Ratiometric Fluorescence Changes Research Articles

A Ratiometric Benzimidazole-Based Fluorescent Probe for The Recognition of Phosgene in Solution and Gaseous Phases.

Considering the high toxicity and widespread application of phosgene, there is an urgent need to develop a simple and sensitive method for detecting phosgene. In this work, we designed and synthesized a novel ratiometric fluorescent probe 1 containing fluorophores of benzimidazole and benzothiazole. Probe 1 showed excellent sensitivity (< 30s) and selectivity (LOD = 3.82 nM) for phosgene and significant ratiometric fluorescence changes. In addition, 1-loaded polystyrene membrane test strips were used to conveniently and efficiently detect phosgene gas (0.5 ppm) via the naked eye and the RGB APP of the smartphone, indicating that this probe has great potential for phosgene detection in the gaseous phase.

An AIE and ESIPT based ratiometric fluorescent hydrogel sensor for detecting biogenic amines and chicken breast freshness

Meat quality is closely linked to food safety and human health, with freshness being a key indicator. Therefore, it is crucial to explore reliable and effective methods for detecting meat freshness. This study presented a ratiometric fluorescent hydrogel sensor based on aggregation-induced emission (AIE) and excited state intramolecular proton transfer (ESIPT) for this purpose. Tetraphenylene (TPE) and 2-(2′-hydroxyphenyl)-benzothiazole (HBT) fluorophore were intersected to generate TPE-HBT, and then a novel biogenic amines (BAs) detection ratiometric fluorescent probe, TPE-HBTAc, was successfully prepared by hydroxyl acetylation. TPE-HBTAc displayed a large Stokes shift and good photostability. It showed a significant response to the representative biogenic amine trimethylamine (TMA), with a ratiometric fluorescence change and low detection limit (LOD = 65 nM). Furthermore, BAs detection hydrogel sensor was created by mixing the fluorescent probe TPE-HBTAc in an agarose hydrogel with a 3D polymer network. The hydrogel sensor displayed a distinct color change from blue to yellow when exposed to TMA vapor under UV light and had a low detection limit (LOD = 5.88 ppm). The hydrogel sensor was utilized in conjunction with a smartphone RGB analysis system to determine the freshness of chicken breast samples. Consumers can easily observe the chicken breast freshness in real-time and non-destructively through UV flashlight illumination. The results of this work suggest that ratiometric fluorescent hydrogel sensor based on AIE and ESIPT can serve as a promising strategy to monitor food freshness.

Swift and quantitative naked-eye detection of cyanide: A dual-mode approach using an ICT-based colorimetric and ratiometric fluorescent chemodosimeter

A chemodosimeter (1) based on dicyanovinyl with a strong intramolecular charge transfer (ICT) mechanism has been devised for the selective and sensitive detection of cyanide (CN−) in a tetrahydrofuran aqueous solution. In polar solvents, chemodosimeter 1 exhibits robust ICT-induced emission; however, in the solid state, its fluorescence weakens owing to the formation of molecular aggregates prompted by intermolecular π–π interactions. The colorimetric and ratiometric fluorescent changes observed in the chemodosimeter upon exposure to CN− result from the incorporation of CN− at the β-conjugated site of the dicyanovinyl moiety of chemodosimeter 1, effectively hindering the ICT process. This alteration is supported by 1H NMR titration experiments and density functional theory calculations, which corroborate the cyanide-induced ICT on–off switching mechanism. The detection limit of chemodosimeter 1 (5.8 × 10−7 M) for CN− falls below the maximum allowable level of cyanide in drinking water (1.9 × 10−6 M), as established by the World Health Organization. Test strips utilizing chemodosimeter 1 offer a potential solution for swift and quantitative naked-eye detection of CN− in real-time scenarios. Moreover, chemodosimeter 1 was effectively employed for detecting cyanide in actual environmental water samples.

Construction of an ultrasensitive hypochlorite fluorescent probe based on a novel chromophore fragmentation strategy

The excess intake of hypochlorite (ClO−) in the human body and excessive emission in wastewater can pose serious health risks and environmental pollution. Therefore, it is vital to develop an efficient method for detecting ClO− in foodstuff and water. In this work, we reported a lactam-fused aza-BODIPY (LAB1) for ultrasensitive ClO− detection based on novel chromophore fragmentation strategy for the first time. It exhibited distinct advantages of good selectivity, high sensitivity, fast response (60 s) and low detection limit of 9.65 nM. The sensing mechanism revealed LAB1 core was fragmented by ClO−, leading to significantly colorimetric and ratiometric fluorescence changes. As a result, 320 nm blue-shift in absorption maximum (from green to colorless) and 340 nm blue-shift in emission maximum (from dark to bright blue) allowed for visual detection by the naked eyes. The potential applicability of LAB1 for ClO− detection with satisfactory recovery in the real samples (tap water and lake water) and vegetables (spinach, lettuce, Chinese cabbage, bean sprouts), and fluorescence “turn on” imaging in mung bean sprout were demonstrated. In addition, LAB1-loaded test paper was suitable for semi-quantitative scanning ClO− analysis by using color recognition APP in a smartphone. Therefore, this work highlights a promising approach based on novel sensing mechanism for monitoring ClO− in food samples.

Ratiometric fluoroprobe based on Eu-MOF@Tb3+ for detecting tetracycline hydrochloride in freshwater fish and its application in rapid visual detection

Tetracycline hydrochloride (TCH), a prevalent antibiotic in aquaculture for treating bacterial infections, poses challenges for on-site detection. This study employed the reversed-phase microemulsion method to synthesize a uniform nano metal-organic framework (MOF) material, europium-benzene-p-dicarboxylic acid (Eu-BDC), doped with Tb3+ to form a dual-emission fluorescence probe. By leveraging the combined a-photoinduced electron-transfer (a-PET) and inner filter effect (IFE) mechanisms, high-sensitivity TCH detection in Carassius auratus and Ruditapes philippinarum was achieved. The detection range for TCH is 0.380–75 μM, with a low limit of detection (LOD) at 0.115 μM. Upon TCH binding, Eu-BDC fluorescence rapidly decreased, while Tb3+ fluorescence remained constant, establishing a ratiometric fluorescence change. Investigation into the TCH quenching mechanism on Eu-BDC was conducted using time-dependent density functional theory (TD-DFT) calculations and fluorescence quenching kinetic equations, suggesting a mixed quenching mechanism. Furthermore, a novel photoelectric conversion fluorescence detection device (FL-2) was developed and evaluated in conjunction with high-performance liquid chromatography-diode-array detection (HPLC-DAD). This is the first dedicated fluorescence device for TCH detection, showcasing superior photoelectric conversion performance and stability that reduces experimental errors associated with smartphone photography methods, presenting a promising avenue for on-site rapid TCH detection.

Aptamer Conjugate-Based Ratiometric Fluorescent Probe for Precise Imaging of Therapy-Induced Cancer Senescence.

Therapy-induced cellular senescence has been increasingly recognized as a key mechanism to promote various aspects of carcinogenesis in a nonautonomous manner. Thus, real-time imaging monitoring of cellular senescence during cancer therapy is imperative not only to further elucidate its roles in cancer progression but also to provide guidance for medical management of cancer. However, it has long been a challenging task due to the lack of effective imaging molecule tools with high specificity and accuracy toward cancer senescence. Herein, we report the rational design, synthesis, and evaluation of an aptamer conjugate-based ratiometric fluorescent probe for precise imaging of therapy-induced cancer senescence. Unlike traditional senescence imaging systems, our probe targets two senescence-associated markers at both cellular and subcellular dimensions, namely, aptamer-mediated membrane marker recognition for active cell targeting and lysosomal marker-triggered ratiometric fluorescence changes of two cyanine dyes for site-specific, high-contrast imaging. Moreover, such a two-channel fluorescence response is activated after a one-step reaction and at the same location, avoiding the diffusion-caused signal decay previously encountered in dual-marker activated probes, contributing to spatiotemporally specific imaging of therapy-induced cancer senescence in living cells and three-dimensional multicellular tumor spheroids. This work may offer a valuable tool for a basic understanding of cellular senescence in cancer biology and interventions.

Construction of a ratiometric fluorescent probe for discriminative detection of SO2 derivatives and Cys and its bio-imaging application

Endogenous sulfur dioxide (SO2) and cysteine (Cys) are important species and interacted with each other. However, due to the reactivity of these species, it is difficult to differentiated detection them. Thus, it is necessary to develop new fluorescent probe for discriminative detect these reactive sulfur species in biological environment. Herein, A new hemicyanine derivative Mito-AE with dual recognition sites for SO2 derivatives and Cys detection was constructed and applied in biological detection. Mito-AE exhibited ratiometric fluorescence change (F470/F610) of over 90-fold when interacted with SO2, and a dramatic fluorescence turn-on at 610 nm when interacted with Cys. The probe can monitor both SO2 derivatives and Cys with fast response rate (within 1 min), high sensitivity and selectivity. As proved by biological experiments, Mito-AE was able to successfully detect exogenous and endogenous SO2 in living cells as well as in mitochondria area. More importantly, the detection of SO2 derivatives and Cys in zebrafish model suggesting a potential application for studying the multiple interaction of biological sulfurous species in live organism.

An AIE-based ratiometric fluorescent probe for reversible detection of bisulfite and hydrogen peroxide and its application in food samples and biological imaging

Reversible detection of bisulfite (HSO3-) and hydrogen peroxide (H2O2) is highly desirable in biology and food safety owing to their redox pair function in biological systems and their utilization in food industry. In this work, a ratiometric fluorescent probe (TPA-Y) with aggregation-induced emission (AIE) properties based on triphenylamine fluorophore was designed and synthesized for reversibly monitoring of HSO3-/H2O2. Reaction of HSO3- with TPA-Y can result in ratiometric fluorescence changes (I444/I629), and the emission spectrum blue shift reaches 185 nm, which can effectively avoid spectral overlap. Meanwhile, the solution color changed obviously from orange to colorless, enabling naked eye detection of HSO3-. TPA-Y was capable of quantitatively detect HSO3- in sugar and wine samples with the recovery rates ranging from 94.52 to 102.18%. In addition, TPA-Y is suitable to prepare paper strips and anti-counterfeiting ink for HSO3- detection. In addition, the original TPA-Y can be released after the addition product (TPA-Y-HSO3-) is oxidized by H2O2, and the HSO3-/H2O2 redox cycle can repeat for at least six times. The probe TPA-Y can be applied to fluorescence imaging of reversible and dynamic interconversion between HSO3- and H2O2 in living MCF-7 cells.

A ratiometric fluorescent probe based on cyclization mechanism to identify hydrazine in environment and living cells

A colorimetric and ratiometric fluorescent probe containing hydroxyl-chalcone moiety as sensing site has been investigated to monitor hydrazine in actual water/soils, gas environment, and living cells. After adding hydrazine, the chalcone structure was cyclized and dihydropyrazole ring was formed, realizing the obvious fluorescence change from red (590 nm) to blue (480 nm) with 110 nm fluorescence peak shift. The probe has low detection limit (0.45 µM), large upgraded ratiometric fluorescence change (I480/I590, 66-fold), and wide pH work range (3.0-10.0). Probe CCA also can monitor hydrazine from actual water/soil samples, liquid/vapor hydrazine with portability and living cells.

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.

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.

NMN sensor cocktail: selective sensing of nicotinamide mononucleotide over citric acid.

The fluorescent probe pair, NBD-B2 and Styryl-51F, selectively detects NMN over citric acid. NBD-B2 exhibits increased fluorescence, while Styryl-51F shows decreased fluorescence upon NMN addition. Their ratiometric fluorescence change enables highly sensitive and wide-range detection of NMN, effectively distinguishing it not only from citric acid but also other NAD boosters.

A reaction-based scenario for fluorescence probing of Au(III) ions in human cells and plants.

A BODIPY-based fluorophore decorated with a gold specific reactive handle (e.g., 2-alkynylallyl alcohol) displayed a ratiometric fluorescence change in response to Au3+ ions with extraordinary selectivity over other competing metal species, including Hg2+, Cu2+, Zn2+ and Pd2+. By way of a gold-catalyzed intramolecular cyclisation-isomerisation reaction sequence, a BODIPY construct with an extended π-conjugation transformed into a new structure with a relatively short π-system. This unique chemical transformation was accompanied by, and resulted in, a dramatic shift in the emission and absorption wavelength, which could be monitored as distinct changes in the color of the solution's emission. Apart from its outstanding analytical performance in solution, including a quick response time (<10 s), unique specificity, a high-fold ratiometric change (62-fold), and a remarkably low detection limit (358 nM), the probe also proved useful in monitoring Au3+ ions in human cells and plants (e.g., Nicotiana benthamiana).

Reversible Ratiometric Mechanochromic Fluorescence Switching in Highly Stretchable Polyurethane Elastomers with Ultratoughness Enhanced by Polyrotaxane

Multistimuli-responsive polymers containing mechanophoric motifs are highlighted as promising mechano-luminescent materials upon stretching via optical fluorescence signals. Herein, we report a distinct ratiometric force-induced fluorescence changes from green-emissive napthalimide stopper (donor) embedded in polyrotaxane (PR) cross-linkers to red-emissive rhodamine mechanophore (acceptor) incorporated in polyurethane (PU) backbones. The utilization of PR (1 wt %) can significantly enhance both toughness and stretchability in our targeted PU elastomers, where the mechanical work is largely dissipated by the ring-sliding motion and pulley effects of PR cross-linkers during stretching. Therefore, the simple soft robotic behavior with ultrafast shape memory and reversible ratiometric mechanochromic fluorescence switching by heating (60 °C) in PR-based PU films provide a distinctive strategy for the construction of molecular machines in the high-performance elastomers, which also offer pathways for practical applications of stimuli-responsive polymers in highly stretchable artificial muscles featuring both outstanding pulley effects on enhanced mechanical properties and novel signal variations of mechanochromic fluorescence simultaneously.

Fe2+ imaging in ferroptosis and drug-induced liver injury with a ratiometric near-infrared fluorescent probe

Recently, great attention has been given to the detection of ferrous ion (Fe2+) in live organisms because it plays a vital role in life and is associated with ferroptosis and many diseases. Near-infrared (NIR) ratiometric fluorescence probes are essential tools, however, such probes for tracking Fe2+ in iron-associated diseases in vivo are rarely reported. Herein, we report a novel NIR ratiometric fluorescent probe NRF-Fe2+ for Fe2+ based on a fluorescence resonance energy transfer (FRET) system using the N-oxide chemistry. This probe shows significant ratiometric fluorescence changes (λem shifts from 460 nm to 675 nm) for Fe2+ with high selectivity and sensitivity, and can image both exogenous and endogenous Fe2+ in cells with low cytotoxicity and ratiometric fluorescence signals. The imaging of Fe2+ in mice with NRF-Fe2+ is also successfully applied. Finally, we demonstrate that the probe can be applied for monitoring the level changes of Fe2+ in ferroptosis and drug-induced liver injury. All the results show that NRF-Fe2+ is a useful tool for the detection of biological Fe2+ and the study of iron-related diseases.

Near‐Infrared Colorimetric and Ratiometric Fluorescence Sensor for Fluoride Ions

AbstractTwo novel benzothiadiazole derivatives were prepared. Clear color changes from orange‐red to blue (DPCN) and pink to green (DPTPE) were observed after the addition of fluoride ions (F−). DPCN and DPTPE displayed ratiometric fluorescence changes in the presence of F−. 1H‐NMR titration and DFT calculations confirmed deprotonation in the presence of F−. Compared with DPTPE, the hydrogen proton of the imine group in DPCN had higher activity due to the influence of the strong electron‐withdrawing cyano group, such that it was more easily deprotonated and the detection limit for F− was much lower. This work provided guidance for the further design and preparation benzothiadiazole based colorimetric and ratiometric fluorescence sensor for F−.