High Fluorescence Enhancement Research Articles

Fabrication and Characterization of Planar Plasmonic Substrates with High Fluorescence Enhancement

The use of plasmonic nanostructures for fluorescence signal amplification is currently a very active research field. The detection of submonolayers of proteins labeled with organic dyes is a widely used technique in surface-based immunoassays and DNA hybridization. There is a strong interest in the development of new optical and chemical methods to increase the signal from ultralow concentrations of dyes on the surface of sensor substrates. Herein, we have explored the possibility of using vacuum-deposited silver nanostructures on dielectric layers and silver mirrors as potential plasmonic substrates that effectively amplify fluorescence over a broad spectral range. By optimizing deposition parameters for dielectric layers and silver nanostructures and applying thermal annealing processes, we observed large fluorescence amplifications from three different dye-strept(avidin) conjugates: about 7-fold for a UV/blue dye AF350-Av, 49-fold for a blue-green dye AF488-SA, and up to 208-fold for red-emitting AF647-SA dye. The observed amplification factors for the ensemble of fluorophores are very promising for development of surface-based bioassays. These substrates can be prepared using simple vacuum deposition in which we circumvent using the expensive nanofabrication methods. In addition, unlike most nanofabrication methods, the present approach is appropriate for large scale fabrication of substrates with microscope slide surface area suitable for sensing applications.

Determination of Protein by Fluorescence Enhancement of Curcumin in Lanthanum-Curcumin-Sodium Dodecyl Benzene Sulfonate-Protein System

We found that the fluorescence intensity of the lanthanum (La(3+))-curcumin (CU) complex can be highly enhanced by proteins in the presence of sodium dodecyl benzene sulphonate (SDBS). Based on this finding, a new fluorimetric method for the determination of protein was developed. Under optimized conditions, the enhanced intensities of fluorescence are quantitatively in proportion to the concentrations of proteins in the range 0.0080-20.0 μg·mL(-1) for bovine serum albumin (BSA) and 0.00080-20.0 μg·mL(-1) for human serum albumin (HSA) with excitation of 425 nm, and 0.00020-20.0 μg·mL(-1) for bovine serum albumin (BSA) and 0.00080-20.0 μg·mL(-1)for human serum albumin (HSA) with excitation of 280 nm, while corresponding qualitative detection limits (S/N ≥ 3) are as low as 5.368, 0.573, 0.049, 0.562 µg·mL(-1), respectively. Study on reaction mechanism reveals that proteins can bind with La(3+), CU and SDBS through self-assembling function with electrostatic attraction, hydrogen bonding, hydrophobic interaction and van der Waals forces, etc. The proteins form a supermolecular association with multilayer structure, in which La(3+)-CU is clamped between BSA and SDBS. The unique high fluorescence enhancement of CU is resulted through synergic effects of favorable hydrophobic microenvironment provided by BSA and SDBS, and efficient intermolecular energy transfer among BSA, SDBS and CU. In energy transfer process, La(3+) plays a crucial role because it not only shortens the distance between SDBS and CU, but also acts as a "bridge" for transferring the energy from BSA to CU.

Deposition of Silver Dentritic Nanostructures on Silicon for Enhanced Fluorescence

Silver dendritic (“fractal”) structures exhibit very high fluorescence enhancement, but their nonuniformity limits practical applications. Here, we present a novel, electroless deposition approach to produce uniform silver dendritic nanostructures on silicon for enhanced fluorescence. These metal-modified surfaces were allowed to bind a protein bovine serum albumin (BSA) labeled with the fluorescent dye Deep Purple. The effect of silver nanostructures on fluorescence intensity and lifetime in the presence of a conductive, absorbing substrate was analyzed, and high enhancement factors between 30 and 40 times were found. Such silicon-based structures with high fluorescence enhancement factors are suitable for integration with lab-on-chip and biosensing microelectronic devices.

Highly sensitive and selective reversible sensor for the detection of Cr 3+

A new fluorescent sensor capable of sensing Cr 3+ has been synthesized. Complexing with Cr 3+ triggers the formation of a highly fluorescent ring-open form which is pink in color. The sensor shows extremely high fluorescence enhancement upon complexation with Cr 3+ and it can be used as a ‘naked eye’ sensor. Binding of Cr 3+ was found to be reversible as the pink color disappears with excess EDTA.

Dansyl-based fluorescent chemosensors for selective responses of Cr(iii)

Three chemosensors DN1, DN2 and DN3, incorporating dansyl dye as a fluorophore and various carboxhydrazones as ionophores, are reported. DN1 contains a pyridine-carboxhydrazone tridentate coordination site, forming a 2:1 stoichiometric complexation species with Cr3+, and exhibits selectivity for Cr3+ over alkali and alkaline earth metals and most first-row transition metals in aqueous media. DN1 displays high quantum yield (Φ = 0.86) and fluorescence enhancement following Cr3+ coordination within a wide pH range. DN2 contains a 8-hydroxyquinoline-carboxhydrazone tetradentate metal-binding moiety, forming a 1:1 complex with Cr3+. DN2 also exhibits significantly fluorescence enhancement but a much lower quantum yield following Cr3+ binding in aqueous solution. In contrast, their congener DN3, having a salicyl-carboxhydrazone tridentate binding site, does not exhibit any significant fluorescence variation following Cr3+ binding. These results demonstrate that the hydroxyl group is an important factor influencing the fluorescence response to Cr3+ in aqueous media.

Chiral Mono Boronic Acid As Fluorescent Enantioselective Sensor for Mono α-Hydroxyl Carboxylic Acids

New mono boronic acid was found to be an enantioselective fluorescent chemosensor for mono alpha-hydroxyl carboxylic acids, such as mandelic acid and lactic acid. The chiral sensor shows lower background fluorescence, higher fluorescence enhancement, and enantioselective recognition kinetics toward mandelic acids and lactic acids.

Complexation of the mycotoxin zearalenone with β-cyclodextrin: Study of the interaction and first promising applications

This work reports the study of the interactions between native and substituted β-cyclodextrins and zearalenone and its derivatives α- and β-zearelonol. The data obtained by fluorescence and NMR experiments suggested that zearalenone, α- and β-zearalenol and cyclodextrins give rise to host-guest complexation, with the inclusion of the phenolic moiety inside the cyclodextrin cavity. The high stability of these complexes induces a high fluorescence enhancement upon complexation. These results have been successfully applied to the spectrofluorimetric determination of zearalenone in maize raw samples, without any chromatographic separation.

Fluorescence of zirconium–naphthalene complexes: Effect of ortho-naphthalene substitution

The effect of the position of substituents on the formation of metal–naphthalene complexes has been investigated. Two positional isomers, 1-hydroxy-2-naphthoic acid (1H2NA) and 3-hydroxy-2-naphthoic acid (3H2NA), have been chosen. A comparative study of the luminescence behaviour of the two isomers in the presence of Zr(IV) has been performed. Interesting results were obtained. While 1-hydroxy-2-naphthoic acid is quenched in the presence of Zr(IV), 3-hydroxy-2-naphthoic acid produced high-fluorescence enhancement. Several pH studies were performed between pH 2.5 and 5.0 and the stoichiometries of the complexes were also established at the different pH values tested, by use of the Benesi–Hildebrand method. In addition, the formation constants have been calculated. Finally, quenching and lifetime studies were performed in an attempt to establish the type of quenching (static or dynamic) that is produced when a complex is formed between 1-hydroxy-2-naphthoic acid and zirconium metal ion.

Determination of Micro Amounts of Nucleic Acids Based on Shifting the Aggregate‐Monomer Equilibrium of Fluorescent Dye

A sensitive spectrofluorimetric method for the determination of nucleic acids based on shifting the aggregate‐monomer equilibrium of the fluorescent dye phenosafranine (PF) was proposed. Formation of aggregate induced by the pre‐micellar aggregation of an anionic surfactant, sodium dodecyl sulfate (SDS), was observed. The possibility of using the in situ–formed aggregate as a fluorescent probe for nucleic acids was also studied. The results showed that the fluorescence intensity of the system increased dramatically when nucleic acids were added to the solution. The fluorescence enhancement effect was thought to be based on the nucleic acid‐modulated shift of the aggregate‐monomer equilibrium of PF in the anionic surfactant solution. Intercalation of the monomer in nucleic acids caused the dissociation of the aggregate and led to a very high fluorescence enhancement. It seemed that the aggregate molecules acted as a source of monomer molecules ready for interaction with nucleic acids. A linear dependence of fluorescence intensity enhancement on the concentration of fish sperm DNA (fsDNA) over the range 0.04–20 µg/mL fsDNA allowed sensitive quantification of fsDNA by a simple fluorescence method. The detection limit was 17 ng/mL and the RSD was 1.2% for 2 µg/mL fsDNA (n=7). Furthermore, calibration graphs for calf thymus DNA (ctDNA) and yeast RNA were also obtained.

Two regioisomeric and exclusively selective Hg(ii) sensor molecules composed of a naphthalimide fluorophore and an o-phenylenediamine derived triamide receptor

This communication presents two regioisomeric fluorescent PET Hg(II) sensors RS, which contain a novel o-phenylenediamine based triamide receptor; RS could be used to detect Hg(II) with exclusive selectivity, high fluorescence enhancement, and fast and reversible response in a neutral buffered aqueous solution.

A Tryptophan-Containing Open-Chain Framework for Tuning a High Selectivity for Ca2+ and 13C NMR Observation of a Ca2+−Indole Interaction in Aqueous Solution

Two molecular architectures featuring the cation-responsive tryptophan indole were designed and investigated for the development of a novel fluorescent chemosensor for Ca2+. We observed that the Trp-based open-framework chemosensor EW2 exhibits remarkable selectivity for Ca2+ over Mg2+, Ba2+, K+, Na+, and Li+ in water between pH 4.6 and 7.0 on the basis of Ca2+-induced high fluorescence enhancement of the Trp residue. A combined 13C NMR and CD spectroscopic study has demonstrated a dynamic reorientation of the indole ring due to the cation-indole interaction accompanying the Ca2+-induced dramatic fluorescence enhancement. The results suggest that the highly sensitive, metal-ion-dependent Trp indolyl C(3) chemical shifts may serve as a promising indicator for monitoring metal ion-indole noncovalent interaction in solution.

Fluorescence response of mono- and tetraazacrown derivatives of 4-aminophthalimide with and without some transition and post transition metal ions

The fluorescence response of two fluorophore–spacer–receptor systems, 1 and 2, wherein a 4-aminophthalimido moiety is linked to a monoaza- and a tetraazacrown macrocycle via a dimethylene spacer, has been explored in the absence and in the presence of various transition and post transition metal ions. Unlike the parent fluorophore, these systems are weakly fluorescent because of photoinduced electron transfer (PET) between the terminal moieties of the molecules. Of the two systems, PET is found to be more efficient in 2, which contains the tetraazacrown moiety as the receptor. Both systems display complex fluorescence decay behaviour with the average fluorescence lifetime much shorter than that of the parent fluorophore. The systems exhibit fluorescence enhancement in the presence of the metal ions, some of which are notorious quenchers of fluorescence. While the fluorescence output of 1 is rather similar with different metal ions, 2 exhibits high fluorescence enhancement with metal ions such as Zn2+, Cd2+, Pb2+, Hg2+ and Mn2+ while producing negligible enhancement with the remaining metal ions studied. This specific signaling behaviour of 2 has been rationalized taking into consideration somewhat unusual binding ability of the tetraazacrown receptor moiety.

Single-molecule spontaneous emission close to absorbing nanostructures

The spontaneous emission of a single molecule is substantially modified close to a metallic nanostructure. We study the spectral behavior of the radiative and nonradiative decay rates and of the local-field factor in the vicinity of a plasmon resonance. We show that the highest fluorescence enhancement is obtained for an emission wavelength redshifted from the plasmon resonance, and that quenching always dominates at plasmon resonance. These results may have experimental implications in spectroscopy and monitoring of elementary light sources.

Cyclodextrin-, UV-, and high pH-induced fluorescence enhancement of the pesticide azinphos-methyl: Applications to its trace analysis

Various methods for the enhancement of the fluorescence of the pesticide azinphos-methyl are reported. The addition of hydroxypropyl-β-cyclodextrin was found to moderately enhance the fluorescence by a factor of three, presumably via inclusion of the pesticide into the cyclodextrin cavity. This complexation was found to occur with an association constant of 690 ± 140 M–1. This enhancement was found to be too low to be useful in a fluorescence-based analytical method for this pesticide. Exposure of azinphos-methyl to UV light was also found to result in enhanced fluorescence, with much larger enhancement than in the case of addition of cyclodextrins. This enhancement was presumed to occur via photolysis of azinphos-methyl to a more fluorescent photoproduct. However, the difficulty of providing a constant UV dosage prevents its useful application as a fluorescence-based analytical method. Finally, it was found that base hydrolysis of azinphos-methyl resulted in a very large fluorescence enhancement. Although this enhancement was previously reported in the literature, it was found that contrary to the published reports, the hydrolysis occurred rapidly at room temperature, with no need for carrying out the reaction at increased temperature. Fluorescence enhancements of a factor of 300 were obtained by simply adding the appropriate amount of an aqueous NaOH solution to the aqueous azinphos-methyl sample. This procedure was used as the basis of a simple fluorescence-based analytical method for azinphos-methyl in water, with excellent linear calibration curves obtained down to concentrations of 5 ppb.Key words: fluorescence spectroscopy, pesticides, azinphos-methyl, fluorescence enhancement, host–guest inclusion.

Mg2+-Selective Fluorescence Enhancement of Benzo-15-crown-5 Derivative Bearing Vinylanthracene Fluorophore

Abstract A fluoroionophore, 1-(anthryl)-2-(benzo-15-crown-5)ethene, was synthesized. This crown ether derivative showed remarkably high cation-induced fluorescence enhancement for magnesium ion.

Unusually High Fluorescence Enhancement of Some 1,8-Naphthalimide Derivatives Induced by Transition Metal Salts

Three-component systems, 1a−c and 2a,b, comprising 1,8-naphthalimide and 4-methoxy-1,8-naphthalimide as fluorophore, a dimethylamino moiety as guest binding site and a polymethylene group as spacer, have been synthesized and the fluorescence behavior of these systems has been studied in the absence and in the presence of the salts of several transition metal ions. The systems are found to be very weakly fluorescent compared to their constituent fluorophores (3 and 4) and this observation has been ascribed to photoinduced intramolecular electron transfer (PIET) between the electron rich amino moiety (donor) and relatively electron deficient fluorophore component (acceptor). Spectral and electrochemical data indicate the thermodynamic feasibility of PIET (exergonic free energy changes) in these multicomponent systems and PIET is found to be most efficient in systems where the fluorophore and the amino moiety are separated by two methylene groups. Fluorescence decay behavior of the systems suggest that PIET ...

Unusually high cation-induced fluorescence enhancement of a structurally simple intrinsic fluoroionophore with a donor–acceptor–donor constitution

Upon cation complexation, donor–acceptor–donor–substituted intrinsic fluoroionophore 3 shows red-shifted emission spectra accompanied by an extraordinarily high fluorescence enhancement.

Study on the dimer–monomer equilibrium of a fluorescent dye and its application in nucleic acids determination

A novel spectrofluorimetric method has been proposed for the determination of nucleic acids based on shifting the dimer–monomer equilibrium of the fluorescent dye, acridine yellow (AY). Induced by the premicellar aggregation of an anionic surfactant, sodium dodecyl sulphate (SDS), AY formed a nonfluorescent homodimer (AYAY) which largely quenches the fluorescence intensity of the dimer system. However, the fluorescence intensity of the system increased dramatically when nucleic acids were added to the solution. The fluorescence enhancement is probably based on the DNA modulated shift of the dimer–monomer equilibrium of AY in the anionic surfactant solution. Intercalation of the monomer in DNA caused the dissociation of AYAY, and led a very high fluorescence enhancement. A linear dependence of fluorescence intensity on Calf thymus (CT) DNA concentration over the rang of 0∼40 μg/ml CT DNA allowed sensitive quantification of CT DNA by a simple fluorescent method. The detection limit was 0.023 μg/ml and the RSD was 1.5% for 2 μg/ml CT DNA ( n=7). Furthermore, calibration graphs for yeast RNA, polynucleotides, such as poly (A) and poly (I) were also obtained.

Transition Metal (II)/(III), Eu(III), and Tb(III) Ions Induced Molecular Photonic OR Gates Using Trianthryl Cryptands of Varying Cavity Dimension

Three heteroditopic cryptands with different cavity dimensions have been synthesized in high yields at 278 K without employing any templating metal ion. The three secondary amino nitrogens in each cryptand could be derivatized with anthryl groups to have a fluorophore−spacer−receptor configuration. The fluorophores in these systems do not show any fluorescence due to an efficient photoinduced intramolecular electron transfer (PET) from nitrogen lone pairs. However, the fluorescence can be recovered to different extents in the presence of different metal ions and protons as well. On complexation by a transition metal ion or on protonation in a solvent like dry THF, each exhibits large fluorescence enhancement as the nitrogen lone pairs responsible for PET are engaged in bonding. Inner-transition-metal ions like Eu(III) or Tb(III) show remarkable discrimination and give high fluorescence enhancement only in one case where the cavity size is smaller than that of other two. Each system exhibits large fluoresc...

DNA—Dye Fluorescence Enhancement Based on Shifting the Dimer—Monomer Equilibrium of Fluorescent Dye

In this paper, the investigation of DNA–dye fluorescence enhancement based on shifting the dimer–monomer equilibrium of a fluorescent dye, acridine orange (AO), is reported. Formation of a virtually nonfluorescent dimeric dye, acridine orange homodimer (AOAO), induced by the pre-micellar aggregation of an anionic surfactant, sodium dodecyl sulfate (SDS), was observed. The possibility of using the in situ formed AOAO as a fluorescent probe for nucleic acids and polynucleotides was studied. The results showed that a nearly 1000-fold fluorescence enhancement was observed upon addition of calf thymus DNA (CT DNA). The fluorescence enhancement effect of DNA was thought to be based on the DNA modulated shift of the dimmer monomer equilibrium of AO in the anionic surfactant solution. Intercalation of the monomer in DNA caused the dissociation of AOAO and led to a very high fluorescence enhancement. It seemed that the dimeric dye molecules acted as a source of monomer molecules ready for interacting with nucleic acids and, at the same time, decreased the inherent fluorescence of monomer molecules, which proved to be unfavorable to the detection of fluorescence enhancement. A linear dependence of fluorescence intensity on CT DNA concentration over a range from 7.8 ng/mL to 10.0 g/mL, in the presence of AO at a concentration of 1.65 × 10−6mol/L and of SDS at a concentration of 8.0 × 10−4 mol/L, allowed sensitive quantitation of CT DNA in a conventional fluorometer. Calibration graphs for yeast RNA and polynucleotides, such as poly A, poly U, and poly I, were also obtained.