the NMR titration method which indicated the intensity of N–H protons is halved upon addition of the respective metal ion solution in DMSO‑d6. Reversibility of the detection was also established using Na2EDTA solution. DFT/TD-DFT calculation supported the experimentally observed red-shift of the absorption band.

RNA-seq analysis identifies age-dependent changes in expression of mRNAs - encoding N-glycosylation pathway enzymes in mouse gonadotropes

Follicle-stimulating hormone (FSH) is a glycoprotein that is assembled as a heterodimer of α/β subunits in gonadotropes. Each subunit contains two N-glycan chains. Our previous in vivo genetic studies identified that at least one N-glycan chain must be present on the FSHβ subunit for efficient FSH dimer assembly and secretion. Moreover, macroheterogeneity observed uniquely on human FSHβ results in ratiometric changes in age-specific FSH glycoforms, particularly during menopausal transition. Despite the recognition of many prominent roles of sugars on FSH including dimer assembly and secretion, serum half-life, receptor binding and signal transduction, the N-glycosylation machinery in gonadotropes has never been defined. Here, we used a mouse model in which gonadotropes are GFP-labeled in vivo and achieved rapid purification of GFP+ gonadotropes from pituitaries of female mice at reproductively young, middle, and old ages. We identified by RNA-seq analysis 52 mRNAs encoding N-glycosylation pathway enzymes expressed in 3- and 8-10-month-old mouse gonadotropes. We hierarchically mapped and localized the enzymes to distinct subcellular organelles within the N-glycosylation biosynthetic pathway. Of the 52 mRNAs, we found 27 mRNAs are differentially expressed between the 3- and 8-10-month old mice. We subsequently selected 8 mRNAs which showed varying changes in expression for confirmation of abundance in vivo via qPCR analysis, using more expanded aging time points with distinct 8-month and 14-month age groups. Real time qPCR analysis indicated dynamic changes in expression of N-glycosylation pathway enzyme-encoding mRNAs across the life span. Notably, computational analysis predicted the promoters of genes encoding these 8 mRNAs contain multiple high probability binding sites for estrogen receptor-1 and progesterone receptor. Collectively, our studies define the N-glycome and identify age-specific dynamic changes in mRNAs encoding N-glycosylation pathway enzymes in mouse gonadotropes. Our studies suggest the age-related decline in ovarian steroids may regulate expression of N-glycosylation enzymes in mouse gonadotropes and explain the age-related N-glycosylation shift previously observed on human FSHβ subunit in pituitaries of women.

Construction of a Dual-Functional, Reversible, Ratiometric, Golgi-Targeting Fluorescent Probe for Real-time Monitoring of Dynamics of Intracellular Redox Homeostasis.

Intracellular redox homeostasis is highly important for the physiological processes of living organisms. Real-time monitoring of the dynamics of this intracellular redox process is pivotal but challenging because the biological redox reactions involved in the process are reversible and require at least one pair of oxidizing and reducing species. Thus, biosensors for investigating intracellular redox homeostasis need to be dual-functional, reversible, and, ideally, ratiometric in order for them to have real-time monitoring capacity and to provide accurate imaging information. In light of the importance of the redox pair between ClO- and GSH in living organisms, herein, we used the phenoselenazine (PSeZ) moiety as an electron donor and a reaction site to design a coumarin-based fluorescent probe, PSeZ-Cou-Golgi. After successive treatment with ClO- and GSH, the probe PSeZ-Cou-Golgi experienced an oxidation of selenium (Se) to selenoxide (Se═O) by ClO- and a subsequent reduction of Se═O to Se by GSH. The redox reactions alternatively changed the electron-donating strength of the donor in the probe PSeZ-Cou-Golgi, in turn affecting the intramolecular charge transfer process that resulted in the reversible, ratiometric change of fluorescence from red to green. After four cycles of reversible ClO-/GSH detection during in vitro experiments, the probe PSeZ-Cou-Golgi still had good performance. With the Golgi-targeting group, the probe PSeZ-Cou-Golgi was able to monitor the dynamic change of the ClO-/GSH-mediated redox state during Golgi oxidative stress, making it a versatile molecular tool. More importantly, the probe PSeZ-Cou-Golgi could facilitate the imaging of the dynamic redox state during acute lung injury progression.

Phenotyping of Methicillin-Resistant Staphylococcus aureus Using a Ratiometric Sensor Array.

Chemical tools capable of classifying multidrug-resistant bacteria (superbugs) can facilitate early-stage disease diagnosis and help guide precision therapy. Here, we report a sensor array that permits the facile phenotyping of methicillin-resistant Staphylococcus aureus (MRSA), a clinically common superbug. The array consists of a panel of eight separate ratiometric fluorescent probes that provide characteristic vibration-induced emission (VIE) profiles. These probes bear a pair of quaternary ammonium salts in different substitution positions around a known VIEgen core. The differences in the substituents result in varying interactions with the negatively charged cell walls of bacteria. This, in turn, dictates the molecular conformation of the probes and affects their blue-to-red fluorescence intensity ratios (ratiometric changes). Within the sensor array, the differences in the ratiometric changes for the probes result in "fingerprints" for MRSA of different genotypes. This allows them to be identified using principal component analysis (PCA) without the need for cell lysis and nucleic acid isolation. The results obtained with the present sensor array agree well with those obtained using polymerase chain reaction (PCR) analysis.

Simple and effective detection of water in hygroscopic organic solvents using smartphone-based device with dithiophene-conjugated benzothiazole

A dithiophene-bearing benzothiazole derivative (DTBz) was synthesized as a moisture-sensitive fluorescent probe for the detection of water in hygroscopic solvents. In a mixture of water and organic solvents, such as THF, 1,4-dioxane, MeOH, and EtOH, the fluorescence intensity of DTBz showed ratiometric changes in response to the content of water in the organic solvents. Moreover, the emission color of DTBz changed drastically from blue to red, which facilitated the development of the smartphone-assisted fluorometric device using image analysis. The custom smartphone-based device allowed water detection over the range of 0–60% with a resolution of 0.1% in the range of 0–1%. The detection sensitivity was as low as 0.05%. The total assay time was estimated to be approximately 6 min. The custom device would be very useful for determining the water content of various hygroscopic organic solvents over a wide range.

A naphthalimide functionalized fluoran with AIE effect for ratiometric sensing Hg2+ and cell imaging application

The pollution caused by mercury ions (Hg2+) poses a potential threat to public health. Therefore, monitoring Hg2+ concentration in the environment is necessary and significant. In this work, a naphthalimide functionalized fluoran dye NAF has been prepared, which shows a new red-shift in emission at 550 nm with the maximum intensity in a mixture of water-CH3CN (v/v = 7/3) due to aggregating induced emission (AIE) effect. Meanwhile, NAF can be employed as a Hg2+ ions sensor, which displays a selective and sensitive response to Hg2+ ions by the reduced fluorescence of naphthalimide fluorophore and increased fluorescence of fluoran group, respectively, showing ratiometric fluorescence signal changes with more than 65-fold emission intensity ratio increase and naked eyes visible color change. In addition, the response time is fast (within 1 min) and the sensing can be conducted in a wide pH range (4.0–9.0). Moreover, the detection limit has been evaluated to be 5.5 nM. The sensing mechanism may be attributed to the formation of a π-extended conjugated system due to the Hg2+ ions-induced conversion of spironolactone to the ring-opened form, partially accompanied by the fluorescence resonance energy transfer (FRET) process. Significantly, NAF exhibits suitable cytotoxicity to living HeLa cells, which allows it to be utilized for ratiometric imaging of Hg2+ ions assisted by confocal fluorescence imaging.

Multifunctional 1,3-benzoxazole-merocyanine-based probe for the ratiometric fluorescence detection of pH/HSO3−/viscosity in mitochondria

pH, HSO3−, and viscosity are crucial bio-markers for evaluating the status of mitochondria in the cell micro-environment. With this research, we developed a ratiometric mitochondria-targeting fluorescent probe 1 that was responsive toward bisulphite, pH and viscosity. Hydroxylphenyl 1,3-benzoxazole (D) acted as a pH recognition unit; benzo[e]indolium (A) acted as a fluorescent rotor to achieve a viscosity response; the C = C bond constructed by bridging D and A was susceptible to nucleophilic attack and hence responded to HSO3−. Probe 1 exhibits significant ratiometric signal changes, high sensitivity, outstanding selectivity, and good stability for detecting pH, viscosity, and SO2 in solution. Probe 1 was used for imaging pH, viscosity, and SO2 derivatives in live cells and zebrafish, indicating its potential for identifying mitochondrial dysfunctions.

Dual-Emission Metal–Organic Framework for Highly Selective Ratiometric Sensing of Lithium(I) Ions in Aqueous Solution

The development of highly selective and sensitive detection methods for lithium ions in various environments, such as aqueous or battery application, is highly sought. However, it remains elusive due to the small radius and weak coordination ability of lithium ions. Considering a metal–organic framework (MOF) possesses plentiful open coordination sites and an adjustable pore size, the well-designed MOF would be an ideal platform for the selective detection of Li+. Herein, a novel dual-emission luminescent metal–organic framework with three-dimensional structure, namely, Co–HIAT, was prepared by the hydrothermal method and structurally characterized. The Co–HIAT MOF displays the ligand-based emission at 340 nm and the charge transition emission between the metal ions and ligand at 410 nm simultaneously. Hence, the first example of ratiometric fluorescence detecting of Li+ can be achieved by measuring the ratio of fluorescence at 410 to 340 nm in the fluorescent spectra of the Co–HIAT, which exhibits the outstanding sensitivity and selectivity, giving a detection limit down to 0.17 μM. Detailed experimental studies showed that the sensing mechanism involves the strong interactions of Li+ with the reasonable hydroxyl and carboxyl oxygen atoms in the Co–HIAT framework, which is responsible for the ratiometric change in fluorescence emission properties in the inclusion of Li+. It is worth noting that electrochemical experiments further confirmed its superior affinity for lithium ions. This work represents an important and feasible pathway to design MOFs for the detection of Li+.

Ultrathin C3N4 nanosheets-based oxidase-like 2D fluorescence nanozyme for dual-mode detection of organophosphorus pesticides

Engineering efficient dual-mode portable sensor with built-in cross reference correction is of great significance for onsite reliable and precise detection of organophosphorus pesticides (OPs) and evading the false-positive outputs, especially in emergency case. Currently, most nanozyme-based sensors for OPs monitoring primarily replied on the peroxidase-like activity, which involved unstable and toxic H2O2. In this scenario, a hybrid oxidase-like 2D fluorescence nanozyme (PtPdNPs@g-C3N4) was yielded by in situ growing PtPdNPs in the ultrathin two-dimensional (2D) graphitic carbon nitride (g-C3N4) nanosheet. When acetylcholinesterase (AChE) hydrolyzed acetylthiocholine (ATCh) to thiocholine (TCh), it ablated O2−• from the dissolved O2 catalyzed by PtPdNPs@g-C3N4’s oxidase-like activity, hampering the oxidation of o-phenylenediamine (OPD) into 2,3-diaminophenothiazine (DAP). Consequently, with the increasing concentration of OPs which inhibited the blocking effect by inactivating AChE, the produced DAP caused an apparent color change and a dual-color ratiometric fluorescence change in the response system. Through integrating into a smartphone, a H2O2-free 2D nanozyme-based onsite colorimetric and fluorescence dual-mode visual imaging sensor for OPs was proposed with acceptable results in real samples, which holds vast promise for further development of commercial point-of-care testing platform in early warning and controlling of OPs pollution for safeguarding environmental health and food safety.

Dipyrene-Terminated Oligosilanes Enable Ratiometric Fluorescence Response in Polymers toward Mechano- and Thermo-Stimuli

Developing fluorescent motifs capable of displaying mechano- and thermo-stimuli reversibly and ratiometrically is appealing for monitoring the deformation or temperature to which polymers are subjected. Here, a series of excimer-type chromophores Sin-Py (n = 1-3) consisting of two pyrenes linked with oligosilanes of one to three silicon atoms is developed as the fluorescent motif incorporated in a polymer. The fluorescence of Sin-Py is steered with the linker length where Si2-Py and Si3-Py with disilane and trisilane linkers display prominent excimer emission accompanied by pyrene monomer emission. Covalent incorporation of Si2-Py and Si3-Py in polyurethane gives fluorescent polymers PU-Si2-Py and PU-Si3-Py, respectively, where intramolecular pyrene excimers and corresponding combined emission of excimer and monomer are obtained. Polymer films of PU-Si2-Py and PU-Si3-Py display instant and reversible ratiometric fluorescence change during the uniaxial tensile test. The mechanochromic response arises from the reversible suppression of excimer formation during the mechanically induced separation of the pyrene moieties and relaxation. Furthermore, PU-Si2-Py and PU-Si3-Py show thermochromic response toward temperature, and the inflection point from the ratiometric emission as a function of temperature gives an indication of the glass transition temperature (Tg) of the polymers. The design of the excimer-based mechanophore with oligosilane provides a generally implementable way to develop mechano- and thermo-dual-responsive polymers.

Green synthesis of carbon dots from spent coffee grounds via ball-milling: Application in fluorescent chemosensors

Carbon dots (CDs) are nanoparticles that have gained widespread attention due to their unique properties including multicolored fluorescence, photochemical stability, and biocompatibility. However, the conventional approaches for the preparation of CDs typically require high energy input and toxic reagents. Herein, a sustainable, high throughput approach is reported for producing uniform CDs. Specifically, spent coffee grounds (SCGs) are used to produce coffee ground-derived carbon dots (CFCDs) via a simple wet ball-milling process. The versatility of our approach can be extended to the synthesis of heteroatom-doped CDs and the preparation of CDs from various SCG sources. Also, the functional groups of the CFCDs are manipulated by the addition of citric acids during the ball-milling process to produce carboxylic acid-functionalized carbon dots (CA-CFCDs). CA-CFCDs exhibit highly selective and sensitive detection of Fe3+ ions in aqueous solution via fluorescence quenching, and the relevant quenching mechanism is investigated. Finally, we demonstrate the fluorescent microgel sensor exhibiting a rapid, ratiometric fluorescence change upon the addition of Fe3+ ion by encapsulating the CA-CFCDs within the microgel matrix.

A Novel Near-Infrared Ratiometric Fluorescence Probe for Hg2+ Based on Quinoline-Fused Rhodamine Dye.

As one of the most toxic metals, Mercury ions cause serious environmental pollution and threaten the health of living organisms. Hence, we designed and synthesised a new near-infrared (NIR) ratiometric fluorescent probe toward monitoring of Hg2+ based on quinoline-fused rhodamine dye. Owing to the specific spirolactam ring-opening reaction, the probe exhibits a ratiometric fluorescent change after treatment of Hg2+ with increased emission in NIR and significantly reduced emission in visible region. The specific response mechanism and dual-channel fluorescence change allow the probe to have remarkable detection selectivity, fast response and high detection sensitivity. Moreover, with the properties of excellent cell permeability and low cytotoxicity, probe can be applied as detection tool for mercury ions with dual-channel ratiometric fluorescence imaging in living cell.

Photoswitchable hemithioindigo inspired copper ion selective sensing with excellent selectivity and versatile operational modes

Copper is an essential element in living organisms and the monitoring of copper ions in aquatic environments and biological systems is of great significance. Inspired by a family of visible light responsive photoswitchable compounds, we report here a fluorescent probe (HTI-Q) for Cu2+ with excellent selectivity, high sensitivity, and a limit of detection (LOD) of ca. 0.02 μM. While the central carbon-carbon double bond of HTI-Q is photoisomerizable between the Z and E configurations, it is locked upon binding with Cu2+ into the E configuration, resulting in a large bathochromic shift (102 nm) and ratiometric fluorescence changes. Different sensing modes were demonstrated including in mixed solvents, a two-phase sensing system containing cation exchanger, and fluorescent nanoprobes containing a reference dye. The absorbance change of HTI-Q upon 470 nm light illumination also depended on the concentration of Cu2+. HTI-Q-based sensors were successfully applied to determine Cu2+ in real water samples with excellent recovery. Further, fluorescent nanoprobes incorporating HTI-Q were successfully applied to image endolysosomal Cu2+ changes upon external stimulation.