Two-photon nano-PEBBLE sensors: subcellular pH measurements

Intracellular pH mapping is of great importance as it plays a critical role in many cellular events. Also, in tissue, pH mapping can be an indicator for the onset of cancer. Here we describe a biocompatible, targeted, ratiometric, fluorescent, pH sensing nano-PEBBLE (Photonic Explorer for Biomedical use with Biologically Localized Embedding) that is based on two-photon excitation. Two-photon excitation minimizes the photobleaching and cell autofluorescence drastically, leading to an increase in the signal-to-noise ratio. PEBBLE nanosensors provide a novel approach for introducing membrane impermeant dyes, like HPTS, into cells. We use both non-targeted and F3 peptide targeted PEBBLE nanosensors for intracellular pH measurement of 9L cells. The intracellular measurements suggest that the non-targeted nanosensors are mostly trapped in endosomes, whereas the F3 peptide targeting enables them to escape/avoid these acidic compartments. Combining the advantages of pH sensitive PEBBLE nanoparticles, including their specific targeting, with the advantages of two-photon microscopy provides an attractive and promising prospect for non-invasive real-time monitoring of pH inside cancer cells and tissues.     

Higgs decay into two photons in a warped extra dimension

A detailed five-dimensional calculation of the Higgs-boson decay into two photons is performed in both the minimal and the custodially protected Randall–Sundrum (RS) model, where the Standard Model (SM) fields propagate in the bulk and the scalar sector lives on or near the IR brane. It is explicitly shown that the $R_\xi $ gauge invariance of the sum of diagrams involving bosonic fields in the SM also applies to the case of these RS scenarios. An exact expression for the $h\rightarrow \gamma \gamma $ amplitude in terms of the five-dimensional (5D) gauge-boson and fermion propagators is presented, which includes the full dependence on the Higgs-boson mass. Closed expressions for the 5D $W$ -boson propagators in the minimal and the custodial RS model are derived, which are valid to all orders in $v^2/M_{\text {KK}}^2$ . In contrast to the fermion case, the result for the bosonic contributions to the $h\rightarrow \gamma \gamma $ amplitude is insensitive to the details of the localization of the Higgs profile on or near the IR brane. The various RS predictions for the rate of the $pp\rightarrow h\rightarrow \gamma \gamma $ process are compared with the latest LHC data, and exclusion regions for the RS model parameters are derived.     

Near-Field Optical Microscopy,Spectroscopy, and Chemical Sensors

Optical microscopy and spectroscopy have long been key techniques in medicine, biology, chemistry, and materials science. Among their advantages are:

• 1. Universality. All materials and samples attenuate light and have spectroscopic states.

• 2. Noninvasiveness. Most often the sample is not altered in a microscopic and/or spectroscopic investigation. Moreover, biological samples usually can be studied in their native environment. Most chemical reactions are not perturbed by light of long enough wavelength.

• 3. Real-time observation. Biological phenomena, chemical reactions, crystallization, and so on can be observed under the microscope as they happen in situ (even with one's eyes); spectroscopic measurements can be performed on line in an industrial process or other setting.

• 4. Energy and chemical state resolution. The obvious advantages of spectroscopy and photochemistry, at ambient temperature, can be trivially added to the optical methods mentioned above. By contrast, this is not easily accomplished with other techniques such as electron microscopy or x-ray crystallography.

• 5. Safety. Optical and spectroscopic analyses usually are very safe, and precautions are mostly limited to wearing optically protective eyeglasses.

• 6. Low price. Optical microscopy is much cheaper than, say, electron microscopy; optical spectroscopy is usually a bargain compared with, say, NMR instruments. Obviously, there are exceptions.

• 7. Speed, zoom, and human factors. Optical techniques are usually fast and can be extended even into the femtosecond time domain. They can be used from astronomical to microscopic distances. Preliminary or concomitant observations can be made using our most developed sense—sight, and in living color—even without the brokerage services of an analog or digital interface.

     

Dynamics of energy transport in ternary molecular solids. II. Time evolution of naphthalene fluorescence

The spectrally resolved time-evolution of free and trapped singlet excitons was obtained at liquid-helium temperature for ternary crystals of perdeuteronaphthalene/naphthalene/betamethylnaphthalene (host/guest/supertrap). The naphthalene guest (donor) concentration varied between 0.30 and 0.99 mole fraction, while the supertrap (acceptor) concentrations were 10^?4–10^?5. At the lower guest concentrations (0.50 and below) the naphthalene-exciton decay time approaches the natural lifetime (≈ 122 ns). At higher concentrations, the decay is much shorter and extremely non-exponential. This behavior is inconsistent with simple homogeneous kinetics schemes that use a time-independent rate constant for energy transport. Above the percolation concentration (0.60 naphthalene) we fitted the experimental results with a random-flight-kinetic model, incorporating correlated random walks on the percolating guest cluster. The best fit was obtained for a “coherence length” (mean free path) of ≈ 10² lattice units. These results are in good agreement with previous steady-state studies on the same samples, and seem to indicate a partial coherence of the exciton transport in both pure and substitutionally disordered crystals at these low temperatures.     

On the application of group theory to molecular excitons

In this paper a group theoretical approach was employed for the classification and construction of molecular exciton wavefunctions for two important crystal structures (naphthalene—anthracene and benzene), utilizing the representation theory of finite groups. The generally valid scheme requires only cyclic boundary conditions (being explicitly imposed on all space group operations, including rotations and reflections). Even though these symmetry considerations are insufficient to determine crystal wavefunctions belonging to a general k vector, it is still possible to write a simple expression for such wavefunctions. This is achieved for cases where the nonvanishing exciton transfer integrals are confined to molecular interactions along symmetry axes and/or planes.     

Collision-induced dissociation of alkali metal cationized and permethylated oligosaccharides: Influence of the collision energy and of the collision gas for the assignment of linkage position

Tandem mass spectrometry has been used to study the collision-induced decomposition of [M+Na]⁺ ions of permethylated oligosaccharides. It is shown that many linkage positions in one compound may be determined by the presence or absence, in a single spectrum, of specific fragment ions that arise from the cleavage of two ring bonds and that the yield of such ions depends strongly on the collision energy and nature of the collision gas. In contrast to the behavior of monolithiated native oligosaccharides, the collision-induced decomposition of the sodiated and permethylated oligosaccharide samples at low energy leads to preferential cleavage of glycosidic linkages. At high collision energies, the fragment ions formed by cleavage of more than one bond are greatly enhanced, especially when helium is replaced by argon as the collision gas. Furthermore, argon is the more efficient collision gas in inducing fragmentation of the precursor ions. As an example of the application of this method, the discrimination between the 1 → 3 and 1 → 6-linked mannose residues in the common core of N-glycans is described.