Fluorescence Switching Research Articles

Isolation and Detection of Exosomal Mir210 Using Carbon Nanomaterial-Coated Magnetic Beads.

MicroRNAs (miRNAs) are short non-coding RNAs that are found in various cellular compartments and play an important role in regulating gene expression. Extracellular miRNAs, such as those found within extracellular vesicles such as exosomes are involved in cell-to-cell communication. The intercellular transfer of miRNAs has been implicated in various diseases' pathogenesis including cancer and has been studied extensively as potential cancer biomarkers. However, the extraction of miRNA from exosomes is still a challenging task. The current nucleic acid extraction assays are expensive and labor-intensive. In this study, we demonstrated a microfluidic device for aptamer-based magnetic separation of the exosomes and subsequent detection of the miRNA using a fluorescence switching assay, which was enabled by carbon nanomaterials coated on magnetic beads. In the OFF state, the fluorophore-labelled cDNA is quenched using carbon nanomaterials. However, when the target miRNA210 is introduced, the cDNA detaches from the bead's surface, which leads to an increase in the fluorescence intensity (ON state). This increment was found to be proportional to miRNA concentration within the dynamic range of 0-100 nM with a detection limit of 5 pM. The assay was validated with spiked miRNA using the standard RT-PCR method. No notable cross-reactivity with other closely related miRNAs was observed. The developed method can be utilized for the minimally invasive detection of cancer biomarkers.

An "on-off-on" fluorescent switch based on luminous covalent organic framework for the rapid and selective detection of glyphosate.

Glyphosate, the most used herbicide in the world, has a residue problem that cannot be ignored. However, glyphosate itself does not have fluorescence emission and lacks the conditions for fluorescence detection. In this work, a rapid and selective fluorescence detection method of glyphosate was designed by an "on-off-on" fluorescent switch based on luminous covalent organic framework (L-COF). Only the fixed concentration of Fe3+ as intermediate could trigger the fluorescent switch and no incubation step was required. The proposed method showed good accuracy with correlation coefficient of 0.9978. The method's limits of detection and quantitation were 0.88 and 2.93 μmol/L, which were lower than the maximum allowable residue limits in some regulations. Environmental water samples and tomatoes were selected as actual samples to verify the application in complex matrix. A satisfactory mean recovery from 87% to 106% was gained. Furthermore, Fe3+ could induce fluorescence quenching of L-COF through photo-induced electron transfer (PET) effect, while the addition of glyphosate could block PET effect to achieve the detection. These results demonstrated the proposed method had abilities to detect glyphosate, and broadened the application of L-COF.

Bell pepper derived nitrogen-doped carbon dots as a pH-modulated fluorescence switching sensor with high sensitivity for visual sensing of 4-nitrophenol

Recently, converting bio-waste into bio-asset and implementing a portable sensing instrument for pollutant monitoring has been highly desirable and challenging. Herein, biomass-derived nitrogen-doped carbon dots (CDs) are prepared hydrothermally and emit blue fluorescence (470 nm) with a high quantum yield of 23.2%. Significantly, CDs can serve as a pH-modulated fluorescence switching nano-sensor to detect 4-NP from 0.054 to 68 μM with low detection limit (LOD, 54 nM) and limit of quantification (LOQ, 181 nM) based on inner filter effect. Moreover, the satisfactory recovery of 101.8–107.5% is gained in practical sample monitoring. Furthermore, a smartphone-integrated optosensing device with CDs-based film is developed for detecting 4-NP with LOD and LOQ of 0.110 μM and 0.350 μM. Concomitantly, the practicability of this device is further validated in several crop samples with satisfactory recovery rates of 101.6–108.6%. Therefore, this work provides a reliable way and a prospective application for on-site 4-NP monitoring in food.

AIE gels based on Schiff base with stimuli-responsive fluorescence switching behaviors as chemosensors

Based on Schiff base unit with/without a perfluoroalkyl group, novel multi-functional compounds 1 and 2 were proven to be able to form gels with different solvents. The difference in the molecular structure of compounds 1 and 2 was the presence of a perfluoroalkyl chain. The self-assembly pattern was studied by the employment of rheological analysis, UV–vis absorption, fluorescence spectrum, field emission scanning electron microscopy (FESEM), fourier transforms infrared (FTIR) spectra, and X-ray powder diffraction (XRD). The gelation behaviors showed a sensitive and selective “turn-off” fluorescence response with Cu2+. Due to the protonation or deprotonation of compounds 1 and 2 with trifluoroacetic acid (TFA) or triethylamine (TEA), the xerogel films which were prepared from DMSO:H2O (9:1, v/v) at 5 wt% presented the emission quenching and recovery upon TFA and TEA vapors. In this sense, the work will open up a novel pathway to detect Cu2+, TFA, and TEA in the environment, using stimuli-responsive fluorescent materials with aggregation-induced emission (AIE) effect.

Low-Pressure Sensitive Piezochromic Fluorescence Switching of Tetraphenylethylene-Anthraquinone.

Invited for the cover of this issue are Prof. Wenjing Tian and co-workers at Jilin University. The image depicts the highly sensitive piezochromic fluorescence switching of tetraphenylethylene-anthraquinone under low-pressure regimes (∼60 kPa). Read the full text of the article at 10.1002/chem.202301070.

2-Pyridone-based stilbazoles containing cyano and trifluoromethyl acceptors: Synthesis and fluorescence properties in solutions and in solid state

A novel simple and efficient stilbazole-based D-π-А system containing cyano and trifluoromethyl acceptors was designed. The developed system demonstrated pronounced (fluoro)solvatochromic properties. The behavior of compound in solution was studied and three forms were identified, namely pyridone (PY), hydroxypyridine (HP), and anionic form (AN). Synthetic equivalents of these forms were prepared and their photophysical characteristics were investigated. It was shown that fluorescence of the stilbazole-based D-π-А chromophore is originated exclusively from hydroxypyridine form, while the pyridone form makes a significant contribution to the absorption properties of the compound. Basing on the obtained 6-(4-(dimethylamino)styryl)-2-oxo-4-(trifluoromethyl)-1,2-dihydropyridine-3-carbonitrile a three position solid-state fluorescent acid-base switch was developed.

Proton-Coupled Photochromic Hemithioindigo: Toward Photoactivated Chemical Sensing and Imaging.

We report photoswitchable fluorescent hemithioindigos (HTIs) where the metastable E isomers were stabilized by the proton-bridged intramolecular hydrogen bond. Titration experiments and computational analysis indicated that the E isomers were much more basic than the Z isomers, which enabled photoactivated colorimetric and fluorescent pH response in solvents and polypropylene films. The HTIs exhibited reversibly switchable fluorescence with the Z isomers being the most fluorescent. Moreover, the HTIs were lysosomotropic and the kinetic fluorescence evolution during photoswitching was able to differentiate subcellular compartments with different pH. The combination of photoenhanced basicity, switchable fluorescence, and proton-coupled photochromism lay the groundwork for a broad range of chemical and biological applications.

Temperature-directed fluorescent switchable nanoparticles based on P3OT–PNIPAM nanogel composite

Poly(N-isopropylacrylamide) (PNIPAM) is a unique stimuli-responsive material that exhibits a lower critical solution temperature (LCST). Owing to this characteristic temperature-dependent behavior, PNIPAM has found extensive utilization as an active material in various applications, including sensors, drug delivery, and cellular imaging. Herein, we demonstrate temperature-directed fluorescent switchable nanoparticles based on poly(3-octylthiophene-2,5-diyl) (P3OT) nanoaggregate-embedded PNIPAM nanogel composites (POPNs) featuring different crosslinker contents. The amount of P3OT loading in the nanogel composites can be gradually controlled by varying the crosslinking density of the PNIPAM matrix; this may be attributable to the efficient entrapment of P3OT nanoaggregates in case of a dense polymeric network with the increase in crosslinking density. POPNs exhibit dramatic temperature-dependent fluorescence enhancement (by a factor of 2.11). This is based on the environmental changes affecting fluorescent P3OT chains at temperatures below and above the LCST of the PNIPAM matrix. Based on this temperature-directed fluorescent switching capability, POPN could find potential applications in various fields, including biomedical imaging and sensors.

Dual-signal and one-step monitoring of Staphylococcus aureus in milk using hybridization chain reaction based fluorescent sensor

Food-borne pathogens in dairy products that was contaminated from raw ingredients or improper food handling can cause a major threaten to human health. Here, to construct the pathogens detection, a dual-signal readout fluorescent switching sensor was designed for one-step determination of Staphylococcus aureus (S. aureus), which was a marker of food contamination. Graphene oxide (GO) was used as a fluorescence quencher, while fluorophore-labeled hairpin DNA was used as a donor, resulting in fluorescence resonance energy transfer (FRET) from the fluorophore to GO (signal off). Enzyme-free hybridization chain reaction could generate remarkable signal amplification, which avoided the nonspecific desorption caused by any enzymatic proteins in GO surface. With the strong binding ability of aptamer to S. aureus, a long bifluorescent molecules-labeled double-stranded DNA product was formed, bringing in dual-signal readout responses (signal on). Consequently, a reliable, sensitive and selective sensor was obtained for one-step quantification of S. aureus concentration from 10 to 108 CFU/mL with a detection limit of 1 CFU/mL. Furthermore, satisfactory stability, reproducibility, specificity and good recovery efficiency in milk samples revealed that the proposed sensor could be served as a prospective tool for food safety analysis.

A photo-controlled fluorescent switching based on carbon dots and photochromic diarylethene for bioimaging.

Carbon dots (CDs) as luminescent zero-dimensional carbon nanomaterials have good aqueous dissolution, photostability, high quantum yield, and tunability of emission color. It has great application potential in many fields, including bioimaging, labeling of biological species, drug delivery, and sensing in biomedical. However, controlling the fluorescence emission of carbon dots remains a formidable challenge. Herein, we designed and exploited a photo-controlled fluorescent switching based on photochromic diarylethene (DT) and CDs for bioimaging. It could be modulated reversibly between "ON" and "OFF" under UV/vis light exposure. The fluorescent modulation efficiency was as high as 95.3%. The fluorescent switching could be used to the bioimaging in HeLa cells with low cell toxicity. Therefore, this fluorescent switching could be a promising candidate in many potential application areas, especially in bioimaging.

Optical Control of Invertebrate nAChR and Behaviors with Dithienylethene-Imidacloprid.

Photopharmacology involving azobenzene or dithienylethene has changed established methods of studying receptor functions, allowing for increasing the spatiotemporal resolution. There are no photopharmacological tools available for the invertebrate nicotinic acetylcholine receptor (nAChR). Here, we report a photochromic ligand, dithienylethene-imidacloprid (DitIMI), using a dithienylethene photoswitch embedded in the nAChR agonist imidacloprid. It was found that DitIMI displayed good photochromism and fluorescence switching behaviors upon irradiation with UV/vis light in aqueous solution. We demonstrated that open-DitIMI has low spontaneous in vitro and in vivo activity but can be photoisomerized to a highly active closed-form. Surprisingly, the photoswitchable DitIMI showed a large difference in insecticidal activity between the open and closed forms, in which the insecticidal activity against Aphis craccivora of the ring-closed isomers for DitIMI was 355 times that of the corresponding ring-open isomers. This photoisomerization can further be translated to photomodulation of neuron membrane potential and behavioral responses of living mosquito larvae and American cockroaches. The photomanipulation of nACh neurotransmission opens new avenues to understanding inhibitory circuits in intact animals.

Fabrication of diarylethene-based reversible fluorescent switch encapsulated in silicone material and its photostimulus response mechanism

Photoresponsive materials, altering their properties such as color, luminescence, and luminescence lifetime under light as external stimulus, would be ideal candidates for application in fluorescent anti-counterfeiting and information encryption. In this paper, we develop a water-dispersive photo-stimuli response hybrid by encapsulating lanthanide complexes and photochromic molecules with an organosilicon material (OSM) via the reprecipitation-encapsulation method. Interestingly, repeated cycles of UV/Vis light irradiation switch the color and structure of photochromic molecules, which in turn influence the Förster resonance energy transfer (FRET) between photochromic molecules and lanthanide complexes, resulting in reversible luminescence ON/OFF switches, accompanied by reduction and recovery of luminescence lifetime of Eu3+ complexes. Considering the above-mentioned interesting characteristics, we realized the application of Eu(DBM)3·phen/BTHFC@OSM suspension as a light-driven fluorescent ink for fingerprint depth encryption. We expect our findings can expand the application scope of photochromic luminescence materials and provide a powerful approach for information encryption and anti-counterfeiting.

Biodegradable and switchable near-infrared fluorescent probes for hypoxia detection.

Aims: Among solid tumors, hypoxia is a common characteristic and responsible for chemotherapeutic resistance. Hypoxia-sensitive imaging probes are therefore essential for early tumor detection, growth monitoringand drug-response evaluation. Despite significant efforts, detecting hypoxic oxygen levels remains challenging. Materials & methods: This paper demonstrates the use of an amine-rich carbon dot probe functionalized with an imidazole group that exhibits reversible fluorescence switching in normoxic and hypoxic environments. Results & conclusion: We demonstrate the ability to emit near-infrared light only under hypoxic conditions. The probes are found to be biodegradable in the presence of human digestive enzymes such as lipase. Exvivo tissue imaging experiments revealed promising near-infrared signals even at a depth of 5mm for the probe under exvivo imaging conditions.

Unique mechanofluorochromism and reversible multicolor switching of triphenylamine-functionalized sulfonyl hydrazone derivatives

Two new simple triphenylamine-based sulfonyl hydrazone derivatives DBBS ((E)-N'-(4-(diphenylamino)benzylidene)benzenesulfonohydrazide) and DBMS ((E)-N'-(4-(diphenylamino)benzylidene)-4-methylbenzenesulfonohydrazide) were designed and synthesized via one-step aldimine condensation reaction to investigate the influence of terminal methyl group on their photophysical, crystal stacking and mechanofluorochromic (MFC) properties. Interestingly, reversible multi-color fluorescence tuning and switching mechanofluorochromism was found for DBBS due to the nature of polymorphs, and DBMS exhibited reversible bicolor switching mechanofluorochromism. Additionally, the reversible MFC behavior was ascribed to the phase transition between the crystalline and amorphous states, which have been confirmed by powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FESEM) and differential scanning calorimetry (DSC) results. The obtained results showed that terminal methyl group did not only regulate molecular conformations and/or intermolecular interactions in crystals, but also affect the force-stimuli responsiveness. The present study provided insight into the development of multicolor switching materials by rational modification of classic luminogens.

Electrochemical fluorescence switching of enhanced green fluorescent protein

Switchable fluorescent proteins, for which fluorescence can be switched ON and OFF, are widely used for molecule tracking and super resolution imaging. However, the robust use of the switchable fluorescent proteins is still limited as either the switching is not repeatable, or such switching requires irradiation with coupled lasers of different wavelengths. Herein, we report an electrochemical approach to reversible fluorescence switching for enhanced green fluorescent proteins (EGFP) on indium tin oxide coated glass. Our results demonstrate that negative and positive electrochemical potentials can efficiently switch the fluorescent proteins between the dim (OFF) and bright (ON) states at the single molecule level. The electrochemical fluorescence switching is fast, reversible, and may be performed up to hundreds of cycles before photobleaching occurs. These findings highlight that this method of electrochemical fluorescence switching can be incorporated into advanced fluorescence microscopy.

Ultrasensitive recognition performance of a folded π-based 1,8-naphthalimide-phthalocyanine fluorescence sensor

Designing ultrasensitive and smart molecules as molecular switches is highly valued in molecular recognition. In this work, a folded π-based molecular switch (NAPC) containing 1,8-naphthalimide and zinc(II) phthalocyanine functional modules was synthesized via cyclo tetramerization of four synthesized 1,8-naphthalimide sensors (NA). The photophysical properties of the folded molecular switch were investigated. This peripherally 1,8-naphthalimide substituted zinc(II) phthalocyanine possessed superior sensitivity in near-infrared “off-on” detection of Al3+, Fe3+, and Cr3+ compared with NA, and the detection limits were calculated to be 0.077 μmol/L for Al3+, 0.073 μmol/L for Fe3+ and 0.067 μmol/L for Cr3+, which were far less than that of NA. Due to the sensitive detection of Fe3+, NAPC was also applied in detecting NO2−. The ultrasensitive recognition mechanism of NAPC was determined to be the level-by-level linkage in the molecule in which the photo-induced electron transfer process in 1,8-naphthalimide sensor module was inhibited by complexing with metal ions first and then caused the inhibition of π-π stacking between two modules. This new folded molecule with a cascade linkage effect has the potential as an excellent fluorescence switch that could be applied in molecular recognition and environmental management.

Heat-induced ʻparallelʼ to ʻorthogonalʼ switching of fluorophores and reversible luminescence changes in divinylbenzene-benzoxazole crystals

Organic crystals that exhibit reversible solid-state luminescence triggered by heat stimulus have garnered great research interest in recent years. In this work, we demonstrate thermoresponsive, reversible color and photoluminescence switching in divinylbenzene-benzoxazole derivatives. The fluorescence switching is caused by differential chromophore packing and the resulting charge transfer On/Off states induced by heat. It is noteworthy that the reversibility, range of colors, and transition temperature associated with the luminescence switching are dependent on the length of the alkyl chains. Our results suggest that controlling charge-transfer interactions in chromophore assemblies may offer a versatile approach for creating functional organic materials with switchable, high-contrast solid-state luminescence. These findings have implications for the development of sensors, data storage devices, dynamic optical materials, and security inks.

Multi-stimuli responsive carbazole-imidazole derivatives: Effect of phenyl substitution and UV light-oxygen induced photochemical transformation

New carbazole-imidazole derivatives, (3-(4,5-diphenyl-1H-imidazole-2-yl)-9-(3-methoxyphenyl)-9H-carbazole (Cz-DPIM)) and 9-(3-methoxyphenyl)-3-(1,4,5-triphenyl-1H-imidazole-2-yl)-9H-carbazole (Cz-TPIM) are synthesized and investigated the effect of phenyl substitution on the fluorescence and stimuli-induced fluorescence properties. Cz-DPIM exhibited relatively strong fluorescence in solution compared to Cz-TPIM (Quantum yield (Φf, compared to quinine sulphate standard) = 0.28 (Cz-DPIM) and 0.09 (Cz-TPIM)). In contrast, Cz-DPIM is weakly fluorescence in solid-state but Cz-TPIM showed strong fluorescence (Φf = 1.3% (Cz-DPIM) and 18.2% (Cz-TPIM)). Cz-TPIM displayed mechanoresponsive reversible fluorescence switching upon crushing and solvent fuming. Both Cz-DPIM and Cz-TPIM exhibited reversible halofluorochromsim upon exposure of trifluoroacetic acid (TFA) and ammonia (NH3). Interestingly, Cz-DPIM and Cz-TPIM exhibited photocleavage upon UV light irradiation in presence of oxygen in CH3CN and produced green emissive fluorescence product. The controlled studies revealed that the presence of oxygen is important for exhibiting photocleavage by UV light exposure and suggest potential use for oxygen sensing application. The UV light and oxygen induced photocleavage of Cz-DPIM and Cz-TPIM also demonstrated in thin films.

Fluoride Induced Dual Mode Moisture Detection in Organic Solvents, Food, and Agricultural Materials using Benzothiazole Based Azo Dye Sensor

AbstractMoisture detection through naked eye is important in various fields, including pharmaceuticals, fuels, materials, and agriculture. In this study, we demonstrate the use of a strategically designed organic molecule, 2AMBP, for the detection of moisture in organic solvents and real‐life samples. The principle behind this sensory system involves fluoride‐induced deprotonation followed by water‐induced re‐protonation. The deprotonated form of 2AMBP displays a color‐changing response (yellow to pink) even in trace amounts of water (LOD: 0.0207 % by spectrophotometric analysis), making it a highly sensitive probe for detecting moisture. We show that the anionic receptor moieties of 2AMBP can be employed for the quantification of water impurity in various real‐life samples, and we develop inexpensive, reusable, dye‐coated paper sensor for quick onsite moisture detection and quantification. Interestingly, a smart phone camera can be used to provide relative RGB values that directly correlate to the amount of moisture present in the sample. The 2AMBP‐F‐ exhibits significant changes in fluorescence properties in the presence and absence of water, which makes it an effective fluorescent switch for detecting moisture. Overall, 2AMBP is a highly sensitive, sustainable material that can be conveniently used by laymen for moisture detection without the need for specific instruments or expertise.

Construction of a Reversible Solid-state Fluorescence Switching Via Photochromic Diarylethene and Si-ZnO Quantum Dots.

Developing fluorescence switching as functional system is highly desirable for potential applications in the fields of light-responsive materials or devices. Attempt to construct fluorescence switching system tend to focus on the high fluorescence modulation efficiency, especially in solid state. Herein, a photo-controlled fluorescence switching system was constructed with photochromic diarylethene and trimethoxysilane modified zinc oxide quantum dots (Si-ZnO QDs) successfully. It was verified by the measurement of modulation efficiency, fatigue resistance as well as theoretical calculation. Upon irradiation with UV/Vis lights, the system exhibited excellent photochromic property and photo-controlled fluorescence switching performance. Furthermore, the excellent fluorescence switching characters could also be realized in solid state and the fluorescence modulation efficiency was determined to be 87.4%. The results will provide new strategies to the construction of reversible solid-state photo-controlled fluorescence switching for the application in the fields of optical data storage and security labels.