Search

In this work, we investigated for the first time morin in MeOH at different pH values by picosecond time-resolved fluorescence. We identified the two species responsible for the fluorescence at low and high pH. The solvated morin-solvent hydrogen-bonded complex has been experimentally observed for the first time. We give also the typical fluorescence spectra as well as the fluorescence lifetimes of the probable emitting species. In this work we put forward new insights concerning the contribution of free morin to the fluorescence. We hope that these new data improve the accuracy of the interpretation of the cation:morin complexes titration using fluorescence signal., (© 2020 Wiley-VCH GmbH.)

Fluorescent probes for detecting the physical properties of cellular structures have become valuable tools in life sciences. The fluorescence lifetime of molecular rotors can be used to report on variations in local molecular packing or viscosity. We used a nucleoside linked to a meso-substituted BODIPY fluorescent molecular rotor (dC(bdp)) to sense changes in DNA microenvironment both in vitro and in living cells. DNA incorporating dC(bdp) can respond to interactions with DNA-binding proteins and lipids by changes in the fluorescence lifetimes in the range 0.5-2.2 ns. We can directly visualize changes in the local environment of exogenous DNA during transfection of living cells. Relatively long fluorescence lifetimes and extensive contrast for detecting changes in the microenvironment together with good photostability and versatility for DNA synthesis make this probe suitable for analysis of DNA-associated processes, cellular structures, and also DNA-based nanomaterials., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Fluorescing proteins emitting in the near-infrared region are of high importance in various fields of biomedicine and applied life sciences. Promising candidates are phytochromes that can be engineered to a small size and genetically attached to a target system for in vivo monitoring. Here, we have investigated two of these minimal single-domain phytochromes, miRFP670nano3 and miRFP718nano, aiming at a better understanding of the structural parameters that control the fluorescence properties of the covalently bound biliverdin (BV) chromophore. On the basis of resonance Raman and time-resolved fluorescence spectroscopy, it is shown that in both proteins, BV is deprotonated at one of the inner pyrrole rings (B or C). This protonation pattern, which is unusual for tetrapyrroles in proteins, implies an equilibrium between a B- and C-protonated tautomer. The dynamics of the equilibrium are slow compared to the fluorescence lifetime in miRFP670nano3 but much faster in miRFP718nano, both in the ground and excited states. The different rates of proton exchange are most likely due to the different structural dynamics of the more rigid and more flexible chromophore in miRFP670nano3 and miRFP718nano, respectively. We suggest that these structural properties account for the quite different fluorescent quantum yields of both proteins. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: The problem of molecular diffusion in the soup of chemical reactions attracts mounting interest across fields ranging from chemistry to biophysics to material science. Chemical reactions involve bond breakup and formation, whose time scale is typically on the orders of fs to ps, while molecular diffusion occurs at time scales of μs to ms. The two processes are often considered orthogonal, given the vastly different scales. The serial results show that the enzyme's diffusion is enhanced in a substrate‐dependent manner, which was further extended to small molecule reaction systems, challenging this classical paradigm. However, the results from different groups using different techniques do not quantitatively agree, and a general mechanism is yet to be understood. We summarize experimental studies on diffusion problems and seek to reconcile the interpretation with understanding the limits of measurement tools and the chemical nature of reaction systems. Understanding molecular diffusion in chemical reactions will provide fresh thoughts in designing chemical systems such as molecular machines that harvest work at the nanoscale in a controllable manner. [ABSTRACT FROM AUTHOR]

Parametric superfluorescence (PSF), which originated from the optical amplification of vacuum quantum noise, is the primary noise source of femtosecond fluorescence non-collinear optical parametric amplification spectroscopy (FNOPAS). It severely affects the detection limit of FNOPAS to collect the femtosecond time-resolved spectra of extremely weak fluorescence. Here, we report the development of femtosecond fluorescence conical optical parametric amplification spectroscopy (FCOPAS), aimed at effectively suppressing the noise fluctuation from the PSF background. In contrast to traditional FNOPAS configurations utilizing lateral fluorescence collection and dot-like parametric amplification, FCOPAS employs an innovative conical fluorescence collection and ring-like amplification setup. This design enables effective cancellation of noise fluctuation across the entire PSF ring, resulting in an approximate order of magnitude reduction in PSF noise compared to prior FNOPAS outcomes. This advancement enables the resolution of transient fluorescence spectra of 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) dye molecules in ethanol, even at an optically dilute concentration of 10−6 mol/l, with significantly enhanced signal-to-noise ratios. This improvement will be significant for extremely weak fluorescence detection on the femtosecond time scale. [ABSTRACT FROM AUTHOR]

Latent fingerprints were successfully visualized using fluorescence lifetime imaging (FLIM) on paper which emits strong fluorescence with a lifetime close to that of fingerprints and thus from which it is difficult for time‐resolved spectroscopy to visualize fingerprints. Latent fingerprint samples on paper were excited using a 450 nm or 532 nm nanosecond pulsed‐laser, and time‐resolved fluorescence images were obtained at a delay time of 6–16 ns in intervals of 1 ns, to the excitation pulse. The excitation beam was expanded using a lens, and the fluorescence from the fingerprints was captured using an intensified CCD camera. Because of the large fluorescence intensity of the background paper of approximately two to four orders of magnitude larger than that of the fingerprint, the fingerprint was not visualized on each fluorescence image by time‐resolved spectroscopy. However, the fingerprint was visualized in a FLIM image constructed using a series of the fluorescence images for the case with the fluorescence intensity of the background paper being four orders of magnitude larger than that of the fingerprint. The difference in fluorescence lifetime in the FLIM image of the visualized fingerprint and background paper was in the order of 0.1 ns, which was an order of magnitude smaller than the inherent fluorescence lifetime of a few nanoseconds for the fingerprints and paper. It was demonstrated that, at a background fluorescence intensity with a certain order of magnitude larger than that of fingerprints, FLIM has the potential to visualize latent fingerprints which cannot be visualized by time‐resolved spectroscopy. [ABSTRACT FROM AUTHOR]

Conventional single-component quantum dots (QDs) suffer from low recombination rates of photogenerated electrons and holes, which hinders their ability to meet the requirements for LED and laser applications. Therefore, it is urgent to design multicomponent heterojunction nanocrystals with these properties. Herein, we used CdSe quantum dot nanocrystals as a typical model, which were synthesized by means of a colloidal chemistry method at high temperatures. Then, CdS with a wide band gap was used to encapsulate the CdSe QDs, forming a CdSe@CdS core@shell heterojunction. Finally, the CdSe@CdS core@shell was modified through the growth of the ZnS shell to obtain CdSe@CdS@ZnS heterojunction nanocrystal hybrids. The morphologies, phases, structures and performance characteristics of CdSe@CdS@ZnS were evaluated using various analytical techniques, including transmission electron microscopy, X-ray diffraction, UV-vis absorption spectroscopy, fluorescence spectroscopy and time-resolved transient photoluminescence spectroscopy. The results show that the energy band structure is transformed from type II to type I after the ZnS growth. The photoluminescence lifetime increases from 41.4 ns to 88.8 ns and the photoluminescence quantum efficiency reaches 17.05% compared with that of pristine CdSe QDs. This paper provides a fundamental study and a new route for studying light-emitting devices and biological imaging based on multicomponent QDs. [ABSTRACT FROM AUTHOR]

The aim of this study was to demonstrate the utility of time-resolved fluorescence spectroscopy in the detection of subtle changes in the local microenvironment of a tryptophan chromophore in a confined and crowded medium of AOT reverse micelles, which mimic biological membranes and cell compartmentalization. For this purpose, fluorescence properties of L-tryptophan and several newly synthesized tryptophan-containing peptides in buffer and in an AOT reverse micelle medium were determined. It was shown that insertion of tryptophan and its short di- and tripeptides inside micelles led to evident changes in both the steady-state emission spectra and in fluorescence decay kinetics. The observed differences in spectral characteristics, such as a blue shift in the emission maxima, changes in the average fluorescence lifetime, and the appearance of environmental-dependent fluorescent species, showed the utility of time-resolved fluorescence spectroscopy as a sensitive tool for detecting subtle conformational modifications in tryptophan and its peptides induced by changes in polarity, viscosity, and specific interactions between chromophores and water molecules/polar groups/ions that occur inside reverse micelles. [ABSTRACT FROM AUTHOR]

The development of biocompatible composites constituted by polydopamine and fluorescent carbon dots represents a promising way of exploiting the extraordinary adhesive properties of polydopamine for multi-purpose technologies. Here, a supramolecular complex is realized by the assembly of dopamine on the carbon dots surface, and the optical and structural properties are investigated by means of different spectroscopic techniques, from time-resolved fluorescence to Raman and NMR spectroscopies. The results suggest that the catechol unit of dopamine plays the main role in the formation of the supramolecular complex, in which carbon nanodot fluorescence emission is quenched by a photoinduced electron transfer process. The interaction with the nanodots' basic surface sites promotes the oxidation of dopamine and drives to its oligomerization/polymerization on the nanodot surface. [ABSTRACT FROM AUTHOR]

The dynamics of molecular systems can be studied with time-resolved spectroscopy combined with model-based analysis. A Python framework for global and target analysis of time-resolved spectra is introduced with the help of three case studies. The first study, concerning broadband absorption of intersystem crossing in 4-thiothymidine, demonstrates the framework's ability to resolve vibrational wavepackets with a time resolution of ≈10 fs using damped oscillations and their associated spectra and phases. Thereby, a parametric description of the "coherent artifact" is crucial. The second study addresses multichromophoric systems composed of two perylene bisimide chromophores. Here, pyglotaran's guidance spectra and lego-like model composition enable the integration of spectral and kinetic properties of the parent chromophores, revealing a loss process, the undesired production of a radical pair, that reduces the light harvesting efficiency. In the third, time-resolved emission case study of whole photosynthetic cells, a megacomplex containing ≈500 chromophores of five different types is described by a combination of the kinetic models for its elements. As direct fitting of the data by theoretical simulation is unfeasible, our global and target analysis methodology provides a useful 'middle ground' where the theoretical description and the fit of the experimental data can meet. The pyglotaran framework enables the lego-like creation of kinetic models through its modular design and seamless integration with the rich Python ecosystem, particularly Jupyter notebooks. With extensive documentation and a robust validation framework, pyglotaran ensures accessibility and reliability for researchers, serving as an invaluable tool for understanding complex molecular systems. [ABSTRACT FROM AUTHOR]

In this work, we monitored the fluorescence quantum efficiency (η) and the fluorescence lifetime (τ) of natural dye extracts from the leaves of Tradescantia pallida purpurea. The natural dye was extracted from leaves in aqueous solutions as a function of the potential of hydrogen (pH). The η was determined from conical diffraction (CD) pattern measurements due to thermally-driven self-phase modulation. The fluorescence spectra and time-resolved fluorescence measurements corroborate the CD results, and the average η ≈ 0.28 and τ ≈ 3.1 ns values were obtained in the pH range 3.96–8.02. In addition, the extracted natural dye was tested as a possible colorimetric and/or fluorometric pH indicator in milk.

Possible use of Thioflavin T based fluorescent molecular rotors as temperature sensors was assessed in this work. Fluorescent properties of Thioflavin T and its derivative 6-Me-BTA-2C in 99% glycerol were studied using steady-state and time-resolved fluorescence spectroscopy methods. For Thioflavin T in glycerol it has been found that temperature growth from 261 to 353 K results in ~3 orders of magnitude increase of non-radiative decay rate constant knr for the excited state of the molecule. Fluorescence decay studies by time-correlated single photon counting method showed that fluorescence decay kinetics of Thioflavin T in glycerol can be used for temperature measurements in the range 260–290 K. For 6-Me-BTA-2C molecule the range of the maximal sensitivity was shifted to higher temperatures (280–320 K). The obtained results about fluorescent properties and decay kinetics of Thioflavin T based dyes in highly viscous media can be used to develop nanoscale temperature sensors. [ABSTRACT FROM AUTHOR]

Two four-coordinate organoboron N,C-chelate complexes with different functional terminals on the PEG chains are studied with respect to their photophysical properties within human MCF-7 cells. Their excited-state properties are characterized by time-resolved pump-probe spectroscopy and fluorescence lifetime microscopy. The excited-state relaxation dynamics of the two complexes are similar when studied in DMSO. Aggregation of the complexes with the carboxylate terminal group is observed in water. When studying the light-driven excited-state dynamics of both complexes in cellulo, i. e., after being taken up into human MCF-7 cells, both complexes show different features depending on the nature of the anchoring PEG chains. The lifetime of a characteristic intramolecular charge-transfer state is significantly shorter when studied in cellulo (360±170 ps) as compared to in DMSO (-960 ps) at 600 nm for the complexes with an amino group. However, the kinetics of the complexes with the carboxylate group are in line with those recorded in DMSO. On the other hand, the lifetimes of the fluorescent state are almost identical for both complexes in cellulo. These findings underline the importance to evaluate the excited-state properties of fluorophores in a complex biological environment in order to fully account for intra- and intermolecular effects governing the light-induced processes in functional dyes. [ABSTRACT FROM AUTHOR]

The flavin derivatives 10-methyl-isoalloxazine (MIA) and 6-fluoro-10-methyl-isoalloxazine (6F-MIA) were incorporated in two alternative metal-organic frameworks, (MOFs) MIL-53(Al) and MOF-5. We used a post-synthetic, diffusion-based incorporation into microcrystalline MIL-53 powders with one-dimensional (1D) pores and an in-situ approach during the synthesis of MOF-5 with its 3D channel network. The maximum amount of flavin dye incorporation is 3.9 wt% for MIA@MIL-53(Al) and 1.5 wt% for 6F-MIA@MIL-53(Al), 0.85 wt% for MIA@MOF-5 and 5.2 wt% for 6F-MIA@MOF-5. For the high incorporation yields the probability to have more than one dye molecule in a pore volume is significant. As compared to the flavins in solution, the fluorescence spectrum of these flavin@MOF composites is broadened at the bathocromic side especially for MIA. Time-resolved spectroscopy showed that multi-exponential fluorescence lifetimes were needed to describe the decays. The fluorescence-weighted lifetime of flavin@MOF of 4 ± 1 ns also corresponds to those in solution but is significantly prolonged compared to the solid flavin dyes with less than 1 ns, thereby confirming the concept of "solid solutions" for dye@MOF composites. The fluorescence quantum yield (ΦF) of the flavin@MOF composites is about half of the solution but is significantly higher compared to the solid flavin dyes. Both the fluorescence lifetime and quantum yield of flavin@MOF decrease with the flavin loading in MIL-53 due to the formation of various J-aggregates. Theoretical calculations using plane-wave and QM/MM methods are in good correspondence with the experimental results and explain the electronic structures as well as the photophysical properties of crystalline MIA and the flavin@MOF composites. In the solid flavins, π-stacking interactions of the molecules lead to a charge transfer state with low oscillator strength resulting in aggregation-caused quenching (ACQ) with low lifetimes and quantum yields. In the MOF pores, single flavin molecules represent a major population and the computed MIA@MOF structures do not find π-stacking interactions with the pore walls but only weak van-der-Waals contacts which reasons the enhanced fluorescence lifetime and quantum yield of the flavins in the composites compared to their neat solid state. To analyze the orientation of flavins in MOFs, we measured fluorescence anisotropy images of single flavin@MOF-5 crystals and a static ensemble flavin@MIL53 microcrystals, respectively. Based on image information, anisotropy distributions and overall curve of the time-resolved anisotropy curves combined with theoretical calculations, we can prove that all fluorescent flavins species have a defined and rather homogeneous orientation in the MOF framework. In MIL-53, the transition dipole moments of flavins are orientated along the 1D channel axis, whereas in MOF-5 we resolved an average orientation that is tilted with respect to the cubic crystal lattice. Notably, the more hydrophobic 6F-MIA exhibits a higher degree order than MIA. The flexible MOF MIL-53(Al) was optimized essentially to the experimental large-pore form in the guest-free state with QuantumEspresso (QE) and with MIA molecules in the pores the structure contracted to close to the experimental narrow-pore form which was also confirmed by PXRD. In summary, the incorporation of flavins in MOFs yields solid-state materials with enhanced rigidity, stabilized conformation, defined orientation and reduced aggregations of the flavins, leading to increased fluorescence lifetime and quantum yield as controllable photo-luminescent and photo-physical properties. [ABSTRACT FROM AUTHOR]

In this work, we monitored the fluorescence quantum efficiency (η) and the fluorescence lifetime (τ) of natural dye extracts from the leaves of Tradescantia pallida purpurea. The natural dye was extracted from leaves in aqueous solutions as a function of the potential of hydrogen (pH). The η was determined from conical diffraction (CD) pattern measurements due to thermally-driven self-phase modulation. The fluorescence spectra and time-resolved fluorescence measurements corroborate the CD results, and the average η ≈ 0.28 and τ ≈ 3.1 ns values were obtained in the pH range 3.96–8.02. In addition, the extracted natural dye was tested as a possible colorimetric and/or fluorometric pH indicator in milk. [ABSTRACT FROM AUTHOR]

Amine groups are common constituents of organic dyes and play important roles in tuning fluorescence properties. In particular, intensive research works have demonstrated the tendency and capabilities of amines in influencing chromophore brightness. Such properties have been explained by multiple mechanisms spanning from twisted intramolecular charge transfer (TICT) to the energy gap law and beyond, which introduce additional nonradiative energy dissipation pathways. In this review, we aim to provide a focused overview of the mechanistic insights mainly for the TICT mechanism, accompanied by a few other less common or influential fluorescence quenching mechanisms in the amine-containing fluorescent molecules. Various aspects of current scientific findings including the rational design and synthesis of organic chromophores, theoretical calculations, steady-state and time-resolved electronic and vibrational spectroscopies are reviewed. These in-depth understandings of how the amine groups with diverse chemical structures at various atomic sites affect excited-state nonradiative decay pathways will facilitate the strategic and targeted development of fluorophores with desired emission properties as versatile chemosensors for broad applications. [ABSTRACT FROM AUTHOR]

Dopamine (DA) and its analogues are compounds of interest in polymer science where their properties provide a multitude of applications. However, in elucidating polydopamine structure, there are ambiguities related to the types of bonds, the structure of monomeric units, their ratio, and influence of synthesis parameters. In order to minimize these variables, isotopic labeling presents an optimal alternative. In the diversification and understanding of these polymers, we aim to investigate analogues that by selective isotopic labeling provide possibilities for structure elucidation both of the polymerized analogues as well as polydopamine. In the present paper we report the synthesis of three new dopamine derivatives, labeled *CL ((Z)-3-(3,4-bis(benzyloxy)phenyl)-2-cyano-2-propenamide) and both labeled and unlabeled DL/*DL (2-aminomethyl-3-(3,4-dihydroxyphenyl)propionamide). The labeled *CL and *DL compounds contain selective 13C and 15N labeling in the alkyl chain. For these new compounds, NMR, FT-IR and fluorescence characterization, including by time-resolved laser spectroscopy, are reported. [ABSTRACT FROM AUTHOR]

It is challenging to decouple typical protein-like chromophoric dissolved organic matter (CDOM) fluorophores from oil-related fluorophores in natural waters using standard steady-state fluorescence techniques. In the present work, time-resolved florescence spectroscopy was explored as a means of differentiating between these two types of fluorophores. Fluorescence lifetimes of oil products were measured as a function of excitation and emission wavelength in artificial seawater. A triexponential model gave τ 1 = ~1–10 ns, τ 2 = ~3–30 ns, and τ 3 = ~0.2–2 ns. Time-resolved fluorescence amplitudes were dominated by τ 3 (τ 3 55–65 %; τ 1 25–29 %; τ 2 11–16 %) and contributions to steady-state fluorescence were dominated by τ 1 and τ 2. Lifetimes increased with decreasing λ ex. Fluorescence was quenched by halide ions, but ion concentrations in natural waters are insufficient for quenching to significantly change lifetimes. Heavier, denser oils had red-shifted emission and lower lifetimes. Results suggest that time-resolved spectroscopy can decouple oil and protein-like CDOM fluorophores at λ ex < 300 nm. [Display omitted] • Fluorescence lifetimes of oils were measured in artificial seawater. • Oil and protein-like DOM fluorophores could be decoupled using lifetimes. • Photochemical aging of oils did not significantly affect lifetimes. • Fluorescence was quenched by halide ions found in seawater. [ABSTRACT FROM AUTHOR]

[Display omitted] • High Quantum Yield: The synthesized coumarin dyes exhibited high quantum yields, ranging from 0.55 to 0.94, indicating their efficiency in fluorescence. This property is essential for their potential use in sensitive fluorescence-based applications. • Solvent Sensitivity: The dyes demonstrated varying degrees of sensitivity to different solvents. This was assessed using UV fluorescence, time-correlated single photon counting (TCSPC), and time-resolved spectroscopy (TRES). This sensitivity is crucial for applications in solvent-based systems and molecular sensing. • Fluorescence Decay Characteristics: The study revealed that most dye-solvent combinations exhibited single exponential decay with lifetimes ranging from 2.3 to 3 ns. However, deviations from single exponential behavior were observed in specific solvent environments, providing insights into the dynamic interactions between the dyes and their solvent matrices. • Effect of Structural Modifications: The impact of different substituents on the coumarin core was significant. For instance, dyes with a piperazine moiety showed significant deviations in fluorescence behavior compared to those with methoxy groups, suggesting that the electronic properties of the substituents greatly influence the photophysical outcomes. • Interaction with Silica Nanoparticles: The interactions of the dyes with silica nanoparticles (Ludox) were explored, showing changes in the spectroscopic properties of the dyes. This result suggests potential applications in nanoparticle-based systems and could lead to new developments in nano-bio conjugates for imaging and sensing. • Potential for FRET Applications: Based on the fluorescence characteristics and quantum yields, the dyes were evaluated for their potential in fluorescence resonance energy transfer (FRET) experiments. This could be pivotal for developing advanced biosensors and molecular probes. Coumarin dyes are highly versatile and widely employed as fluorescent chemosensors in a variety of fields, including molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, biology, and medical science. Thanks to their outstanding photostability and high quantum yield, they represent an ideal choice for developing sensitive and selective sensing platforms. In this study, we successfully designed and synthesized four new dyes based on the coumarin dye molecular skeleton, investigating their solvent sensitivity and spectroscopic properties. Our novel coumarin dyes were synthesized by a straightforward approach, reacting coumarin-3-carboxylic acid succinimidyl ester derivatives with corresponding amines in 1,4-dioxane as a solvent. We carefully monitored the completion of the reactions using thin-layer chromatography (TLC) and characterized these dyes using spectral and elemental analyses. We further investigated the UV, fluorescence, time-correlated single photon counting (TCSPC) technique and time-resolved spectroscopy (TRES) of these dyes in different solvents and on polymer film poly(methyl methacrylate) (PMMA). The quantum yield of the synthesized dyes was determined, with values observed to range between 0.55 and 0.94. Most of the dye-solvent and dye-polymer combinations exhibited single exponential decay, with lifetimes ranging from 2.3 to 3 ns. Minor deviations from single exponential behavior were observed for most of the dyes in toluene, while significant deviations were observed for coumarin dyes with piperazine moiety. We have provided a rationalization of these results in terms of the chemical functionalities of the various dyes. Furthermore, we investigated the effect of interactions between 7-methoxy-2-oxo-N-(2-(piperazin-1-yl)ethyl)–2H-chromene-3-carboxamide and silica nanoparticles (Ludox) on the spectroscopic properties of these dyes, with charge transfer being one possible mechanism contributing to the behavior of the dyes. Additionally, we explored the effect of trifluoroacetic acid (TFA) on the dyes' emission intensity and fluorescence decay. Based on our UV and fluorescence measurements of the dyes in different solvents, we have concluded that these dyes can create excellent donor–acceptor pairs for our upcoming fluorescence resonance energy transfer (FRET) experiments. [ABSTRACT FROM AUTHOR]

Biocompatible luminophores based on organic dyes, which have fluorescence characteristics that are highly sensitive to the properties of the solvating medium, are of particular interest as highly sensitive, selective, and easy-to-use analytical agents. We found that BODIPY dimers (2,2′-, 2,3′-3,3′-CH2-bis(BODIPY) (1–3)) demonstrate fluorescence characteristics with a high sensitivity to the presence of polar solvents. The intense fluorescence of 1–3 in nonpolar/low-polarity solvents is dramatically quenched in polar media (acetone, DMF, and DMSO). It has been established that the main reason for CH2-bis(BODIPY) fluorescence quenching is the specific solvation of dyes by electron-donating molecules (Solv) with the formation of stable supramolecular CH2-bis(BODIPY)·2Solv structures. Using steady-state absorption and fluorescence spectroscopy, time-resolved fluorescence spectroscopy, and computational modeling, the formation mechanism, composition, and structure of CH2-bis(BODIPY)·2Solv supramolecular complexes have been substantiated, and their stability has been evaluated. The results show the promise of developing fluorescent probes based on CH2-bis(BODIPY)s for detecting toxic N/O-containing compounds in solutions. [ABSTRACT FROM AUTHOR]

Three benzofluorenone derivatives, benzo[a]fluorenone (BFA), benzo[b]fluorenone (BFB), and benzo[c]fluorenone (BFC), were studied spectroscopically in comparison with 9‐fluorenone (9‐FL) in solvents of various polarities to better understand the solvatochromism and excited‐state deactivation processes in these molecules. Time‐resolved transient absorption, steady‐state absorption, emission, and fluorescence lifetimes were utilized in this endeavor. Differences in the excited‐state deactivation processes are observed which can be attributed to the varied characters of the singlet and triplet excited states in these molecules which arise from structural differences and solvatochromism. The main deactivation pathway in all of the studied molecules was internal conversion (IC). Ignoring IC, the competition between intersystem crossing (ISC) and fluorescence is highly dependent on the molecule‐solvent system. BFA was found to decay mainly via a triplet state in cyclohexane but via fluorescence in ethyl acetate and acetonitrile. BFB was found to decay via both ISC to a triplet state and emission from the singlet state in cyclohexane but only via ISC in ethyl acetate and acetonitrile. Only emission from the singlet state was observed in BFC in all solvents. [ABSTRACT FROM AUTHOR]

The real-time monitoring of the intracellular pH in live cells with high precision represents an important methodological challenge. Although genetically encoded fluorescent indicators can be considered as a probe of choice for such measurements, they are hindered mostly by the inability to determine an absolute pH value and/or a narrow dynamic range of the signal, making them inefficient for recording the small pH changes that typically occur within cellular organelles. Here, we study the pH sensitivity of a green-fluorescence-protein (GFP)-based emitter (EGFP-Y145L/S205V) with the alkaline-shifted chromophore's pKa and demonstrate that, in the pH range of 7.5–9.0, its fluorescence lifetime changes by a factor of ~3.5 in a quasi-linear manner in mammalian cells. Considering the relatively strong lifetime response in a narrow pH range, we proposed the mitochondria, which are known to have a weakly alkaline milieu, as a target for live-cell pH measurements. Using fluorescence lifetime imaging microscopy (FLIM) to visualize the HEK293T cells expressing mitochondrially targeted EGFP-Y145L/S205V, we succeeded in determining the absolute pH value of the mitochondria and recorded the ETC-uncoupler-stimulated pH shift with a precision of 0.1 unit. We thus show that a single GFP with alkaline-shifted pKa can act as a high-precision indicator that can be used in a specific pH range. [ABSTRACT FROM AUTHOR]

Carbon nanomaterials endowed with significant luminescence have been synthesized for the first time from an abundant, highly localized waste, the wet pomace (WP), a semi-solid by-product of industrial olive oil production. Synthetic efforts were undertaken to outshine the photoluminescence (PL) of carbon nanoparticles through a systematic search of the best reaction conditions to convert the waste biomass, mainly consisting in holocellulose, lignin and proteins, into carbon dots (CDs) by hydrothermal carbonization processes. Blue-emitting CDs with high fluorescence quantum yields were obtained. Using a comprehensive set of spectroscopic tools (FTIR, Raman, XPS, and 1H/13C NMR) in combination with steady-state and time-resolved fluorescence spectroscopy, a rational depiction of WP-CDs structures and their PL properties was reached. WP-CDs show the up-conversion of PL capabilities and negligible cytotoxicity against two mammalian cell lines (L929 and HeLa). Both properties are excellent indicators for their prospective application in biological imaging, biosensing, and dynamic therapies driven by light. [ABSTRACT FROM AUTHOR]

Time-resolved fluorescence anisotropy (TRFA) provides key information on the dynamics of biomolecules and their interaction with ligands. However, since natural nucleosides are almost non-fluorescent, its application to DNA duplexes (dsDNA) requires fluorescent labels, which can alter dsDNA stability, hinder protein binding, and complicate interpretation of TRFA experiments due to their local motion. As shown here, thienoguanosine ( th G), a fluorescent analogue of guanosine, overcomes all these limitations. We recorded the TRFA decays of th G -labelled dsDNA of different lengths. th G behaved as a rigid, non-perturbing reporter, since no fast correlation time was recorded for any tested dsDNA. Due to its perfect stacking, only two correlation times, instead of the typical three, describe th G -labelled dsDNA rotational dynamics. Thanks to these features, we provided a complete description of the tumbling of the different dsDNA and their complexes with the Set and Ring Associated (SRA) domain of UHRF1, a key epigenetic regulator, obtaining values in excellent agreement with theoretical predictions. Moreover, th G was also found sensitive to SRA-induced base flipping of neighboring nucleobases. In the DNA label toolbox, th G thus stands out as a unique reporter for investigating the rotational dynamics of dsDNA and protein/dsDNA complexes. Thienoguanosine, a fluorescent analogue of guanosine, stands out in the DNA probe toolkit, as a rigid, non-perturbing reporter, with only two correlation times to describe dsDNA rotational dynamics. It allows a comprehensive description of the tumbling of dsDNA and their complexes with proteins, fully matching theoretical predictions. [Display omitted] • Thienoguanosine ( th G) behaves as a rigid, non-perturbing reporter in dsDNA. • Time-resolved fluorescence anisotropy of th G allows full dsDNA tumbling description. • Rotational correlation times of thG-labelled dsDNA ± protein fully match with theory • th G is sensitive to protein-induced base flipping of neighboring nucleobases • th G is unique in the toolkit of fluorescent DNA labels for monitoring DNA dynamics. [ABSTRACT FROM AUTHOR]

Electrospinning is an efficient technique to fabricate nanofibers of controlled diameter and uniform morphology. Herein, we report a low‐cost and high‐yield route to fabricate PAN/DAC composite nanofibers and its use for vapor sensing of 2,4‐Dinitrotoluene (DNT) and 2,4,6‐Trinitrotoluene (TNT) with a detection level in the range of parts‐per‐billion. Furthermore, the sensing ability and photo‐induced electron transfer mechanism of DAC towards DNT and TNT in the solution phase were also investigated in detail via absorption, steady‐state, and time‐resolved fluorescence spectroscopy and further supported by density function theory (DFT). The calculated Stern‐Volmer quenching constants, 810 M−1 (DNT) and 1170 M−1 (TNT), revealed that DAC is not much sensitive in solution‐phase because of the self‐condensation phenomenon of DAC molecules. This concern was addressed by the development of a fluorescent nanofiber probe constituting π‐electron‐rich carbazole (CZ) derivatives, namely 3,6‐Diaminocarbazole (DAC) as a fluorescent material and polyacrylonitrile (PAN) as a support polymatrix. This fluorophore‐doped nanofiber matrix was fabricated at a relatively lower wt% ratio (PAN:DAC::10:6), obtaining an average diameter of 857 nm and exhibited promising features in the vapor detection of DNT and TNT such as fast response time, excellent sensitivity and selectivity. Reduction of self‐condensation caused DAC molecules' fluorescence self‐quenching by simply employing the electrospinning technique to cast PAN/DAC nanofibrous film. This work promises a new aspect of sensitivity enhancement of carbazole molecular unit by amine modification and further incorporation into the polymer matrix. This nanofiber‐based sensor can lead to the design and development of highly efficient and field‐deployable vapor sensors for the detection of nitroaromatic compounds, with application in both explosive sensing and environment pollution. [ABSTRACT FROM AUTHOR]

Fluorescence properties of quantum dots (QDs) are critically affected by their redox states, which is important for practical applications. In this study, we investigated the optical properties of MoSe2-metallic phase quantum-dots (MoSe2-mQDs) depending on the pH variation, in which the MoSe2-mQDs were dispersed in water with two sizes (Φ~3 nm and 12 nm). The larger MoSe2-mQDs exhibited a large red-shift and broadening of photoluminescence (PL) peak with a constant UV absorption spectra as varying the pH, while the smaller ones showed a small red-shift and peak broadening, but discrete absorption bands in the acidic solution. The excitation wavelength-dependent photoluminescence shows that the PL properties of smaller MoSe2-mQDs are more sensitive to the pH change compared to those of larger ones. From the time-resolved PL spectroscopy, the excitons dominantly decaying with an energy of ~3 eV in pH 2 clearly show the shift of PL peak to the lower energy (~2.6 eV) as the pH increases to 7 and 11 in the smaller MoSe2-mQDs. On the other hand, in the larger MoSe2-mQDs, the exciton decay is less sensitive to the redox states compared to those of the smaller ones. This result shows that the pH variation is more critical to the change of photophysical properties than the size effect in MoSe2-mQDs. [ABSTRACT FROM AUTHOR]

KaiC, a core protein of the cyanobacterial circadian clock, consists of an N-terminal CI domain and a C-terminal CII domain, and assembles into a double-ring hexamer upon binding with ATP. KaiC rhythmically phosphorylates and dephosphorylates its own two adjacent residues Ser431 and Thr432 at the CII domain with a period of ~24 h through assembly and disassembly with the other clock proteins, KaiA and/or KaiB. In this study, to understand how KaiC alters its conformation as the source of circadian rhythm, we investigated structural changes of an inner-radius side of the CII ring using time-resolved Trp fluorescence spectroscopy. A KaiC mutant harboring a Trp fluorescence probe at a position of 419 exhibited a robust circadian rhythm with little temperature sensitivity in the presence of KaiA and KaiB. Our fluorescence observations show a remarkable environmental change at the inner-radius side of the CII ring during circadian oscillation. Crystallographic analysis revealed that a side chain of Trp at the position of 419 was oriented toward a region undergoing a helix-coil transition, which is considered to be a key event to allosterically regulate the CI ring that plays a crucial role in determining the cycle period. The present study provides a dynamical insight into how KaiC generates circadian oscillation. [ABSTRACT FROM AUTHOR]

We investigate the two-photon fluorescence (TPF) of conjugated polymer (CP) microspheres with diameters up to tens of micrometers. Two polymers, emitting in either the violet or red, were first synthesized and characterized in terms of their one-photon fluorescence and three-dimensional internal microstructure. Under femtosecond infrared excitation, both types of microspheres showed a strong TPF, which was investigated by the excitation intensity dependence, emission spectroscopy, time-resolved luminescence, and photobleaching dynamics. While the violet-fluorescent microspheres performed similarly compared to dye-doped polystyrene counterparts emitting at a similar wavelength, the red-fluorescent microspheres showed a two-orders-of-magnitude stronger TPF. This excellent performance is attributed to enhanced hyperpolarizability associated with intermolecular interactions in the polymer solid, indicating a route toward designed CP microspheres that could outperform currently-available microparticles for sensing or imaging applications involving two-photon fluorescence. [ABSTRACT FROM AUTHOR]

In this work, a donor–acceptor substituted aromatic system ((E)-N-((E)-3-(4 (dimethylamino)phenyl) allylidene)-4-(trifluoromethyl) benzenamine (DPATB) has been synthesized and its detailed photophysics of intramolecular charge transfer process have been explored on the basis of steady state absorption, fluorescence and time resolved spectroscopy in combination with density functional theory calculations. Large solvent dependency fluorescence spectral shift and the calculated large excited state dipole moment clearly indicate an efficient charge transfer occurring from the donor group to the acceptor moiety in the excited state. Effect on addition of acid and pH on steady state spectral properties further reveals excited state charge transfer character. Quantum chemical calculations were performed in order to study the conformation and polarity of DPATB at their ground as well as excited electronic states. The HOMO and LUMO molecular orbital pictures are obtained at DFT level using B3LYP functional and 6–311 + g(d,p) basis set which clearly support excited state intramolecular charge transfer process. The molecular electrostatic potential maps for the optimized ground state, donor twisted and acceptor twisted geometry shed insight on the electrostatic potential and charge distribution in a system which gives information about the reacting site of the probe and nature of the reaction. In this work, detailed photophysics of excited state intramolecular charge transfer process in donor–acceptor system (DPATB) was evaluated using steady state and time-resolved fluorescence spectroscopy in combination with density functional theory calculations. Large solvent dependency fluorescence spectral shift and the calculated large excited state dipole moment clearly indicate an efficient charge transfer occurring in DPATB. Molecular orbital pictures as obtained from DFT based computational analysis reveals a significant change in the distribution of electron density upon transition from HOMO to LUMO which confirms an ICT process occurring from the donor group to the acceptor moiety in the excited state. [ABSTRACT FROM AUTHOR]

To improve and diversify the quantification of reactive oxygen species (ROS) in mitochondria of single cells, we connected pyrene derivatives (PB) to a triphenylphosphonium salt (TPP+) as a mitochondrial vector forming PB-TPP+ probes. Two pyrene isomers with the n-butyltriphenylphosphonium moieties attached at their 1- or 2- positions were synthesized and characterized. Using the long fluorescence lifetime of pyrene, it was possible to monitor the variation of cellular free radicals and oxygen and to follow the reversibility of both quenchers in real-time. We compared the behavior of these new probes to the previously published pyrene-probes, functionalized by a mitochondrial-penetrating peptide, allowing their transfer to the mitochondria (Mito-PB) or to the cytosolic membrane for pyrene butyric acid (PBA). The high cellular uptake of the new probes allows cells to be loaded with an initial concentration 40 times lower than that for Mito-PB probes, without inducing perturbations in cell growth. The variation in free radicals and oxygen levels was monitored within cells under different stress conditions through the fluorescence lifetime of the new TPP+-based probes giving comparable results to those obtained for MPP-based probes. However, at a loading concentration as low as 25 nM, our technique allows the detection of increased production of free radicals in the mitochondria in the presence of the TPP+ vector, a warning to the user of this well-known vector. [ABSTRACT FROM AUTHOR]

Strategic incorporation of a meta‐dimethylamino (–NMe2) group on the conformationally locked green fluorescent protein (GFP) model chromophore (m‐NMe2‐LpHBDI) has drastically altered molecular electronic properties, counterintuitively enhancing fluorescence of only the neutral and cationic chromophores in aqueous solution. A ~200‐fold decrease in fluorescence quantum yield of m‐NMe2‐LpHBDI in alcohols (e.g., MeOH, EtOH and 2‐PrOH) supports this GFP‐derived compound as a fluorescence turn‐on water sensor, with large fluorescence intensity differences between H2O and ROH emissions in various H2O/ROH binary mixtures. A combination of steady‐state electronic spectroscopy, femtosecond transient absorption, ground‐state femtosecond stimulated Raman spectroscopy (FSRS) and quantum calculations elucidates an intermolecular hydrogen‐bonding chain between a solvent –OH group and the chromophore phenolic ring –NMe2 and –OH functional groups, wherein fluorescence differences arise from an extended hydrogen‐bonding network beyond the first solvation shell, as opposed to fluorescence quenching via a dark twisted intramolecular charge‐transfer state. The absence of a meta‐NMe2 group twisting coordinate upon electronic excitation was corroborated by experiments on control samples without the meta‐NMe2 group or with both meta‐NMe2 and para‐OH groups locked in a six‐membered ring. These deep mechanistic insights stemming from GFP chromophore scaffold will enable rational design of organic, compact and environmentally friendly water sensors. [ABSTRACT FROM AUTHOR]

Polyphenol oxidase (PPO) is an enzyme associated with the browning process that can occur from mechanical injury and postharvest storage. Thus, its inactivation to inhibit this process is of great interest to the food industry. Recently a nonthermal technology, high frequency ultrasound (100–1 MHz), has found usage in this aspect. In this work, the application of high-frequency (378 kHz, 583 kHz, 1144 kHz, and 1175 kHz) and low frequency (20 kHz) treatment on a PPO extract (from mushrooms) by monitoring the residual enzymatic activity is described. A control thermal treatment at 40 °C was also performed for comparison purposes. High-frequency inactivation data fitted well using the Weibull model, whereas those obtained upon low frequency followed first-order kinetics. The inactivation rate constant obtained ranged from 0.0054 (20 kHz) to 0.028 min−1 (at 583 kHz). To elucidate changes in the enzyme structure time-resolved spectroscopy of a commercial PPO enzyme model was employed. Results indicated that ultrasound-induced structural changes in PPO, in keeping with the activity behaviour upon sonication. [ABSTRACT FROM AUTHOR]

Strategic incorporation of a meta‐dimethylamino (–NMe2) group on the conformationally locked green fluorescent protein (GFP) model chromophore (m‐NMe2‐LpHBDI) has drastically altered molecular electronic properties, counterintuitively enhancing fluorescence of only the neutral and cationic chromophores in aqueous solution. A ~200‐fold decrease in fluorescence quantum yield of m‐NMe2‐LpHBDI in alcohols (e.g., MeOH, EtOH and 2‐PrOH) supports this GFP‐derived compound as a fluorescence turn‐on water sensor, with large fluorescence intensity differences between H2O and ROH emissions in various H2O/ROH binary mixtures. A combination of steady‐state electronic spectroscopy, femtosecond transient absorption, ground‐state femtosecond stimulated Raman spectroscopy (FSRS) and quantum calculations elucidates an intermolecular hydrogen‐bonding chain between a solvent –OH group and the chromophore phenolic ring –NMe2 and –OH functional groups, wherein fluorescence differences arise from an extended hydrogen‐bonding network beyond the first solvation shell, as opposed to fluorescence quenching via a dark twisted intramolecular charge‐transfer state. The absence of a meta‐NMe2 group twisting coordinate upon electronic excitation was corroborated by experiments on control samples without the meta‐NMe2 group or with both meta‐NMe2 and para‐OH groups locked in a six‐membered ring. These deep mechanistic insights stemming from GFP chromophore scaffold will enable rational design of organic, compact and environmentally friendly water sensors. [ABSTRACT FROM AUTHOR]

Multiplexed mRNA profiling in the spatial context provides new information enabling basic research and clinical applications. Unfortunately, existing spatial transcriptomics methods are limited due to either low multiplexing or complexity. Here, we introduce a spatialomics technology, termed Multi Omic Single-scan Assay with Integrated Combinatorial Analysis (MOSAICA), that integrates in situ labeling of mRNA and protein markers in cells or tissues with combinatorial fluorescence spectral and lifetime encoded probes, spectral and time-resolved fluorescence imaging, and machine learning-based decoding. We demonstrate MOSAICA's multiplexing scalability in detecting 10-plex targets in fixed colorectal cancer cells using combinatorial labeling of five fluorophores with facile error-detection and removal of autofluorescence. MOSAICA's analysis is strongly correlated with sequencing data (Pearson's r = 0.96) and was further benchmarked using RNAscopeTM and LGC StellarisTM. We further apply MOSAICA for multiplexed analysis of clinical melanoma Formalin-Fixed Paraffin-Embedded (FFPE) tissues. We finally demonstrate simultaneous co-detection of protein and mRNA in cancer cells. Spatial-omics methods with ease-of-use and high multiplexing are in demand. Here the authors report Multi Omic Single-scan Assay with Integrated Combinatorial Analysis (MOSAICA) which uses Spectral and Fluorescence Lifetime Imaging and Microscopy; they apply this to co-detection of mRNA and protein. [ABSTRACT FROM AUTHOR]

Gold nanotriangles (AuNTs) and nanocubes (NCs) coated with silica shell and fluorescein were synthesized to study the effects of metal‐enhanced fluorescence. The interaction between gold nanoparticles (GNPs) and fluorescein with silica shells of different thicknesses as spacers was investigated by using time‐resolved fluorescence spectroscopy. From the biexponential decay of fluorescence of fluorophore and the kinetic mechanism for the interaction, we obtained the rate constants of energy transfer processes. Both energy transfer rates from fluorophore to the bright and dark modes of gold nanoparticles decreased with distance d (= silica thickness) with a dependence ∝ d−n and n ≈ 2. The rate constant of nanosurface energy transfer kNEST, considering dipolar interaction between fluorophore and metal surface, has an estimated value 1.7 times slower at d = 9 nm and about four times slower at 25 nm than the obtained rate constant for energy transfer from fluorophore to GNP dipolar mode in the AuNT system. For the AuNC system, the rate constants are greater than the AuNT system because of better spectral overlap between emission of fluorescein and surface plasmon resonance. [ABSTRACT FROM AUTHOR]

Microfluidic droplet sorting systems facilitate automated selective micromanipulation of compartmentalized micro- and nano-entities in a fluidic stream. Current state-of-the-art droplet sorting systems mainly rely on fluorescence detection in the visible range with the drawback that pre-labeling steps are required. This limits the application range significantly, and there is a high demand for alternative, label-free methods. Therefore, we introduce time-resolved two-photon excitation (TPE) fluorescence detection with excitation at 532 nm as a detection technique in droplet microfluidics. This enables label-free in-droplet detection of small aromatic compounds that only absorb in a deep-UV spectral region. Applying time-correlated single-photon counting, compounds with similar emission spectra can be distinguished due to their fluorescence lifetimes. This information is then used to trigger downstream dielectrophoretic droplet sorting. In this proof-of-concept study, we developed a polydimethylsiloxane-fused silica (FS) hybrid chip that simultaneously provides a very high optical transparency in the deep-UV range and suitable surface properties for droplet microfluidics. The herein developed system incorporating a 532-nm picosecond laser, time-correlated single-photon counting (TCSPC), and a chip-integrated dielectrophoretic pulsed actuator was exemplarily applied to sort droplets containing serotonin or propranolol. Furthermore, yeast cells were screened using the presented platform to show its applicability to study cells based on their protein autofluorescence via TPE fluorescence lifetime at 532 nm. [ABSTRACT FROM AUTHOR]

The conformational distribution and mutual interconversion of thermally activated delayed fluorescence (TADF) emitters significantly affect the exciton utilization. However, their influence on the photophysics in amorphous film states is still not known due to the lack of a suitable quantitative analysis method. Herein, we used temperature‐dependent time‐resolved photoluminescence spectroscopy to quantitatively measure the relative populations of the conformations of a TADF emitter for the first time. We further propose a new concept of "self‐doping" for realizing high‐efficiency nondoped OLEDs. Interestingly, this "compositionally" pure film actually behaves as a film with a dopant (quasi‐equatorial form) in a matrix (quasi‐axial form). The concentration‐induced quenching that may occur at high concentrations is thus expected to be effectively relieved. The "self‐doping" OLED prepared with the newly developed TADF emitter TP2P‐PXZ as a neat emitting layer realizes a high maximum external quantum efficiency of 25.4 % and neglectable efficiency roll‐off. [ABSTRACT FROM AUTHOR]

Carbon quantum dots (CQDs) are a new class of carbon-rich materials with a range of unique optical and structural properties. They can be defined as carbon nanoparticles, with sizes in the range of 1–10 nm, displaying absorption and emission activities in the UV-VIS range. Depending on the structure, CQDs display a wide variability of properties, which provides the possibility of finely tuning them for several applications. The great advantages of CQDs are certainly the ease of synthesis, non-toxicity, and the strong interactions with the surrounding environment. Based on this, CQDs are especially promising as selective chemosensors. The present study reports on carbon quantum dots synthesized with a top-down (TD) approach, and characterized by different optical, spectroscopic, and morphological techniques to identify the selectivity for metal ions belonging to the first transition series. In particular, the study focuses on the interaction between two samples, namely TD and TDA, featuring different surface functionalization, and heavy metal ions. Their sensing towards Co2+, Cu2+, Fe3+, Zn2+, and Ni2+ has been tested by fluorescence (PL), steady state absorption spectroscopy, and time-resolved PL spectroscopy, in order to determine the fluorescence quenching. We found a PL quenching in the presence of concentrations of metal salts starting from 0.5 µM, and a selectivity towards the interacting ions, depending on CQDs' surface features paving the way for their use for sensing. [ABSTRACT FROM AUTHOR]

Fluorescence spectroscopy and time-resolved study have successfully explored the impact of supramolecular assembly, cucurbit[6]uril (CB6) on the dynamics of proton transfer in 2-(4'-pyridyl) benzimidazole (4-PBI). It has been observed that the guest molecules are capable of binding in three different states of protonation: cation C, tautomer T, and neutral N. While the acid–base equilibria is altered by the host molecule in the ground and excited states. Binding modes of the dye molecule with cucurbit[6]uril have been investigated by proton NMR spectroscopy. The binding of the guest with the supramolecular host is further confirmed by Quantum chemical calculations. The current study successfully recognises how the convoluted acid–base equilibria of dye molecule (4-PBI) are affected by cucurbit[6]uril (CB6) supramolecular assembly upon complexation. [ABSTRACT FROM AUTHOR]

Herein, a computational platform FluorSimStudio was developed for processing fluorescence decay curves in molecular systems, which implements the concept of complex analysis of experimental information based on the simulation modeling and data mining methods. Data analysis includes partitioning the fluorescence decay curves into clusters according to the degree of likeness in some measure of similarity, finding the median cluster members (medoids), applying the data reduction method and visualizing the experimental data in a two-dimensional space. Analysis of the decay curves is carried out by the analytical or simulation models of optical processes occurring in molecular systems. The visualization of data clusters in the original and transformed time spaces is done with the aim of user interaction. A functional scheme of the platform is proposed, the choice of software for ensuring high computing performance is substantiated, a web application of the platform is implemented (https://dsa-cm.shinyapps.io/FluorSimStudio), and the results of a comparative analysis of the simulation algorithms are presented. The performance of the computational platform was confirmed by examples of the analysis of data sets representing systems of free fluorophores and in the presence of the Förster electronic excitation energy transfer process. The computational platform is an open system and allows permanent addition of complex analysis models, taking into account the development of new algorithms for modeling the energy transfer processes in molecular systems, studied with the use of time-resolved fluorescence spectroscopy systems. [ABSTRACT FROM AUTHOR]

Hydrogels, natural and synthetic origin, are actively studied for their use for implants and payload carriers. These biomaterials for delivery systems have enormous potential in basic biomedical research, drug development, and long-term delivery of biologics. Nanofibrillated cellulose (NFC) hydrogels, both natural and anionic (ANFC) ones, allow drug loading for immediate and controlled release via the slow drug dissolution of solid drug crystals into hydrogel and its subsequent release. This property makes NFC originated hydrogels an interesting non-toxic and non-human origin material as drug reservoir for long-term controlled release formulation or implant for patient care. A compelling tool for studying NFC hydrogels is Raman spectroscopy, which enables to resolve the chemical structures of different molecules in a high-water content like hydrogels, since Raman spectroscopy is insensitive to water molecules. That offers real time investigation of label-free drugs and their release in high-water-content media. Despite the huge potential of Raman spectroscopy in bio-pharmaceutical applications, the strong fluorescence background of many drug samples masking the faint Raman signal has restricted the widespread use of it. In this study we used a Raman spectrometer capable of suppressing the unpleasant fluorescence background by combining a pulsed laser and time-resolved complementary metal-oxide-semiconductor (CMOS) single-photon avalanche diode (SPAD) line sensor for the label-free investigation of Metronidazole and Vitamin C diffusivities in ANFC. The results show the possibility to modulate the ANFC-based implants and drug delivery systems, when the release rate needs to be set to a desired value. More importantly, the now developed label free real-time method is universal and can be adapted to any hydrogel/drug combination for producing reliable drug diffusion coefficient data in complex and heterogeneous systems, where traditional sampling-based methods are cumbersome to use. The wide temporal range of the time-resolved CMOS SPAD sensors makes it possible to capture also the fluorescence decay of samples, giving rise to a combined time-resolved Raman and fluorescence spectroscopy, which provides additional information on the chemical, functional and structural changes in samples. [Display omitted] [ABSTRACT FROM AUTHOR]

A novel and sensitive approach has been presented for the determination of methamphetamine (METH) based on fluorescence resonance energy transfer-thermal lens spectrometry (FRET-TLS). Due to the affinity of fluorescein molecules to the surface of AuNPs through the electrostatic interaction and thereby caused reduction of the distance between fluorescein and AuNPs, the best way for de-excitation of excited fluorescein is FRET. The energy absorbed by fluorescein transferred to AuNPs causes enhancement of the thermal lens effect. The thermal lens of the fluorescence molecule could be enhanced through a proper acceptor. Upon the addition of methamphetamine, the fluorescein molecules are detached from the surface of AuNPs, due to the stronger adsorption of methamphetamine. As a result, the fluorescence of fluorescein recovered, and the thermal lens effect of fluorescein decreased. The mechanism of energy transfer was evaluated by two different methods including time-resolved spectroscopy and thermal lens spectrometry. Under the optimal conditions, the thermal lens signal was linearly proportional to methamphetamine concentration in the range 5 – 80 nM. The limit of detection and limit of quantitation were 1.5 nM and 4.5 nM, respectively. The detection volume and limit of molecules in the detection volume were 960 attoliter and 87 molecules, respectively. The method was successfully applied for the determination of methamphetamine in human blood plasma and urine. [ABSTRACT FROM AUTHOR]

Enhancement of the luminescence efficiency of two new diazapentacenium salts (D1 and D2) of more than 55 for D1 and 22 times for D2) in poor solvents, acetonitrile and/or dichloromethane, was observed and rationalized as formation of emissive J‐aggregates. Both compounds displaying 4‐n‐decylphenyl substituents at the 7,14‐carbons and phenyl (D1) or 2,6‐difluorophenyl (D2) substituents at the quaternary nitrogen atoms in 5,12‐positions have been synthetized in a two‐step procedure involving a two‐fold Buchwald‐Hartwig‐type CN cross‐coupling and an electrophilic Friedel‐Crafts‐type cyclization. The optical properties of the dicationic diazapentacenium salts in various solvents and in thin films have been investigated by steady‐state and time‐resolved absorption and photoluminescence spectroscopies. In thin films and in good solvents, isolated molecules coexist with aggregates. Nonetheless, D1 is seven times more emissive than D2, reflecting a higher J‐aggregate contribution in the former. [ABSTRACT FROM AUTHOR]

Human aromatase is a member of the cytochrome P450 superfamily, involved in steroid hormones biosynthesis. In particular, it converts androgen into estrogens being therefore responsible for the correct sex steroids balance. Due to its capacity in producing estrogens it has also been considered as a promising target for breast cancer therapy. Two single-nucleotide polymorphisms (R264C and R264H) have been shown to alter aromatase activity and they have been associated to an increased or decreased risk for estrogen-dependent pathologies. Here, the effect of these mutations on the protein dynamics is investigated by UV/FTIR and time resolved fluorescence spectroscopy. H/D exchange rates were measured by FTIR for the three proteins in the ligand-free, substrate- and inhibitor-bound forms and the data indicate that the wild-type enzyme undergoes a conformational change leading to a more compact tertiary structure upon substrate or inhibitor binding. Indeed, the H/D exchange rates are decreased when a ligand is present. In the variants, the exchange rates in the ligand-free and –bound forms are similar, indicating that a structural change is lacking, despite the single amino acid substitution is located in the peripheral shell of the protein molecule. Moreover, the fluorescence lifetimes data show that the quenching effect on tryptophan-224 observed upon ligand binding in the wild-type, is absent in both variants. Since this residue is located in the catalytic pocket, these findings suggest that substrate entrance and/or retention in the active site is partially compromised in both mutants. A contact network analysis demonstrates that the protein structure is organized in two main clusters, whose connectivity is altered by ligand binding, especially in correspondence of helix-G, where the amino acid substitutions occur. Our findings demonstrate that SNPs resulting in mutations on aromatase surface modify the protein flexibility that is required for substrate binding and catalysis. The cluster analysis provides a rationale for such effect, suggesting helix G as a possible target for aromatase inhibition. [ABSTRACT FROM AUTHOR]

Immunochromatographic assays are good analytical tools for the detection of drug residues. We report a nanosphere-based time-resolved fluorescence immunoassay (nano-TRFIA) based on a monoclonal antibody and a portable TRFIA analyzer for the rapid quantification of chlorpromazine (CPZ) residues in pork. Under optimal conditions, the nano-TRFIA detected CPZ residues within 6 min of sample pretreatment. The results showed good linearity (R2 = 0.991), with a limit of detection (LOD) of 0.32 μg/kg, a wide dynamic range of 0.46–10.0 μg/kg, and coefficients of variation (CVs) of the overall intrabatch and interbatch assays of 7.34% and 7.65%, respectively. The nano-TRFIA was also used to detect CPZ at different spiked concentrations in pork, and the results were confirmed via ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The nano-TRFIA was evaluated for the analysis of six commercial pork samples, and the results agreed well with those obtained via UPLC-MS/MS, without significant differences (P > 0.05). Therefore, the proposed nano-TRFIA is a powerful alternative for the rapid and accurate quantification of CPZ residues in pork to meet the required Chinese maximum residue limits for veterinary drugs in foods. [ABSTRACT FROM AUTHOR]

Six pyrimidine‐based push–pull systems substituted at positions C2 and C4/6 with phenylacridan and styryl moieties, employing methoxy or N,N‐diphenylamino donors, have been designed and synthesized through cross‐coupling and Knoevenagel reactions. X‐ray analysis confirmed that the molecular structure featured the acridan moiety arranged perpendicularly to the residual π system. Photophysical studies revealed significant differences between the methoxy and N,N‐diphenylamino chromophores. Solvatochromic studies revealed that the methoxy derivatives showed dual emission in polar solvents. Time‐resolved spectroscopy revealed that the higher energy band involved very fast (<80 ps) fluorescence, whereas the lower energy one included long components (≈30 ns) due to long‐lived intramolecular charge‐transfer fluorescence. In contrast to N,N‐diphenylamino chromophores, the methoxy derivatives also showed aggregation‐induced emission in mixtures of THF/water, as well as dual emission in thin films, covering almost the whole visible spectrum with corresponding chromaticity coordinates not far from that of pure white light. These properties render the methoxy derivatives as very promising organic materials for white organic light‐emitting diodes. [ABSTRACT FROM AUTHOR]

The lipophilic nature of organic dyes complicates their effectiveness in aqueous solutions. In this work we investigate three different strategies for achieving water‐solubility of the diazaoxatriangulenium (DAOTA+) chromophore: hydrophilic counter ions, aromatic sulfonation of the chromophore, and attachment of charged side chains. The long fluorescence lifetime (FLT, τf=20 ns) of DAOTA+ makes it a sensitive probe to analyze solvation and aggregation effects. Direct sulfonation of the chromophore was found to increase solubility drastically, but at the cost of greatly reduced quantum yields (QYs) due to enhanced non‐radiative deactivation processes. The introduction of either cationic (4) or zwitterionic side chains (5), however, brings the FLT (τf=18 ns) and QY (ϕf=0.56) of the dye to the same level as the parent chromophore in acetonitrile. Time‐resolved fluorescence spectroscopy also reveals a high resistance to aggregation and non‐specific binding in a high loading of bovine serum albumin (BSA). The results clearly show that addition of charged flexible side chains is preferable to direct sulfonation of the chromophore core. [ABSTRACT FROM AUTHOR]

Fluorescent color centers in diamond are invaluable room temperature quantum systems in fundamental scientific studies and vital for many emerging applications from inertial navigation to quantum sensing in biology. Yet, controlled production of specific color centers in synthetic diamond at scale remains challenging. Characteristics of silicon‐ and nickel‐based defects with strong fluorescence in the 700–950 nm spectral region formed in Si‐ and Ni‐doped diamond, created via high‐pressure high‐temperature synthesis in commercial quantities without irradiation, are reported. Using electron paramagnetic resonance spectroscopy and fluorescence spectroscopy, the presence of defects including the negatively charged silicon‐vacancy (SiV−), silicon‐boron (SiB) and positively charged substitutional nickel center (Nis+) in micrometer‐sized particles is identified and quantified. The color centers' optical properties are investigated via time‐resolved and steady‐state fluorescence spectroscopy below 10 K and at room temperature. In ensemble measurements, the particles show no detectable signals from nitrogen‐vacancy (NV−) defects. The particles' relative fluorescence brightness is quantified and compared to particles containing ≈1 ppm NV− centers. It is demonstrated that the Nis+ center fluorescence characteristics are preserved in 50 nm nanoparticles. The work paves the way for the use of fluorescent nanodiamonds in the first near‐infrared biological window between 700 nm and 950 nm in biomedical applications. [ABSTRACT FROM AUTHOR]