Extensive elemental mapping unlocks Mg/Ca ratios as climate proxy in seasonal records of Mediterranean limpets.

Elemental analysis of biogeochemical archives is an established technique used to study climate in a range of applications, including ocean circulation, glacial/interglacial climates, and anthropogenic climate change. Data from mollusc archives are especially important because of their global abundance and sub-annual resolution. Despite this potential, they are underrepresented among palaeoclimate studies, due to enigmatic physiological influences skewing the elemental record. Understanding the patterns behind these influences will improve data interpretation and lead to the development of new climate proxies. Here, we show for the first time that extensive spatial mapping of multiple mollusc specimens using Laser Induced Breakdown Spectroscopy (LIBS) across a wider region can resolve enigmatic patterns within the elemental record caused by physiological influences. 2D elemental (Mg/Ca) maps of whole limpet shells (Patella caerulea) from across the Mediterranean revealed patterns of variability within individual mollusc records as well as within isochronous parts of specimens. By registering and quantifying these patterns, we established previously uninterpretable correlations with temperature (R2 > 0.8, p < 0.01). This outcome redefines the possibilities of accessing sub-annual climate proxies and presents the means to assess annual temperature ranges using oxygen isotope analysis requiring only 2 samples per shell.

Investigation of the laserlike behavior of polymeric scattering gain media under subpicosecond laser excitation.

The narrowing effects of scatterers on the lifetime and the spectral width of the laser-induced fluorescence of organic dyes hosted in poly(methyl methacrylate) polymer sheets were studied. The excitation source was a distributed-feedback dye laser emitting 0.5-ps pulses at 496 nm. Spectral and temporal features were recorded simultaneously on a spectrograph-streak-camera detection system. The results were then compared with those obtained from dye solutions in methanol that were recorded in previous studies. The effects of the different host environments on the fluorescence characteristics of the dye were thus investigated. These effects are currently studied when the dye is inserted into human tissue in an attempt to boost tumor detection and photodynamic-therapy efficiency. Some initial results are presented.

Corneal hydration monitored by laser-induced breakdown spectroscopy.

BACKGROUND: Corneal hydration is an important factor in laser corneal ablation. In photorefractive keratectomy (PRK), corneal ablation rate and final ablation surface quality are strongly dependent on corneal hydration. We used a spectroscopic technique for monitoring corneal hydration during PRK. METHODS: Hydroxyethlymethacrylate (HEMA) was employed for corneal hydration modeling. Hydrated HEMA samples were irradiated with a pulsed Nd:YAG laser (1064 nm, 10 mJ/pulse, pulse duration 15 nsec). Successive emission spectra corresponding to different degrees of hydration were recorded on a gated optical multichannel analyzer. The weight of the sample and hence its water content was monitored during the entire procedure with a sensitive balance. One rabbit and one human cornea were used to demonstrate the spectral analogy between the model and corneal tissue. RESULTS: The most noticeable dependence on water content of the substrate was that of atomic emission lines of Ca at 393 nm and 396 nm. CONCLUSION: Plasma emission spectra exhibited significant dependence on sample hydration. This dependence can be used for estimation of water content of irradiated model material and real cornea.

Fluorescence quenching in a strongly helical peptide series: the role of noncovalent pathways in modulating electronic interactions.

The very strong helical propensity of peptides rich in alpha-aminoisobutyric acid (Aib) has enabled the design of a set of helices containing as guest amino acids one fluorescent chromophore, beta-(1'-naphthyl)-L-alanine, and one heavy atom perturber, p-bromo-L-phenylalanine. The fluorescence of the chromophoric residue was monitored in this set to explore heavy atom induced enhanced intersystem crossing as a potentially useful tool for exploring remote electronic interactions in biomolecules. The peptides in this set were sequence isomers of each other and were designed such that the chromophore and the perturber were separated by two, one, or zero Aib residues. The respective distances between the aromatic side chains are then modulated by the twist of the helix. All peptides showed steady-state fluorescence quenching, and on the basis of further time-resolved triplet-triplet absorption experiments, two mechanisms for the heavy atom induced fluorescence quenching were established: (i) a weak and nominally spin-forbidden singlet-triplet energy transfer and (ii) the remote heavy atom effect (RHAE) on the intersystem crossing within the fluorophore. Both the rate of singlet-triplet energy-transfer and the RHAE are at their maxima in the peptide with the largest sequence separation but the smallest direct distance between the chromophore and the perturber. Thus neither quenching mechanism is controlled by the length of the intervening covalent pathway. Subtle factors arising from the structure of the intervening peptide backbone apparently contribute to the RHAE for the peptides with shorter sequence separation. Because the sensitivity to the remote heavy atom is a measure of electronic delocalization, this result may have significance for the understanding of the role of helices in biological electron-transfer interactions.