Time-resolved Luminescence Techniques Research Articles

Fluorescence and Electrochemical Recognition of Nucleosides and DNA by A Novel Luminescent Bioprobe Eu(lll) -TNB

The luminescence arising from lanthanide cations offers several advantages over organic fluorescent molecules: sharp, distinctive emission bands allow for easy resolution between multiple lanthanide signals; long emission lifetimes (μs -ms) make them excellent candidates for time-resolved measurements; and high resistance to photo bleaching allow for long or repeated experiments. A method is presented for determination of nucleosides using the effect of enhancement of fluorescence of the easily accessible europium(III)-TNB in presence of different nucleosides. The latter coordinates to Eu(III) -TNB and enhances its luminescence intensity as a result of the displacement of water from the inner coordination sphere of the central metal. A similar method for the determination of DNA based on the quenching of Eu(III)-TNB has been established. The interaction of Eu(III)-4,4,4 trifluoro-1-(2-naphthyl)1,3-butanedione (TNB) complex with nucleosides (NS) (guanosine, adenosine, cytidine, inosine) and DNA has been studied using normal and time-resolved luminescence techniques. Binding constants were determined at 293 K, 298 K, 303 K, 308 K and 313 K by using Benesi-Hildebrand equation. A thermodynamic analysis showed that the reaction is spontaneous with ΔG being negative. The enthalpy ΔH and the entropy ΔS of reactions were all determined. The formation of binary and ternary complexes of Eu(III) with nucleosides and TNB has been studied potentiometrically at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol.dm(-3) (KNO3) . The formation of the 1:1 binary and 1:1:1 ternary complexes are inferred from the corresponding titration curves. Initial estimates of the formation constants of the resulting species and the protonation constants of the different ligands used have been refined with the HYPERQUAD computer program. Electrochemical investigations for the systems under investigations have been carried out using cyclic voltammetry (CV), differential pulse polarography (DPP), and square wave voltammetry (SWV) on a glassy carbon electrode in I = 0.1 mol/L p-toluenesulfonate as supporting electrolyte.

New Strategy for Label-Free and Time-Resolved Luminescent Assay of Protein: Conjugate Eu3+ Complex and Aptamer-Wrapped Carbon Nanotubes

We report here a carbon nanotube-based approach for label-free and time-resolved luminescent assay of lysozyme (LYS) by engineering an antilysozyme aptamer and luminescent europium(III) (Eu(3+)) complex. The sensing mechanism of the approach is based on the exceptional quenching capability of carbon nanotubes for the proximate luminescent Eu(3+) complex and different propensities of single-stranded DNA and the DNA/protein complex to adsorb on carbon nanotubes. The luminescence of a mixture of chlorosulfonylated tetradentate β-diketone-Eu(3+) and the antilysozyme aptamer was efficiently quenched by single-walled carbon nanotubes (SWNTs) unless the aptamer interacted with LYS. Due to the highly specific recognition ability of the aptamer for the target and the powerful quenching property of SWNTs for luminescence regents, this proposed approach has a good selectivity and high sensitivity for LYS. In the optimum conditions described, >700-fold signal enhancement was achieved for micromolar LYS, and a limit of detection as low as 0.9 nM was obtained, which is about 60-fold lower than those of commonly used fluorescent aptamer sensors. Moreover, due to the much longer lifetime of the Eu(3+) luminescence than those of the ubiquitous endogenous fluorescent components, the time-resolved luminescence technique could be conveniently used for application in complicated biological samples. LYS concentrations in human urine were thus detected using time-resolved luminescence measurement with satisfactory recoveries of 95-98%.

A long-lived luminescence and EPR bimodal lanthanide-based probe for free radicals

We developed a novel spin-labeled terbium complex Tb(3+)/cs124-DTPA-TEMPO (1) by covalently labeling a nitroxide radical on the terbium complex for monitoring free radicals of various areas. This lanthanide complex probe shows a high EPR signal which resulted from the nitroxide radical moiety, and is weakly luminescent which resulted from the intramolecular quenching effect of the nitroxide radical on sensitised terbium luminescence. The intensity of both the EPR and luminescence can be modulated by eliminating the paramagnetism of the nitroxide radical through recognition of a carbon-centered radical analyte and thus gives a quantification of the analyte. We have preliminarily applied this probe in the luminescent detection of model carbon-centered radicals and hydroxyl radicals (·OH). This probe is water-soluble and contains lanthanide-luminescence properties, favorable for the time-resolved luminescence technique. The investigation of the intramolecular quenching process has showed that the labeled nitroxide radical quenches multiple excited states of the terbium complex, resulting in highly efficient quenching of terbium luminescence. This probe is the first example of intramolecular modulation of lanthanide luminescence by a nitroxide radical.

Biolabeling with nanoparticles based on Y2O3: Nd3+ and luminescence detection in the near-infrared

Neodymium based fluorescence presents several advantages in comparison to conventional rare earth or enzyme–substrate based fluorescence emitting sources (e.g.Tb, HRP) . Based on this fact we have herein explored a Nd-based fluoroimmunoassay. We efficiently detected the presence of an oxidized low-density lipoprotein (oxLDL) in human plasma a well-known marker for cardiovascular diseases, which causes around 30% of deaths worldwide. Conventional fluoroimmunoassay uses time-resolved luminescence techniques, with detection in the visible range, to eliminate the fluorescence background from the biological specimens. By using an immunoassay based on functionalized Y2O3:Nd3+ nanoparticles, where the excitation and emission processes in the Nd3+ ion occur in the near-infrared (NIR) region, we have succeeded in eliminating the interferences from the biological fluorescence background, avoiding the use of time-resolved techniques. This yields higher emission intensity from the Nd3+-nanolabels and efficient detection of anti-oxidized low-density lipoproteins (anti-oxLDL) by Y2O3:Nd3+-antibody–antigen conjugation, leading to a novel biolabeling method.

Formation of Eu(III) Nanoparticles on Borosilicate Sol−Gel Studied with Time-Resolved Luminescence Techniques

The formation of Eu(III) nanoparticles in borosilicate sol−gels and the glass formation heat treatment effect on those particles were studied using luminescence techniques. The presence of the particles was observed using transmission electron microscopy (TEM) images followed by analysis with energy dispersive X-ray spectroscopy (EDS). These experiments showed the presence of particles with a large quantity of europium and chlorine and only small amounts of oxygen with sizes ranging from 30 to 100 nm. Heat treatment at 400, 600, and 800 °C lead to glass samples in which those particles were no longer observed. Steady-state and time-resolved luminescence techniques allowed a detailed study of Eu(III) photophysics in sol−gel and glass samples. In sol−gel matrices, the 5D0 → 7F0 transition is very weak, hinting at Eu(III) species experiencing a rather symmetric crystal field. The 5D0 → 7F2 transition intensity is not very strong, which according to a Judd−Ofelt analysis indicates low interaction with the ani...

Synthesis, Structure, and Photophysical Characterization of Blue-Green Luminescent Zinc Complexes Containing 2-Iminophenanthropyrrolyl Ligands

New 2-iminophenanthro[9,10-c]pyrrole ligand precursors containing phenyl or 2,6-diisopropylphenyl groups at the imine nitrogen substituent, 2-arylformiminophenanthro[9,10-c]pyrroles (aryl = phenyl IIa, 2,6-diisopropylphenyl IIb) were synthesized and deprotonated in situ with NaH, originating solutions of the corresponding sodium salts (IVa, IVb). The reaction of these salts with zinc chloride gave the homoleptic bis-ligand Zn(II) complexes [Zn(kappa(2)N,N'-2-arylformiminophenanthro[9,10-c]pyrrolyl)(2)] (aryl = phenyl 2a, 2,6-diisopropylphenyl 2b). The new ligand precursors and complexes were characterized by NMR, elemental analysis, UV/vis spectroscopy, and X-ray crystallography, when possible. The photophysical characterization was carried out using steady-state and picosecond time-resolved luminescence techniques in solution. The influence of the pi-extended conjugation of the condensed phenanthro group on the deprotonated iminopyrrolyl ligands coordinated to Zn(2+) greatly enhances fluorescence quantum yields of the complexes (2a, 2b) in relation to those of their ligand precursors (IIa, IIb). Complex 2a shows emission in the green spectral region (lambda(max) = 494 nm), presenting the highest fluorescence quantum yield (phi(f) = 8.8%). In the case of the complex 2b (phi(f) = 3.9%), the bulkiness of the 2,6-diisopropyl substituents of the arylimino group highly restricts the aryl ring rotation toward coplanarity with the ligand framework, inducing a shift in the emission to the blue region (lambda(max) = 459 nm). The values of the radiative (k(f)) and radiationless rate constants (k(nr)) show that the fluorescence quantum yield enhancement in the complexes results from a 50-fold increase in k(f) values, indicating much more allowed pi-pi* transitions in complexes 2a and 2b than those occurring in the ligand precursors IIa and IIb, with an essentially n-pi* character. These assignments were confirmed by density-functional theory (DFT) and time-dependent DFT (TD-DFT) molecular orbital calculations. Simple 2-aryliminopyrrole ligand precursors (Ia, Ib) and their Zn(II) complexes (1a, 1b) were also prepared to compare their photophysical properties with those of the corresponding 2-aryliminophenanthro[9,10-c]pyrrolyl compounds.

The third-order optical nonlinearity and upconversion luminescence of CdTe quantum dots under femtosecond laser excitation

The aqueous CdTe quantum dots (QDs) were synthesized by the electrostatic reaction method. The optical properties of CdTe QDs were investigated by femtosecond Z-scan and time-resolved luminescence technique in nonresonant spectral region. The nonlinear absorption and refraction are ascribed to two-photon absorption, and time-resolved upconversion photoluminescence produces biexponential decay pattern at infrared femtosecond laser excitation. Upconversion luminescence is composed of a band-edge excitonic state and a photoinduced trapping state. The short-lived band-edge excitonic emission is independent of the detection wavelengths, and long-lived species becomes even longer with the increase of detection wavelengths, which indicates the size dependence of surface excitonic emission.

Time-resolved luminescent lateral flow assay technology

We here report a detection technology that integrates highly sensitive time-resolved luminescence technique into lateral flow assay platform to achieve excellent detection performance with low cost. We have developed very bright, surface-functionalized and mono-dispersed phosphorescent nanoparticles of long lifetime under ambient conditions. The phosphorescent nanoparticles have been used to conjugate with monoclonal antibody for C-reactive protein (CRP), an inflammatory biomarker. Lateral flow immunoassay devices have been developed using the conjugate for highly sensitive detection of CRP. The CRP assay can achieve a detection sensitivity of <0.2 ng mL −1 in serum with a linear response from 0.2 to 200 ng mL −1 CRP. We have also developed a low cost time-resolved luminescence reader for the lateral flow immunoassay (LFIA) devices. The reader does not use expensive band pass filter and still provide very low detection background and high detection sensitivity on solid substrates such as nitrocellulose membranes. The reader can detect less than 2.5 ng phosphorescent particles captured on a nitrocellulose membrane strip with more than three orders of magnitude linear detection dynamic range. The technology should find a number of applications, ranging from clinical diagnostics, detection of chemical and biological warfare agents, to food and environmental monitoring.

In vitro characterization of the Gd complex of [2,6-pyridinediylbis(methylene nitrilo)] tetraacetic acid (PMN-tetraacetic acid) and of its Eu analogue, suitable bimodal contrast agents for MRI and optical imaging

Gd and Eu complexes of PMN-tetraacetic acid show interesting properties either for MRI or for optical imaging; that is, for the Gd-complex, a high proton relaxivity with favorable water residence time; for the Eu-complex, a luminescence lifetime of 400 μs at room temperature compatible with the use of time-resolved luminescence technique. Both complexes have a good stability in physiological medium.

Stimulated Emission in InGaN/GaN Quantum Wells

The origin of the luminescence of InGaN/GaN multiple quantum-wells has been studied at high optical excitation by means of time-resolved luminescence technique combined with the variable-stripe method. Spontaneous transitions from localized states and stimulated emission of free carriers both from the quantum well and the barrier or buffer layers have been identified. The estimated room-temperature optical gain coefficient of 8000 cm -1 was found to be close to the theoretical value.

Some properties of luminescence lifetimes from quartz stimulated by blue light

Measurements have been made of recombination lifetimes as a function of stimulation time in quartz, a natural dosimeter. Time-resolved luminescence techniques were used to study the influence on lifetimes of sustained 470nm optical stimulation of luminescence and modifications associated with beta irradiation of samples. Results are reported for samples differing in sensitivity to luminescence stimulation.

Femtosecond midinfrared-induced luminescence study of the ultrafast dynamics of split-off holes in GaAs

The ultrafast relaxation dynamics of split-off holes in GaAs are studied using a time-resolved two-wavelength excitation luminescence technique. Following valence-to-conduction-band transitions that are excited by near-infrared femtosecond pulses, delayed midinfrared femtosecond pulses are used to promote holes from the heavy-hole band to the split-off-hole band. The subsequent conduction-to-split-off-hole luminescence indicates that the room-temperature lifetime of split-off holes in GaAs is approximately 50 fs. The accompanying changes in conduction-to-heavy-hole-and-light-hole luminescence when holes are transferred to the split-off band are also observed.

Association of Nitrophenols to Sodium Dodecylsulfate Micelles

The luminescence quenching of tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy)32+) by 2-, 3-, and 4-nitrophenol (NO2PhOH), in their protonated forms, has been studied by static and time-resolved techniques in water and sodium dodecyl sulfate (SDS) aqueous solution. In water, the bimolecular rate constants were obtained separately from both techniques and they were coincident. The values were close to the diffusional limit. In the presence of SDS micelles at a fixed detergent concentration, the Stern–Volmer plots of τ0/τ vs quencher total concentration ([Q]t) were linear in the whole range of [Q]tused. However, the Stern–Volmer plots of the ratioI0/Ivs [Q]tin SDS micelles showed an upward deviating curve. From these plots ofI0/I, the concentrations of the NO2PhOHs in the micellar pseudophase were measured. The treatment of the data of both types of measurements let us determine the association constants (K) of the NO2PhOHs to SDS micelles and the exit (k−) and entrance (k+) rate constants of NO2PhOHs to the micelles. TheKvalues obtained from either static or time-resolved luminescence techniques were in agreement within experimental error. An electron-transfer mechanism was also proposed for the quenching reaction of the excited state Ru(bpy)32+by nitrophenols in which the metallic complex is oxidized.

Studies on quenching reactions in the excited electronic states of tetrahydronaphthols both at the ambient temperature as well as at 77 K

The present investigation was carried out at the ambient temperature as well as at 77 K both by steady-state and time-resolved luminescence techniques to reveal the mechanisms of non-radiative transitions of the lowest excited singlet (S 1) and triplet (T 1) states of tetrahydronaphthol donors 5,6,7,8-tetrahydro-1-naphthol (THN1OH) and 5,6,7,8-tetrahydro-2-naphthol (THN2OH) in presence of the electron acceptor 2-nitrofluorene (2NF) in solvents of different polarity. At room temperature large negative values of ΔG ° (~ −1.9 eV), Gibbs free energy for photo-induced electron transfer (ET) reaction, indicate highly exothermic ET reaction occurs within the present donor-acceptor systems possibly in the Marcus inverted region. At this temperature evidence of concurrent occurrence of Förster's-type singlet-singlet (S D 1→S A 1) energy transfer process is also found. In presence of the acceptor 2NF, the fluorescence of the donor molecule is strongly quenched and the large dynamic (as there is absence of ground-state complex) fluorescence quenching rate constant k q , of the order of 10 12 M −1s −1 is observed. This quenching has been ascribed mainly due to two concurrent processes: non-radiative energy transfer and ET. Radiative energy transfer is found to have negligible role. In 2NF, apart from the quenching in fluorescence spectra of the present donor molecules a longer wavelength band of broad nature was observed due to formation of contact charge transfer (CT) complex in non-polar solvent. In highly polar acetonitrile (ACN) this band was absent but instead another broad band at a far longer wavelength region due to formation of donor anion (confirmed from metallic sodium experiment and excitation spectra) was found. It was suggested that this anion was produced from its initially formed cationic species, resulted from ET reaction with 2NF. The reaction scheme showing this mechanism is given. At 77 K it seems the Förster mechanism of singlet-singlet energy transfer is still operative resulting the observed fluorescence quenching of the donor in presence of the acceptor 2NF. A reaction mechanism has been proposed for the observed lowering of donor phosphorescence intensity in presence of the acceptor. The possibility of the occurrence of photo-induced ET reaction between excited (T 1) donor and ground-state acceptor is hinted from time-resolved phosphorescence measurements and thermodynamic considerations.

Time-resolved luminescence technique as a probe for phase transitions in some polysiloxane liquid crystals bearing the chromophore 2,7-dimethoxy-N-methyl carbazole (DMNMC) as a pendant group

Solid films of poly(methylsiloxanes) with side chains containing 2,7-dimethoxy-N-methyl-carbazole (DMNMC) pendant groups attached through aliphatic spacers (CH 2) m where m = 3, 5 and 6 were studied photophysically. Time-correlated single-photon-counting measurements were performed on these films at temperatures encompassing the various mesophases obtained by differential thermal analysis (DTA). The decays are multiexponential in all cases. No rise time of excimer emission was observed such that the analysis was based on a three exponential decay. These decays have been attributed tentatively to quenched monomer-like emission, to dimers possibly made of antiparallel sandwich configurations and to ground state preformed excimer type-II emission. The fluorescence intensity fraction of the latter was shown to be the most sensitive to any mesophases in these polymer films. The smectic and nematic mesophases of polymer C 5 have been detected. It is shown that the length of the spacer is playing a major role in the appearance of the mesogenic properties in these polymers.

Luminescence quenching by nitroxide spin labels in aqueous solution: studies on the mechanism of quenching

The mechanism of luminescence quenching by spin labels was investigated in aqueous solution by steady-state and time-resolved luminescence techniques. Water-soluble nitroxide radicals strongly quenched the luminescence emitted by Tb3+ chelates and by fluorescein, either free or conjugated to proteins. The following features of the quenching reaction were established: (I) the rate constant for quenching of triplet-state Tb3+ by nitroxides was about 4 orders of magnitude smaller (ca. 10(5) M-1 s-1) than those of the singlet-state probes; (II) the quenchers reduced the excited-state lifetime of both probes; (III) the rate constants for quenching of both probes were found to be apparently independent of the temperature (between 6 and 42 degrees C) and viscosity (up to 60 mPa.s) of the solutions; (IV) both singlet and triplet quenching rates were sensitive to solvent polarity; (V) there is a small but significant spectral overlap between the absorption band of weekly absorbing nitroxide radicals and the emission spectra of luminophores, the extent of which, however, does not correlate with the extent of quenching; (VI) the quenching rate declines sharply with an increasing luminophore to nitroxide distance. The distance dependence of the quenching rate showed a satisfactory fit to an exponential function. These findings indicate that the quenching reaction is dominated by an electron exchange between the excited singlet- or triplet-state luminophore and the nitroxide radical rather than controlled by diffusional properties of the reactants.(ABSTRACT TRUNCATED AT 250 WORDS)

Luminescence thermal quenching of Cr3+ in zirconium-barium-based fluoride glasses investigated by time-resolved laser spectroscopy.

The optical properties of trivalent chromium ions in zirconium-barium-lanthanum fluoride glasses [${62\mathrm{Z}\mathrm{r}\mathrm{F}}_{4}$-${30\mathrm{B}\mathrm{a}\mathrm{F}}_{2}$-${8\mathrm{L}\mathrm{a}\mathrm{F}}_{3}$, ${57\mathrm{Z}\mathrm{r}\mathrm{F}}_{4}$-${34\mathrm{B}\mathrm{a}\mathrm{F}}_{2}$-${5\mathrm{L}\mathrm{a}\mathrm{F}}_{3}$-${4\mathrm{A}\mathrm{l}\mathrm{F}}_{3}$, and 58 ${\mathrm{ZrF}}_{4}$-${18\mathrm{B}\mathrm{a}\mathrm{F}}_{2}$-5.${5\mathrm{L}\mathrm{a}\mathrm{F}}_{3}$-${3\mathrm{A}\mathrm{l}\mathrm{F}}_{3}$-15NaF] have been investigated by using steady-state and time-resolved luminescence techniques. The thermal quenching of the broadband emission is discussed in terms of the quantum-mechanical single-configurational-coordinate model using the Struck-Fonger method, and good agreement with the experimental results is obtained. The quantum efficiencies for the three glasses are low in accordance with the strong thermal quenching of the luminescence, and the influence of the host material on their values can be well related with the parameters of the quantum-mechanical single-configurational-coordinate model. In order to correlate glass-matrix composition with emission spectral properties, detailed time-resolved measurements have been performed. The results obtained provide evidence for the assumption of two main statistical site distributions for ${\mathrm{Cr}}^{3+}$ in these glasses.

Effect of anionic molecular assembly environments on fluorescence quenching by electron transfer

The quenching of the excited state of [tris(2,2'-bipyridine) ruthenium(II)][Ru(bpy) 2+ 3] by cationic quenchers [methylviologen, diquat, copper(II) and thallium(I)] in molecular assemblies such as polyelectrolytes, polysoaps and micelles have been investigated by steady-state and time-resolved luminescence techniques. The emission quenching of photoexcited positively charged sensitizers was greatly enhanced in anionic molecular assemblies in comparison to neat water. The quenching in poly(styrenesulfonate)—(PSS) solution is found to be dynamic in nature. In the absence of a quencher, the emission decay ∗Ru(bpy) 2+ 3 in polyelectrolyte solution is single exponential. Upon addition of cationic quencher the emission decay is clearly nonexponential. The detailed studies showed that emission decay of ∗Ru(bpy) 2+ 3 over the whole range of cationic quencher concentration, is well described by a general model of dispersed kinetics, in which there is a Gaussian distribution of the logarithm of the rate constants about some mean. The distribution can be characterized by a mean rate constant, k̄, and parameter γ—the width of the Gaussian distribution. Laser flash photolysis was used to study the yield of electron transfer as well as the rate of the back reaction. Addition of the polyelectrolyte markedly decreases the efficiency of charge separation in the organized system as compared to the aqueous solution. Steady-state spectroscopic and pulsed laser techniques have been used to investigate electron transfer from excited Ru(bpy) 2+ 3 to methylviologen in the PSS film. The kinetics of luminescence quenching are consistent with electron-tunneling mechanism where the rate constant k( r) has an exponential dependence on the reactant separation distance, r, with the matrix vibration, and is shown to be quite temperature dependent. No quenching of ∗Ru(bpy) 2+ 3 by methylviologen was observed in glassy solutions or polymer films at 77 K.

Electron-hole plasma relaxation in CdTe

We have studied the relaxation of photo-generated electron-hole pairs in CdTe using a time resolved luminescence technique. Temperature kinetics are deduced from the line shape analysis using first a free particle model and second including the carrier damping in the frame of the plasmon pole approximation. The latter model leads to significantly lower plasma temperatures which are compared to plasma cooling theory including hot phonon effects. The agreement is satisfactory for the densities ranging from 5 X 10 16 to 4 X 10 17 cm -3.

Photophysical studies of tin(IV)-protoporphyrin: potential phototoxicity of a chemotherapeutic agent proposed for the prevention of neonatal jaundice.

The strongly light-absorbing metalloporphyrin tin(IV)-protoporphyrin IX (SnPP) is currently being considered as a chemotherapeutic agent for preventing severe hyperbilirubinemia in newborns, a condition usually treated by phototherapy with visible light. To assess the potential phototoxicity of SnPP we studied the photophysics of the drug in aqueous and nonaqueous solutions using laser flash photolysis and pulse radiolysis. Quantum yields for formation of triplet-state excited SnPP were measured, along with triplet lifetimes and extinction coefficients. In addition, we measured quantum yields for the SnPP-photosensitized formation of singlet oxygen in MeO2H and 2H2O containing cetyltrimethylammonium bromide, using a time-resolved luminescence technique. Quantum yields for formation of triplet SnPP from monomeric ground-state SnPP are high (approximately equal to 0.6-0.8), and triplet lifetimes are long (approximately equal to 0.1-0.2 ms). Efficient quenching of triplet SnPP by molecular oxygen was seen with rate constants greater than 10(9) M-1.s-1. SnPP-photosensitized formation of singlet oxygen in aqueous and nonaqueous solvents was confirmed by the detection of the characteristic luminescence at 1270 nm (phi delta = 0.58 in MeO2H). The photophysical parameters and singlet oxygen-sensitizing efficiency of SnPP are similar to those reported for hematoporphyrin and other metal-free porphyrins known to be phototoxic to humans. These observations suggest that cutaneous photosensitivity arising from singlet-oxygen damage is likely to be an undesirable side-effect of SnPP therapy.