Selective Fluorescence Enhancement Research Articles

Fluorescent Selectivity-Enhanced FRET Based on 3D Photonic Crystals for Multianalyte Sensing.

Fluorescence resonance energy transfer (FRET) finds widespread utility in biochemical sensing, single-molecule experiments, cell physiology, and various other domains due to its inherent simplicity and high sensitivity. Nevertheless, the efficiency of energy transfer between the FRET donor and acceptor is significantly contingent on the local photonic environment, a factor that limits its application in complex systems or multianalyte detections. Here, a fluorescent selectivity-enhanced acridine orange (AO)-aflatoxins (AFs) FRET system based on a range of 3D topological photonic crystals (PCs) was developed with the aim of enhancing the selectivity and discrimination capabilities of FRET. By exploring the angle-dependent characteristics of the photonic stopband, the stopband distribution across different 3D topological PCs pixels was investigated. This approach led to selective fluorescence enhancement in PCs that matched the stopbands, enabling the successful discrimination of six distinct aflatoxins and facilitating complex multianalysis of moldy food samples. In particular, the stopband, which was strategically positioned within the blue-purple structural color range, exhibited a strong alignment with the fluorescence peaks of both the FRET donor and acceptor. This alignment allowed the 3D three-pointed star PCs to be effectively employed for the identification of mixed samples containing six distinct aflatoxins as well as the detection of real aflatoxin samples present in moldy potatoes, bread, oats, and peanuts. Impressively, this approach achieved a remarkable accuracy rate of 100%. This innovative strategy not only presents a novel avenue for developing a multitarget discrimination analysis system but also offers a convenient pretreatment method for the quantitative detection of various aflatoxins.

Cd2+-Selective Fluorescence Enhancement of Bisquinoline Derivatives with 2-Aminoethanol Skeleton.

The development of fluorescent Cd2+ sensors requires strict selectivity over Zn2+ because of the high availability of Zn2+ in the natural environment. In this paper, bisquinoline-based fluorescent sensors with a 2-aminoethanol backbone were investigated. The weak coordination ability of quinoline compared to well-studied pyridine is suitable for Cd2+ selectivity rather than Zn2+. In the presence of 3 equiv. of metal ions, TriMeO-N,O-BQMAE (N,O-bis(5,6,7-trimethoxy-2-quinolylmethyl)-2-methylaminoethanol (3)), as well as its N,N-isomer TriMeO-N,N-BQMAE (N,N-bis(5,6,7-trimethoxy-2-quinolylmethyl)-2-methoxyethylamine (6)), exhibits Cd2+-selective fluorescence enhancement over Zn2+ in DMF-HEPES buffer (1:1, 50 mM HEPES, 0.1 M KCl, pH = 7.5) (IZn/ICd = 26-34%), which has similar selectivity in comparison to the corresponding ethylenediamine derivative TriMeOBQDMEN (N,N'-bis(5,6,7-trimethoxy-2-quinolylmethyl)-N,N'-dimethylethylenediamine) under the same experimental condition (IZn/ICd = 24%). The fluorescence mechanisms of N,O- and N,N-isomers of BQMAE are quite different, judging from the fluorescence lifetimes of their metal complexes. The Cd2+ complex with TriMeO-N,O-BQMAE (3) exhibits a long fluorescence lifetime similar to that of TriMeOBQDMEN via intramolecular excimer emission, whereas the Cd2+ complex with TriMeO-N,N-BQMAE (6) exhibits a short lifetime from monomer emission.

Quantification and visualization of hydrogen peroxide in an ischemic model and serum samples from stroke patients using a reaction-based fluorescence sensor

Stroke is a cerebral vascular disease resulting in an imbalance of oxidative stress and the generation of reactive oxygen species (ROS). As a significant member of the ROS family, hydrogen peroxide (H2O2) is a potential biomarker candidate for stroke evaluation. Herein, we report a reaction-based fluorescent sensor, HYTZ-1, which showed selective fluorescent enhancement towards H2O2, to be successfully applied to visualize H2O2 in HeLa cells and C. elegans. In ischemic models, HYTZ-1 exhibited outstanding H2O2 imaging capabilities in mice brain tissue sections and demonstrated that hypoxia-ischemia could raise H2O2 concentration. Establishing standard curves facilitated quantitative detection in the peripheral serum of ischemic stroke patients. A relationship between H2O2 content, stroke severity, and patients’ age was discovered, proving the clinical potential of HYTZ-1 for future application.

A fluorescence and colorimetric bifunctional probe for recognition of Al3+ and Cu2+ and its applications in cells and environmental water systems

A highly sensitive bifunctional probe (1) for Al3+ and Cu2+ by the reaction of 2-hydroxyl-1-naphthalene formaldehyde with indole-3-formyl hydrazine was synthesized. In THF-H2O (v/v = 3:7) solution, 1 only shows fluorescence enhanced recognition for Al3+ in 17 common metal ions, which shows that 1 can be used as a highly selective fluorescence enhancement probe for Al3+. When the concentration of Al3+ is 20.0 µM (1.0 equivalent), the fluorescence intensity of 1 is increased by 195 times, and the detection limit of 1 for Al3+ is calculated to be 3.8 nM, which shows that 1 is fluorescence probe for Al3+ with an ultra-high sensitivity. Trace Al3+ (For example, the WHO drinking water quality standard 7.4 μM) can be clearly observed by the fluorescence test paper covering 1 through the change of fluorescence color. In addition, the vivo-detection ability of 1 is verified by detected the Al3+ in living GS cells of epinephelus coioides. Furthermore, 1 can also be used as a high selective and sensitive colorimetric probe for Cu2+. In THF-H2O (v/v = 3:7) buffer solution (pH = 7.0), the addition of Cu2+ results in a 69 nm red shift in the UV–visible absorption spectrum of 1 solution, causing the color of 1 solution to change from colorless to yellow. In addition, 1 shows a low detection limit of 39.3 nM, a fast response time, excellent recyclability and anti-interference for Cu2+. Therefore, 1 can be used for fluorescence detection of Cu2+ in environmental water systems.

A terpyridyl functionalized rhodamine dye for viscosity sensing with fluorescence enhancement and mitochondria-targeting imaging

Exploring new fluorescent organic dyes with mitochondria-targeted and viscosity-sensitive functions attracts extensive attention because they may provide access to a better understanding of the microenvironments of the subcellular level via biological imaging. Herein a terpyridyl functionalized rhodamine dye (TRMe) has been facilely designed and prepared, which shows a highly selective fluorescence enhancement response to viscosity (1.0–1238.0 cp) in water-glycerol mixtures with the increased glycerol content. In addition, TRMe can respond to viscosity enhancement over a wide pH range (1.0–10.0) and presents low cell toxicity. Besides, a good linearity between the viscosity and fluorescence lifetime of TRMe can be observed. Significantly, TRMe shows excellent mitochondria-targeted performance with a Pearson's colocalization coefficient of 0.958 and can be employed as a tracer for viscosity imaging in Nystatin-stimulated living HeLa cells.

Rapid Colorimetric and Fluorometric Discrimination of Maleic Acid vs. Fumaric Acid and Detection of Maleic Acid in Food Additives.

An anthracene thiazole based Schiff base L was synthesized and employed for fluorescence switch-on detection of maleic acid in aqueous DMSO. The non-fluorescent L (10-5M) showed an instantaneous and selective fluorescence enhancement at 506nm upon interaction with maleic acid (10-5M). Other potential carboxylic acids (10-5M), such as malic acid, citric acid, acetic acid, cinnamic acid, tartaric acid, succinic acid, fumaric acid, oxalic acid and malonic acid failed to alter the chromo-fluorogenic properties of L. Probe L can be employed to detect maleic acid down to 2.74 × 10-6M. The probe L showed good linearity from 2.97 to 6.87µM. Analytical utility of L was examined by detecting maleic acid in various food additives and drosophila larvae.

Comprehensive monitoring of mitochondrial viscosity variation during different cell death processes by a NIR mitochondria-targeting fluorescence probe

Cell death is a fundamental feature of multicellular organisms, in which mitochondria play crucial roles. Therefore, revealing and monitoring the microenvironment of mitochondria are significant to investigate cell death process. Herein, the mitochondrial viscosity variation behaviors of a series of different cell death processes were monitored with a NIR mitochondria-targeting fluorescence probe FLV. FLV was designed based on a rotatable flavylocyanine fluorophore that presented selective and sensitive NIR fluorescence enhancement response with the increase of environmental viscosity. Fluorescence imaging experiments of living cells incubated with nystatin or under different temperature indicated that FLV was capable of imaging the change of mitochondrial viscosity. Finally, FLV was applied for monitoring the mitochondrial viscosity variation during different cell death processes. It was found that there were obvious mitochondrial viscosity increases during apoptosis, necrosis and autophagy; however, no detectable mitochondrial viscosity variation was observed in ferroptosis process incubated with ferroptosis inducer erastin or RSL3 for 6 h. These results demonstrated that FLV is a viable tool for monitoring the mitochondrial viscosity variation and is likely to be used in the diagnosis of the mitochondrial viscosity-associated cell processes and diseases.

Synthesis of a BINOL-Based C3 Symmetric Schiff Base and Its Fluorescence Response to Zn2.

A novel C3 symmetric 1,1'-bi-2-naphthol-based Schiff base (R,R,R)-6 has been synthesized which shows highly selective fluorescence enhancement with Zn2+ among 21 metal cations examined. Its sensitivity and selectivity are found to be greater than other related C2 (1) and C1 [(R)-9] symmetric compounds in the fluorescent recognition of Zn2+ . The mechanistic study reveals that the selective fluorescence enhancement of the probe can be attributed to the formation of a unimolecular multidentate 6-coordinated Zn2+ complex.

Dual-Emission 2D Blue Luminescent Organic Silver Chalcogenide for Highly Selective Pb2+ Detection in an Aqueous Medium

Crystalline organic metal chalcogenides (OMCs) are a class of organic-inorganic hybrid semiconducting materials with continuous M-X (X = S, Se, Te) networks formed by the combination of metal nodes and chalcogen atoms from the organic ligands, which display great potentials in the fields of optoelectronics, catalysis, sensing, as well as energy conversion and storage. Here, we synthesized a wave-like 2D OMC material, [(AgBF4)2Me6BHS]n (Ag-BHSMe), from AgBF4 and 1,2,3,4,5,6-hexa(methylselanyl)benzene (Me6BHS) through a simple homogeneous reaction. In the solid state, Ag-BHSMe exhibits both fluorescence emission at room temperature and phosphorescent emission at 77 K. TEM, SEM, and confocal microscopy revealed that it is an intrinsic blue luminescent microcrystalline material. In addition, we found that it exhibited a highly selective fluorescence enhancement response to Pb2+ in an aqueous solution in the range of 10-4 to 10-2 mol L-1, which demonstrates its potential as a turn-on probe for the detection of lead ions.

'AIE + ESIPT' Active 2-hydroxy-naphthalene Hydrazone for the Fluorescence Turn-on Sensing of Al3.

The aggregation-induced emission (AIE) behaviour of an easy-to-prepare Schiff base 2-hydroxy-naphthalene hydrazone (L) was explored in mixed DMSO/HEPES medium by selecting DMSO as a good solvent, whereas HEPES buffer (H2O, 10mM, pH 7.4) as a poor solvent. The weakly fluorescent L in pure DMSO showed a fluorescence enhancement at 532nm upon increasing the fraction of HEPES above 70% because of the self-aggregation of L and excited state intramolecular proton transfer (ESIPT) process. The AIE luminogen (AIEgen) L was applied for the sensing of metal ions in HEPES buffer (5% DMSO, 10mM, pH 7.4). Among the fourteen different metal ions (Cu2+, Co2+, Ni2+, Mn2+, Mg2+, Fe3+, Fe2+, Zn2+, Cd2+, Hg2+, Pb2+, Al3+, Cr3+), AIEgen L showed a selective fluorescence enhancement at 435nm in the presence of Al3+ without disturbing the fluorescence intensity at 532nm due to the chelation-enhanced fluorescence effect (CHEF). The detection limit of 20nM was estimated by performing the fluorescence titration of AIEgen L with Al3+. The reversibility of the Al3+ selective AIEgen L was demonstrated by adding a strong chelating agent EDTA. Finally, the practical utility of AIEgen L was validated by quantifying Al3+ in river and tap water samples.

Effect of methoxy substituents on fluorescent Zn2+/Cd2+ selectivity of bisquinoline derivatives with a N,N'-dimethylalkanediamine skeleton.

BQDMEN (N,N'-bis(2-quinolylmethyl)-N,N'-dimethylethylenediamine) and its 6-methoxyquinoline derivative (6-MeOBQDMEN) are fluorescent Zn2+ sensors with minor response to Cd2+ (IZn/ICd = 3.9 for BQDMEN and IZn/ICd = 2.2 for 6-MeOBQDMEN in the presence of 1 equiv. of metal ion). Nevertheless, the introduction of three methoxy substituents at the 5,6,7-position of both quinoline rings of BQDMEN reversed the fluorescent metal ion selectivity to favor Cd2+ (IZn/ICd = 0.22 for TriMeOBQDMEN in the presence of 1 equiv. of metal ion). This reversal of Zn2+/Cd2+ preference in fluorescence enhancement by trimethoxy substitution was also valid for 1,3-propanediamine derivatives. The X-ray crystallography, ESI-MS, fluorescence lifetime and pH profile of the fluorescence intensity suggest that the dinuclear cadmium complex is a key component of the fluorescent Cd2+ selectivity in TriMeOBQDMEN.

Chemoselective and Enantioselective Fluorescent Recognition of Prolinol

A highly chemoselective and enantioselective fluorescent probe has been discovered for the recognition of prolinol among various primary and secondary amine-based amino alcohols. The mechanistic studies including 1D and 2D 1H/13C NMR and mass spectroscopic analyses and DFT calculations have shown that the aldehyde group of the probe can react with prolinol to generate a bicyclic oxazolidine unit which, through a possible intramolecular hydrogen bond interaction, will lead to highly selective fluorescence enhancement.

Fluorescent turn-on sensing of albumin proteins (BSA and ovalbumin) using vitamin B6 cofactor derived Schiff base.

The detection of albumin proteins with high accuracy by facile analytical approaches is important for the diagnosis of various diseases. This manuscript introduced an easy-to-prepare Schiff base L by condensing vitamin B6 cofactor pyridoxal 5'-phosphate (PLP) with 2-aminothiophenol for the fluorescence turn-on sensing of bovine serum albumin (BSA) and ovalbumin (OVA). The weakly emissive L showed a significant fluorescence enhancement at 485 and 490 nm in the presence of OVA and BSA with an estimated sensitivity limit of 1.7 µM and 0.3 µM, respectively. The formation of protein-ligand complex restricted the free intramolecular rotation of L is expected to show the selective fluorescence enhancement. The molecular docking and molecular dynamics simulations were performed to examine the binding affinity and modes between BSA/OVA and L. The practical utility of L as a fluorescent turn-on sensor was validated by quantifying BSA and OVA in various real biological samples of milk, serum, egg white and urine with good recovery percentages.

Basic Fluorescent Protonation-Type pH Probe Sensitive to Small ΔpKa of Methanol and Ethanol

An optical pH probe is a simple and effective tool for determining an accurate pH value in its localized area. However, basic pH probes with pKBH+ values above 8 have rarely been reported, although many components with high pKa such as arginine play important roles in vivo. Herein, we introduce novel colorimetric and fluorescent basic probes 1-5, which are designed using push-pull-type aminoquinoline and aminobenzoquinoline fluorophores, with pKBH+ values ranging from 8.4 to 9.9. After the basicity of the remarkably sensitive basic probe 4 was tuned, it was able to successfully distinguish between the pKa values of MeOH (15.5) and EtOH (15.9), thus displaying selective protonation and fluorescence enhancement in MeOH over EtOH. Our pH probes can be used to detect MeOH poisoning in commercial EtOH products such as hand sanitizers, providing an effective solution to this problem observed during the COVID-19 pandemic.

A novel spectrofluorimetric method based on a reaction with an azoisoxazoles-benzenesulfonamide derivative for determination of uranium (VI) ions in water samples.

Selective fluorometric detection and determination of uranium ions is provided here using a novel fluorescent reagent, namely (E)-4-([4-hydroxynaphthalen-1-yl]diazenyl)-N-(5-methyleisoxazol-3-yl) benzenesulfonamide (UVI reagent). The UVI reagent offers a selective fluorescence enhancement behaviour at emission wavelength = 557 nm. The parameters affecting fluorometric detection of uranium ions, such as the pH, solvent type, ligand concentration, interaction time, and interfering ions, were investigated and adjusted. The proposed UVI reagent can detect and determine uranium ions even at low concentrations, for which the obtained limit of detection was 0.1 ppm. Additionally, this proposed determination protocol was successfully used to detect, monitor, and determine uranium ions in actual water samples.

Cd2+-selective fluorescence response of TQEN (N,N,N',N'-tetrakis(2-quinolylmethyl)ethylenediamine) derivatives bearing ether oxygen-binding sites.

Moderate Zn2+ selectivity over Cd2+ (IZn/ICd = 1.6) in the fluorescence enhancement of TQEN (N,N,N',N'-tetrakis(2-quinolylmethyl)ethylenediamine) was changed to Cd2+ preference via the introduction of a methoxymethyloxy (MOMO) substituent at the 8-position of one of the four quinoline rings (IZn/ICd = 0.2). Thus, 8-MOMOTQEN (N-(8-methoxymethyloxy-2-quinolylmethyl)-N,N',N'-tris(2-quinolylmethyl)ethylenediamine) showed not only high Cd2+-selectivity but also an enhanced fluorescence quantum yield upon Cd2+ binding and high sensitivity for Cd2+ detection as shown by ϕCd = 0.065 and LOD (limit of detection) = 19 nM. The two oxygen atoms of the MOMO group in 8-MOMOTQEN play a crucial role in the fluorescent metal-ion selectivity because the corresponding hydroxy (8-OHTQEN) and methoxy (8-MeOTQEN) derivatives resulted in a poor fluorescent response and metal selectivity, respectively. Another N6O2 ligand, N,N'-bis(8-methoxy-2-quinolylethyl)-N,N'-bis(2-quinolylmethyl)ethylenediamine ((8-MeO)2TQEN) exhibited a Zn2+-selective fluorescence enhancement (IZn/ICd = 2.2), indicating the superiority of the MOMO group for the selective sensing of Cd2+.

A nitroreductase-responsive near-infrared phototheranostic probe for in vivo imaging of tiny tumor and photodynamic therapy

The hypoxia-activated and nitroreductase-responsive phototheranostic probe has been developed by incorporating a nitro group into a hemicyanine fluorophore. The probe displays extremely sensitive and selective near-infrared fluorescence enhancement to nitroreductase with the detection limit of 2.10 ng/mL. The detection mechanism relies on the nitroreductase-catalyzed reduction of the nitro group to an amino group, along with the generation of the fluorophore. The availability of the probe in fluorescence imaging and photodynamic therapy was demonstrated at cellular level and in vivo. The probe can image endogenous nitroreductase and the hypoxia status of living cells. The probe also exhibits significant phototoxicity to hypoxia tumor cells under the 660 nm laser irradiation. More importantly, the probe has been successfully utilized in imaging tiny tumor (about 6 mm3) and tumor photodynamic therapy in vivo. The proposed probe integrates accurate near-infrared fluorescence imaging and photodynamic therapy into the same molecule, which probably become a promising agent in the early diagnosis and therapy of tumors.

Fluorescent Sensor for Copper(II) and Cyanide Ions via the Complexation-Decomplexation Mechanism with Di(bissulfonamido)spirobifluorene.

A novel spirobifluorene derivative bearing two bissulfonamido groups is successfully synthesized by Sonogashira coupling. This compound exhibits a strong fluorescence quenching by Cu(II) ion in a 50% mixture between acetonitrile and 20 mM pH 7.0 N-(2-hydroxyethyl)piperazine-N′-ethanesulfonic acid (HEPES) buffer with a detection limit of 98.2 nM. However, this sensor also shows ratiometric signal shifts from blue to yellow in the presence of Zn(II), Pb(II), and Hg(II) ions. The static quenching mechanism is verified by the signal reversibility using ethylenediaminetetraacetic acid (EDTA) and the Stern–Volmer plots at varying temperatures. The Cu(II)–spirobifluorene complex shows a highly selective fluorescence enhancement upon the addition of CN– ion with the detection limit of 390 nM. The application of this complex for quantitative analysis of spiked CN– ion in real water samples resulted in good recoveries.

Rational Design of Crystallization‐Induced‐Emission Probes To Detect Amorphous Protein Aggregation in Live Cells

AbstractUnlike amyloid aggregates, amorphous protein aggregates with no defined structures have been challenging to target and detect in a complex cellular milieu. In this study, we rationally designed sensors of amorphous protein aggregation from aggregation‐induced‐emission probes (AIEgens). Utilizing dicyanoisophorone as a model AIEgen scaffold, we first sensitized the fluorescence of AIEgens to a nonpolar and viscous environment mimicking the interior of amorphous aggregated proteins. We identified a generally applicable moiety (dimethylaminophenylene) for selective binding and fluorescence enhancement. Regulation of the electron‐withdrawing groups tuned the emission wavelength while retaining selective detection. Finally, we utilized the optimized probe to systematically image aggregated proteome upon proteostasis network regulation. Overall, we present a rational approach to develop amorphous protein aggregation sensors from AIEgens with controllable sensitivity, spectral coverage, and cellular performance.

Rational Design of Crystallization-Induced-Emission Probes To Detect Amorphous Protein Aggregation in Live Cells.

Unlike amyloid aggregates, amorphous protein aggregates with no defined structures have been challenging to target and detect in a complex cellular milieu. In this study, we rationally designed sensors of amorphous protein aggregation from aggregation-induced-emission probes (AIEgens). Utilizing dicyanoisophorone as a model AIEgen scaffold, we first sensitized the fluorescence of AIEgens to a nonpolar and viscous environment mimicking the interior of amorphous aggregated proteins. We identified a generally applicable moiety (dimethylaminophenylene) for selective binding and fluorescence enhancement. Regulation of the electron-withdrawing groups tuned the emission wavelength while retaining selective detection. Finally, we utilized the optimized probe to systematically image aggregated proteome upon proteostasis network regulation. Overall, we present a rational approach to develop amorphous protein aggregation sensors from AIEgens with controllable sensitivity, spectral coverage, and cellular performance.