Enhanced Ratiometric pH Sensing Using SNAFL-2 on Silver Island Films: Metal-enhanced Fluorescence Sensing

We have explored the opportunities for enhanced ratiometric pH sensing using the well-known carboxy seminaphthofluorescein (SNAFL-2) and silver island films (SiFs). Our results show that the metallic surfaces can provide up to a 40-fold increase in probe fluorescence intensity as compared to nonmetallic surfaces with the same probe coverage. However, while the S/N is significantly better for pH sensing, the emission wavelength ratiometric values are similar to that obtained in solution, due to the fact that the emission of both the acidic and basic forms of the probe are enhanced to similar extents. To the best of our knowledge this is the first report of enhanced ratiometric fluorescence sensing on metallic surfaces.     

Editorial: Plasmonics

Editorial Introduction

Editorial: Plasmonics     

Fluorescence Enhancements on Silver Colloid Coated Surfaces

We observed a strong, more than 16-fold, enhancement of Texas Red-labeled BSA fluorescence emission when deposited on silver colloid coated surfaces (SCCS). The same labeled protein deposited on silver island films (SIFs) showed an approximate 8-fold fluorescence enhancement. The lifetimes of Texas Red-BSA fluorescence are significantly shorter on silvered surfaces than on uncoated quartz substrate indicating a strong change in radiative decay rate of the dyes. We also observed a 36-fold increased brightness of overlabeled fluorescein-HSA deposited on silver colloid coated surface. Stronger enhancement observed for overlabeled Fl-HSA protein indicates that presence of silver particles partially decreased self-quenching. Our results indicate that surfaces coated with silver colloids are valuable substrates for metal-enhanced fluorescence.     

Long-Lived Luminescent Re(I) Complexes Containing cis-Carbonyl and Bidentate Phosphine Ligands

Highly emissive Re(I) complexes, hydrophobic cis-Re(CO)₂(c-dppene)(dpphen) and water-soluble cis-Re(CO)₂(c-dppene)(SO₃-dpphen) with a negative charge, were synthesized [where c-dppene is cis-(bis(diphenylphosphino)ethylene, dpphen is 4,7-diphenyl-1,10-phenanthroline, and SO₃-dpphen is its disulfonate derivative]. These Re(I) complexes have significantly higher molar absorption in the 350- to 490-nm region compared to their tricarbonyl Re(I) counterparts and their emission spectra are similar to those of Ru(II) polypyridyl complexes. The luminescence lifetimes of these Re(I) complexes approach 10 s in the absence of oxygen in both aqueous and less polar solvents. The complexes have limiting anisotropy values exceeding 0.3. As both ligands, the diimine and the bidentate phosphine, can be modified by adding different substituents, it should be possible to make cis-Re(CO)₂(diimine)(P-P) derivatives which are capable of labeling biomacromolecules for biochemical and biophysical studies.     

Long-term retention of ice-nucleating active Pseudomonas fluorescens by overwintering colorado potato beetles

Ice nucleating-active Pseudomonas fluorescens F264C was fed to Colorado potato beetles to determine bacterial retentioin in the beetle gut and its effect on the cold hardiness of this insect pest. The bacrterium was present in beetles recovered after overwintering in the field, seven months after their exposure to P. fluorescens. Retention was evident not only in the detection of the P. fluorescens ice nucleating gene, inaW, in bacterial cultures from beetle guts but also in the elevated supercooling points of some treated beetles.     

Breakdown of stabilization of atoms interacting with intense, high-frequency laser pulses

An analysis of the influence of the magnetic field of an intense, high-frequency laser pulse on the stabilization of an atomic system is presented. We demonstrate that at relatively modest intensities the magnetic field can significantly alter the dynamics of the system. In particular, a breakdown of stabilization occurs, thereby restricting the intensity regime in which the atom is relatively stable against ionization. Counterpropagating pulses do not negate the detrimental effects of the magnetic field. We compare our quantum mechanical results with classical Monte Carlo simulations.     

Calcium imaging using fluorescence lifetimes and long-wavelength probes

We describe imaging of calcium concentrations using the long-wavelength Ca²⁺ indicators, Calcium Green, Orange, and Crimson. The lifetimes of these probes were measured using the frequency-domain method and were found to increase from 50% to severalfold in response to calcium. The two-dimensional images of the calcium concentration were obtained using a new apparatus for fluorescence lifetime imaging (FLIM). We also describe procedures to correct for the position-dependent frequency response of the gain-modulated image intensifier used in the FLIM apparatus. Importantly, the FLIM method does not require the probe to display shifts in the excitation or emission spectra. Using the FLIM method, calcium imaging is possible using probes which display changes in lifetime in response to calcium. Consequently, calcium imaging is possible with excitation wavelengths ranging from 488 to as long as 620 nm, where autofluorescence and/or photochemical damage is minimal. These probes are also suitable for calcium measurements of single cells using lifetime-based flow cytometry.     

Two photon-induced fluorescence intensity and anisotropy decays of diphenylhexatriene in solvents and lipid bilayers

We measured the fluorescence intensity and anisotropy decays of 1,6-diphenyl-1,3,5-hexatriene (DPH)-labeled membranes resulting from simultaneous two-photon excitation of fluorescence. Comparison of these two-photon data with the more usual one-photon measurements revealed that DPH displayed identical intensity decays, anisotropy decays, and order parameters for one- and two-photon excitation. While the anisotropy data are numerically distinct, they can be compared by use of the factor 10/7, which accounts for the two-photon versus one-photon photoselection. The increased time 0 anisotropy of DPH can result in increased resolution of complex anisotropy decays. Global analysis of the one- and two-photon data reveals consistency with a single apparent angle between the absorption and the emission oscillators. The global anisotropy analysis also suggests that, except for the photoselection factor, the anisotropy decays are the same for one-and two-photon excitation. This ideal behavior of DPH as a two-photon absorber, and its high two-photon cross section, makes DPH a potential probe for confocal two-photon microscopy and other systems where it is advantageous to use long-wavelength (680- to 760-nm) excitation.