Fluorescence Enhancement Phenomenon Research Articles

Fluorescence enhancement upon magnesium hydroxide micro/nanoparticles in the detection of ferulic acid

We found an exciting fluorescence enhancement phenomenon of ferulic acid (FA) and magnesium ions in strong alkaline medium. In KCl/NaOH buffer solution with pH = 12.30, Mg2+ ions could coordinate with FA to generate Mg-FA complex ions and also combined with hydroxide ions to form Mg(OH)2 nanosheets, and then the nanosheets further aggregated into Mg(OH)2-micro/nanoparticles (Mg(OH)2-MNPs). The Mg(OH)2-MNPs acted as potential matrix materials for surface-enhanced fluorescence (SEF). In this work, the fluorescence quantum yield and the fluorescence intensity of FA were significantly increased by about 50 times and hundreds of times by freshly formed Mg(OH)2-MNPs, respectively. Then, a highly sensitive method was developed for quantitative detection of FA. The fluorescence intensity at 440 nm under 370 nm light irradiation showed a good linearity with FA concentration in the range of 9.0 × 10−10 to 1.0 × 10–6 M (R2 = 0.9984), and the limit of detection (at S/N = 3) was 2.7 × 10−10 M. And then a convenient method for FA detection by smartphone assisted was also proposed. These methods were applied for detecting FA in real samples, and the recovery rates were range from 98.3 % to 103.1 %. This work provided an effective way for improving FA analytical sensitivity.

High‐Efficiency Luminescent Solar Concentrators Based on Carbon Dots with Simultaneously Ultrabright Solid‐State and Liquid‐State Luminescence

AbstractCarbon dots (CDs) are ideal fluorophores for optoelectronic devices. However, it is still a great challenge to obtain CDs with high solid‐state photoluminescence quantum yields (PLQYs). In this work, it is first reported that the barium‐doped CDs (Ba‐CDs), which can be simply synthesized on a large scale via a direct one‐step heating approach using an open vessel. The as‐synthesized Ba‐CDs exhibit ultrabright luminescence both in liquid and solid states. The as‐synthesized Ba‐CDs with a scale of 8.6 g per batch show a Stokes shift of ≈0.68 eV and high PLQYs of 80.8% and 66.8% in liquid and solid state, respectively. Interestingly, an efficient fluorescence enhancement phenomenon occurs when Ba‐CDs are mixed with polyvinylpyrrolidone (PVP), which reveals the critical issue of compatibility between CDs and polymer matrix can be well resolved. As a proof‐of‐concept, the Ba‐CDs are employed as fluorophores for high‐efficiency luminescent solar concentrator (LSC) fabrication. The Ba‐CDs@PVP‐based LSC has a PLQY of 88.78%, showing a breakthrough optical conversion efficiency of 7.16% and power conversion efficiency of 6.87% under natural light irradiation (40 mW cm−2). The results demonstrate the potential application of the ultrabright Ba‐CDs in efficient photovoltaic devices.

Isomeric fluorescence sensors for wide range detection of ionizing radiations

In order to achieve a wider range of ionizing radiations detection, novel fluorescence sensing materials have been developed that utilize the fluorescence enhancement phenomenon caused by the intramolecular photoinduced electron transfer (PET) effect. Two perylene diimide isomers PDI-P and PDI-B were designed and synthesized, and their molecular structures were characterized by high-resolution Fourier transform mass spectrometry (HRMS), nuclear magnetic resonance hydrogen and carbon spectroscopy (1H and 13C NMR). The interaction between ionizing radiation and fluorescent molecules was simulated by HCl titration. The results show that combining PDIs and HCl can improve fluorescence through the retro-PET process. Despite the similarities in chemical structures, the fluorescent enhancement multiple of PDI-B with aromatic amine as electron donor is much higher than that of PDI-P with alkyl amine. In the direct irradiation experiments of ionizing radiation, the emission enhancement multiples of PDI-P and PDI-B are 2.01 and 45.4, respectively. Furthermore, density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations indicate that the HOMO and HOMO-1 energy ranges of PDI-P and PDI-B are 0.54 eV and 1.13 eV, respectively. A wider energy range has a stronger driving force on electrons, which is conducive to fluorescence quenching. Both femtosecond transient absorption spectroscopy (fs-TAS) and transient fluorescence spectroscopy (TFS) tests show that PDI-B has shorter charge separation lifetime and higher electron transfer rate constant. Although both isomers can significantly reduce LOD during PET process, PDI-B with aromatic amine has a wider detection range of 0.118–240 Gy due to its larger emission enhancement, which is a leap of three orders of magnitude. It breaks through the detection range of gamma radiation reported in existing studies, and provides theoretical support for the further study of sensitive and effective new materials for ionizing radiation detection.

BODIPY-Based Fluorescent Probes for Selective Visualization of Endogenous Hypochlorous Acid in Living Cells via Triazolopyridine Formation.

In this work, the two pyridylhydrazone-tethered BODIPY compounds (2 and 3) were synthesized. These compounds aimed to detect hypochlorous acid (HOCl) species via cyclic triazolopyridine formation. The open forms and the resulting cyclic forms of BODIPYs (2, 3, 4, and 5) were fully characterized by nuclear magnetic resonance, mass spectrometry, infrared spectroscopy, and single-crystal X-ray diffraction. These two probes can selectively detect HOCl through a fluorescence turn-on mechanism with the limit of detections of 0.21 µM and 0.77 µM for compounds 2 and 3, respectively. This fluorescence enhancement phenomenon could be the effect from C = N isomerization inhibition due to HOCl-triggered triazolopyridine formation. In cell imaging experiments, these compounds showed excellent biocompatibility toward RAW 264.7 murine live macrophage cells and greatly visualized endogenous HOCl in living cells stimulated with lipopolysaccharide.

Investigation of intense mid-infrared emission in Ho3+/Yb3+/Er3+ triple-doped tellurite glass

Rare earth ion doping is considered to be a feasible way to improve the optical properties of glass in recent years. We investigate the luminescence characteristics of Ho3 + -Er3 + -Yb3 + triple-doped tellurite glass (TeO2-ZnO-WO3-La2O3) at 2.0 μm. A series of characterization analyses on the prepared samples, such as x-ray diffractometer (XRD) pattern, Raman spectrum, differential scanning calorimetry (DSC) curve analyses, absorption spectrum, emission spectrum, and fluorescence decay curve, were performed. XRD pattern and DSC curve analyses indicate that the glass sample exhibits a typical amorphous structure with excellent thermodynamic stability. Through the absorption spectrum, the position and intensity of the absorption peak of the glass sample can be detected. Under an excitation of 980 nm laser, the 2.0-μm emission peak intensity of the glass sample increases by about 1500%, which is attributed to the energy level transition among Ho3 + , Er3 + , and Yb3 + . By analyzing the energy level transition of Ho3 + , Yb3 + , and Er3 + ions, the energy transfer mechanism and fluorescence lifetime can be obtained, and then the fluorescence enhancement phenomenon of Ho3 + -Er3 + -Yb3 + triple-doped tellurite glass at 2.0 μm can be explained. It is demonstrated that the as-prepared Ho3 + -Er3 + -Yb3 + triple-doped tellurite glass has potential for the application of fiber lasers and fiber amplifiers.

Effects of the Surface Charge Density of Clay Minerals on Surface-Fixation Induced Emission of Acridinium Derivatives.

Surface-fixation induced emission is a fluorescence enhancement phenomenon, which is expressed when dye molecules satisfy a specific adsorption condition on the anionic clay surface. The photophysical behaviors of two types of cationic acridinium derivatives [10-methylacridinium perchlorate (Acr+) and 10-methyl-9-phenylacridinium perchlorate (PhAcr+)] on the synthetic saponites with different anionic charge densities were investigated. Under the suitable conditions, the fluorescence quantum yield (Φf) of PhAcr+ was enhanced 22.3 times by the complex formation with saponite compared to that in water without saponite. As the inter-negative charge distance of saponite increased from 1.04 to 1.54 nm, the Φf of PhAcr+ increased 1.25 times. In addition, the increase in the negative charge distance caused the increase in the integral value of the extinction coefficient and the radiative deactivation rate constant (kf) and the decrease in the nonradiative deactivation rate constant. It should be noted that the 2.3 times increase in kf is the highest among the reported values for the effect of clay. From these results, it was concluded that the photophysical properties of dyes can be modulated by changing the charge density of clay minerals.

Piperidine based effective chemosensor for Zn(II) with the formation of binuclear Zn complex having specific Al(III) detection ability in aqueous medium and live cell images

A schiff base chemosensor HL [4-chloro-(((2-(piperidine-1-yl)imino)methyl)phenol], constructed by one step condensation of 2-aminoethyl piperidine and 5- Chloro Salicylaldehyde is illustrated to have its usefulness for selective and sensitive detection of Zn(II) among other metal ions in aqueous solution (HEPES buffer) displaying the colour changes from light blue to turquoise under UV light. The specific detection phenomena of Zn (II) is monitored by the remarkable fluorescence enhancement and notable change in NMR spectral data of fluorescence active HL after addition of Zn(II) to it. The impressive high binding constant in 106 orders, determined by electronic spectral titration after introduction of Zn(II) to HL assure the formation of a Zinc complex during sensing phenomena. In order to check whether the nuclearity of the constructed complex can be increased or not fluorescence enhancement phenomenon is further monitored in presence of different bridging ligands and the results display that only in presence of azide a significant enhancement of Zn(II)-HL domain is exposed where as for other bridging ligand the spectra remain unaltered. This observation insists to conduct the reaction between HL and ZnCl2 in presence of sodium azide which lead the formation of a Zn complex [Zn2(HL)2(N3)4] (complex 1) employing azide as the secondary anionic residue instead of bridging. The single crystal structure of the complex unveils the unique protonation of the piperidine N during the crystallization of the dinuclear motif of the complex 1. Furthermore the Zn complex due to the presence of remarkable luminescence property have been effectively used for selective sensing of Al(III) ion as metalloreceptor in HEPES buffer solution via turn of fluorescence with remarkable fluorescence quenching constant. In aqueous solution, complex 1 induces a 1:2 complex formation with Al(III) ion indicated by Job’s plot analysis. The DFT study suggests the formation of bimetal complex during sensing of Al(III) with complex 1 as metalloreceptor. The in vitro cell imaging study gives a authentic hints for in vivo biomedical application of HL as a selective and easy Zn(II) sensor. The two step sensing phenomena of HL and complex 1 is further established by advanced molecular logic gate formation.

A miniaturized optoelectronic biosensor for real-time point-of-care total protein analysis

A miniaturized optoelectronic sensor is demonstrated that measures total protein concentration in serum and urine with sensitivity and accuracy comparable to gold-standard methods. The sensor is comprised of a vertical cavity surface emitting laser (VCSEL), photodetector and other custom optical components and electronics that can be hybrid packaged into a portable, handheld form factor. In conjunction, a custom fluorescence assay has been developed based on the protein-induced fluorescence enhancement (PIFE) phenomenon, enabling real-time sensor response to changes in protein concentration. Methods are described for the following:•Standard curves: Used to determine the sensitivity, dynamic range, and linearity of the VCSEL biosensor/PIFE assay system in buffer as well as in human blood and urine samples.•Comparison of VCSEL biosensor performance with a benchtop fluorimetric microplate reader.•Accuracy of the VCSEL biosensor/PIFE assay system: Evaluated by comparing sensor measurements with gold-standard clinical laboratory measurements of total protein in serum and urine samples from patients with diabetes.

Preparation of Ag@SiO2@NH2 core-shell nanocomposites for the fluorescence enhancement of carbon quantum dots

In this paper, the fluorescence enhancement phenomenon of carbon quantum dots (C-QDs) via metal fluorescence effect has been investigated. Firstly, uniform Ag nanoparticles was prepared, which theoretically can supply a strong enhancement effect with a diameter as small as 20 nm. Then SiO2 shell was utilized to control the distance between Ag core and C-QDs while surface charge of as-synthesized Ag@SiO2 was further modified to bond C-QDs via electrostatic effect. Four different kinds of SiO2 shell, with thickness 12 nm, 15 nm, 20 nm, and 27 nm, were synthesized to study the enhancement effect of distance. With the increase of SiO2 shell, the fluorescence of Ag@SiO2@NH2-C-QDs nanocomposites rise first but then fall while the sample with the 20-nm shell obtained the best enhancement effect as high as 3.92-fold. Surface charge vibration of metal particles was used to explain this phenomenon.

Fluorescence Enhancement Induced by Curing Reaction in Nanostructured Epoxy Thermosets Containing a Diblock Copolymer.

In this work, a novel curing-induced fluorescence (FL) enhancement phenomenon in the nanostructuring process of epoxy thermosets was investigated. Toward this end, a diblock copolymer composed of poly(ethylene oxide) and poly(((4-vinylphenyl)ethene-1,1,2-triyl)tribenzene) (PTPEE) blocks was introduced into epoxy thermosets. Before curing reaction, the mixtures of epoxy precursors with the diblock copolymer only emitted feeble FL under ultra-visible (UV) irradiation. However, photoluminescence was significantly enhanced after the curing reaction was carried out. It was found that the novel FL enhancement phenomenon resulted from the aggregation-induced emission behavior of PTPEE blocks, which was triggered by curing reaction. In the nanostructured thermosets, the fluorophore blocks (viz. PTPEE) of this diblock copolymer were segregated into aggregates, that is, a reaction-induced microphase separation occurred. Owing to the generation of PTPEE microdomains, the epoxy nanocomposites significantly displayed the enhanced dielectric constants due to the promoted contribution from electron polarizations via π-π conjugation in the materials.

A Luminescent Dicyanodistyrylbenzene-based Liquid Crystal Polymer Network for Photochemically Patterned Photonic Composite Film

A novel photonic composite film based on a luminescent dicyanodistyrylbenzene-based liquid crystal polymer network (LCN) was fabricated by using a silica colloidal crystal as a template. The upper part of inverse opal structure and the luminescence characteristics of dicyanodistyrylbenzene-based moiety endowed the resulting bilayer photonic film with structural color arising from coherent Bragg reflection and fluorescence properties, respectively. A fluorescence enhancement phenomenon was observed in the photonic film due to the overlap between the reflection band and emission band of the fluorescent LCN. More importantly, the photo-induced irreversible Z/E photoisomerization of dicyanodistyrylbenzene-based moiety in the photonic film led to both a reflection spectral shift and an observable fluorescence variation. On the basis of this effective phototuning process, microscopic patterning of photonic film was developed under both fluorescence mode and reflection mode. The work demonstrated here provides a new route to construct photo-responsive photonic film.

Fluorescence enhancement via varied long-chain thiol stabilized gold nanoparticles: A study of far-field effect

Metal enhanced fluorescence of carbon dots has been reported in aqueous solution. Moderately fluorescing carbon dots (λex=360nm and λem=440nm) of 6–8nm diameters (CDA) have been synthesized from freshly prepared aqueous ascorbic acid solution under modified hydrothermal treatment. The CDA fluorescence is quenched at the close proximity with gold nanoparticles (AuNPs). Here, a substrate specific near-field electric field distribution is pronounced. Anticipating distance dependent fluorescence enhancement phenomenon, long-chain aliphatic thiol capped AuNPs are introduced to improve fluorescence of moderately fluorescing CDAs. The long-chain aliphatic thiols act as spacers between CDA and AuNP. Interestingly, the fluorescence of CDA is observed to be enhanced successively as the chain lengths of aliphatic thiols are increased. Fluorescing CDA, upon excitation, transfers energy to the nearby AuNP and a plasmon is induced. This plasmon radiates in the far-field resulting in fluorescence enhancement of CDAs. Such an interesting enhancement in emission with metallic gold is termed as gold enhanced fluorescence. This far-field effect for fluorescence enhancement of CDA particles becomes a general consensus in solution with varied long-chain aliphatic amine ligand capped silver nanoparticles (AgNPs). Finally, consequence of far-field effect of fluorescence enhancement has been observed while derivatized AuNP and AgNP are introduced into the CDA solution simultaneously which is described as reinforced fluorescence enhancement due to coupled plasmonic radiation.

The Effect of Temperature on Photoluminescence Enhancement of Quantum Dots in Brain Slices.

In this paper, we investigated the effect of temperature on photoluminescence of quantum dots immobilized on the surface of an optical fiber in a rat brain slice. The optical fiber was silanized with 3-aminopropyl trimethoxysilane (APTMS), following which quantum dots with carboxyl functional group were immobilized on the optical fiber via amide bond formation. The effect of temperature on the fluorescence intensity of the quantum dots in rat brain slices was studied. This report shows that the fluorescence intensity of quantum dots increases with the increase of temperature of the brain slice. The fluorescence enhancement phenomenon appears to take place via electron transfer related to pH increase. With the gradual increase of temperature, the fluorescence intensity of quantum dots in solution decreased, while that in the brain slice increased. This enhanced thermal performance of QDs in brain slice makes suggestion for the study of QDs-based brain temperature sensors.

The study of metal enhanced fluorescence property of Ag/ZnO composite structure

In this paper, Ag nanoparticles were successfully prepared by chemical reduction, and then Ag/ZnO composite particles were successfully prepared and deposited onto glass substrates to form Ag/ZnO thin films. Hereafter, the structure, the morphology and the metal enhanced fluorescence (MEF) property of Ag nanoparticles and ZnO/Ag composite particles were studied by XRD, SEM, EDS, TEM, UV-vis absorption and fluorescence (FL) spectrometer. The results showed that the average size of Ag nanoparticles increased with the increase of prepared time. Moreover, ZnO layer consisted of polycrystalline structure and amorphous interface layer, but nano-Ag particle was polycrystalline structure. Annealing process was carried out to investigate the influence of annealing process parameters on MEF property of Ag/ZnO composite structure. Due to annealing treatment, the amorphous component of Ag/ZnO thin films was reduced, which might improve the density of Ag/ZnO thin films and the diameter of composite particles. Furthermore, FL enhancement phenomenon of fluorescein isothiocyanate (FITC) molecules might be attributed to the joint influence of the roughness and the density of these films and the average diameter of composite particles.

Pinpoint the Positions of Single Nucleotide Polymorphisms by a Nanocluster Dimer.

Single nucleotide polymorphisms (SNPs) are the most fundamental internal causes for many genetic diseases. However, the location information on SNPs in a specific DNA sequence is not well acquired through current SNPs detection methods, except for accurate DNA sequencing. Here we report a fluorescence enhancement phenomenon in the process of two silver nanoclusters (AgNCs) approaching closely to form a nanocluster dimer (NCD). The fluorescence intensity is sensitive to the distance between two AgNCs; therefore, the NCD lights into different fluorescence intensities upon binding SNPs targets with mismatched bases at different positions. Interestingly, the fluorescence intensities of the NCD decrease linearly when the position of single mismatched base moves gradually from the middle point to the end of the target DNA. The NCD is a single probe acting as a universal platform to pinpoint various SNP positions. With this single probe, we cannot only identify the existence of SNPs but also pinpoint the location of a specific single mismatched base in the adjacent positions. This strategy is feasible to detect specific gene point mutations in clinical samples.

Identification of molecules through the fluorescence enhancement by a metal tip

A fluorescence enhancement phenomenon, which is realized as a result of a sharp increase in the radiative decay rate of a quantum dipole emitter (QDE) is investigated theoretically in the vicinity of a conical metal tip. The QDE relaxation process is considered as a self-stimulated transition from an excited state into the ground state due to the feedback field formation from the tip. The dynamics of the system shows a stepped relaxation behavior that differs significantly from the conventional exponential decay. This effect can be observed in a small region of the resonance frequency, which is defined by an angle of conical tip. The increase of fluorescence when approaching of molecule to the metal tip on the surface enables one to determine its location.

Demystifying PIFE: The Photophysics Behind the Protein-Induced Fluorescence Enhancement Phenomenon in Cy3.

Protein-induced fluorescence enhancement (PIFE) is a term used to describe the increase in fluorescence intensity observed when a protein binds to a nucleic acid in the proximity of a fluorescent probe. PIFE using the single-molecule dye Cy3 is gaining popularity as an approach to investigate the dynamics of proteins that interact with nucleic acids. In this work, we used complexes of DNA and Klenow fragment and a combination of time-resolved fluorescence and transient spectroscopy techniques to elucidate the photophysical mechanism that leads to protein-enhanced fluorescence emission of Cy3 when in close proximity to a protein (PIFE). By monitoring the formation of the cis isomer directly, we proved that the enhancement of Cy3 fluorescence correlates with a decrease in the efficiency of photoisomerization, and occurs in conditions where the dye is sterically constrained by the protein.

Study on the Cofluorescence Effect of Europium (III)–Yttrium (III)–Balofloxacin–Sodium Dodecyl Sulfate System and Its Analytical Application

A new fluorescence enhancement phenomenon in the europium(III)–balofloxacin–sodium dodecyl sulfate system was observed when yttrium(III) was added. Based on this, a sensitive cofluorescence assay for the estimation of balofloxacin was established. Under the optimized conditions, the enhanced fluorescence signal was linear over the concentration of balofloxacin ranging from 3.0 × 10−9 to 7.0 × 10−6 mol L−1 with a correlation coefficient of 0.9993. The detection limit (3 σ) was determined as 8.3 × 10−10 mol L−1. The presented method was successfully applied to determination of balofloxacin in pharmaceutical preparations, human serum, and urine. The possible fluorescence enhancement mechanism was also discussed.

Metal-enhanced fluorescence using aggregated silver nanoparticles

A simple strategy to prepare aggregated Ag nanoparticle composites in solution by self-assembly is developed. Sodium citrate is used as the reduction agent to produce negatively charged Ag nanoparticles which are then aggregated using cationic polyacrylamide (PAM) to form self-assembled Ag-PAM microcomposites. In these microcomposites, the degree of aggregation of Ag nanoparticles can be controlled by changing the Ag/PAM ratio. This special structural feature can be applied in the study of metal-enhanced fluorescence. Confocal laser scanning microscopy and time-resolved fluorescence measurements are used to examine the fluorescence enhancement phenomenon of the Ag-PAM microcomposites. The microcomposites considerably enhanced the fluorescence intensity of fluorescein isothiocyanate isomer (FITC).

Modulated fluorescence properties in fluorophore-containing gold nanorods@mSiO2

The influencing factors and mechanism of fluorescence enhancement or quenching in mesoporous nanocarriers consisting of gold nanorod cores and mesoporous silica shells (GNR@mSiO2) with controlled thicknesses were investigated. Mesoporous silica can act as a tool to change the distance between the fluorophores and GNRs as well as a vehicle to load the fluorescence molecules in this system. We found that the distance between the GNRs’ surface and the fluorophores, the distribution of fluorophores in mesoporous silica and the kind of fluorophore used were the three main reasons for the fluorescence change. The shell-thickness-dependent fluorescence enhancement of doxorubicin (DOX)-containing GNR@mSiO2 was observed. The maximum metal-enhanced fluorescence (MEF) was obtained when GNR@mSiO2–DOX had the thinnest mesoporous silica shell. Moreover, changing the concentration ratio between GNR@mSiO2 and DOX resulted in different fluorescence enhancement factors. Upon combination of GNR@mSiO2 with other fluorophores, such as hematoporphyrin dihydrochloride (HP) and rhodamine 6G (R6G), the fluorescence enhancement phenomenon was also observed. On the other hand, we found that the fluorescence enhancement factor was reduced when the emission wavelength of the fluorophores was generally close to the surface plasmon resonance wavelength of the gold nanorods. This mechanism was confirmed by fluorescence quenching on fluorescein isothiocyanate (FITC)-containing GNR@mSiO2.