Fluorescence line-narrowing measurements at low temperature were performed on the Fenna-Matthews-Olson complex of Prosthecochloris aestuarii. Superimposed on the phonon wing, several vibronic bands could be observed. By use of these data, the temperature dependence of the lowest-energy absorption band was modeled based on the linear harmonic Franck-Condon approximation. The overall Huang-Rhys factor was estimated to be 0.45. The maximum of the phonon distribution was located at 20 cm-1. Thirty vibrational modes could be observed, and their Franck-Condon factors were estimated. The strongest modes were located at 36, 70, and ∼195 cm-1. For the full width at half-maximum of the inhomogeneous broadening, a value of 80 cm-1 was determined. We did not find any evidence for the presence of different excitonic states in the lowest-energy absorption band.

New absorption, linear dichroism (LD) and circular dichroism (CD) measurements at low temperatures on the Fenna-Matthews-Olson complex from Prosthecochloris aestuarii are presented. Furthermore, the anisotropy of fluorescence excitation spectra is measured and used to determine absolute LD spectra, i.e. corrected for the degree of orientation of the sample. In contrast to previous studies, this allows comparison of not only the shape but also the amplitude of the measured spectra with that calculated by means of an exciton model. In the exciton model, the point-dipole approximation is used and the calculations are based on the trimeric structure of the complex. An improved description of the absorption and LD spectra by means of the exciton model is obtained by simply using the same site energies and coupling strengths that were given by Louwe et al. (1997, J Phys Chem B 101: 11280-11287) and including three broadening mechanisms, which proved to be essential: Inhomogeneous broadening in a Monte Carlo approach, homogeneous broadening by using the homogeneous line shape determined by fluorescence line-narrowing measurements [Wendling et al. (2000) J Phys Chem B 104: 5825-5831] and lifetime broadening. An even better description is obtained when the parameters are optimized by a global fit of the absorption, LD and CD spectra. New site energies and coupling strengths are estimated. The amplitude of the LD spectrum is described quite well. The shape of the CD spectrum is modelled in a satisfactory way but its size can only be simulated by using a rather large value for the index of refraction of the medium surrounding the chromophores. It is shown that the estimated coupling strengths are compatible with the value of the dipole strength of bacteriochlorophyll a, when using the empty-cavity model for the local-field correction factor.

Abstract:Time-resolved fluorescence data was collected from a series of 23 bulk crude petroleum oils and 6 microscopic Hydrocarbon-bearing Fluid Inclusions (HCFI). The data was collected using a Diode Laser Fluorescence Lifetime Microscope (DLFLM) over the 460-700 nm spectral range using a 405 nm excitation source. The correlation between intensity averaged lifetimes (τ ) and chemical and physical parameters was examined with a view to developing a quantitative model for predicting the gross chemical composition of hydrocarbon liquids trapped in HCFI. It was found that τ is nonlinearly correlated with the measured polar and corrected alkane concentrations, and that oils can be classified on this basis. However, these correlations all show a large degree of scatter, preventing accurate quantitative prediction of gross chemical composition of the oils. Other parameters such as API gravity and, asphaltene, aromatic, and sulphur concentrations do not correlate well with τ measurements. Individual HCFI were analysed using the DLFLM and time resolved fluorescence measurements were compared with τ data from the bulk oils. This enabled the fluid within the inclusions to be classified as either low alkane/high polar or high alkane/low polar. Within the high alkane/low polar group, it was possible to clearly discriminate HCFI from different locales and to see differences in the trapped hydrocarbon fluids from a single geological source. This methodology offers an alternative method for classifying the hydrocarbon content of HCFI, and observing small variations in the trapped fluid composition, that is less sensitive to fluctuations in the measurement method than fluorescence intensity based methods.

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Aim: Face masks are an important addition to our arsenal in the fight against COVID-19. The aim of this study is to present a novel method of measuring mask performance which can simultaneously assess both fabric penetration and leakage due to poor fit. Materials & methods: A synthetic aerosol is introduced into the lung of a medical dummy. A conical laser sheet surrounds the face of the dummy where it illuminates the aerosol emitted during a simulated breath. The system is demonstrated with five mask types. Conclusions: The curved laser sheet highlights both penetration through the mask fabric and leakage around the edges of the mask. A large variation in both material penetration and leakage was observed.

We report on the coherent coupling of whispering gallery modes (WGMs) in a photonic molecule formed from two melamine-formaldehyde spherical microcavities coated with a thin shell of light-emitting CdTe nanocrystals (NCs). Utilizing different excitation conditions, the splitting of the WGM resonances originating from bonding and antibonding branches of the photonic states is observed, and fine structure consisting of very sharp peaks resulting from lifting of the WGM degeneracy has been detected. Time-resolved measurements showed a slight increase in the spontaneous emission rate of NCs in a photonic molecule when compared to the spontaneous emission rate for NCs coating a single microsphere.

The addition of contaminated powdered spices and seasonings to finished products which do not undergo further processing represents a significant concern for food manufacturers. To reduce the incidence of bacterial contamination, seasoning ingredients should be subjected to a decontamination process. Ultraviolet light emitting diodes (UV-LEDs) have been suggested as an alternative to UV lamps for reducing the microbial load of foods, due to their increasing efficiency, robustness and decreasing cost. In this study, we investigated the efficacy of UV-LED devices for the inactivation of four bacteria (Listeria monocytogenes, Escherichia coli, Bacillus subtilis and Salmonella Typhimurium) on a plastic surface and in four powdered seasoning ingredients (onion powder, garlic powder, cheese and onion powder and chilli powder). Surface inactivation experiments with UV mercury lamps, UVC-LEDs and UVA-LEDs emitting at wavelengths of 254 nm, 270 nm and 365 nm, respectively, revealed that treatment with UVC-LEDs were comparable to, or better than those observed using the mercury lamp. Bacterial reductions in the seasoning powders with UVC-LEDs were less than in the surface inactivation experiments, but significant reductions of 0.75–3 log10 colony forming units (CFU) were obtained following longer (40 s) UVC-LED exposure times. Inactivation kinetics were generally nonlinear, and a comparison of the predictive models highlighted that microbial inactivation was dependent on the combination of powder and microorganism. This study is the first to report on the efficacy of UV-LEDs for the inactivation of several different bacterial species in a variety of powdered ingredients, highlighting the potential of the technology as an alternative to the traditional UV lamps used in the food industry.

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