Steady-state Lifetime Research Articles

Observations of N2O5 and NO3 at a suburban environment in Yangtze river delta in China: Estimating heterogeneous N2O5 uptake coefficients

The nitrate radical (NO3) and dinitrogen pentoxide (N2O5) play an important role in the nocturnal atmosphere chemistry. Observations of NO3 radicals and N2O5 were performed in a semirural ground site at Tai'Zhou in polluted southern China using cavity ring down spectroscopy (CRDS) from 23 May to 15 June 2018. The observed NO3 and N2O5 concentrations were relatively low, with 1 min average value of 4.4 ± 2.2 and 26.0 ± 35.7 pptV, respectively. The N2O5 uptake coefficient was determined to be from 0.027 to 0.107 based on steady state lifetime method. Fast N2O5 hydrolysis was the largest contributor to the loss of NO3 and contributed to substantial nitrate formation, with an average value of 14.83 ± 6.01 µg/m3. Further analysis shows that the N2O5 heterogeneous reactions dominated the nocturnal NOx loss and the nocturnal NOx loss rate is 0.14 ± 0.02 over this region.

A Spectroscopic Study of Xanthene Dyes on a Polystyrene Surface: an Investigation of Ion-π Interactions at Polymer Interfaces.

Thin films of three differently charged xanthene dyes: rhodamine 6G (Rh6G, cationic), fluorescein 27 (F27, neutral), and disodium fluorescein (DSF, anionic) were cast onto a polystyrene (PS) coated glass substrate to investigate ion-π interactions. Absorbance spectroscopy was used to determine the aggregation state of the dyes on the PS surface. Deconvolution of the spectra of films revealed multiple peaks for all dyes assigned to isolated monomers, aggregates, and complexes between the dye and the polymer substrate. The shift of the low energy peak relative to the monomer peak was used as an indication of interaction strength of that species with the PS π system, which followed the trend of Rh6G > DSF > F27. Increase in the interaction energy is attributed to stabilization from ion-π interactions. Steady-state emission spectra and excited state lifetime measurements were performed on all films. The formation of a weakly emissive exciplex was found for Rh6G and DSF, consistent with ion-π interactions, but no evidence of an exciplex is found for the F27 films.

A Spectroscopic Marker for Structural Transitions Associated with Amyloid-β Aggregation.

An amyloid aggregate evolves through a series of intermediates that have different secondary structures and intra- and intermolecular contacts. The structural parameters of these intermediates are important determinants of their toxicity. For example, the early oligomeric species of the amyloid-β (Aβ) peptide have been implicated as the most cytotoxic species in Alzheimer's disease but are difficult to identify because of their dynamic and transitory nature. Conventional aggregation monitors such as the fluorescent dye thioflavin T report on only the overall transition of the soluble species to the final amyloid fibrillar aggregated state. Here, we show that the fluorescent dye bis(triphenylphosphonium) tetraphenylethene (TPE-TPP) identifies at least three distinct aggregation intermediates of Aβ. Some atomic-level features of these intermediates are known from solid state nuclear magnetic resonance spectroscopy. Hence, the TPE-TPP fluorescence data may be interpreted in terms of these Aβ structural transitions. Steady state fluorescence and lifetime characteristics of TPE-TPP distinguish between the small oligomeric species (emission wavelength maximum, λmax = 465 nm; average fluorescence lifetime, τFl measured at 420 nm = 3.58 ± 0.04 ns), the intermediate species (λmax = 452 nm; τFl = 3.00 ± 0.03 ns), and the fibrils (λmax = 406 nm; τFl = 5.19 ± 0.08 ns). Thus, TPE-TPP provides a ready diagnostic for differentiating between the various, including the toxic, Aβ aggregates and potentially can be utilized to screen for amyloid aggregation inhibitors.

Cationic Organic Nanoaggregates as AIE Luminogens for Wash-Free Imaging of Bacteria and Broad-Spectrum Antimicrobial Application.

The increase in the use of bactericides is a matter of grave concern and a serious threat to human health. The present situation demands rapid and efficient detection and elimination of antibiotic-resistant microbes. Herein, we report the synthesis of a simple C3-symmetric molecular system (TGP) with an intrinsic positive charge through a single-step Schiff base condensation. In a water-dimethyl sulfoxide (DMSO) solvent mixture (80:20 v/v), TGP molecules self-aggregate to form spherical nanoparticles with a positively charged surface that displays efficient fluorescence owing to the aggregation-induced emission (AIE) phenomenon. Both Gram-positive and Gram-negative bacteria could be effectively detected through "turn-off" fluorescence spectroscopy as the electrostatic interaction of the resultant nanoaggregates with the negatively charged bacterial surface induced quenching of fluorescence of the nanoparticles. The fluorescence analysis and steady-state lifetime studies of TGP nanoparticles suggest that a nonradiative decay through photoinduced electron transfer from the nanoparticles to the bacterial surface leads to effective fluorescence quenching. Further, the TGP nanoaggregates demonstrate potent antimicrobial activity against microbes such as multidrug-resistant bacteria and fungi at a concentration as low as 74 μg/mL. A combination of factors including ionic surface characteristics of the nanoparticles for strong electrostatic binding on the bacterial surface followed by possible photoinduced electron transfer from the nanoaggregates to the bacterial membrane and enhanced oxidative stress in the membrane resulting from reactive oxygen species (ROS) generation is found accountable for the high antimicrobial activity of the TGP nanoparticles. The effective disruption of membrane integrity in both Gram-positive and Gram-negative bacteria upon interaction with the nanoaggregates can be observed from field emission scanning electron microscopy (FESEM) studies. The development of simple pathways for the molecular design of multifunctional broad-spectrum antimicrobial systems for rapid and real-time detection, wash-free imaging, and eradication of drug-resistant microbes might be crucial to combat pathogenic agents.

Systematic spectroscopic investigation of structural changes and corona formation of bovine serum albumin over magneto-fluorescent nanoparticles.

Magneto-fluorescent nanoparticles have attracted great attention because of their dual nature as multimodal imaging probes in various biomedical applications. Particulary, it is desirable to understand how these nanoparticles interact with human serum proteins before they are used in biological systems. In this work, the physiological interactions between magneto-fluorescent nanoparticles (MFNPs) and bovine serum albumin (BSA) were systematically investigated. The present observations identified that the collision of MFNPs and BSA caused fluorescence quenching of BSA. Steady state fluorescence, lifetime and anisotropy measurements in the presence of MFNPs supported dynamic quenching of the BSA emission. Furthermore, in the presence of MFNPs, the conformation changes in the BSA structure indicate merely the secondary structural changes. The findings demonstrated that random interactions and hydrophobic forces play a major role in the dynamic quenching. Further, subsequent coating of BSA over MFNPs result in protein corona formation, as is evident through spectroscopic measurements. In light of the present work, MFNPs could serve a purpose in magnetic separation and optical detection of serum proteins from blood plasma in real-time disease diagnosis.

Tracking the Fluorescence Lifetimes of Cesium Lead Halide Perovskite Nanocrystals During Their Synthesis Using a Fully Automated Optofluidic Platform

Semiconductive metal halide perovskites have opened exciting opportunities in a range of optoelectronic applications including solar cells, photodetectors, lasers, and light emitting devices. Recently, all-inorganic cesium lead halide (CsPbX3; X = Cl, Br, I) nanocrystals have become attractive light sources due to their high photoluminescence quantum yields, narrow emission linewidths, and emission color tunable over the entire visible region. Their radiative rates are higher (i.e., luminescence lifetimes shorter) than those of more conventional quantum dots, making perovskite NCs brighter emitters, highly attractive as both classical and quantum light sources. Multiple factors—primarily synthesis parameters and postsynthetic experience—govern the observed radiative lifetime and other optical characteristics. High-throughput experimentation in microfluidic platforms equipped with in-line optical characterization had proven to be highly instrumental for rapid and accurate assessment of optical properties, mainly in a steady-state mode. Thus far, in-line measurement of the radiative lifetimes and hence the proper use of high-throughput experimentation for tailored engineering of radiative rates have been elusive. Herein, we showcase a fully automated optofluidic platform that integrates time-correlated single photon counting measurements in droplet-based flow for the rigorous extraction of fluorescence lifetimes of CsPbX3 nanocrystals. The sensitivity of the experimental setup allows for measurements at a single-droplet level. Such concurrent time-resolved photoluminescence allows mapping the parametric space in a time-efficient manner (∼1000 lifetime measurements in 5 h of operation) and with high reagent economy (200 nL reaction volume per measurement). We elucidated the effects of composition and ratios of judiciously chosen reagents, as well as temperature on the fluorescence lifetimes (5–42 ns). Specifically, the average lifetime as well as the emission spectra of all halide compositions tested was strongly dependent on Pb-to-Cs variations. Accordingly a correlation between the steady-state luminescence amplitude and fluorescence lifetimes was established, thus providing a simple method to differentiate between the photoluminescence quantum yields, concentration effects, and effects due to the nonradiative recombination at the surface traps. Such a microfluidic tool will aid in analyzing the physicochemical and photophysical properties of diverse perovskite nanocrystals and other luminescent materials produced in the liquid-state synthesis.

NO3 and N2O5 chemistry at a suburban site during the EXPLORE-YRD campaign in 2018

During the EXPLORE-YRD campaign (EXPeriment on the eLucidation of the atmospheric Oxidation capacity and aerosol foRmation, and their Effects in Yangtze River Delta) in May–June 2018, we measured N2O5, NO2, O3 and relevant parameters at a regional site in Taizhou, Jiangsu Province. The nocturnal average NO3 production rate was 1.01 ± 0.47 ppbv h−1, but the mixing ratio of N2O5 was low, with a maximum of 220 pptv in 1 min, suggesting rapid loss of NO3 and N2O5. The nocturnal steady-state lifetime of N2O5 was 43 ± 52 s on average, which may be attributed to the elevated monoterpene and fast N2O5 uptake. VOCs (mainly monoterpenes) dominated daily NO3 loss with the percentage of 36.4% and N2O5 uptake accounted for 14.4%, when taking NO + NO3 and NO3 photolysis into consideration. We demonstrated that the nonnegligible daytime NO3 oxidation of monoterpene in YRD region, which contributes to the daytime formation of organic nitrate and secondary organic aerosol. The daily average NOx consumption rate via rapid NO3 reaction reached 0.63 ppbv h−1, corresponding to 57.3% NOx loss in comparison with the OH oxidation pathway at this site, highlighting the key role of NO3 and N2O5 in NOx removal and subsequent photochemistry in the YRD region.

Luminescence and nonlinear optical properties of Er3+- doped ZnWO4 nanostructures

Monoclinic ZnWO4 nanostructures with various concentration of Er were prepared by hydrothermal approach. The synthesized nanostructures were characterized by UV–vis spectra, X-ray diffraction (XRD) technique, steady-state and time-resolved fluorescence lifetime measurements. XRD results confirmed that Er3+ ions were successfully incorporated into ZnWO4 lattice without any secondary phase formation. The incorporation and energy transfer of Er into ZnWO4 were revealed by emission spectra and lifetime decay curves. The nonlinear optical properties of the nanostructures were studied by continuous wave Z-scan technique at 532 nm using Nd: YAG laser. From the open aperture and closed aperture Z-scan traces, the extracted nonlinear absorption and refraction data are attributed to reverse saturable absorption and self-defocusing nature of the samples. The optical nonlinearity of the nanostructures was found to be increasing with increased Er3+ dopant concentration. The observed nonlinearity suggests that the synthesized nanostructures could be explored for its applications in advanced photonic devices.

Aluminum chloride phthalocyanine in MCF-7: Rationally accounting for state of aggregation of photosensitizers inside cells

Current limited understanding of the intracellular self-aggregation process of several photosensitizers is one of the obstacles in the progress of Photodynamic Therapy (PDT) as a clinically viable option to photomodulate the biological responses. This is further intensified by the higher in vitro experimental complexity as compared to the experiments carried out in simple solution. This study describes the monomer(photoactive)/aggregate(non-active) equilibrium of aluminum chloride phthalocyanine (AlClPc) within the human breast adenocarcinoma cell line, MCF-7. Steady-state fluorescence and fluorescence lifetime imaging microscopy demonstrated that there was an upper limit of the amount of monomeric AlClPc inside cells, which might be influenced by the high water content inside the biological tissue. In this process, high AlClPc concentrations triggered the aggregation process while lowering its monomeric active form. The monomer/aggregates equilibrium can be modulated even inside cell typically through cell replication process, which decreases the AlClPc content inside each cellular unit. The results underline the need for new strategies in order to enhance the AlClPc monomerization within cells, especially in key organelles for PDT including mitochondria and lysosome membrane. This study demonstrates a rational approach for the study of the state of aggregation of photosensitizers inside cells, which is a critical issue to be considered for PDT efficacy.

Time Dependence of Transient Radiative Excess Carrier Lifetimes and Carriers Density in Indium Antimonide(InSb) Semiconductor in the Presence and Absence of Illumination

In this work, we models the optical generation and transient radiative recombination excess carrier lifetimes in direct band gap semiconductors Indium antimonide (Insb) during illumination and after switching off the illumination. The time dependence of excess carrier density and excess carrier lifetimes are determined by using the doping level 1017cm-3 and absorption rate 1:21x1024cm-3s-1. The transient mean times for each excess carrier lifetimes to reach their steady-state values and excess carrier lifetime are determined.

Silver Nanoparticle Gradient Arrays: Fluorescence Enhancement of Organic Dyes.

Noble metal nanoparticles show pronounced extinction peaks in the visible wavelength range due to their localized surface plasmon resonances. The excitation of these resonances leads to strong confinement of electromagnetic energy at nanometer scales, which is critical for ultrasensitive, fluorescence-based detection of analytes. The strength and spatial distribution of this near-field zone depend on particle size, shape, and composition. To determine how these near-field effects depend on the particle size, we have prepared nanoparticle gradients on centimeter-scale substrates using a colloid-based approach. This plasmonic gradient is used to study the steady-state emission and fluorescence lifetime of a common organic dye that was embedded into the monolayer.

Switchable Dual-Emissive DNA-Stabilized Silver Nanoclusters.

We investigated an ss-DNA sequence that can stabilize a red- and a green-emissive silver nanocluster (DNA-AgNC). These two emitters can convert between each other in a reversible way. The change from red- to green-emitting DNA-AgNCs can be triggered by the addition of H2O2, while the opposite conversion can be achieved by the addition of NaBH4. Besides demonstrating the switching between red- and green-emissive DNA-AgNCs and determining the recoverability, we fully characterized the photophysical properties, such as steady-state emission, quantum yield, fluorescence lifetime, and anisotropy of the two emissive species. Understanding the mechanism behind the remarkable conversion between the two emitters could lead to the development of a new range of DNA-AgNC-based ratiometric sensors.

Steady-state recombination lifetimes in polar InGaN/GaN quantum wells by time-resolved photoluminescence

Both the steady-state radiative and nonradiative recombination lifetimes of excess carriers in polar InGaN/GaN quantum wells are extracted by a novel technique. Instead of the conventional ultrashort-pulsed laser, a modulated CW laser is utilized as the excitation source in time-resolved photoluminescence (PL) experiments to obtain the steady-state lifetimes. By analyzing the dependence of the PL lifetime and the integrated PL intensity on the injected power density simultaneously, both the radiative and Shockley–Read–Hall (SRH) recombination lifetimes can be determined accurately. The proposed method is applied to study the radiative and nonradiative processes in polar InGaN/GaN quantum wells with various well widths. The results suggest that both the SRH lifetime of holes and the radiative recombination lifetime increase drastically with increasing well width, while the SRH lifetime of electrons exhibits a weaker dependence on well width.

Metal substituted metalloporphyrins as efficient photosensitizers for enhanced solar energy conversion

The electron transfer dynamics of tetra(4-carboxyphenyl)porphyrin with different central metal ions Fe(III), Cu(II), Co(II),Ni(II), Zn(II) adsorbed on ZnO nanorods have been investigated by using photophysical and electrochemical studies. Spectroscopic studies confirmed that metalloporphyrins anchored onto ZnO through the carboxylic group. XPS studies indicated that replacement of free base porphyrin with different metals resulted in change in symmetry with uniform distribution of electron density of nitrogen atom of pyrrole ring which gives one broad peak of N1S state. Absorption studies revealed the bathochromic shift of soret band in ZnO-TCPPM nanocomposites as compare to free base porphyrin and metalloporphyrins owing to the electronic coupling between ZnO and TCPPM which stabilize the π* orbital. The photoluminescence properties of metalloporphyrins are shown to be highly dependent on central metal atom. Steady state and PL lifetime measurements studies shows the electron transfer in ZnO-TCPPM occurred feasibly for TCPPZn sensitizer as Zn(II)porphyrin have long lived excited state as compare to other metalloporphyrins. Improved photovoltaic properties of the metalloporphyrins are originated from electron injection driving force from dye to ZnO. Introduction of metal in porphyrin cavity increase the electron transfer process. Incase of TCPPCo, TCPPNi fast recombination exists between metal cation and photogenerated electron that inhibits the photocurrent generation. J–V Characteristics revealed there is 4.5 fold increases in efficiency for ZnO-TCPPM device as compare to device composed of free base porphyrin.

The Effect of Lithium Binding on Secondary and Tertiary Structure, Hydrophobicity, Thermodynamics, and Interactions with Interacting Partners of Dream

Li+ is widely used for the treatment of manic-depressive illness. Studies on neuronal calcium sensor protein1 (NCS-1) have found that Li+ can inhibit the interaction between NCS-1 and inositol 1,4,5-triphosphate receptor protein, alleviating hyperarousal of insomnia patient. Li+ can have neuroprotective or neurotoxic effects depending on its concentration. In a rat model, chronic exposure to Li+ has shown a significant decrease in membrane-associated protein kinase C (PKC) in the hippocampus, suggesting potential clinical relevance. Here, we show that Li+ binds to a neuronal calcium sensor protein named Downstream Element Antagonist Modulator (DREAM), a protein homologous to NCS-1 and expressed in the hippocampus region of the brain. Li+ association results in a decrease in the emission intensity of tryptophan, suggesting rearrangements of the tertiary structure of the protein. Li+ binding also exposes hydrophobic cavity of the protein as evidenced by binding of the hydrophobic molecule 1,8-ANS. CD data reveal that Li+ binding alters the protein secondary structure. Tryptophan emission and CD data are further supported by steady-state lifetime data. Thermodynamic parameters for Li+ association to DREAM have been obtained through isothermal titration calorimetry (ITC) measurements. Li+-bound DREAM interactions with binding partners have been probed by titrating FITC-tagged presenilin-1 and potassium channel against Li+-bound DREAM. Findings of this project suggest potentials for the Li+-based compounds in the animal model to investigate whether acute and chronic exposure to Li+ has any effect on the expression level of DREAM and whether Li+-based compounds influence interactions between DREAM and intracellular partners.

Multicharacteristic Behavior of Tyrosine Present in the Microdomains of the Macromolecule Gum Arabic at Various pH Conditions.

Gum arabic (GA), the dried exudates of Acacia seyal and Acacia senegal trees, being a biopolymer, has found many applications in the food, pharmaceutical, cosmetic, and lithography industries. GA, a water-soluble food hydrocolloid, is a complex and variable mixture of arabinogalactan oligosaccharides, polysaccharides, and glycoproteins. It has been a subject of great interest and a wide range of research has been done on the polysaccharide structural aspects and the emulsifying properties only. In the present study, fluorescence spectral technique is employed as an analytical tool to understand the photophysics of GA. The tyrosine microenvironment of GA was explored by studying the steady-state absorption, emission, fluorescence lifetime, and three-dimensional (3D) emission contour spectra of GA at various pH conditions in aqueous solution. The multiple emissive states are attributed to the presence of intrinsic fluorophore tyrosine in a heterogeneous microenvironment. The study portrays the multicharacteristic behavior of tyrosine in various pH conditions and in different microdomains. The exposure of the buried tyrosine to the heterogeneous aqueous phase was authenticated by 3D emission contour spectral studies. An interesting visualization of tyrosine involving in hydrogen-bonding network with another tyrosine moiety at neutral pH was ascertained. The coexistence of hydrophilic carbohydrate and hydrophobic protein in GA enables its emulsification and stabilization properties. Hence, any advancement toward understanding the protein microenvironment of GA is of great significance for chemists, as the molecular modeling and biosynthesis of the gum with desired end product are underway in many research institutes.

Temperature-dependent photoluminescence spectra and decay dynamics of MAPbBr3 and MAPbI3 thin films

The steady-state spectra and fluorescence lifetimes are investigated under vacuum for methylammonium lead bromide and iodide (CH3NH3PbBr3 or MAPbBr3, and CH3NH3PbI3 or MAPbI3) thin films by stably controlling the sample temperature in the range of 78 K to 320 K. The transformation of spectrum features and lifetime components are proved to be quite sensitive to the temperatures in accordance with the phase transition of structures. Our work demonstrates that the halide anions I- and Br- lead to remarkable differences on optical characteristics. Due to the distinct behaviors of excitons, electron-hole pairs and free carriers in decay channels, MAPbI3 has much longer lifetime and higher low-temperature fluorescence efficiency than those of MAPbBr3. The findings provide possible choices for certain perovskites under various ambient temperature conditions to display photovoltaic or luminescent advantage.

On the nature of interaction between Pd nanoparticles and C3N4 support

C3N4 samples were prepared by thermal decomposition of urea and Pd nanoparticles were uniformly dispersed on it by electron beam irradiation technique. From XRD, FTIR and TEM studies it is inferred that C3N4 network and its morphology are unaffected with Pd incorporation. However, UV–Visible optical absorption, steady state luminescence and lifetime measurements have confirmed that, there exists charge transfer from C3N4 network to Pd nanoparticles. Effective mixing of Pd nanoparticles with C3N4 and subsequent Pd catalyzed decomposition of C3N4 is inferred from Thermo-gravimetric studies. Hydrogen storage capacity of C3N4 increases with Pd nanoparticle incorporation.

Mesoporous silica for drug delivery: Interactions with model fluorescent lipid vesicles and live cells

Formulated mesoporous silica nanoparticle (MSN) systems offer the best possible drug delivery system through the release of drug molecules from the accessible pores. In the present investigation, steady state and time resolved fluorescence techniques along with the fluorescence imaging were applied to investigate the interactions of dye loaded MSN with fluorescent unilamellar vesicles and live cells. Here 1,2-dimyristoyl-sn-glycero-3-phospocholine (DMPC) was used to prepare Small Unilamellar Vesicles (SUVs) as the model membrane with fluorescent 1,6-diphenyl-1,3,5-hexatriene (DPH) molecule incorporated inside the lipid bilayer. The interaction of DPH incorporated DMPC membrane with Fluorescein loaded MSN lead to the release of Fluorescein (Fl) dye from the interior pores of MSN systems. The extent of release of Fl and spatial distribution of the DPH molecule has been explored by monitoring steady-state fluorescence intensity and fluorescence lifetime at physiological condition. To investigate the fate of drug molecule released from MSN, fluorescence anisotropy has been used. The drug delivery efficiency of the MSN as a carrier for doxorubicin (DOX), a fluorescent chemotherapeutic drug, has also been investigated at physiological conditions. The study gives a definite confirmation for high uptake and steady release of DOX in primary oral mucosal non-keratinized squamous cells in comparison to naked DOX treatment.

An Eccentricity Based Data Routing Protocol with Uniform Node Distribution in 3D WSN.

Due to nonuniform node distribution, the energy consumption of nodes are imbalanced in clustering-based wireless sensor networks (WSNs). It might have more impact when nodes are deployed in a three-dimensional (3D) environment. In this regard, we propose the eccentricity based data routing (EDR) protocol in a 3D WSN with uniform node distribution. It includes network partitions called 3D subspaces/clusters of equal member nodes, an energy-efficient routing centroid (RC) nodes election and data routing algorithm. The RC nodes election conducts in a quasi-static nature until a certain period unlike the periodic cluster heads election of typical clustering-based routing. It not only reduces the energy consumption of nodes during the election phase, but also in intra-communication. At the same time, the routing algorithm selects a forwarding node in such a way that balances the energy consumption among RC nodes and reduces the number of hops towards the sink. The simulation results validate and ensure the performance supremacy of the EDR protocol compared to existing protocols in terms of various metrics such as steady state and network lifetime in particular. Meanwhile, the results show the EDR is more robust in uniform node distribution compared to nonuniform.