Excited Dye Research Articles

Spatial and temporal pulse shaping for lateral and depth resolved two-photon excited fluorescence contrast

We report combined temporal and spatial laser pulse shaping to perform lateral and depth dependent two-photon excited fluorescence of dyes. For generating the specific spatially and temporally phase tailored pulses a temporal pulse shaper and a subsequent spatial pulse shaper are employed. Simultaneous spatial and temporal shaping is presented for two-photon excited fluorescence by applying temporal third order phase functions on spatially different light field components. Moreover, the prospects of spatial shaping are demonstrated by applying various lateral two-photon fluorescence pattern. In particular, a depth dependent excitation of different dyes is performed which leads to a high axially resolved fluorescence contrast. The introduced spatial and temporal shaping technique provides new perspectives for biophotonic imaging applications.

Hydrogel Fluorescence Microsensor with Fluorescence Recovery for Prolonged Stable Temperature Measurements

This work describes a hydrogel fluorescence microsensor for prolonged stable temperature measurements. Temperature measurement using microsensors has the potential to provide information about cells, tissues, and the culture environment, with optical measurement using a fluorescent dye being a promising microsensing approach. However, it is challenging to achieve stable measurements over prolonged periods with conventional measurement methods based on the fluorescence intensity of fluorescent dye because the excited fluorescent dye molecules are bleached by the exposure to light. The decrease in fluorescence intensity induced by photobleaching causes measurement errors. In this work, a photobleaching compensation method based on the diffusion of fluorescent dye inside a hydrogel microsensor is proposed. The factors that influence compensation in the hydrogel microsensor system are the interval time between measurements, material, concentration of photo initiator, and the composition of the fluorescence microsensor. These factors were evaluated by comparing a polystyrene fluorescence microsensor and a hydrogel fluorescence microsensor, both with diameters of 20 µm. The hydrogel fluorescence microsensor made from 9% poly (ethylene glycol) diacrylate (PEGDA) 575 and 2% photo initiator showed excellent fluorescence intensity stability after exposure (standard deviation of difference from initial fluorescence after 100 measurement repetitions: within 1%). The effect of microsensor size on the stability of the fluorescence intensity was also evaluated. The hydrogel fluorescence microsensors, with sizes greater than the measurement area determined by the axial resolution of the confocal microscope, showed a small decrease in fluorescence intensity, within 3%, after 900 measurement repetitions. The temperature of deionized water in a microchamber was measured for 5400 s using both a thermopile and the hydrogel fluorescence microsensor. The results showed that the maximum error and standard deviation of error between these two sensors were 0.5 °C and 0.3 °C, respectively, confirming the effectiveness of the proposed method.

Investigation of triphenylamine-based sensitizer characteristics and adsorption behavior onto ZnTiO3 perovskite (1 0 1) surfaces for dye-sensitized solar cells using first-principle calculation

Four different Triphenylamine-based dyes, named as TPA-1, TPA-2, TPA-3 and TPA-4 as shown below, with substituents containing different linkages, earlier described inTiO2dye-sensitized solar cells (DSSCs), are described. The dyes are examined as potential dyes for perovskite ZnTiO3 based dye sensitized solar cells (DSSCs). The simulated characteristics include: Electronic absorption spectra, light harvesting efficiency, energy of dye adsorption to the semiconductor ZnTiO3 electrode, energy level alignment and spontaneity of charge transfer across the dye interfaces with ZnTiO3 and with solution redox couple. The characteristics have been comparatively investigated for all dyes. The absorption spectra for each dye, in its free and adsorbed forms, are discussed. Energy levels and electrochemical parameters are investigated to assess electron transfer efficiency between the excited dyes and the ZnTiO3 particles. Among the series, the dye TPA-3 shows superior behaviors, in terms of spontaneity of charge transfer with ZnTiO3 conduction band. The dye exhibits bidentate mode bonding with the semiconductor surface (1 0 1) as evidenced from its high adsorption energy. Such bonding enables stronger adherence between the dye and the semiconductor and enables more efficient charge transfer. The results encourage more theoretical and experimental study on TPA-3@ZnTiO3 DSSCs, with promising conversion efficiency and stability.

Raman Spectroscopy and Surface Enhanced Raman Scattering (SERS) for the Analysis of Blue and Black Writing Inks: Identification of Dye Content and Degradation Processes.

Raman spectroscopy and Surface Enhanced Raman Scattering (SERS) were applied to the analysis of blue and black writing inks. SERS was performed by application of plasmonic nanopastes constituted by Ag nanoparticles and Au nanorods directly on inks deposited on paper substrates under laser irradiation of 514 nm. It was found that SERS spectra were largely enhanced compared to Raman spectra and that Ag nanopastes produced much larger enhancements than Au nanopastes, due to a combination of plasmonic resonance, charge transfer, and molecular resonance effects. All analyzed writing inks resulted constituted by Crystal Violet and other triarylmethane dye mixtures, to which sometimes phthalocyanine dyes were also added (for example in Bic pens). SERS was also used for the identification of degradation processes occurring in artificially aged blue pens deposited on paper substrates. It was found that color alteration changed from ink to ink and varied from darkening to discoloration to slight fading, depending on the initial chemical composition. For inks containing Crystal Violet, two mechanisms associated to de-methylation and photo-reduction of excited dye to colorless leuco forms were identified.

Two-photon excitation of FluoVolt allows improved interrogation of transmural electrophysiological function in the intact mouse heart

Background & aimsTwo-photon excitation of voltage sensitive dyes (VSDs) can measure rapidly changing electrophysiological signals deep within intact cardiac tissue with improved three-dimensional resolution along with reduced photobleaching and photo-toxicity compared to conventional confocal microscopy. Recently, a category of VSDs has emerged which records membrane potentials by photo-induced electron transfer. FluoVolt is a novel VSD in this category which promises fast response and a 25% fractional change in fluorescence per 100 mV, making it an attractive optical probe for action potential (AP) recordings within intact cardiac tissue. The purpose of this study was to characterize the fluorescent properties of FluoVolt as well as its utility for deep tissue imaging. MethodsDiscrete tissue layers throughout the left ventricular wall of isolated perfused murine hearts loaded with FluoVolt or di-4-ANEPPS were sequentially excited with two-photon microscopy. ResultsFluoVolt loaded hearts suffered significantly fewer episodes of atrio-ventricular block compared to di-4-ANEPPS loaded hearts, indicating comparatively low toxicity of FluoVolt in the intact heart. APs recorded with FluoVolt were characterized by a lower signal-to-noise ratio and a higher dynamic range compared to APs recorded with di-4-ANEPPS. Although both depolarization and repolarization parameters were similar in APs recorded with either dye, FluoVolt allowed deeper tissue excitation with improved three-dimensional resolution due to reduced out-of-focus fluorescence generation under two-photon excitation. ConclusionOur results demonstrate several advantages of two-photon excitation of FluoVolt in functional studies in intact heart preparations, including reduced toxicity and improved fluorescent properties.

Tunable Fluorescence from Dye-Modified DNA-Assembled Plasmonic Nanocube Arrays.

Colloidal crystal engineering with DNA on template-confined surfaces is used to prepare arrays of nanocube-based plasmonic antennas and deliberately place dyes with sub-nm precision into their hotspots, on the DNA bonds that confine the cubes to the underlying gold substrate. This combined top-down and bottom-up approach provides independent control over both the plasmonic gap and photonic lattice modes of the surface-confined particle assemblies and allows for the tuning of the interactions between the excited dyes and plasmonically active antennas. Furthermore, the gap mode of the antennas can be modified in situ by utilizing the solvent-dependent structure of the DNA bonds. This is studied by placing two dyes, with different emission wavelengths, under the nanocubes and recording their solvent-dependent emission. It is shown that dye emission not only depends upon the in-plane structure of the antennas but also the size of the gap, which is regulated with solvent. Importantly, this approach allows for the systematic understanding of the relationship between nanoscale architecture and plasmonically coupled dye emission, and points toward the use of colloidal crystal engineering with DNA to create stimuli responsive architectures, which can find use in chemical sensing and tunable light sources.

Pseudodimeric complexes of 4-styrylpyridine derivatives: Structure–property relationships and a stereospecific [2+2]-cross-photocycloaddition in solution

The study addresses the spectral and photochemical properties of N-(3-ammoniopropyl)-4-styrylpyridinium diperchlorate and its substituted analogs containing either electron-donating (OMe, SMe, NMe2) or electron-withdrawing (NO2, Cl) groups on the benzene ring. These styryl dyes in MeCN form pseudodimeric complexes with uncharged 18-crown-6-containing 4-styrylpyridine due to hydrogen bonding between the ammonium group and the crown ether oxygen atoms. The stability constants of the complexes were determined by spectrophotometric and 1H NMR titration methods. Owing to complexation, the dyes containing OMe or SMe groups and the dye with unsubstituted benzene ring undergo a stereospecific [2 + 2]-cross-photocycloaddition to the crown-containing styrylpyridine to give unsymmetrical cyclobutane derivatives as single rctt isomers. The structure of cyclobutanes was confirmed by X-ray diffraction analysis. The most probable conformations of the pseudodimeric complexes in MeCN were determined by density functional theory calculations. The cross-photocycloaddition quantum yields, measured upon selective excitation of the styryl dye, and other relevant data suggested that the barrier for this photoreaction increases with an increase in the reorganization energy of the singlet excited state of the dye.

Enhanced intramolecular charge transfer of organic dyes containing hydantoin donor: A DFT study

As a key factor for promoting electron transfer to the semiconductor, the intramolecular charge transfer (ICT) process in dye-sensitized solar cells (DSSCs) is crucial to enhancing the conversion efficiency. In this study, the effects of anchoring groups on charge transfer during dye excitation and interfacial electron injection from the dyes to the semiconductor were theoretically investigated. The calculation results indicate that the sensitizers with hydantoin anchoring groups, namely HY-4, HY-3, HQ-4, and HQ-3, can significantly adjust the orbital energy levels and increase the HOMO-LUMO energy gaps. Importantly, the ICT process of sensitizers before and after binding TiO2 cluster were detected via frontier molecular orbitals, electronic transition processes and transferred charges on the basis of the excitation (qCT), the transferred charge distance (dCT) and the dipole moment (μCT). The calculation results confirm that HY-4 and HY-3 greatly improve ICT performances relative to CA-4, which successfully interprets the experimentally observed efficiency difference. Moreover, the inserting acceptor moiety quinoxaline and hydantoin anchoring groups, namely HQ-4 and HQ-3, play an important role in raising the efficiency of ICT process. The finding can promote further understanding of the relationship between structure and performance of organic dyes containing hydantoin anchoring groups, so as to help them become more efficient dyes for DSSCs.

Bioorthogonal labeling with tetrazine-dyes for super-resolution microscopy

Genetic code expansion (GCE) technology allows the specific incorporation of functionalized noncanonical amino acids (ncAAs) into proteins. Here, we investigated the Diels-Alder reaction between trans-cyclooct-2-ene (TCO)-modified ncAAs, and 22 known and novel 1,2,4,5-tetrazine-dye conjugates spanning the entire visible wavelength range. A hallmark of this reaction is its fluorogenicity - the tetrazine moiety can elicit substantial quenching of the dye. We discovered that photoinduced electron transfer (PET) from the excited dye to tetrazine is the main quenching mechanism in red-absorbing oxazine and rhodamine derivatives. Upon reaction with dienophiles quenching interactions are reduced resulting in a considerable increase in fluorescence intensity. Efficient and specific labeling of all tetrazine-dyes investigated permits super-resolution microscopy with high signal-to-noise ratio even at the single-molecule level. The different cell permeability of tetrazine-dyes can be used advantageously for specific intra- and extracellular labeling of proteins and highly sensitive fluorescence imaging experiments in fixed and living cells.

Delayed Photoluminescence in Metal-Conjugated Fluorophores.

Assemblies of metal nanostructures and fluorescent molecules represent a promising platform for the development of biosensing and near-field imaging applications. Typically, the interaction of molecular fluorophores with surface plasmons in metals results in either quenching or enhancement of the dye excitation energy. Here, we demonstrate that fluorescent molecules can also engage in a reversible energy transfer (ET) with proximal metal surfaces, during which quenching of the dye emission via the energy transfer to localized surface plasmons can trigger delayed ET from metal back to the fluorescent molecule. The resulting two-step process leads to the sustained delayed photoluminescence (PL) in metal-conjugated fluorophores, as was demonstrated here through the observation of increased PL lifetime in assemblies of Au nanoparticles and organic dyes (Alexa 488, Cy3.5, and Cy5). The observed enhancement of the PL lifetime in metal-conjugated fluorophores was corroborated by theoretical calculations based on the reverse ET model, suggesting that these processes could be ubiquitous in many other dye-metal assemblies.

Photoluminescence Activation of Organic Dyes via Optically Trapped Quantum Dots.

Laser tweezers afford quantum dot (QD) manipulation for use as localized emitters. Here, we demonstrate fluorescence by radiative energy transfer from optically trapped colloidal QDs (donors) to fluorescent dyes (acceptors). To this end, we synthesized silica-coated QDs of different compositions and triggered their luminescence by simultaneous trapping and two-photon excitation in a microfluidic chamber filled with dyes. This strategy produces a near-field light source with great spatial maneuverability, which can be exploited to scan nanostructures. In this regard, we demonstrate induced photoluminescence of dye-labeled cells via optically trapped silica-coated colloidal QDs placed at their vicinity. Allocating nanoscale donors at controlled distances from a cell is an attractive concept in fluorescence microscopy because it dramatically reduces the number of excited dyes, which improves resolution by preventing interferences from the whole sample, while prolonging dye luminescence lifetime due to the lower power absorbed from the QDs.

Study of dye sensitized solar cells photoelectrodes consisting of nanostructures

Abstract An important element that allows the dye sensitized solar cells (DSSC) photovoltaic assemblies to achieve high efficiency is the photoelectrode. In this kind of solar devices photoanode is mostly in the form of a meso-porous oxide layer composed of nanostructures with attached dye molecules through bonds between the hydroxyl group of the oxide material and the carboxylic group in the dye structure. It is responsible for the separation of charge carriers, which plays the most important role in the photovoltaic effect. The used dyes should be characterized by: higher dye excitation energy than the edge of the oxide semiconductor, the wide absorption spectrum, presence of groups that allow permanent bonding to the surface, resistance to photodegradation and photocorrosion, lower level of the basic state than the redox potential of the electrolyte allowing dye regeneration, thermal and electrochemical stability. Nowadays the most commonly used dyes are ruthenium, osmium, copper, iridium complexes as well as porphyrins and phthalocyanines. The work involved the production of two types of photoelectrodes, containing TiO2 nanoparticles and TiO2 nanoparticle/nanowire. The nanowires of TiO2 have been produced with use electrospinning method. The both photoelectrodes have been obtained by screen printing method ensuring dimensional accuracy and repeatability of production. In order to determine the properties of photoanodes, topographical studies were performed using atomic force microscope (AFM), allowing through RMS Ra roughness coefficients determination to quantify of surface of the electrodes, qualitative studies of chemical composition using Energy Dispersive Spectrometer (EDS), X-ray structural studies, and investigations of optical properties in the wavelength range 200 to 800 nm. The I-V characteristics of dye sensitized solar cells were measured using PV Test Solutions Tadeusz Zdanowicz Solar Cell I-V Tracer System and Keithley 2410 source meter under Standard Test Conditions (AM 1.5, 100 W/m2). The research confirmed that the use of selected method of producing TiO2 nanowires and the method of photoelectrode production allows to obtain a large specific surface area as well as homogeneity of the electrodes. Investigations of optical properties indicate good absorption of the dye used to the semiconductor TiO2 layer, both composed of nanoparticles and the nanoparticle/nanowire system. Obtained cell efficiency results at 4.5–5% make photovoltaic structures promising from the point of view of further development and further application.

Photoinduced Intercomponent Processes in Selectively Addressable Bichromophoric Dyads Made of Linearly Arranged Ru(II) Terpyridine and Expanded Pyridinium Components.

Three new linearly arranged bichromophoric systems 1-3 have been prepared, and their photophysical properties have been studied, taking also advantage of femtosecond pump-probe transient absorption spectroscopy. The three compounds contain the same chromophores, that is a Ru(II)-terpy-like species and a fused expanded bipyridinium (FEBP) unit, separated by three different, variously methylated biphenylene-type bridges. The chromophores have been selected to be selectively addressable, and excitation involving the Ru-based or the FEBP-based dyes results in different excited-state decays. Upon Ru-based excitation at 570 nm, oxidative photoinduced electron transfer (OPET) takes place in 1-3 from the 3MLCT state; however, the charge-separated species does not accumulate, indicating that the charge recombination rate constant exceeds the OPET rate constant. Upon excitation of the organic dye at 400 nm, the FEBP-based 1π-π* level is prepared, which undergoes a series of intercomponent decay events, including (i) electron-exchange energy transfer leading to the MLCT manifold (SS-EnT), which successively decays according to 570 nm excitation, and (ii) reductive photoinduced electron transfer (RPET), leading to the preparation of the charge-separated (CS) state. Reductive PET, involving the FEBP-based singlet state, is much faster than oxidative PET, involving the MLCT triplet state, essentially because of driving force reasons. The rate constant of CR is intermediate between the rate constants of OPET and RPET, and this makes 1-3 capable to selectively read the 400 nm excitation as an active input to prepare the CS state, whereas excitation at wavelengths longer than 480 nm is inefficient to accumulate the CS state. Moreover, intriguing differences between the rate constants of the various processes in 1-3 have been analyzed and interpreted according to the superexchange theory for electron transfer. This allowed us to uncover the role of the electron-transfer and hole-transfer superexchange pathways in promoting the various intercomponent photoinduced decay processes occurring in 1-3.

Optical imaging and spectroscopy of SnO2-rhodamine 6G composite's desiccation patterns

In this study, we produced self-assembly structures (desiccation patterns) in the drying sessile drops of SnO2-R6G colloidal suspension that have functional applications. Colloidal suspensions of SnO2 nanoparticles were synthesized using the sol-gel method and, subsequently, R6G molecules were added into the suspension. Centimeter-sized honeycomb- or tree-like self-assembled structures of the nanoparticle-dye composite are formed from the evaporating droplets on a flat glass surface. The usual “coffee ring” effect observed in the case of drying of a sessile drop of dye solution is inhibited this way, which is desirable in many applications. The structures were investigated using optical microscopy and spectroscopy. The resemblance between transmission and fluorescence images illustrates the feasibility of organizing dye molecules in a specific way using self-assembled nanoparticles as a template. However, dye fluorescence from the self-assembly is very weak, which might be due to photoinduced interfacial electron transfer from the excited dye molecules to the nanoparticles.

Designing new quinoline-based organic photosensitizers for dye-sensitized solar cells (DSSC): a theoretical investigation.

In this work, 27 new quinoline-derivative dyes were proposed, and their geometries, electronic structures, and absorption spectra were investigated using density functional theory (DFT) calculations. An important feature found in most of the new compounds was that the lowest unoccupied molecular orbital (LUMO) was above the TiO2 conduction band, facilitating electron transfer from the excited dye to the semiconductor. The energy of the highest occupied molecular orbital (HOMO) was below the reduction potential energy of the electrolyte (I-/I3-), improving the charge regeneration process after photooxidation. Here we present compounds with a small band gap, favorable absorption properties, a D-π-A-type structure that exhibits maximum absorption above 540nm, and a high light harvesting efficiency (LHE > 0.78). The results show that the compounds D1C, D2C, D3C, and R3C could be used as dye sensitizers for dye-sensitized solar cells (DSSCs).

Quantitative zeptomolar imaging of miRNA cancer markers with nanoparticle assemblies

Multiplexed detection of small noncoding RNAs responsible for posttranscriptional regulation of gene expression, known as miRNAs, is essential for understanding and controlling cell development. However, the lifetimes of miRNAs are short and their concentrations are low, which inhibits the development of miRNA-based methods, diagnostics, and treatment of many diseases. Here we show that DNA-bridged assemblies of gold nanorods with upconverting nanoparticles can simultaneously quantify two miRNA cancer markers, namely miR-21 and miR-200b. Energy upconversion in nanoparticles affords efficient excitation of fluorescent dyes via energy transfer in the superstructures with core-satellite geometry where gold nanorods are surrounded by upconverting nanoparticles. Spectral separation of the excitation beam and dye emission wavelengths enables drastic reduction of signal-to-noise ratio and the limit of detection to 3.2 zmol/ngRNA (0.11 amol or 6.5 × 104 copies) and 10.3 zmol/ngRNA (0.34 amol or 2.1 × 105 copies) for miR-21 and miR-200b, respectively. Zeptomolar sensitivity and analytical linearity with respect to miRNA concentration affords multiplexed detection and imaging of these markers, both in living cells and in vivo assays. These findings create a pathway for the creation of an miRNA toolbox for quantitative epigenetics and digital personalized medicine.

Engineering a Coiled Coil Protein as pH Sensor

To design our pH sensor, we decided on using an anti-parallel coiled-coil protein. The protein consists of two α-helices connected by a loop, adopting a super-coiled tertiary structure. Designing and engineering of coiled-coil proteins are already parametrized, so length of the helices can be controlled as desired. The approach for our sensor design incorporates the ‘binding coupled to folding’ design-principle with grafting of histidines (H). The partially protonated side chain of histidine has a pKa close to physiological pH and can switch between protonated (general acid) and unprotonated (general base) states. This switching from an aromatic (at higher pH) to positively charged (at lower pH) state, can have a role in (un)stabilizing the folded structure of the protein. We mutated H into the hydrophobic core to manipulate the coiled-coil structure stability, resulting in an intrinsically unstable native state. The protein populates the unfolded state when the concentration of protons is low and as the concentration of protons is increased, the protein ensemble shifts to the folded state. To monitor this transition, we used quenching of fluorescent dye (Atto 655). As the protein folds, photo-induced electron transfer (PET) occurs between the excited state dye and the ground-state of tryptophan (W). Our results show quenching of about 80% of florescence intensity as the pH is lowered from 8-4, also corroborating our circular dichroism studies.

Multi-wavelength photo-acoustic microscopy in the frequency domain for simultaneous excitation and detection of dyes.

An optical-resolution photoacoustic microscope with modulated CW laser diodes allowing multi-channel imaging is presented that can be used for both imaging biological tissues and for targeted photo-dynamic therapy (PDT) varying the optical power and exposure time. The effects of this therapy are immediately monitored in order to optimize the time of irradiation. After the description of the experimental setup, in vitro and in vivo applications are presented on a synthetic sample and on the mouse ear using hemoglobin as endogenous and methylene blue as exogenous dye for imaging and PDT, respectively.

Optical pH measurement system using a single fluorescent dye for assessing susceptibility to dental caries.

.Sugar-rich diets and poor dental hygiene promote the formation of a biofilm (plaque) that strongly adheres to the dental enamel surface and fosters the evolution of aciduric bacteria. The acid contributes to demineralization of the exterior tooth enamel, which accelerates after the pH drops below a critical value () for extended time periods resulting in the need for restorative procedures. Preventative techniques to alert the dentist and caries-susceptible patients regarding vulnerability to dental decay require a clinical measure of plaque activity. Therefore, there is a need to evaluate the acid production capability of plaque deposits in the pits and fissures of occlusal and interproximal regions. A ratiometric fluorescence pH-sensing device has been developed using an FDA-approved dye and LED excitation. Fluorescein spectral profiles were collected using a spectrometer and analyzed with a spectral unmixing algorithm for calibration over the pH range of 4.5 to 7. An in vivo pilot study on human subjects was performed using a sucrose rinse to accelerate bacterial metabolism and to measure the time-dependent drop in pH. The optical system is relatively immune to confounding factors such as photobleaching, dye concentration, and variation in excitation intensity associated with earlier dye-based pH measurement techniques.

Investigation of Fluorescent Optical Properties of Fluorine-Boron Cored Dye

In this contribution, an F-B containing dye is readily synthesized. In chloro-carbon medium, it exhibit good solubility and stability. The emission peak value is determined to be 519 nm in chloroform. The highly emissive character is ascribed to the coordination lock, which inhibits the free rotation of methoxybenzene around the single bond. This BF2 locker inhibits the energy dissipation by thermal vibration to an extent and results strong fluorescence emission. In addition, electron deficiency feature of B atom also contributes to its strong emission character. Even though the π-conjugate system is small, the emission shifted significantly and the Stoke’s shift reaches to 170 nm. In addition, the film by doping into polycarbonate is also emissive. In solid state, the emission maximum reaches to 529 nm. Both in film and in solid, only slightly redshift are observed, demonstrating less interference of intermolecular interaction toward the excited dye molecules.