Fluorescence Lifetime Spectroscopy Research Articles

Biological activities of biogenically synthesized fluorescent silver nanoparticles using Acanthospermum hispidum leaves extract

Silver nanoparticles (AgNPs) synthesized by an implicitly environmentally gracious route using Acanthospermum hispidum aqueous leaves extract at room temperature reported. This approach is facile, swift, cost-effective and stable for a long time, reproducible at room temperature and in an eco-friendly manner to obtain a self-assembly of AgNPs. These fabricated AgNPs were investigated by ultraviolet–visible spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscope with selected area electron diffraction, X-ray diffraction, Fourier transform Infrared spectroscopy, particle size, zeta potential, photoluminescence with fluorescence life-time spectroscopy and surface area with porosity studies of synthesized nanoparticles were analyzed by Brunauer–Emmett–Teller and Barrett–Joyner–Halenda curve. Besides, these AgNPs displayed antibacterial, antifungal antimycobacterial and antimalarial activity against some bacterial pathogens. From the outcomes obtained it is suggested that AgNPs could be used effectively in future nanobiotechnology and medical concerns.

Langmuir-Blodgett Films from Fluorescently Labelled Phospholipids Deposited on Surface Acoustic Wave Devices

Over the years several new effects in fluorescently labelled Langmuir monolayers or Langmuir-Blodgett (LB) films, deposited on solid support plates, have been reported. Mostly layers from Dipalmytoyl Phosphatidyl Ethanolamine head labelled with Nitrbenzoxadiazole (DPPE-NBD) have been studied. This molecule behaves exactly as the DPPE molecule which is part of biological membranes. So it is expected that DPPE-NBD molecules can serve as an appropriate matrix for implementation of selectively reacting proteins or enzymes while preserving their function. This combination can act as an active layer in biosensor applications for operation in either gas or liquid environments and this molecule could further increase the system sensitivity in such applications. Addition of the chromophore NBD head group also stabilizes the film and allows for multilayer deposition which is not possible for phospholipids. In this study, LB monolayers were deposited on glass substrates at different surface pressures and with or without Cadmium ions in the water subphase. They were studied using fluorescence spectroscopy and Atomic Force Microscopy (AFM). In view of possible biosensor applications, LB layer by layer deposition was performed on Rayleigh Surface Acoustic Wave (SAW) resonant devices working at 440 MHz. These can effectively be used to transduce the biosensor signal from the active layer by providing a mass proportional frequency output. Layers from DPPE-NBD that might also be suitable for possible SAW based biosensor applications were deposited at a surface pressure of 10 mN/m. AFM spectroscopy reveals the phase coexistence of liquid and solid phases as well as higher bilayer nanosized cylinders. Fluorescence intensity was strongly self-quenched at this pressure and fluorescence lifetime spectroscopy shows a complex behaviour with a 3-rd order exponential decay. A frequency downshift of 10 KHz per monolayer was measured with the coated SAW device which results in a deposited mass of about 1 ng/monolayer.

Digital frequency domain approach for fluorescence lifetime spectroscopy of the cornea using an enhanced confocal scanning microfluorometer

We report on enhancement to a confocal scanning microfluorometer (CSMF) for depth-resolved frequency domain lifetime spectroscopy across the cornea. Fluorescence was detected by a photomultiplier tube (PMT; R928P, Hamamatsu) and coupled to computer-controlled data acquisition module (K520, Digital Frequency Domain, ISS Inc.).The digital frequency domain (DFD) module performed acquisition of PMT pulses for further calculation of phase (ϕ) and modulation (M) in the emission of the sample, relative to excitation pulses, at 30 harmonics. As per the DFD approach, fluorescence lifetime (τ) was calculated by tanϕ =ωτ, where ω= 2πf with f being the excitation harmonic in Hz. The modulation depth can be calculated byM=1/√(1+ω2τ2). The DFD module was also used to pulse the excitation laser (450 nm; ISS Model N742) with the repetition rate of up to 10 MHz (fundamental frequency). Apart from coupling to DFD module, two other modifications were incorporated to enhance the CSMF: first, a sighting optic was constructed and placed before the PMT for rapid and precise confocal alignment of the excitation and emission slits, and second, a stepper motor was interfaced to the vertical nanostage for rapid depth scanning. These enhancements have enabled the CSMF to consistently produce a depth resolution of 7 µm during transcorneal scans with a 40x water immersion objective (Zeiss; WD = 1.2 mm, NA= 0.75). Overall, the CSMF is now capable of measuring transcorneal fluorescence lifetime with a wide array of fluorophores exhibiting lifetimes in the range of µs to nanoseconds.

Phase-resolved Fluorometer for Fluorescence Lifetime Measurements in the Human Eye

A slit-lamp is a standard instrument in ocular diagnostics. It consists of an illumination assembly and viewing, binocular optics. The illumination assembly projects a beam of visible light into the eye as a thin sheet, and its interaction with intraocular structures is then viewed at an angle with binocular optics. To perform fluorescence lifetime spectroscopy, we have modified a slit lamp to form an ocular spot fluorometer in the frequency domain (FD). To ensure depth-resolved fluorescence measurements, an adjustable collection slit has been positioned confocal to the excitation slit (i.e., the slit of the illumination optics) at the image plane of the slit lamp. This has enabled measurements exclusively from any desired spot in the eye, which corresponds to the focal point of the excitation beam. Thus, the sampling volume, referred to as the focal diamond, is formed by the intersection of the emission and illumination/excitation beams. For purposes of implementation in FD, we modulated the excitation (10-100 kHz) by driving a white LED (10 W) with a power amplifier connected to a function generator. The emission was detected by an analog photomultiplier tube (PMT). The output of the PMT was connected to a lock-in amplifier to measure the phase delay (ϕ) and demodulation (M), which are related to the fluorescence lifetime in the emission relative to the excitation sine wave. Both ϕ and M, measured with Ru phenanthroline, were sensitive to pO2 and could be acquired at frequencies greater than 100 Hz. Overall, the findings of this study indicate the potential of our instrument to sense rapid pO2 dynamics in the eye.

Interaction between trelagliptin and pepsin through spectroscopy methods and molecular dynamics simulation

The interaction between trelagliptin and pepsin was probed through spectroscopy methods and molecular dynamics simulation. Results of fluorescence lifetime and fluorescence spectroscopy analysis showed that trelagliptin can spontaneously interact with pepsin through a static quenching. This interaction was mainly driven by hydrogen bonding and van der Waals, as evident from thermodynamic parameters and molecular dynamics simulation. The microenvironment of tyrosine residues and the secondary structure of pepsin were slightly influenced by trelagliptin based on synchronous fluorescence, three-dimensional fluorescence, and circular dichroism spectra. In addition, the activity of pepsin was hardly affected by the insertion of trelagliptin. Molecular dynamics simulations were used to further analyze the pepsin–trelagliptin complex. This study provides useful information for binding mechanisms of trelagliptin on pepsin.

Label-free fluorescence lifetime spectroscopy detects radiation-induced necrotic changes in live brain in real-time.

Current clinical imaging modalities do not reliably identify brain tissue regions with necrosis following radiotherapy. This creates challenges for stereotaxic biopsies and surgical-decision making. Time-resolved fluorescence spectroscopy (TRFS) provides a means to rapidly identify necrotic tissue by its distinct autofluorescence signature resulting from tissue breakdown and altered metabolic profiles in regions with radiation damage. Studies conducted in a live animal model of radiation necrosis demonstrated that necrotic tissue is characterized by respective increases of 27% and 108% in average lifetime and redox ratio, when compared with healthy tissue. Moreover, radiation-damaged tissue not visible by MRI but confirmed by histopathology, was detected by TRFS. Current results demonstrate the ability of TRFS to identify radiation-damaged brain tissue in real-time and indicates its potential to assist with surgical guidance and MRI-guided biopsy procedures.

Reducing parasitic capacitance in single‐photon avalanche diodes

Page ***, ‘Triple epitaxial single-photon avalanche diode for multichannel timing applications’, Ivan Labanca, Francesco Ceccarelli, Angelo Gulinatti, Massimo Ghioni and Ivan Rech. Cross section of the new SPAD structure. A lightly doped n- Intermediate Layer has been introduced between the Buried Layer and the Substrate to reduce the parasitic capacitance. An array of SPADs that have been fabricated using the new custom technology. A single-photon avalanche diode with picosecond temporal resolution and low parasitic capacitance is presented by researchers at the Politecnico di Milano, Italy. Single-photon avalanche diodes (SPADs) are solid-state devices that provide a digital current pulse every time they are hit by a single photon. They record not only the number of photons impinging on the detector but they also determine the arrival time of each photon within an accuracy of tens of picoseconds. SPAD development is driven by the widespread and growing interest in low-level light detection in several scientific and industrial applications, such as fluorescence spectroscopy in life and material sciences, quantum computing and cryptography, profiling of remote objects with optical radar techniques, particle sizing, and more. In particular, the use of fluorescence lifetime spectroscopy as an analytical research tool has increased substantially in recent years, finding remarkable applications in chemistry, biochemistry and biology. In this Issue of Electronics Letters, Francesco Ceccarelli and colleagues have modified the typical structure of SPADs to introduce an additional layer that reduces the parasitic capacitance between the detector anode and the chip substrate. This was made possible due to the use of a fully custom technology, namely a fabrication process in which each step can be finely optimised in order to achieve the best overall device performance. The new structure reported by the authors increases the fraction of avalanche current that can be fed into the front-end electronics. This means that the same timing jitter can be attained with a higher detection threshold and is especially important when more than one SPAD is integrated on the same chip and the disturbances generated by a detector during operation can degrade the timing jitter on adjacent pixels. “By simplifying the problem of reading the avalanche current with a low timing jitter, the device structure reported in this Letter opens the way to fabricating photon detection systems that are based on custom-technology SPADs with a large number of pixels and picosecond temporal resolution” explains Ceccarelli. The fabrication of large arrays of SPADs, which are truly parallel and attain high detection efficiency and picosecond timing resolution, is certainly a long-term objective in this field. This work represents one of the milestones towards achieving this goal. Ceccarelli says “we aim at arrays with many thousands of pixels which can have a dramatic impact on very critical fields like new drugs discovery.” Ceccarelli and his colleagues at the Politecnico di Milano will now work on combining this new technology with a recently developed integrated front-end circuit to build a multichannel time-resolved single-photon detection module. They will also continue to develop the detector to improve its performance. Ceccarelli explains “we are looking in particular at very high detection efficiency in the visible / near infrared region and at removing the slow components in the temporal response.” The interest in single-photon detection has grown considerably in the last few years and is expected to increase even further in the coming decade, due to emerging consumer and scientific applications, like autonomous cars and new drug discoveries. Most of the attention will likely be devoted to the development of a high-throughput, time-resolved, single-photon imager with a large number of pixels. On the one hand, this requires the design of detectors with always increasing performance, especially in terms of detection efficiency, temporal response and scalability. On the other hand, a lot of work must be done to devise new architectures for handling the huge amount of data produced by large, time-resolved arrays. “Beside this mainstream development, we expect also a lot of activity in emerging fields, especially in quantum information processing” concludes Ceccarelli.

Noninvasive Optical Assessment of Implanted Engineered Tissues Correlates with Cytokine Secretion.

Fluorescence lifetime sensing has been shown to noninvasively characterize the preimplantation health and viability of engineered tissue constructs. However, current practices to monitor postimplantation construct integration are either qualitative (visual assessment) or destructive (tissue histology). We employed label-free fluorescence lifetime spectroscopy for quantitative, noninvasive optical assessment of engineered tissue constructs that were implanted into a murine model. The portable system was designed to be suitable for intravital measurements and included a handheld probe to precisely and rapidly acquire data at multiple sites per construct. Our model tissue constructs were manufactured from primary human cells to simulate patient variability based on a standard protocol, and half of the manufactured constructs were stressed to create a range of health states. Secreted amounts of three cytokines that relate to cellular viability were measured in vitro to assess preimplantation construct health: interleukin-8 (IL-8), human β-defensin 1 (hBD-1), and vascular endothelial growth factor (VEGF). Preimplantation cytokine secretion ranged from 1.5 to 33.5 pg/mL for IL-8, from 3.4 to 195.0 pg/mL for hBD-1, and from 0.1 to 154.3 pg/mL for VEGF. In vivo optical sensing assessed constructs at 1 and 3 weeks postimplantation. We found that at 1 week postimplantation, in vivo optical parameters correlated with in vitro preimplantation secretion levels of all three cytokines (p < 0.05). This correlation was not observed in optical measurements at 3 weeks postimplantation when histology showed that the constructs had re-epithelialized, independent of preimplantation health state, supporting the lack of a correlation. These results suggest that clinical optical diagnostic tools based on label-free fluorescence lifetime sensing of endogenous tissue fluorophores could noninvasively monitor postimplantation integration of engineered tissues.

Phytosynthesis and Biological Activities of Fluorescent CuO Nanoparticles Using Acanthospermum hispidum L. Extract

Copper oxide nanoparticles (CuO-NPs) synthesized by an implicitly environmentally benign process using Acanthospermum hispidum L. aqueous plant extract as an effective bio-oxidizing/bio-reducing agent. Phytochemical screening of the fresh aqueous leaves extract showed the presence of coumarins, tannins, saponins, phenols, flavonoids, sterols and volatile oils. Fourier transform infrared spectroscopy confirmed the possible biomolecules responsible for the formation of copper oxide nanoparticles. X-ray diffraction patterns revealed the monoclinic phase of the synthesized copper oxide nanoparticles. The average size, shape and the crystalline nature of the nanoparticles were determined by field emission scanning electron microscopy and transmission electron microscopy analysis. Energy-dispersive X-ray spectroscopy analysis confirmed the presence of elements in the synthesized nanoparticles. Photoluminescence and fluorescence life-time spectroscopy showed luminescence properties of copper oxide nanoparticles. Furthermore, Copper oxide nanoparticles evinced highly robust antimicrobial, antimalarial and antimycobacterial activity against Pseudomonas aeruginosa, Streptococcus pyogenes, Staphylococcus aureus, Escherichia coli, Plasmodium falciparum and Micobacterium tuberculosis H37RV. The current study demonstrates convenient utilization of Acanthospermum hispidum L. extract as a fuel for the efficient synthesis of copper oxide nanoparticles through a green synthesis method to obtain significantly biologically active material.

Portable fluorescence lifetime spectroscopy system for in-situ interrogation of biological tissues.

Fluorescence spectroscopy and lifetime techniques are potential methods for optical diagnosis and characterization of biological tissues with an in-situ, fast, and noninvasive interrogation. Several diseases may be diagnosed due to differences in the fluorescence spectra of targeted fluorophores, when, these spectra are similar, considering steady-state fluorescence, others may be detected by monitoring their fluorescence lifetime. Despite this complementarity, most of the current fluorescence lifetime systems are not robust and portable, and not being feasible for clinical applications. We describe the assembly of a fluorescence lifetime spectroscopy system in a suitcase, its characterization, and validation with clinical measurements of skin lesions. The assembled system is all encased and robust, maintaining its mechanical, electrical, and optical stability during transportation, and is feasible for clinical measurements. The instrument response function measured was about 300ps, and the system is properly calibrated. At the clinical study, the system showed to be reliable, and the achieved spectroscopy results support its potential use as an auxiliary tool for skin diagnostics.

Studies on Structural, Optical, Thermal and Electrical Properties of Perylene-Doped p-terphenyl Luminophors.

A simple solid state reaction technique was employed for the preparation of polycrystalline luminophors of p-terphenyl containing different amounts of perylene followed by spectral characterization techniques viz. XRD, SEM, TGA-DSC, UV-Visible spectroscopy, thermo-electrical conductivity, fluorescence spectroscopy, fluorescence life time spectroscopy and temperature dependent fluorescence. X-ray diffraction profiles of the doped p-terphenyl reveal well-defined and sharp peaks indicate homogeneity and crystallinity. The SEM micrograph of pure p-terphenyl exhibit flakes like grains and then compact and finally gets separately with perylene amounts. The observed results indicate that closed packed crystal structures of doped p-terphenyl during crystal formation. The band gaps estimated from UV-visible spectroscopy decreased from 5.20 to 4.10eV, while thermo-electrical conductivity increases with perylene content. The fluorescence spectra showed partial quenching of p-terphenyl fluorescence and simultaneously sensitization of perylene fluorescence at the excitation wavelength of p-terphenyl (290nm) due to excitation energy transfer from p-terphenyl to perylene. The observed sensitization results are in harmony with intense blue color seen in fluorescence microscopy images and has high demand in scintillation process.

Impact of Shell Thickness on Photoluminescence and Optical Activity in Chiral CdSe/CdS Core/Shell Quantum Dots.

Core/shell quantum dots (QDs) are of high scientific and technological importance as these nanomaterials have found a number of valuable applications. In this paper, we have investigated the dependence of optical activity and photoluminescence upon CdS shell thickness in a range of core-shell structured CdSe/CdS QDs capped with chiral ligands. For our study, five samples of CdSe/CdS were synthesized utilizing successive ion layer adsorption and reaction to vary the thickness of the CdS shell from 0.5 to 2 nm, upon a 2.8 nm diameter CdSe core. Following this, a ligand exchange of the original aliphatic ligands with l- and d-cysteine was carried out, inducing a chiroptical response in these nanostructures. The samples were then characterized using circular dichroism, photoluminescent spectroscopy, and fluorescence lifetime spectroscopy. It has been found that the induced chiroptical response was inversely proportional to the CdS shell thickness and showed a distinct evolution in signal, whereas the photoluminescence of our samples showed a direct relationship to shell thickness. In addition, a detailed study of the influence of annealing time on the optical activity and photoluminescence quantum yield was performed. From our work, we have been able to clearly illustrate the approach and strategies that must be used when designing optimal photoluminescent optically active CdSe/CdS core-shell QDs.

Addition of Fluorescence Lifetime Spectroscopy to the Tool Kit Used to Study the Formation and Degradation of Luminescent Quantum Dots in Solution.

The increasing commercialization of consumer electronic products that make use of II-VI semiconductor quantum dots (QDs) has raised significant concerns about their impact on natural systems and human health once they are released into the environment at the end of the product's lifetime. In this paper, we demonstrate the addition of fluorescence lifetime spectroscopy to the existing tool kit of spectroscopic techniques to quantitatively monitor changes in QD properties as they form and degrade in solution. Our study reveals that because of its rich information content, fluorescence lifetime spectroscopy has a limited utility as a stand-alone technique in the study of QD formation and degradation. However, combining fluorescence lifetime spectroscopy with the commonly used emission quantum yield and peak width measurements along with other analytical methods, including ultraviolet-visible spectroscopy, transmission electron microscopy, and inductively coupled plasma mass spectrometry measurements, significantly enhances the existing analytical tool kit and provides the capability to monitor in real time, the formation and degradation of luminescent QDs in organic and aqueous solutions under environmentally relevant conditions.

Fabrication of Water-Soluble, Green-Emitting Gold Nanoclusters with a 65% Photoluminescence Quantum Yield via Host–Guest Recognition

Metal nanoclusters (NCs) as a new type of fluorescent material have been extensively explored because of their attractive set of features such as their ultrafine size, low toxicity, and excellent photostability. However, little progress has been made in producing water-soluble, homogeneous, and ultrabright metal NCs. In this study, gold NCs (AuNCs) with a photoluminescence quantum yield (QY) as high as 65% are synthesized in water through a simple blending route. Weak emission is observed from the 6-aza-2-thiothymine-protected AuNCs (ATT-AuNCs); however, the fluorescence intensity can be prominently enhanced by introducing l-arginine (Arg) into the capping layer. The fluorescence enhancement mechanism is systematically investigated by the measurements of ultraviolet–visible absorption spectroscopy, photoluminescence spectroscopy, fluorescence lifetime spectroscopy, transmission electron microscopy, dynamic light scattering, X-ray photoelectron spectroscopy, 1H nuclear magnetic resonance, and calculations from density functional theory, with results isolating the vital role of the ligand shell and ruling out the effect of the gold core. The supramolecular host–guest assemblies formed between ATT capped on the gold core and the guanidine group of Arg make the capping ligands of ATT rigid. Subsequently, the intramolecular vibration and rotation of ATT are greatly suppressed, which reduce the nonradiative relaxation of excited states and, as a result, predominantly increase the luminescence QY of ATT-AuNCs. Further experiments demonstrate that a small change in guanidine substituents can arouse obvious changes in the photoluminescence features of NCs. We envision that this work will substantively contribute to the process of developing efficient synthetic routes to high-quality metal NCs.

Tryptophan and Non-Tryptophan Fluorescence of the Eye Lens Proteins Provides Diagnostics of Cataract at the Molecular Level

The chemical nature of the non-tryptophan (non-Trp) fluorescence of porcine and human eye lens proteins was identified by Mass Spectrometry (MS) and Fluorescence Steady-State and Lifetime spectroscopy as post-translational modifications (PTM) of Trp and Arg amino acid residues. Fluorescence intensity profiles measured along the optical axis of human eye lenses with age-related nuclear cataract showed increasing concentration of fluorescent PTM towards the lens centre in accord with the increased optical density in the lens nucleolus. Significant differences between fluorescence lifetimes of “free” Trp derivatives hydroxytryptophan (OH-Trp), N-formylkynurenine (NFK), kynurenine (Kyn), hydroxykynurenine (OH-Kyn) and their residues were observed. Notably, the lifetime constants of these residues in a model peptide were considerably greater than those of their “free” counterparts. Fluorescence of Trp, its derivatives and argpyrimidine (ArgP) can be excited at the red edge of the Trp absorption band which allows normalisation of the emission spectra of these PTMs to the fluorescence intensity of Trp, to determine semi-quantitatively their concentration. We show that the cumulative fraction of OH-Trp, NFK and ArgP emission dominates the total fluorescence spectrum in both emulsified post-surgical human cataract protein samples, as well as in whole lenses and that this correlates strongly with cataract grade and age.

Recent progress on super-resolution imaging and correlative super-resolution microscopy

The diffraction of the finite aperture in the optical imaging system restricts further improvement of the resolution of optical microscopy, which is called the diffraction limit. Since raised by Ernst Abbe in 1873, the problem of diffraction limit has been one of the foci of academic research. In recent years, with the rapid development of related fields such as the development of optoelectronic devices including high energy lasers and high sensitivity detectors and the development of new fluorescent probes, the problem of diffraction limit in optical microscopy ushered in a new opportunity, and super-resolution microscopy (SRM) has made remarkable achievements in the past decade. The basic principles of diffraction limited resolution in both space and frequency domains are reviewed, and on this basis, the mechanisms for the various SRM technologies to circumvent the diffraction limit and improve the resolution are explained in detail. The development trends and research directions of various SRM techniques are also introduced. As a new and important development trend of SRM, correlative super-resolution microscopy and its recent progress are reviewed, including correlative studies on SRM and time-lapse live cell fluorescence microscopy, fluorescence lifetime imaging microscopy, spectrometry and spectroscopy, electron microscopy, atomic force microscopy, etc. The role and significance of various correlative super-resolution microscopy are discussed. The future development of super-resolution microscopy and correlative super-resolution microscopy is also prospected.

Structural, optical and morphological studies of undoped and Zn-doped CdSe QDs via aqueous route synthesis

Undoped and Zn-doped CdSe quantum dots (QDs) were successfully synthesized by the chemical precipitation method. The structural, optical and morphological properties of the synthesized undoped and Zn-doped CdSe QDs were studied by X-ray diffraction (XRD), UV–visible absorption spectroscopy, photoluminescence (PL) spectroscopy, fluorescence lifetime spectroscopy, scanning electron microscopy (SEM), field emission transmission electron microscopy (FE-TEM) and FTIR. The synthesized undoped and Zn-doped CdSe QDs were in cubic crystalline phase, which was confirmed by the XRD technique. From the UV–visible absorption spectral analysis, the absorption wavelengths of both undoped and Zn-doped CdSe QDs show blue-shift with respect to their bulk counterpart as a result of quantum confinement effect. The highest luminescence intensity was observed for CdSe QDs doped with 4% Zn by PL studies. TEM analysis shows that the prepared QDs are spherical in shape.

3,12-Dimethoxy-5,6,9,10-tetrahydro-7,8-dicyano-[5]helicene as a new emitter for blue and white organic light-emitting diodes

In this work, crystallographic data along with thermal, electrochemical and optical properties of 3,12-dimethoxy-5,6,9,10-tetrahydro-7,8-dicyano-[5]helicene (DTDH) were studied and reported. DTDH has an energy band gap of 2.9 eV which enable it to emit blue light in the fluorescence process. Because of high fluorescence quantum yield, i.e. 0.96, it is suitable to be used as an emissive material in an organic light-emitting diode (OLED). The device with a configuration of ITO/PEDOT:PSS/DTDH/Ca/Al emitted blue light with a peak at 475 nm. The best device showed a turn-on voltage at 4.0 V, maximum brightness at 4954 cd/m2, and maximum current efficiency at 2.38 cd/A. However, up on mixing DTDH with N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (NPB), the couple compounds form exciplex when excited resulting in a new emission spectra at lower energy with a peak at 558 nm. Consequently, White OLEDs with the configuration of ITO/NPB/NPB:DTDH(1:1)/DTDH/BCP/Alq3/LiF/Al, in which NPB:DTDH layer was formed by co-evaporation, were fabricated. Performance and color quality of the white OLEDs can be tuned by varying thickness of the mixture layer (NPB:DTDH) and the pure DTDH layer. The best WOLED with CRI of 72 and CCT of 5096 was obtained. Evidences of exciplex formation between NPB and DTDH were observed in fluorescence lifetime and time-resolved emission spectroscopy (TRES) experiments.

Hairpin DNA-functionalized gold nanorods for mRNA detection in homogenous solution.

We report a fluorescent probe for mRNA detection. It consists of a gold nanorod (GNR) functionalized with fluorophore-labeled hairpin oligonucleotides (hpDNA) that are complementary to the mRNA of a target gene. This nanoprobe was found to be sensitive to a complementary oligonucleotide, as indicated by significant changes in both fluorescence intensity and lifetime. The influence of the surface density of hpDNA on the performance of this nanoprobe was investigated, suggesting that high hybridization efficiency could be achieved at a relatively low surface loading density of hpDNA. However, steady-state fluorescence spectroscopy revealed better overall performance, in terms of sensitivity and detection range, for nanoprobes with higher hairpin coverage. Time-resolved fluorescence lifetime spectroscopy revealed significant lifetime changes of the fluorophore upon hybridization of hpDNA with targets, providing further insight on the hybridization kinetics of the probe as well as the quenching efficiency of GNRs.

Quantitative determination of the surfactant-induced split ratio of influenza virus by fluorescence spectroscopy

ABSTRACTThe majority of marketed seasonal influenza vaccines are prepared using viruses that are chemically inactivated and treated with a surfactant. Treating with surfactants has important consequences: it produces ‘split viruses’ by solubilizing viral membranes, stabilizes free membrane proteins and ensures a low level of reactogenicity while retaining high vaccine potency. The formulation stability and potency of split influenza vaccines are largely determined by the specifics of this ‘splitting’ process; namely, the consequent conformational changes of proteins and interactions of solubilized particles, which may form aggregates. Robust methods to quantitatively determine the split ratio need to be developed before optimal splitting conditions can be investigated to streamline production of superior influenza vaccines. Here, we present a quantitative method, based on both steady-state and time-resolved fluorescence spectroscopy, to calculate the split ratio of the virus after surfactant treatment. We use the lipophilic dye Nile Red (NR) as a probe to elucidate molecular interactions and track changes in molecular environments. Inactivated whole influenza viruses obtained from a sucrose gradient were incubated with NR and subsequently treated with increasing concentrations of the surfactant Triton X-100 (TX-100) to induce virus splitting. NR's emission spectra showed that the addition of TX-100 caused ˜27 nm red-shifts in the emission peak, indicative of increasingly hydrophilic environments surrounding NR. The emission spectra of NR at different surfactant concentrations were analyzed with multi-peak fitting to ascertain the number of different micro-environments surrounding NR and track its population change in these different environments. Results from both the emission spectra and fluorescence lifetime spectroscopy revealed that NR showed presence in 3 distinct molecular environments. The split ratio of the virus was then calculated from the percentages of NR in these environments using both fluorescence emission and lifetime data. This study can pave the way for the development of robust methods to rapidly quantify splitting extent during vaccine manufacturing.