Time-resolved Luminescence Signal Research Articles

Determination of Ascorbic Acid in Pharmaceuticals and Biological Fluids by the Quenching of Europium Luminescence

Here we present a novel strategy for the quantification of ascorbic acid (AA) (vitamin C). The developed method is based on the quenching effect produced by AA on the time-resolved luminescence signal of europium ions using excitation and emission wavelengths of 388 nm and 617 nm. The method presents a linear dynamic range from 0.2 to 2 µg mL−1 with a detection limit of 0.06 µg mL−1 and a relative standard deviation lower than 6%. The method was applied to the determination of AA in pharmaceutical preparations, human serum and human urine. The obtained results in pharmaceuticals were compared with a reference method; the recovery yields were close to 100% in all cases. The accuracy of the method was statistically assessed, demonstrating the suitability of this alternative method for the determination of AA in pharmaceuticals and biological samples, requiring no sample treatment except for a dilution step.

Rapid time-resolved luminescence based screening of bacteria in urine with luminescence modulating biosensing phages

Urinary tract infections (UTIs) are a common problem worldwide. The most prevalent causative pathogen of UTI is Escherichia coli, focus of this study. The current golden standard for detecting UTI is bacterial culture, creating a major workload for hospital laboratories - cost-effective and rapid mass screening of patient samples is needed. Here we present an alternative approach to screen patient samples with a single-step assay utilising time-resolved luminescence and luminescence modulating biosensing phages. Filamentous phage M13 was biopanned for binding luminescence quenching metal (copper) and further E. coli. The screening assay luminescence modulation was further enhanced by selecting right chemical environment for the functioning phage clones. Semi-specific interaction between phage, target bacteria and metal was detected by modulation in the signal of a weakly chelating, easily quenchable lanthanide complex. In the presence of the target pathogen, the phages collected quenching metal from solution to the bacterial surface changing the quenching effect on the lanthanide label and thus modulating the signal. Our method was compared with the bacterial culture data obtained from 70 patient samples. The developed proof-of-principle screening assay showed sensitivity and a specificity at the 90% mark when compared to culture method although some samples had high turbidity and even blood. The detection limit of E. coli was in the range of 1000–10 000 colony forming units/mL. Untreated urine sample was screened and time-resolved luminescence signal result was achieved within 10 min in a single incubation step.

Enhanced Quenching Effect of Neonicotinoid Pesticides on Time-Resolved Terbium Luminescence in Presence of Surfactants

A luminescence analytical method for the quantification of neonicotinoid pesticides (acetamiprid, clothianidin, dinotefuran, imidacloprid, nitenpyram, thiacloprid, and thiamethoxam) in water samples is proposed. The method is based on the quenching effect that these analytes produce on the time-resolved luminescence signal of terbium ions (excitation/emission wavelengths of 256/545 nm/nm). An enhancement on the analytical signal is observed when surfactants are used in the system. The use of a 0.01 mol·L−1 sodium dodecyl sulfate produced approximately a 30% increase in the sensitivity of the method. Under the optimum conditions, the method presented detection limits between 0.03 and 0.23 µg·mL−1. Interference studies were performed for ions commonly present in waters, observing no interferences. In addition, recovery experiments were performed in different waters, well, spring, and swamp, observing recovery yields close to 100%, with relative standard deviations lower than 4% in all cases. No sample treatment except a filtration step was required. Hence, this method may represent an alternative to other existing methods for the quick and simple analysis of these ubiquitous insecticides in environmental waters.

Encapsulation-Stabilized, Europium Containing Nanoparticle as a Probe for Time-Resolved luminescence Detection of Cardiac Troponin I.

The use of a robust optical signaling probe with a high signal-to-noise ratio is important in the development of immunoassays. Lanthanide chelates are a promising material for this purpose, which provide time-resolved luminescence (TRL) due to their large Stokes shift and long luminescence lifetime. From this, they have attracted considerable interest in the in vitro diagnostics field. However, the direct use of lanthanide chelates is limited because their luminescent signal can be easily affected by various quenchers. To overcome this drawback, strategies that rely on the entrapment of lanthanide chelates inside nanoparticles, thereby enabling the protection of the lanthanide chelate from water, have been reported. However, the poor stability of the lanthanide-entrapped nanoparticles results in a significant fluctuation in TRL signal intensity, and this still remains a challenging issue. To address this, we have developed a Lanthanide chelate-Encapsulated Silica Nano Particle (LESNP) as a new immunosensing probe. In this approach, the lanthanide chelate is covalently crosslinked within the silane monomer during the silica nanoparticle formation. The resulting LESNP is physically stable and retains TRL properties of the parent lanthanide chelate. Using the probe, a highly sensitive, sandwich-based TRL immunoassay for the cardiac troponin I was conducted, exhibiting a limit of detection of 48 pg/mL. On the basis of the features of the LESNP such as TRL signaling capability, stability, and the ease of biofunctionalization, we expect that the LESNP can be widely applied in the development of TRL-based immunosensing.

On-Chip Generation, Routing, and Detection of Resonance Fluorescence.

Quantum optical circuits can be used to generate, manipulate, and exploit nonclassical states of light to push semiconductor based photonic information technologies to the quantum limit. Here, we report the on-chip generation of quantum light from individual, resonantly excited self-assembled InGaAs quantum dots, efficient routing over length scales ≥1 mm via GaAs ridge waveguides, and in situ detection using evanescently coupled integrated NbN superconducting single photon detectors fabricated on the same chip. By temporally filtering the time-resolved luminescence signal stemming from single quantum dots we use the quantum optical circuit to perform time-resolved excitation spectroscopy on single dots and demonstrate resonance fluorescence with a line-width of 10 ± 1 μeV; key elements needed for the use of single photons in prototypical quantum photonic circuits.

Time-resolved fluorescence-based assay for rapid detection of Escherichia coli

Fast and simple detection of pathogens is of utmost importance in health care and the food industry. In this article, a novel technology for the detection of pathogenic bacteria is presented. The technology uses lytic-specific bacteriophages and a nonspecific interaction of cellular components with a luminescent lanthanide chelate. As a proof of principle, Escherichia coli-specific T4 bacteriophage was used to infect the bacteria, and the cell lysis was detected. In the absence of E. coli, luminescent Eu3+–chelate complex cannot be formed and low time-resolved luminescence signal is monitored. In the presence of E. coli, increased luminescence signal is observed as the cellular contents are leached to the surrounding medium. The luminescence signal is observed as a function of the number of bacteria in the sample. The homogeneous assay can detect living E. coli in bacterial cultures and simulated urine samples within 25min with a detection limit of 1000 or 10,000 bacterial cells/ml in buffer or urine, respectively. The detection limit is at the clinically relevant level, which indicates that the method could also be applicable to clinical settings for fast detection of urine bacteria.

Ion-induced stacking of photosensitizer molecules can remarkably affect the luminescence detection of singlet oxygen inCandida albicanscells

Singlet oxygen (¹O₂) is an important reactive intermediate in photodynamic reactions, particularly in antimicrobial PDT (aPDT). The detection of ¹O₂ luminescence is frequently used to elucidate the role of ¹O₂ in various environments, particularly in microorganisms and human cells. When incubating the fungus, Candida albicans, with porphyrins XF73 (5,15-bis-[4-(3-Trimethylammonio-propyloxy)-phenyl]-porphyrin) or TMPyP (5,10,15,20-Tetrakis(1-methyl-4-pyridinio)-porphyrin tetra(p-toluenesulfonate)), the ¹O₂ luminescence signals were excellent for TMPyP. In case of XF73, the signals showed strange rise and decay times. Thus, ¹O₂ generation of XF73 was investigated and compared with TMPyP. Absorption spectroscopy of XF73 showed a change in absorption cross section when there was a change in the concentration from 1×10⁻⁶M to 1×10⁻³ M indicating an aggregation process. The addition of phosphate buffered saline (PBS) substantially changed ¹O₂ luminescence in XF73 solution. Detailed experiments provided evidence that the PBS constituents NaCl and KCl caused the change of ¹O₂ luminescence. The results also indicate that Cl- ions may cause aggregation of XF73 molecules, which in turn enhances self-quenching of ¹O₂ via photosensitizer molecules. These results show that some ions, e.g., those present in cells in vitro or added by PBS, can considerably affect the detection and the interpretation of time-resolved luminescence signals of ¹O₂, particularly in in vitro and in vivo. These effects should be considered for any other photosensitizer used in photodynamic processes.

Luminescence kinetics of two-component molecular systems in porous glasses

The kinetics of bimolecular photoreactions accompanied by a characteristic delayed emission of reactant molecules is studied in nanoporous silica glasses upon selective activation of a two-component luminophore system (erythrosine-anthracene) by a short (10 ns) pulse of a Nd3+:YAG laser (532 nm). Time-resolved luminescence signals with different shapes are recorded in different spectral regions. The emission at a wavelength of 430 nm is identified as the sensitized delayed annihilation fluorescence of anthracene. The long-time luminescence in the region of 570 nm consists of thermally induced delayed fluorescence of erythrosine and an emission resulting from heterogeneous annihilation of triplet excitations of erythrosine and anthracene. The effect of pore sizes on the triplet-triplet energy transfer efficiency is determined.

Femtosecond excitation correlation spectroscopy of single-walled carbon nanotubes: Analysis based on nonradiative multiexciton recombination processes

We studied the nonlinear time-resolved luminescence signals due to multiexciton recombination processes in single-walled carbon nanotubes (SWNTs) using femtosecond excitation correlation (FEC) spectroscopy. From theoretical analysis of the FEC signals, we found that the FEC signals in the long time range are dominated by the single exciton decay in SWNTs, where the exciton-exciton annihilation process is efficient. Our results provide a simple method to clarify the single exciton decay dynamics in low-dimensional materials.

INVESTIGATION OF OPTICAL PROPERTIES OF SI-NC ER-DOPED FIBER AMPLIFIER WITH THE GAUSSIAN RADIUS DISTRIBUTION OF NC

Optical and electrical properties of Er-doped Sinanocrystal (Si-NC) fiber amplifier are studied. Presence of Si-NC near Er3+ ions in silica matrix induces strong coupling mechanism and improves the efficiency of Er3+ excitation but in this process the size of Si-NC is important. We investigate effect of radius variation of Si-NC in the range of 2–6 nm by studying the steady state and time resolved luminescence signals at 1.54μm. We conclude that by limiting the range of Si-NC sizes the amplifier gain is improved. On the other hand Si-NCs may introduce optical loss mechanism, such as confined carrier absorption loss that affects the possibility of obtaining positive net gain. But this detrimental event can be affected by change in the radius of Si-NC as reported in this article.

Portable tetracycline analyzer based on LED-excitation europium-sensitized luminescence☆

Described in detail here is the design of a portable tetracycline (TC) analyzer based on europium-sensitized luminescence (ESL). The instrument operation and data processing are controlled by a laptop computer running a custom LabVIEW program. A 385-nm light emitting diode (LED) is used in pulse mode as excitation source. Compared to a conventional xenon flashlamp, an LED has a narrow emission bandwidth, weak residual radiation, and orders-of-magnitude-lower cost, weight, and power consumption. The time-resolved luminescence (TRL) signal is detected by a gated photomultiplier tube (PMT), and normalized by monitoring the energy of individual LED pulses with a photodiode (PD). Over three orders of magnitude (0.1–100 ppb TC), the TRL signal maintains linear dependence on TC concentration; beyond 100 ppb filter effects becomes obvious. A 0.060-ppb limit of detection (LOD) is achieved with a typical ∼5% relative standard deviation (R.S.D.). The background noise corresponds to ∼0.05 ppb. At 16 pounds, the analyzer is readily deployable for field analysis.

Time-Resolved Luminescence Screening of Antibiotics in Tissue Matrices without Centrifugation and Filtration: Spiked Recovery Studies

Analyses of chemical residues in animal tissue matrices require multistep sample preparation. To simplify this process, a methodology was developed that combines sorbent extraction and solid-matrix time-resolved luminescence (TRL); it was applied to tetracycline screening in milk. Reported here is an effort to extend its application to tissue matrices, illustrated by oxytetracycline (OTC) screening in catfish muscle. Extraction and enrichment are accomplished by immersing small C18 sorbent strips into tissue homogenates for 20 min, followed by a 3 min rinse in water and a 2 min dip in a reagent solution. After desiccation, TRL is measured directly on the sorbent surface. Tissue particulates no longer interfere via attenuation or scattering, rendering centrifugation and filtration unnecessary. The integrated TRL intensity shows a linear dependence on OTC concentration in the 0-8 microg/g range (R2 = 0.9992) with a 0.026 microg/g limit of detection. To screen OTC at 2 microg/g, the U.S. regulatory tolerance level, a threshold is established at x2-3sigma2, where x2 and sigma2 are the mean and standard deviation, respectively, of the TRL signals from 15 samples fortified at 2 microg/g. Among 45 blind samples randomly fortified at 0-4 microg/g, 41 were screened correctly and 4 negative samples were presumed positive. This method has the potential to improve throughput and save assay costs by eliminating acids, organic solvents, centrifugation, and filtration.

Versatile portable fluorometer for time-resolved luminescence analysis

A robust, filter-based portable fluorometer was designed, prototyped, and tested for time-resolved luminescence (TRL) analysis. Its flexible optical design allows interchangeable configurations to support three measurement modes: liquid-phase TRL using a sample cuvette, solid-matrix TRL using a sorbent strip, and evanescent-field TRL using a quartz-rod waveguide. A xenon flashlamp is used as the light source and a photomultiplier tube (PMT) as the photodetector. A gating technique was implemented to overcome PMT saturation by the intense xenon lamp flash, therefore higher gains can be set to measure weak luminescence signals. The TRL signal is digitized at a 4μs time resolution and a 12bit amplitude resolution. Individual flashes were monitored by a photodiode and its current was integrated to compensate for source light fluctuation. Using tetracycline as a model analyte, a 0.025ppb limit of detection (LOD) with a typical 2% relative standard deviation, and a 3 orders of magnitude (0.5–300ppb) linear dynamic range (r2=0.9996) were achieved.

Time‐Resolved Luminescence Screening Assay for Tetracyclines in Chicken Muscle#

A time‐resolved luminescence (TRL) assay was developed for effective screening of tetracyclines in chicken muscle at the European Union (EU) maximum residue level of 100 ng g−1. The method involves extraction of the tetracyclines with McIlvaine–ethylenediamine tetraacetic acid (EDTA) buffer, centrifugation, solid‐phase extraction (SPE) clean‐up, formation of an Eu(III) complex, and then measurement of the TRL signal at 615 nm (excitation at 388 nm). Samples fortified with tetracycline (TC), oxytetracycline (OTC) or chlortetracycline (CTC) gave a linear response over the range of 0–1000 ng g−1, with relative sensitivities 5.4×, 2.4×, and 1×, respectively. Limits of detection for TC, OTC, and CTC were 3.5, 8, and 19 ng g−1, respectively. Examination of the least sensitive case, CTC, showed no overlap between the TRL of control chicken extracts and those that had been fortified with 100 ng g−1 CTC. The within‐day variation for these samples averaged 3.1% relative standard deviation (RSD), as did the day‐to‐day variation. The method was tested with blind control and fortified samples over the range of 20–500 ng g−1 CTC to illustrate its utility. Other veterinary drugs approved for chickens in the US (enrofloxacin, nicarbazin, tylosin) did not interfere. This method can provide a useful alternative to microbial screening assays for tetracyclines. #Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture.

Coupling and Cooperative Up-conversion Coefficients in Er-doped Si Nanocrystals

AbstractIn the present work, a quantitative understanding of the Er-doped Si nanocrystals interaction is reported. We present a model based on an energy level scheme taking into account the coupling between each Si nanocrystal and the neighboring Er ions. By fitting the steady state and time resolved luminescence signals at both the 1.54 and 0.98 μm Er lines we were able to determine a value of 3×10-15cm3s-1for the coupling coefficient. Moreover, a strong cooperative up-conversion mechanism, active between two excited Er ions and characterized by a coefficient of 7×10-17cm3s-1, will be shown to be active in the system, demonstrating that each Si nanocrystal can actually excite more than one Er ion.

Application of Terbium‐Sensitized Luminescence for the Determination of Grepafloxacin in Human Urine and Serum

Analytical performance and applications of a selective and sensitive lanthanide-sensitized luminescence method for the determination of grepafloxacin is described. The method is based in the time-resolved luminescence signal from a terbium (III)-grepafloxacin complex in a micellar solution of sodium dodecyl sulfate. The optimized method allows the determination of 10-500 ng mL(-1) of grepafloxacin in 7.5 mM sodium dodecyl sulfate solution containing 0.16 M acetic acid-sodium acetate buffer (pH 6.0) and 7.5 mM Na(2)SO(3) (chemical deoxygenation agent), with lambda(exc) = 275 nm and lambda(em) = 546 nm. Grepafloxacin was determined in human serum (by external calibration method) and urine (by standard additions method), spiked at levels found after drug administration at normal clinical doses. Average recoveries found were 89.6 (relative standard deviation 0.9%) and 102 (relative standard deviation 2%), respectively.

Determination of trovafloxacin in human serum by time resolved terbium-sensitised luminescence

A sensitive time-resolved luminescence method for the determination of trovafloxacin is described. The method is based on the time-resolved luminescence signal from the terbium(III)–trovafloxacin complex, in a micellar solution of sodium dodecyl sulfate (SDS), using a chemical deoxygenation agent (Na 2SO 3). The method allows the determination of 20–450 ng ml −1 of trovafloxacin in 7.5 mM SDS solution containing 0.16 M acetic acid–sodium acetate buffer (pH 6.0) and 7.5 mM Na 2SO 3 with λ exc=270 nm and λ em=546 nm. In these experimental conditions luminescence signal for trovafloxacin increases 20-fold with respect to native fluorescence of the compound in aqueous solution at pH 6.5. Terbium-sensitised luminescence was applied to trovafloxacin determination in human serum, spiked at levels found after drug administration at normal clinical doses. Recovery is 90±1% and day-to-day precision is 3.5%. The proposed method tolerates high concentrations of other co-administrated drugs and excipients.

Time resolved photoluminescence in keV proton irradiated a-SiC:H alloys

We have studied the photoluminescence of amorphous hydrogenated silicon–carbon films prepared by plasma enhanced chemical vapour deposited and subsequently irradiated by 150 keV proton at dose ranging from 0.1 to 4×1015cm−2 using both continuum wave and picosecond pulsed laser. We show that proton irradiation induces a consistent number of defects in the films (up to 1019 cm−3) with a strong reduction in the photoluminescence yield detected in the wavelength range 550–800 nm. We have analysed the time resolved luminescence signal in terms of a multiple exponential decay model and the fits give three dominating lifetimes which do not change with proton dose. We observed an increase of the relative weight of the faster decay component with increasing defect density induced by irradiation. The observed photoluminescence decays can be well understood according to the bound exciton model in amorphous semiconductors where the radiative recombination is due to interaction between electrons and localised holes within a region of the order of 0.3 nm.