Modulation Of Fluorescence Intensity Research Articles

Photoswitching electrospun nanofiber based on a spironaphthoxazine–isophorone-based fluorescent dye system

A bistable photoswitching photochromic spironaphthoxazine/isophorone-based fluorescent dye system was investigated. The photoregulated fluorescence switching behavior of a spironaphthoxazine/isophorone dye loaded poly(methyl methacrylate) nanofiber was also studied. Reversible modulation of fluorescence intensity was achieved using alternating irradiation with UV and visible light. The erasable and rewritable optical storage based on spironaphthoxazine/isophorone dye loaded poly(methyl methacrylate) nanofiber has been developed.

Polarization Modulation Spectroscopy of Single Fluorescent Nanodiamonds with Multiple Nitrogen Vacancy Centers

A technique based on polarization modulation spectroscopy (PMS) has been developed to determine quantitatively the number of fluorophores in nanoparticles at the single-molecule level. The technique involves rotation of the polarization of the excitation laser on a millisecond time scale, leading to fluorescence intensity modulation. By taking account of the heterogeneous orientation among the dipoles of the fluorophores and simulating the modulation depth distribution with Monte Carlo calculations, we show that it is possible to deduce the ensemble average and number distribution of the fluorophores. We apply the technique to fluorescent nanodiamonds (FNDs) containing multiple nitrogen vacancy (NV) centers. Comparing the experimental and simulated modulation depth distributions of 11 nm FNDs, we deduce an average number of <N> = 3, which is in good agreement with independent photon correlation measurements. The method is general, rapid, and applicable to other nanoparticles, polymers, and molecular complexes containing multiple and randomly orientated fluorophores as well.

Photoregulated optical switching of poly( N-isopropylacrylamide) hydrogel in aqueous solution with covalently attached spironaphthoxazine and D-π-A type pyran-based fluorescent dye

A thermoresponsive poly(NIPAM- co-SPO- co-fluorophore) hydrogel comprising poly( N-isopropylacrylamide) that was partially modified using an electron donor-π-conjugated-electron acceptor (D-π-A) pyran-based fluorescent dye using radical copolymerization as well as a photochromic spironaphthoxazine unit displayed a lower critical solution temperature transition from 28 to 50 °C in aqueous solution. The poly(NIPAM- co-SPO- co-fluorophore) copolymer exhibited excellent photochromic behavior in both aqueous solution and hydrogel state. The fluorescence intensity of the poly(NIPAM- co-SPO- co-fluorophore) was temperature-dependent. The relationship between fluorescence intensity change and size of the polymer aggregates was determined using dynamic light scattering. Reversible modulation of fluorescence intensity was achieved using alternating irradiation with UV and visible light. The internal microstructure of the poly(NIPAM- co-SPO- co-fluorophore) hydrogel was investigated using SEM.

On the Nature of DNA Self-Assembled Monolayers on Au: Measuring Surface Heterogeneity with Electrochemical in Situ Fluorescence Microscopy

The creation of gold surfaces modified by single- or double-stranded DNA self-assembled monolayers (SAMs) is shown to produce heterogeneous surface packing densities through the use of electrochemical studies coupled with fluorescence imaging. The modified surfaces created by direct adsorption of thiolate DNA [followed by passivation with mecaptohexanol (MCH)] resulted in regions covered by a monolayer of DNA SAM and other regions that were coated by large particles of DNA. The difference in fluorescence intensity measured from these regions was dramatic. More importantly, a regional variance in fluorescence intensity in response to electrochemical potential was observed: the large aggregates showing a significantly different modulation of fluorescence intensity than the monolayer-coated regions. Electrochemical desorption and detection of the fluorescently tagged DNA provided clear evidence of a complete surface modification. These studies have implications for biosensor/biochip development using DNA SAMs. A modification in the method used to produce the DNA SAMs resulted in a significantly different surface with much fewer aggregates and more significant electromodulation of the fluorescence intensity, though at much lower DNA surface density (ca. 1% of maximum theoretical coverage). This method for forming the modified surfaces has clear advantages over the currently accepted practice and emphasizes the importance of studying the nonaveraged nature of the sensor surface using in situ imaging tools like electrofluorescence microscopy.

Exploring the Nature of Photo-Damage in Two-photon Excitation by Fluorescence Intensity Modulation

We investigate the relative photo-damage effects during one- and two-photon excitations and demonstrate that there exist fundamental differences in the damage induced by a high repetition rate laser as compared to that of a CW laser. This difference is evident from the degree of enhanced fluorescence intensity achieved by blanking the excitation with an optical chopper. Such an enhancement in fluorescence intensity provides better signal-to-noise ratio that could have immediate applications in multiphoton imaging of live specimens.

Photomodulated PPV Emission in a Photochromic Polymer Film

We present studies of fluorescence intensity modulation in neat films of a photochromic poly(p-phenylenevinylene) (PPV) derivative. Poly(2-hexyloxy-5-((10-(4-(phenylazo)phenoxy)decyl)oxy)-1,4-phenylenevinylene) (HPA-10-PPV), a PPV derivative functionalized with photoaddressable azobenzene side chains, is known to undergo modulated changes in fluorescence intensity upon azobenzene isomerization in solution. These changes are caused by nonradiative transfer of excitation energy from the PPV backbone to the azobenzene moiety. The efficiency of energy transfer is higher for the cis azobenzene isomer than for trans, a difference that enables fluorescence intensity modulation. Upon film formation, the fluorescence spectra of neat HPA-10-PPV films undergo a red shift of ca. 30 nm compared to those measured in dilute solution. Application of ultraviolet irradiation to induce trans → cis azobenzene isomerization yields a reduction in fluorescence intensity in HPA-10-PPV films that is reversed upon azobenzene cis →...

Host Matrix Dependent Fluorescence Intensity Modulation by an Electric Field in Single Conjugated Polymer Chains

An electric field oscillating at a frequency approximately 1 Hz is found to induce strong modulation of the fluorescence intensity of single poly[2-methoxy,5-(2'-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) molecules (MW approximately 10(6)) embedded in a poly(methyl methacrylate) (PMMA) matrix. The MEH-PPV polymer chains are carefully isolated from the electrodes to avoid effects of injection. In a polystyrene matrix, fluorescence intensity modulations are on average much less pronounced. The difference in average modulation depth can be explained in terms of lower field-induced exciton dissociation rates in the MEH-PPV/polystyrene system compared to MEH-PPV/PMMA because of a lack of suitable acceptor sites. The observed electric field dependence of single-molecule fluorescence strongly suggests that energy transfer from singlet or even triplet excitons to long-living on-chain hole polarons contributes to the observed modulations. The observed large qualitative differences between the responses of different molecules probably reflect differences in chain topology and strongly anisotropic distributions of acceptor sites, while the hysteretic response of some molecules indicates conformational switching.

Multilabeled Pyrene-Functionalized 2‘-Amino-LNA Probes for Nucleic Acid Detection in Homogeneous Fluorescence Assays

Homogeneous fluorescence assays for detection of nucleic acids are widely used in biological sciences. Typically, probes such as molecular beacons that rely on distance-dependent fluorescence quenching are used for such assays. Less attention has been devoted to tethering a single kind of fluorophores to oligonucleotides and exploiting hybridization-induced modulation of fluorescence intensity for nucleic acid detection. Herein, thermal denaturation experiments and fluorescence properties of oligodeoxyribonucleotides containing one or more 2'-N-(pyren-1-yl)carbonyl-2'-amino-LNA monomer(s) X are described. These pyrene-functionalized 2'-amino-LNAs display large increases in thermal stability against DNA/RNA complements with excellent Watson-Crick mismatch discrimination. Upon duplex formation of appropriately designed 2'-N-(pyren-1-yl)carbonyl-2'-amino-LNA probes and complementary DNA/RNA, intensive fluorescence emission with quantum yields between 0.28 and 0.99 are observed. Quantum yields of such magnitudes are unprecedented among pyrene-labeled oligonucleotides. Molecular modeling studies suggest that the dioxabicyclo[2.2.1]heptane skeleton and amide linkage of monomer X fix the orientation of the pyrene moiety in the minor groove of a nucleic acid duplex. Interactions between pyrene and nucleobases, which typically lead to quenching of fluorescence, are thereby reduced. Duplexes between multiple modified probes and DNA/RNA complements exhibit additive increases in fluorescence intensity, while the fluorescence of single stranded probes becomes increasingly quenched. Up to 69-fold increase in fluorescence intensity (measured at lambda(em) = 383 nm) is observed upon hybridization to DNA/RNA. The emission from duplexes of multiple modified probes and DNA/RNA at concentrations down to less than 500 nM can easily be seen by the naked eye using standard illumination intensities.

Using live FRET imaging to reveal early protein–protein interactions during T cell activation[Curr. Opin. Immunol. 16 (2004) 418

The emerging challenge for proteomics in general and lymphocyte biology in particular is to understand protein–protein interactions in the dynamic context of the living cell. Particularly interesting are the molecular dynamics of the T cell receptor–CD3 complex and other immunoreceptors in immune synapses. Fluorescence (or Förster) resonance energy transfer (FRET) is one of the few techniques that are capable of giving dynamic information about the nanometer-range proximity between molecules, as opposed to simply the subcellular co-localization that is provided by fluorescence microscopy. Spectral changes in fluorescence intensity and down modulation of donor lifetime are the basis for rapidly developing approaches to real-time FRET imaging. With two-photon excitation, FRET can now be extended to in vivo imaging.

Metal-Capped Brownian and Magnetically Modulated Optical Nanoprobes (MOONs): Micromechanics in Chemical and Biological Microenvironments

Modulated optical nanoprobes (MOONs) are microscopic (spherical and aspherical) fluorescent particles designed to emit varying intensities of light in a manner that depends on particle orientation. MOONs can be prepared over a broad size range, allowing them to be tailored to applications including intracellular sensors, using submicrometer MOONs, and immunoassays, using 1−10 μm MOONs. When particle orientation is controlled remotely, using magnetic fields (MagMOONs), it allows modulation of fluorescence intensity in a selected temporal pattern. In the absence of external fields, or material that responds to external fields, the particles tumble erratically due to Brownian thermal forces (Brownian MOONs). These erratic changes in orientation cause the MOONs to blink. The temporal pattern of blinking reveals information about the local rheological environment and any forces and torques acting on the MOONs, including biomechanical forces as observed in macrophages. The rotational diffusion rate of Brownian MOONs is inversely proportional to the particle volume and hydrodynamic shape factor, for constant temperature and viscosity. Changes in the particle volume and shape due to binding, deformation, or aggregation can be studied using the temporal time pattern from the probes. The small size and the large number of MOONs that can be viewed simultaneously provide local measurements of physical properties, in both homogeneous and inhomogeneous media, as well as global statistical ensemble properties.

Characterization and Applications of Modulated Optical Nanoprobes (MOONs)

ABSTRACTModulated optical nanoprobes (MOONs) are microscopic (spherical and aspherical) particles designed to emit different fluxes of light in a manner that depends on particle orientation. When particle orientation is controlled remotely using magnetic fields (MagMOONs) it allows modulation of fluorescence intensity in any selected pattern including square and sinusoidal waves. The broad range of sizes over which MOONs can be prepared allows them to be tailored to applications from intracellular sensors using submicron MOONs to immunoassays using larger MOONs (1–10μm). In the absence of external fields, or material that responds to external fields, the particles tumble erratically due to Brownian thermal forces. These erratic changes in orientation cause the MOONs to blink. The temporal pattern of blinking contains information about the local rheological environment and any forces and torques acting on the MOONs.

Epitope-specific differential modulations within the T-cell antigen receptor complex.

The feeding of cloned helper T cells by irradiated spleen cells results in the modulation of T-cell antigen receptors (TCRs) as detected by FACS. When two groups of anti-TCR antibodies--anti-idiotypic and anti-V beta--are compared, time-dependent patterns of modulation of TCR are drastically different. Whereas up to 80% of the idiotypic determinants disappear within 2 days after stimulation, almost no change is observed for the determinants recognized by V beta-specific antibodies within the same period. Sequential immunoprecipitations clearly showed that anti-idiotypic and anti-V beta antibodies recognize the same population of TCR. Moreover, surface labelling followed by immunoprecipitation of TCR did not show rapid and drastic changes in the amount of specifically precipitated material. The modulation is not significantly affected by the addition of specific antigen, but is specific for the clone's MHC restriction element. Functionally, the modulation of TCR epitopes affects the ability of anti-TCR antibody but not of the MHC/antigen complex to stimulate T cells. We conclude that the observed modulation of fluorescence intensity in the TCR complex after MHC recognition (1) is epitope specific, (2) is independent of the presence of nominal antigen and (3) does not affect the efficiency of antigen-specific stimulation.

Analyse der Fluoreszenz von C6D6 -Mischkristallen durch IR-Modulation

Abstract Deuterated benzene mixed crystals are irradiated by intensity modulated i.r. at low temperatures. The i.r. causes a modulation of crystal temperature which in turn causes a modulation of fluorescence intensity of the crystal. Phase sensitive detection of fluorescence allows the assignment of bands to different trap emissions due to their different temperature dependences. A simple kinetic model gives qualitative agreement with experiments.