Strong Fluorescence Enhancement Research Articles

Dual-locked NIR fluorescent probe for detection of GSH and lipid droplets and its bioimaging application in cancer model

Fluorescence probes with outstanding merits have wide applications in tumor diagnosis. However, most of these probes can only detect single tumor biomarker, potentially generating “false positive” signals within intricate biological systems. In contrast, the dual-locked fluorescent probes triggered by two response factors can effectively address the aforementioned limitations. In this work, we fabricated a novel coumarin-based NIR fluorescent probe (CP-GSH), demonstrating dual-responsiveness to high glutathione (GSH) concentrations and high viscosity. Specifically, the probe showed strong fluorescence enhancement at 675 nm ∼ 725 nm in the simultaneous presence of GSH and high viscosity, whereas the presence of either GSH or high viscosity alone could not induce a noticeable change in fluorescence intensity of CP-GSH. More importantly, the bioimaging experiments further validated CP-GSH triggered by endogenous GSH possessed excellent targeting capability towards lipid droplets (LDs), which could be utilized to effective discriminate between cancer cells and normal cells. This work proposes a promising strategy for the design of dual-locked probe for tumor imaging.

A lysosome-targeted fluorescent probe for thiol detection in drug analysis and multiple biological systems.

Biothiols, characterized by their unique sulfhydryl (-SH) groups, possess excellent antioxidant properties, effectively neutralizing the damage to cellular structures caused by reactive oxygen species (ROS) in living organisms. Additionally, lysosomes play a crucial role in decomposing damaged biomolecules through the action of their internal enzymes, regulating the cellular redox state, and mitigating oxidative stress. To facilitate rapid monitoring of intracellular biothiols, particularly within lysosomes, we constructed a lysosome-targeted biothiol fluorescent probe, PHL-DNP, in this study. PHL-DNP exhibited excellent photophysical properties in an aqueous test system, including strong fluorescence enhancement response, excellent selectivity, and low detection limits (Cys 16.5nM, Hcy 16.8nM, GSH 21.3nM, Cap 26.6nM). These attributes enabled easy and efficient qualification of Cys on test strips and accurate determination of the effective content of captopril tablets. Notably, PHL-DNP demonstrated low cytotoxicity and precise lysosomal targeting. Through bioimaging, PHL-DNP not only monitored changes in biothiol levels under oxidative stress but also assessed biothiols in complex biological systems such as live HeLa cells, zebrafish, tumor tissue sections, and radish roots. This provides a promising tool for quantitative analysis of biothiols, disease marker detection, and drug testing.

Carbazole Derivatives Binding to Bcl-2 Promoter Sequence G-quadruplex.

In this study, we used ultraviolet-visible (UV-Vis), fluorescence, and circular dichroism (CD) techniques, as well as molecular modeling, to probe the interactions between carbazole derivatives and the G-quadruplex structure formed in the promoter region of gene Bcl-2. This gene is a rational target for anticancer therapy due to its high expression in a variety of tumors as well as resistance to chemotherapy-induced apoptosis. We employed a sequence with a specific dual G-to-T mutation that may form a mixed-type hybrid G-quadruplex structure in the Bcl-2 P1 promoter region. The three tested carbazole compounds differing in substitution on the nitrogen atom of carbazole interact with the Bcl-2 G-quadruplex by the same binding mode with the very comparable binding affinities in the order of 105 M-1. During absorption and fluorescence measurements, large changes in the ligand spectra were observed at higher G4 concentrations. The spectrophotometric titration results showed a two-step complex formation between the ligands and the G-quadruplex in the form of initial hypochromicity followed by hyperchromicity with a bathochromic shift. The strong fluorescence enhancement of ligands was observed after binding to the DNA. All of the used analytical techniques, as well as molecular modeling, suggested the π-π interaction between carbazole ligands and a guanine tetrad of the Bcl-2 G-quadruplex. Molecular modeling has shown differences in the interaction between each of the ligands and the tested G-quadruplex, which potentially had an impact on the binding strength.

Macrocyclic Conformational Switch Coupled with Pyridinium-Induced PET for Fluorescence Detection of Adenosine Triphosphate.

The binding of nucleotides is crucial for signal transduction as it induces conformational protein changes, leading to downstream cellular responses. Synthetic receptors that bind nucleotides and transduce the binding event into global conformational rearrangements are highly challenging to design, especially those that operate in an aqueous solution. Much work is focused on evaluating functionalized dyes to detect nucleotides, whereas coupling of a nucleotide-induced conformational switching to a sensing event has not been reported to date. We disclose synthetic receptors that undergo a global conformational rearrangement upon nucleotide binding. Integrating naphthalimide and the pyridinium ion into the structure enables stabilization of the folded conformation and efficient fluorescence quenching. The binding of a nucleotide rearranges the receptor conformation and alters the strong fluorescence enhancement. The methylpyridinium-containing receptor demonstrated high sensing selectivity for adenosine 5'-triphosphate (ATP) and a record 160-fold fluorescence enhancement. It can detect fluctuations of ATP in HeLa cells and possesses low cytotoxicity. The developed systems present an attractive approach for designing ATP-responsive artificial molecular switches that operate in water and integrate a strong fluorescence response.

Intramolecular charge transfer-induced fluorochromic covalent organic frameworks for high speed on-line monitoring of volatile amines

Direct and visual evaluation of volatile amine molecules, a group of hazardous gases and indicators, remains challenge in the fields of chemical industry, environmental detection and food safety. Herein, a convenient and reversible intramolecular charge transfer (ICT)-induced fluorescence-colorimetric approach is proposed for on-line, visual and quantitative monitoring on volatile amines at molecular level through skeletal constructing of cationic pyridinium sites in a carbon-conjugated covalent organic framework (COF). In the presence of volatile amine molecules, the deprotonation of pyridinium sites causes a strong fluorescence enhancement (fluorescence quantum yield > 13 %) and a sharp color change. Specifically, with the reversable pyridinium sites, the COFs-based sensor first exhibits an ultrafast response time (τrise) of 0.65 s to ammonia gas (51.8 ppm), which outperforms reported nanostructure-based ammonia sensors. Meanwhile, through studying the relationship between the total volatile basic nitrogen (TVB-N) and Red/Green/Blue (RGB) outputs of home-made COFs membrane on the food spoilage (fish meat: R2 > 0.9987, shrimp meat: R2 > 0.9917), the protonated TPCH-mOBPy COF is fully verified to work as an on-line fluorochromic probe for visually, AI-intelligently and quantitatively monitoring the generation of volatile amines.

Highly Selective Turn-on Fluorescence Sensor for Cd2+ Ions by TripodalOrganic Ligand.

Organic fluorescence sensor for selectively detecting and quantifying toxic heavy metal ions has received significant interest due to their environmental hazards. Herein, we have designed and synthesized a simple tripodal Schiff base ligand (1) based on hydroxy-naphthaldehyde and tris(2-aminoethyl)amine (TREN) and demonstrated highly selective turn-on fluorescence sensing of Cd2+ ions. The free ligand did not show any fluorescence in DMF. In contrast, Cd2+ (10- 4M) addition exhibited a strong enhancement of fluorescence at 450nm. Interestingly, other metal ions including Zn2+, which exhibit similar chemistry, did not show any turn-on fluorescence. The concentration-dependent studies of 1 with Cd2+ showed the detection limit of 6.78 × 10- 8M. NMR spectra of 1 with Cd2+ and computational studies were performed to understand the mechanism of sense.

Cy3 Cyanine Dye with Strong Fluorescence Enhancement for AGRO100 and Its Derivative.

Nucleic acids, as important substances for biological inheritance, have attracted extensive attention in the biomedical field. More and more cyanine dyes are emerging as one of the probe tools for nucleic acid detection due to their excellent photophysical properties. Here, we discovered that the insertion of the AGRO100 sequence can specifically disrupt the twisted intramolecular charge transfer (TICT) mechanism of the trimethine cyanine dye (TCy3), resulting in a clear "turn-on" response. Moreover, the fluorescence enhancement of TCy3 combined with the T-rich AGRO100 derivative is more obvious. One explanation for the interaction between dT (deoxythymidine) and positively charged TCy3 may be that its outer layer carries the most negative charge. This study provides a theoretical basis for the use of TCy3 as a DNA probe, which has promising applications in the DNA detection of biological samples. It also provides the basis for the following construction of probes with specific ability for recognition.

Unraveling the Strong Fluorescence Enhancement of HPBI Molecules by ZIF-8 Colloidal Suspensions via Adsorption Analysis.

Enhancing the fluorescence of organic dye by colloidal particles is one of the most promising routes to optimize fluorescence detection. However, in addition to metallic particles, which serve as the most frequently used particles and have been found to employ the plasmonic resonance to provide strong fluorescence enhancement, neither new types of colloidal particles nor new fluorescence mechanisms have been intensively explored in recent years. In this work, strongly enhanced fluorescence was observed when 2-(2-hydroxyphenyl)-1H-benzimidazole (HPBI) molecules were simply mixed with zeolitic imidazolate framework-8 (ZIF-8) colloidal suspensions. Moreover, the enhancement factor ΔI = IHPBI+ZIF-8/IHPBI does not increase accordingly with the increasing amount of HPBI. To find out how the strong fluorescence was triggered and affected by the amount of HPBI, multiple techniques were applied to analyze the adsorption behavior. By combining analytical ultracentrifugation with first-principles calculations, we proposed that HPBI molecules were adsorbed onto the surface of ZIF-8 particles coordinatively and electrostatically, depending on the concentration of HPBI molecules. The coordinative adsorption would result in a new kind of fluorescence emitter. The new fluorescence emitters tend to distribute on the outer surface of ZIF-8 particles periodically. The distance between each fluorescence emitter is fixed and much smaller than the wavelength of the excitation light. Thus, it can be concluded that collective spontaneous emission might be triggered.

Pyrrole Based Schiff Base as a Highly Sensitive Fluorescent Sensor for Fe3+ and Sn2+ Ions

Condensation product of o-aminophenol and pyrrole-2-carboxylaldehyde behaves as a fluorescent sensor for Fe3+ and Sn2+ ions in aqueous medium over the other metal ions like Na+, K+, Mg2+, Zn2+, Cd2+, Hg2+, Mn2+ and Cr3+. In aqueous solution, Fe3+ and Sn2+ ions coordinate to the receptor through a NON binding site which induces a strong fluorescence enhancement. Receptor can be applied as fluorescence enhanced probes for transition metal ions due to the inhibition of photo induced electron transfer (PET) mechanism.

Supramolecular self-assembled polymeric nanospheres based on hydrazino naphthalimide functionalised pillar[5]arene for long chain aldehyde detection.

A novel fluorescent sensor HNP5A is constructed consisting of bis-hydrazine naphthalimide decorated pillar[5]arene. Interestingly, this sensor possessed the potential for sensitive and selective detection of long-chain aldehydes, particularly nonanal (C9), and subsequently formed supramolecular pseudorotaxane polymeric nanoparticles inducing a strong fluorescence enhancement. In addition, this as-produced HNP5A⊂C9 exhibited an unexpected reduction of Ag+ to produce AgNPs in an aqueous system and the resulting AgNPs-HNP5A⊂C9 demonstrated a significant fluorescence enhancement under metal-enhanced fluorescence (MEF) behaviour.

5-(Thiophene-2-yl)oxazole derived “off-on-off” fluorescence chemosensor for sequential recognition of In3+ and Cr3+ ions

A new fluorescent chemosensor P from 5-(thiophen-2-yl)oxazole-4-carbohydrazide and 4-diethylaminosalicylaldehyde was designed and synthesized for sequential detection of In3+ and Cr3+ ions. P exhibits strong fluorescence enhancement at 512 nm upon binding to In3+. The green fluorescence of complex P-In3+ was selectively quenched by Cr3+. The complex stoichiometry of P with In3+ and Cr3+ was identified as 1:2 for both in conjunction with Job’s Plot analysis, ESI-MS titration and theoretical calculations. Moreover, P was successfully applied to monitor target ions in actual water samples, and a portable paper sensor for the detection of In3+ was investigated to evaluate the versatility application.

CuNCs modified with dual-ligand to achieve fluorescence visualization detection of Tin (Ⅳ)

In this study, polyvinylpyrrolidone (PVP) supported and cysteine (Cys) modified copper nanoclusters (Cys-PVP-CuNCs) with high fluorescence intensity have been synthesized and used to establish a simple and sensitive assay for the determination of trace Sn4+. The presence of Sn4+ can lead to fluorescence quenching based on the aggregation of PVP-CuNCs caused by the coordination of Sn4+ and oxygen atoms. For Cys-PVP-CuNCs, the ligand Cys can transfer electrons to the metal center of the cluster, resulting in strong fluorescence enhancement of CuNCs and intensification of fluorescence quenching after interaction with Sn4+, which is conducive to more sensitive visual detection. The proposed assay allows for the detection of Sn4+ in a linear range from 5 μg L−1 to 100 μg L−1, with a detection limit as low as 4.5 μg L−1 at a signal-to-noise ratio of 3. Moreover, under UV light, the obvious fluorescent color change can be observed by naked eyes at Sn4+ concentration ranging from as low as 5 μg L−1 to 200 μg L−1. Benefiting from the high sensitivity of this assay, satisfactory test results have been obtained when using only 10 mg of canned food samples with rapid digestion. The proposed Cys-PVP-CuNCs fluorescent probe shows excellent stability, simple operation, good selectivity, and high sensitivity, and thus it is expected to be used in the real-time field detection of Sn4+.

Viscosity activated NIR fluorescent probe for visualizing mitochondrial viscosity dynamic and fatty liver mice

Intracellular viscosity plays an important role for maintaining the diffusion, transportation, signal transmission and cell metabolism between biomolecules. And abnormal intracellular viscosity would cause various concurrent diseases such as fatty liver, hyperlipidemia and so on. However, as far as we know, there are quite few tools could be used for imaing of intracellular viscosity, much less in-depth investigation of the viscosity-related dysfunctional and disease. Herein, we have designed and developed a series of NIR fluorescent probes, in which the chemical bond between fluorophore and molecular rotor was designed with single bonds, double bonds, and extended double bonds, respectively. According to the theoretical calculations and experiments results, BP-III with was selected as the most sensitive fluorescence sensor for imaging viscosity change in vitro and in vivo. As the viscosity increasesd, the TICT (twisted intramolecular charge transfer) of BP- III was inhibited, accompanied with a strong red fluorescence enhancement at 740 nm. In addition, BP- III showed excellent mitochondrial target ability and can be used to imaging viscosity changes in mitochondrial of living cells. More importantly, the probe has been used for imaging the abnormal viscosity of fatty liver at the organ level. We expect this work would provide meaningful tool for promoting fundamental research in biological viscous environment and mitochondrial viscosity related diseases.

A chemoselective fluorescent probe for arginine in aqueous phase

As an essential amino acid, arginine (Arg) is of many biological significances. However, the chemoselective detection of Arg using fluorescent techniques remain challenging. Here, a 1,1′-bi-2-naphthol (BINOL)-based fluorescent probe has been synthesized and responds chemoselectively to Arg to give strong fluorescence enhancement within a minute. The probe can report the concentration of Arg in a large window from 10 μM to 5 mM. UV irradiation provides a qualitative method for Arg detection. The fluorescence of the formed imine product can be turned off again by either acid or base. Based on those findings, a simple fluorescence OFF-ON-OFF device has been made for the fast detection of Arg.

Construction of a unique two-photon fluorescent probe and the application for endogenous CO detection in live organisms.

Carbon monoxide (CO) is one of the most significant signal molecules and plays an important role in regulating human physiological and pathological processes. In this study, a novel Pd-based complex (Pd-BNP-OH) was developed for endogenous CO detection. The structure and morphology of Pd-BNP-OH was characterized by SEM, XPS, and NMR analyses. When Pd-BNP-OH was reacted with CO, a strong fluorescence enhancement at 510nm was observed. In addition, Pd-BNP-OH exhibited high stability and selectivity toward CO in PBS buffer. In biological experiments, Pd-BNP-OH exhibited little cytotoxicity in cellular environment, and a bright fluorescence turn on was observed in the presence of exogenous CO and endogenous generated CO. The probe was then applied for CO detection in live zebrafish by both one-photon and two-photon excitation. Significantly, Pd-BNP-OH has excellent two-photon property, controllable structure and high biocompatibility. These features enable the probe to detect endogenously generated carbon monoxide in live organisms successfully.

Bioinspired 3D Hierarchical UiO-66-NH2 Nanoparticle/γ-AlO(OH) Nanowire for Simultaneous Detection and Removal of Fluoride Ions

Excessive fluorine can cause a serious threat to human health. It is significant but challenging to develop a straightforward and rapid way to simultaneously detect and remove excess F– from water. Herein, we presented a three-dimensional (3D) hierarchical UiO-66-NH2 nanoparticle/γ-AlO(OH) nanowire hybrid synthesized by a facile biotemplate route for simultaneous detection and removal of F– from water. We elaborately assembled two kinds of materials in a bioinspired 3D hierarchical structure as a functional unit to achieve detection and removal of dual functions. The outer UiO-66-NH2 nanoparticles served as a fluorescent sensor to detect and capture F– via a strong fluorescence enhancement effect caused by the electron transfer from F– and γ-AlO(OH) and acted as the capture unit of F–. The inner γ-AlO(OH) nanowire layer served as a F– absorbent through ion exchange between F– and γ-AlO(OH). The resulting UiO-66-NH2 nanoparticle/γ-AlO(OH) nanowire hybrid displayed excellent selectivity and sensitivity for F– detection (the detection range was 0–5 mM and the limit of detection was as low as 0.77 μM) and high capacity for F– removal (the maximum equilibrium adsorption capacity qmax was as high as 87.0 mg g–1). This dual-function material provided a strategy for simultaneously selective sensing and efficient removal of anionic pollutants from water.

Novel dimeric dyes based on the acridine orange chromophore: Synthesis, characterization and application in real-time PCR

Novel homodimeric dyes based on the acridine orange (AO) chromophore were synthesized and investigated. The photophysical properties measured free in solution and on binding to double-stranded DNA (dsDNA) were compared to those of widely used nucleic acid labelling dyes, namely SYBR Green I (SG) and YOYO-1. All studied dyes demonstrated negligible intrinsic fluorescence and strong fluorescence enhancement upon binding to dsDNA with quantum yields 0.45–0.55. Contrary to SG and YOYO-1, the obtained dyes showed better resistance to high temperatures, light and oxidizing reagents. The inhibitory effect and the effect on DNA melting temperature in a real-time quantitative polymerase chain reaction (qPCR) for all studied dyes were investigated. In qPCR experiments, dimeric dyes composed of two AO moieties coupled by neutral linkers comprising 2,5- or 2,6-disubstituted five- or six-membered heterocyclic fragments were less inhibitory to qPCR than SG at a broader range of dye concentrations (i.e. 0.75–1.75 μM). Moreover, these dyes are nontoxic when used at concentrations well above the qPCR working concentration. The strong fluorescent signal without inhibiting the qPCR along with the promotion of the formation of specific amplification products make these dyes suitable for high-resolution melt curve analysis and routine qPCR at a broad range of concentrations.

Preparation of 2D Periodic Nanopatterned Arrays through Vertical Vibration-Assisted Convective Deposition for Application in Metal-Enhanced Fluorescence

The performance of a metal-enhanced fluorescence (MEF) substrate is fundamentally based on the orientation of the metal nanostructures on a solid substrate. In particular, two-dimensional (2D) periodic metallic nanostructures exhibit a strong confinement of the electric field between adjacent nanopatterns due to localized surface plasmon resonance (LSPR), leading to stronger fluorescence intensity enhancement. The use of vertical vibration-assisted convective deposition, a novel, simple, and highly cost-effective technique for preparing the 2D periodic nanostructure of colloidal particles with high uniformity, was therefore proposed in this work. The influences of vertical vibration amplitude and frequency on the structure of thin colloidal film, especially its uniformity, monolayer, and hexagonal close-packed (HCP) arrangement, were also investigated. It was found that the vibration amplitude affected film uniformity, whereas the vibration frequency promoted the colloidal particles to align themselves into defect-free HCP nanostructures. Furthermore, the results showed that the self-assembled 2D periodic arrays of monodisperse colloidal particles were employed as an excellent template for a Au thin-film coating in order to fabricate an efficient MEF substrate. The developed MEF substrate provided a strong plasmonic fluorescence enhancement, with a detection limit for rhodamine 6G as low as 10−9 M. This novel approach could be advantageous in further applications in the area of plasmonic sensing platforms.

A dual-responsive nanozyme sensor with ultra-high sensitivity and ultra-low cross-interference towards metabolic biomarker monitoring.

Accurate, sensitive and selective detection of metabolic biomarkers in biofluids are of vital significance for health self-monitoring and chronic disease prevention. Here, for the first time, a smart dual-responsive nanozyme sensor (DNS) was developed for simultaneous analysis of glucose and caffeine utilizing stimuli-responsive yolk-shell gold nanoparticles (GNPs)-embedded MIL-53 (Al) (GNPs@MIL-53) structures. After the introduction of glucose, GNPs@MIL-53 displays excellent glucose oxidase (GOx)-like activity to induce the conversion of glucose to gluconic acid and H2O2. H2O2 can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) with the generation a bright-blue color, enabling in-field visualization and surface enhanced Raman scattering (SERS) detection of glucose. Upon the addition of caffeine, 2-aminoterephthalic acid modified MIL-53 can react with the caffeine to form intermolecular hydrogen-bonded complexes, leading to strong cyan fluorescence and significant Raman enhancements. The DNS with multi-channel signal outputs can simultaneously determine glucose and caffeine at concentrations of as low as 3 × 10-8 M and 1.2 × 10-11 M, respectively. Importantly, the DNS-based analytical system not only enables visual discrimination and accurate assay of glucose and caffeine in biofluids, but also exhibits negligible cross-interference between glucose and caffeine determination. The combined characteristics of high selectivity, enhanced accuracy and superior quantitative performance make our platform suitable for the point-of-care monitoring of chronic-disease-related metabolic biomarkers.

A rhodamine based dye for sensing of Group 13 metal ions

Search for a new reagent for the detection of a particular group members is of significant importance to the researchers of analytical and inorganic chemistry. We report here a rhodamine based compound, L1, for the colorimetric as well as fluorometric sensing of Group 13 cations in 10 mM HEPES buffer in (1:9, v/v) water:ethanol (pH = 7.4). L1 has been obtained from the condensation between rhodamine 6G hydrazide and 4-(4-fluorobenzyloxy)benzaldehyde and characterized by standard methods. Colorless L1 becomes pink in the presence of Al3+, Ga3+, In3+ and Tl3+ ions. Its absorbance increases at ∼530 nm considerably with these cations. L1 is nonfluorescent. However, it exhibits strong fluorescence enhancement at about 555 nm in the presence of Al3+, Ga3+, In3+ and Tl3+.Other metal ions fail to alter any significant change in abosrbance and fluorescence. Opening of spirocyclic ring of L1 occurs with the Group 13 cations followed by the strong complex formation to display its color change and fluorescence increment. Lifetime and quantum yield of L1 increase appreciably with the cations. Limit of detection values of the probe are in order of 10−8 M indicating high sensitivity towards these cations. It has been utilized to sense these cations using river water. Thus, it may be concluded that L1 is effective to sense Group 13 metal ions.