Increment Of Fluorescence Intensity Research Articles

Chelation-enhanced fluorescence-enabled coumarin-hydrazone Schiff bases for the detection of Al3+ ions and its real-time applications

We designed a simple coumarin-hydrazone-based Schiff base fluorescent probe, namely 7-(diethylamino)-N'-(2,4-dihydroxybenzylidene)-2-oxo-2H-chromene-3-carbohydrazide (L), which was successfully synthesized and utilized for selective detection of Al3+ ion via fluorescence ‘turn-on’ method. The Probe L could detect Al3+ by a sharp increment in fluorescence intensity (∼15 times) in a semi-aqueous DMSO medium. The detection limit of L towards Al3+ was calculated to be 50 nM, and the former undergoes a 1:1 stoichiometry binding with a higher binding constant of ∼ 2.14 × 104 M−1. Probe L detects Al3+ by the well-known chelation-enhanced fluorescence (CHEF) mechanism and inhibits C = N isomerization by fluorescence time-resolved measurement. Experimental results from FT-IR, NMR, and ESI mass spectrometry confirm the interaction mechanism between probe L and Al3+ ions, further supported by DFT calculations. In addition, the probe L fabricated paper strips could detect Al3+ in the naked eye under UV light.

Synthesis of selenium-based BOPHY sensor for imaging of Cu(II) in living HeLa cells

NSe2 chelating moiety embedded BOPHY probe was synthesized and characterized. The probe displayed high selectivity and sensitivity for the detection of Cu(II). The probe reacted with Cu(II) in less than 1 s and showed a 6 fold increment in fluorescence intensity. Detection limit of the probe was found to be 10.8 nM and the binding ratio of the complex (Probe:Cu(II)) was determined to be 1:1 from the Job's plot. In addition, the probe exhibited reversibility with S2− ions. The probe possessed cell-membrane permeability and sensitive detection of Cu(II) in live HeLa cells with strong green fluorescence.

Handheld device for on-site sensitive detection of genetically modified crop based on supramolecular fluorescence material

Herein, a handheld device for on-site detection of genetically modified crop was developed. To meet the requirement of highly sensitive detection, single-wavelength light emitting diode was used as excitation light source, silicon photodiode with a dark current of pA level was adopted for photoelectric conversion, and phase-sensitive signal acquisition and amplification were carried out to improve the signal-to-noise ratio. Specially, micron-scale supramolecular fluorescence material was proposed for the first time as the signal label of sandwich immunoassay, which is a luminescent molecule aggregate. It could bring much greater increment in fluorescence intensity by increasing the number of luminescent molecules and accelerating the internal energy recombination, resulting in an excellent detection sensitivity. Under optimal experimental conditions, genetically modified protein PAT/bar as a template could be detected in the range of 0.01 ~ 10,000 ng/mL, with a limit of quantification10 pg/mL. Selectivity, stability, precision and accuracy were all satisfied. And, real GM rice sample could be successfully detected, implying that this high-sensitivity on-site detection platform has broad application prospects in food inspection.

Melamine induced human serum albumin aggregates: Its possible role in amyloidogenesis

Mutation in genes which encode amino acids as well as any other adverse condition can lead to neurodegenerative diseases like Alzheimer's, diabetes mellitus, Huntington’s etc. Transition from α helix to β sheet is the main hallmark of the formation of aggregates which may lead to fibril or amyloid formation. Human Serums Albumin (HSA) being major carrier protein was taken as model protein to investigate the effect of Melamine (an organic compound). Melamine (MM) toxicity has recently attracted worldwide attention as it causes renal failure and the death of humans and animals. In vitro analysis through various spectroscopic methods has revealed that melamine can cause the unfolding of HSA under certain conditions. Increment of fluorescence intensity and disappearance of two negative peaks in circular dichroism spectroscopy have indicated that β sheeted structure is favoured with gradual increase in concentration of melamine upto 225 μM. It was further confirmed by Transmission electron microscopy. Interactions between protein and ligand were also analysed by autodock. Finally, fluorescence microscopy has corroborated the presence of aggregates in our sample of interest.

Rapid recognition of fatal cyanide in water in a wide pH range by a trifluoroacetamido based metal–organic framework

A trifluoroacetamido functionalized Hf-MOF is presented for the selective and fast fluorescence turn-on detection of toxic CN− ions in aqueous environment with tremendous fold increment in fluorescence intensity.

An in-vitro elucidation of inhibitory potential of carminic acid: Possible therapeutic approach for neurodegenerative diseases

Protein misfolding leads to several human pathologies. So far, there has not been much success on the remediations of these protein conformational disorders. Since these diseases arise as a result of protein aggregation, hence inhibition of aggregation could be a promising approach for designing new therapeutics. For which; polyphenols, antibiotics and other small compounds have been tested by the researchers in the recent past, but so far there has not been much success. Here we have investigated the effect of carminic acid over Human serum albumin in an in vitro manner. It was observed that there was severe resistance in the increment of fluorescence intensity in the presence of carminic acid when observed through ANS, ThT and RLS, which was further supported by CD and Congo red assay. Microscopic analysis also confirmed that there was aggregation inhibition in the presence of180μM carminic acid. ROS and SDS-PAGE results also established the same. Furthermore, molecular docking was performed to understand the interacting residues which were found to be Arg, Leu, Glu. It is noteworthy that inhibitory effect was concentration dependent and maximum inhibition was found to be in presence of 180 μM of carminic acid. These results shall be helpful in designing the new therapeutics against amyloidosis.

Study of the Intrinsic Fluorescence of a Highly Branched Cationic Dendrimer, Poly(Ethyleneimine) (PEI).

Poly(ethyleneimine) (PEI) is a weakly basic, synthetic, polycationic polymer, due to the presence of primary, secondary, and tertiary amino groups. The amino groups are responsible for the variety of applications of PEI (e.g., transfection, bioimaging, solar cell, etc.). Our study presents some new and reproducible methods for the quantification of molecular or mass concentration of highly branched PEI of different molecular weights (800–2000–25,000–750,000 MW PEI). In the course of the direct method, spectrophotometry and fluorometry were applied to determine the absorption and fluorescence of PEI dilution series. An increase in the MW at the same concentration produces a higher count number because of the higher number of amino groups in PEI molecules. The character of increment in fluorescence intensity is essentially different in the case of mass concentrations and molar concentrations. The increment of the fluorescence intensity related to the molar concentration is non-linear. In the case of mass concentration, the slope is linear. Moreover, their fluorescence is enhanced with the decrease in pH values. The spectrophotometry is a reliable method for measuring the quantity of PEI molecules in solution. Our data help in recognizing the detailed properties of PEI in dendrimer research.

CHEF-Affected Fluorogenic Nanomolar Detection of Al3+ by an Anthranilic Acid-Naphthalene Hybrid: Cell Imaging and Crystal Structure.

We report the synthesis of a novel hydrazine-bridged anthranilic acid–naphthalene conjugate (E)-2-(benzamido)-N′-((2-hydroxynaphthalen-1-yl) methylene) benzohydrazide (BBHAN) and its crystal structure. BBHAN can detect Al3+ by a sharp increment in fluorescence intensity (∼40 times) in aqueous methanolic medium. The limit of detection of BBHAN towards Al3+ is 1.68 × 10–9 M, and the former undergoes a 2:1 binding with Al3+ with a high binding constant of ∼1.15 × 1011 M2–. BBHAN detects Al3+ by the well-known mechanism of chelation-enhanced fluorescence (CHEF), established by fluorescence time-resolved measurement. The mode of interaction between BBHAN and Al3+ has been explored by 1H NMR and electrospray ionization mass spectrometry techniques. Paper strips coated with BBHAN can detect Al3+ under UV light observed through the naked eye. Lastly, BBHAN can detect Al3+ in MDA-MB-468 cells.

2-hydroxy-5-methylisophthalaldehyde based fluorescent-colorimetric chemosensor for dual detection of Zn2+ and Cu2+ with high sensitivity and application in live cell imaging

A 2-hydroxy-5-methylisophthalaldehyde (HMP) based Schiff-base ligand (HL) was successfully developed as a fluorescent and colorimetric chemosensor for dual detection of Zn2+and Cu2+ions in HEPES buffer medium (H2O:Methanol = 9:1 (v/v), pH= 7.4). Interestingly, in presence of Zn2+ around 16 times increment in fluorescence intensity and in presence of Cu2+ ~ 174 times decrease in fluorescence intensity has been observed. The 1:2 binding modes for both HL-Zn2+/Cu2+complexes are proved by fluorescence measurements, ESI-MS analysis and DFT-Calculations. The reversibility and regeneration process of HL are also established using Na2EDTA. It has been observed that Chemosensor HL exhibits a rapid change in fluorescence intensity within pH range 6–8 against Zn2+and Cu2+ions. Low detection limit was found to be 1.059 × 10-9(M) and 3.53 × 10-9 (M) for Zn2+ and Cu2+ ions respectively. These values also suggest that the chemosensor HL has great potential to detect Zn2+ and Cu2+ ions in environmental and biological studies.

Effects of titanium dioxide (TiO2) nanoparticles on the photodissolution of particulate organic matter: Insights from fluorescence spectroscopy and environmental implications

Widely used titanium dioxide (TiO2) nanoparticles are likely to accumulate ultimately in sediments and potentially pose a risk to water ecosystems. This study evaluated the effect of TiO2 nanoparticles on the photodissolution of particulate organic matter (POM) through fluorescence spectroscopy. Excitation-emission matrices and parallel factor analyses revealed that the fluorescent characteristics of produced dissolved organic matter (DOM) during photodissolution of suspended sediment and synthetic particulate organic matter (SPOM) were primarily humic-like. SPOM particles appeared to simulate well the photodissolution of suspended sediment. Quasi-complete increases in fluorescence intensity and chromophoric DOM (CDOM) abundance were reached after 90, 60, and 50 min irradiation for TiO2 concentrations of 0, 2, and 5 mg L−1, respectively. The faster increment of fluorescence intensity and CDOM abundance indicated the photocatalytic dissolution of SPOM, as opposite charges between TiO2 and SPOM at pH = 4 favored the adsorption of TiO2 onto SPOM. For sediments, the CDOM abundance and fluorescence intensity decreased with increasing TiO2 concentration, resulting from the photocatalytic degradation of photoproduced DOM from sediments. These results demonstrated that pH plays an important role in the photocatalytic dissolution of POM by TiO2. Therefore, appropriate pH controls should be implemented when TiO2 are used to treat sediments contaminated with organic pollutants. Finally, with increasing use of TiO2, its accumulation in sediments may affect the fate of carbon, nutrients, and heavy metals in shallow-water ecosystems.

Hydrazine bridged coumarin-pyrimidine conjugate as a highly selective and sensitive Zn2 + sensor: Spectroscopic unraveling of sensing mechanism with practical application

We report the synthesis and Zn2+ sensing of a novel coumarin-hydrazine conjugate 3-{1-[(4, 6-Dimethyl-pyrimidin-2-yl)-hydrazono]-ethyl}-chromen-2-one (3). Compound 3 can act as a neat fluorescent Zn2+ sensor by an increment in fluorescence intensity along with an appreciable red shift. Fluorescence enhancement is caused by complexation through cis-trans isomerization process in the presence of Zn2+ ion. The practical utility of 3 was demonstrated by successful test kit experiment to detect Zn2+ in water under UV-light.

Rapid and highly sensitive detection of extracellular and intracellular H2S by an azide-functionalized Al(iii)-based metal-organic framework.

A new, azide-functionalized Al(iii)-based metal-organic framework (MOF) denoted as CAU-10-N3 (1, CAU = Christian-Albrechts-University) and consisting of the 5-azido-isophthalic acid (H2IPA-N3) ligand was employed as a reaction-based fluorescent turn-on probe for the detection of H2S. The activated compound (1') showed fast, selective and highly sensitive sensing properties for extracellular H2S in HEPES buffer (10 mM, pH = 7.4). The material retained its high selectivity even in the presence of possibly competing biological species. The limit of detection of 1' for H2S is 2.65 μM, which is lower than the earlier reports on MOFs for H2S sensing. The material displayed a short response time (420 s) and a significant increase (20-fold and 26-fold after 1 and 7 min of addition of Na2S, respectively) in the fluorescence intensity towards H2S. Macrophage cells loaded with probe 1' exhibited blue fluorescence with a response time of 15 min after Na2S addition, indicating the suitability of the probe for intracellular H2S detection. Moreover, CAU-10-N3 featured excellent detection performance (quick response and 32-fold increment in fluorescence intensity after 7 min of Na2S addition) in water. Hence, it can be utilized to regulate the H2S level in aqueous samples collected from the environment.

Highly selective fluorescent chemosensors for the detection of Hg2+ based on photochromic diarylethenes with a terminal terpyridine unit

Two new diarylethenes with a terpyridine unit were synthesized and their photochromic and fluorescent properties were investigated. The diarylethenes exhibited favorable photochromism by UV/vis irradiation. Compared to the one with a vinyl-linked terpyridine unit, the one with a simple benzene linker had a smaller molar absorption coefficient and absorption maximum, and larger cyclization/cycloreversion quantum yields. Hg2+ coordination with the diarylethenes resulted in remarkable photochromism and fluorescence changes. The fluorescence intensity of the diarylethene with a benzene linker was enhanced significantly by 2.5-fold and its emission peak exhibited a notable red-shift from 420 to 463 nm with an evident color change from dark blue to bright cyan. In contrast, the one with a vinyl linker showed a dramatic increment of fluorescence intensity by 35-fold with a color change from darkness to bright green. Both of the diarylethenes were highly selective toward the recognition of Hg2+ without interference from other metal ions.

Construction of an off-on fluorescence system based on carbon dots for trace pyrophosphate sensing.

A novel and simple fluorescence Off-On system is proposed for selective pyrophosphate (PPi) sensing in an aqueous solution. The method is constructed based on the strong blue emission of carbon dots (CDs) owing to its outstanding photoluminescence and easy synthesis, which has shown exciting potential in analytical and biological field. The fluorescence of CDs can be remarkably quenched by some transition metal ions such as Cu(2+), Ni(2+), Mn(2+) and Co(2+) due to the coordination reaction between metal ions and the carboxylic groups on the surface of CDs. When PPi was introduced to CDs-metal ion system the fluorescence of CDs was recovered regularly. The increment of fluorescence intensity was proportional with the concentration of PPi in the range of 1-200μM and correspondingly the limit of detection was calculated as 0.32μM according to the recommendation of IUPAC as 3.29 S B/m. The possible mechanism was discussed for the detection of PPi and the quenching reaction between CDs and metal ions. Furthermore, the proposed system was successfully used to monitor the content of PPi in water samples from artificial wetland.

A fluorescence detection of d-penicillamine based on Cu2+-induced fluorescence quenching system of protein-stabilized gold nanoclusters

In this contribution, a luminescent gold nanoclusters which were synthesized by bovine serum albumin as novel fluorescent probes were successfully utilized for the determination of d-penicillamine for the first time. Cupric ion was employed to quench the strong fluorescence of the gold nanoclusters, whereas the addition of d-penicillamine caused obvious restoration of fluorescence intensity of the Cu2+-gold nanoclusters system. Under optimum conditions, the increment in fluorescence intensity of Cu2+-gold nanoclusters system caused by d-penicillamine was linearly proportional to the concentration of d-penicillamine in the range of 2.0×10−5–2.39×10−4M. The detection limit for d-penicillamine was 5.4×10−6M. With the off–on fluorescence signal at 650nm approaching the near-infrared region, the present sensor for d-penicillamine detection had high sensitivity and low spectral interference. Furthermore, the novel gold nanoclusters-based fluorescent sensor has been applied to the determination of d-penicillamine in real biological samples with satisfactory results.

Study on the luminescence behavior of lanthanide ions using luminol as probe

Using luminol as the probe, the luminescence behavior of trivalent lanthanide ions (Ln3+=La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+ and Lu3+) in aqueous solution was first investigated by fluorescence, and the sensitivity enhanced by 3–5 orders of magnitude compared with the Ln3+ intrinsic fluorescence. It was found that Ln3+ with luminol could form a 1:1 association complex which remarkably enhanced the fluorescence signal of luminol. The increment of fluorescence intensity was proportional to the concentration of Ln3+ in the range of 1.0–70.0nmolL−1, and the linear correlation equation, ΔIF=ACLn+B, was given. The relationships of A (defined as sensitivity factor) with some physical parameters (atomic number Z, ionic radius γ±, standard redox potential Eo and hydration enthalpy ΔHhyd) were discussed. The good symmetry of A vs. Z plot for light lanthanides (LLG) and the heavy lanthanides (HLG) and linear relations of A with Z, γ±, Eo and ΔHhyd should originate in the special features of Ln3+ electronic configurations [Xe]4fn (n=0–14). Using the proposed model of Ln3+–luminol interaction, lg[ΔIF/(IFo–ΔIF)]=rlg[Ln]+lgk, the association constant k was obtained over the range of 1.95×106–2.63×107Lmol−1.

Enzymatic nanolithography of FRET peptide layer using V8 protease-immobilized AFM probe

In our study, a method based on Enzymatic nanolithography was successfully performed in a buffered solution using Staphylococcal serine V8 protease and AFM. To estimate the lithographing activity of the protease immobilized on the AFM tip to peptides immobilized on a substrate, we designed fluorescence resonance energy transfer (FRET) peptides as reporter peptides that showed enzymatic action specific to the V8 protease. When the protease digested the reporter peptide a quencher residue was released from the peptide and resulted in the appearance of fluorescence. In the designed 9-mer peptides, TAMRA functioned as a good quencher for FAM. When the fluorescence resonance energy transfer peptides immobilized on a glass substrate were hydrolyzed by V8 protease at the C-terminal of glutamic acid, fluorescence of a reporter dye was observed because of the release of a quencher from the substrate. After contacting and lateral scanning of the protease-immobilized AFM tip to the reporter peptide layer, a fluorescent area was observed by imaging using total internal refection fluorescence microscopy (TIRFM). The increment of fluorescence intensity of the digested peptide indicates the performance of lithography. Lithographing rates increased in inverse relation to scanning rates of the probe. The maximum limit of the scanning rate, i.e., that was too fast to permit cutting of the peptide on the substrate, and the lithographing performance are discussed in this study.

Effect of detergents on the fluorescence from CdS-Q clusters prepared using variable excess Cd 2+ concentrations

The effect of surfactants Triton X-100 (TX-100, neutral), cetyltrimethylammonium chloride (CTAC, cationic) and sodium dodecyl sulfate (SDS, anionic) on the intensity and lifetime of several fluorescence bands of Q-CdS clusters, which were prepared with variable excess Cd 2+ concentration, was studied. The fluorescence intensity of the several clusters of Q-CdS is strongly increased by adding a little excess of Cd 2+. When more Cd 2+ is added, a moderate increment of fluorescence intensity is observed and then, at higher excess Cd 2+ concentrations, the fluorescence intensity remains nearly constant. The effect of the detergents on the fluorescence was found to depend on the excess of Cd 2+ added to the cluster. The quenching of the fluorescence from Q-CdS by CTAC and SDS render linear Stern–Volmer plots. The corresponding values of the Stern–Volmer constants ( K sv) are lowered when the excess cadmium concentration is increased. For TX-100 the Stern–Volmer plots were non-linear for all the clusters with all the excess cadmium concentrations used. Two different zones, corresponding to different responses of the system in two concentration ranges are observed: the first one at TX-100 concentrations lower (zone I) and the second one at TX-100 concentrations higher (zone II), than 2×10 −4 M, which is equal to the concentration of the polyphosphate used to stabilize the colloid. According to the experimental results, we believe that TX-100 quenching, for all the CdS clusters’ fluorescence bands in the range of final cadmium concentration used for the experiments, is a polyphosphate-assisted process in zone I, while in zone II this assistence is not evident. The fluorescence decay curves were also determined in all the cases. They were not altered, for any of the clusters, by the addition of TX-100 and SDS, pointing to static quenching processes in both cases. On the other side, the fluorescence lifetimes were shortened by the addition of CTAC, which is indicative that, at least in part, the quenching process is dynamic for this cationic detergent.

Magnesium permeability of sarcoplasmic reticulum vesicles monitored in terms of chlortetracycline fluorescence.

The Ca2+ and Mg2+ permeabilities of sarcoplasmic reticulum vesicles were measured by using a fluorescence chelate probe, chlortetracycline. The Mg2+ permeability was studied extensively. The data were analyzed under the assumption that the increment of fluorescence intensity is proportional to the amount of the divalent cations inside the vesicles. The validity of this assumption was confirmed by the tracer method with Ca2+. The presence of Ca2+ or Mg2+ had little effect on the Mg2+ efflux, but greatly affected the Ca2+ efflux. In the absence of extravesicular divalent cations, the permeabilities for Ca2+ and Mg2+ were almost the same, but the Ca2+ permeability was slightly reduced by the presence of Mg2+ and greatly reduced by Ca2+. In the absence of extravesicular divalent cations, the Ca2+ and Mg2+ permeabilities increased in parallel with increasing pH. For example, the permeation times for Mg2+ and Ca2+ were about 3 min at pH 6.5 and 20 s at pH 8.1 at room temperature. Kinetic analysis of the fluorescence change suggested the existence of two kinds of vesicles with different permeabilities.