A comparative study of the fluorescence and photostability of common photoswitches in microstructured optical fibre

Available online 10 August 2016The fluorescence spectra and photostability under 532 nm laser excitation of four different common photoswitches (an azobenzene, spiropyran, indolylfulgide, and a diarylperfluorocyclopentene) were investigated in a silica microstructured optical fibre. An example of each photoswitch was examined in solution and physically adsorbed to the silica fibre surface. This comparison was made to define fluorescence behaviour in these two states and to determine which photoswitch has the best performance in this light intense microenvironment. The azobenzene and the spiropyran switches demonstrated the strongest fluorescence response and the least degradation of the fluorescence signal.Daniel B. Stubing, Sabrina Heng, Tanya M. Monro, Andrew D. Abel

Trophic relationships among Southern Ocean copepods and krill: some uses and limitations of a stable isotope approach

The use of stable isotopes to study food webs has increased rapidly, but there are still some uncertainties in their application. We examined the delta(15)N and delta(13)C values of Antarctic euphausiids and copepods from the Polar Front, Lazarev Sea, and Marguerite Bay against their foodweb baseline of particulate organic matter (POM). Interpretations of trophic level were helped by comparison with other approaches and by calibration experiments with Euphausia superba fed known diets: Results for well-known mesozooplankters (e.g., Calanoides acutus and Metridia gerlachei) were internally consistent and corresponded to those derived from independent methods. This gave confidence in the isotope approach for copepods and probably larval euphausiids. Among the dominant yet poorly known species, it suggested mainly herbivory for Rhincalanus gigas but omnivory for Calanus simillimus and furcilia larvae of Thysanoessa spp. and Euphausia frigida. The delta(15)N values of adult copepods were up to 3parts per thousand higher than those of early copepodites, pointing to ontogenetic shifts in diet. In the Lazarev Sea in autumn, the isotopic signals of E. superba larvae suggested pelagic, mainly herbivorous, feeding rather than feeding within the ice. In contrast to the mesozooplankton, some anomalous results for postlarval krill species indicated problems with this method for micronekton. The experiments showed that postlarval E. superba did not equilibriate with a new diet within 30 d. We suggest that the slower turnover of these larger species, partly in combination with their ability to migrate, has confounded trophic effects with those of a temporally/spatially changing food-web baseline. Interpretations of food sources of micronekton could be helped by analyzing their molts or fecal pellets, which responded faster to a new diet

Feeding and energy budgets of Antarctic krill Euphausia superba at the onset of winter. I. Furcilia III larvae

Physiological condition and feeding behavior of furcilia larvae were investigated in autumn (April 1999) in the southwestern Lazarev Sea prior to the critical overwintering period. Furcilia stage III (FIII) larvae were most abundant, so only these were used for all analyses (dry mass [DM], elemental and biochemical composition, gut content) and experiments (metabolic and ingestion rates, selective feeding behavior). Chlorophyll a (Ch1 a) concentrations in the mixed layer were <0.1 mug L-1. Respiration rates of freshly caught FIII larvae were between 0.4 and 1.2 mul O-2 mg(-1) DM h(-1), similar to larvae fed for 7 d on high food concentrations (4 mug Ch1 a L-1). Excretion rates ranged between 0.01 and 0.02 mug NH4 mg(-1) DM h(-1). Their atomic O:N ratio of 72 indicated that lipids were the main metabolic substrate of FIII larvae in the field. The daily C ration ranged from 0.4% at the lowest food concentration of 3 mug C L-1 to 28% at the highest enriched food concentration of 216 mug C L-1, whereas clearance rates decreased with increasing food concentrations. In natural seawater, 115 ml mg(-1) C h(-1), and in natural seawater enriched with ice biota, 24 ml mg(-1) C h(-1), the clearance rates on specific phytoplankton taxa revealed no significant difference across a food size range of 12-220 mum. The study suggests that during periods of low food supply in the water column, larvae have to exploit ice biota to cover their metabolic demands

Photoswitchable calcium sensor: ‘On’–‘Off’ sensing in cells or with microstructured optical fibers

Calcium is a ubiquitous intracellular signaling ion that plays a critical role in the modulation of fundamental cellular processes. A detailed study of these processes requires selective and reversible sensing of Ca2+ and an ability to quantify and monitor concentration changes in a biological setting. Three new, rationally designed, synthesized and photoswitchable spiropyran-based reversible sensors for Ca2+ are reported. Sensor 1a is highly selective for Ca2+ with an improved profile relative to the other two analogues, 1b and 1c. Formation of the merocyanine–Ca2+ complex is proportional to an increase in Ca2+ released from HEK293 cells on stimulation with ionomycin. The photophysical processes surrounding the binding of Ca2+ to compound 1a were further explored using computational methods based on density functional theory (DFT). The ability of sensor 1a to bind Ca2+ and photoswitch reversibly was also characterized using silica suspended-core microstructured optical fiber (SCF). These SCF experiments (with 100 nM Ca2+) represent a first step toward developing photoswitchable, minimally invasive and highly sensitive Ca2+ sensing platforms for use in a biological setting.Sabrina Heng, Adrian M. Mak, Roman Kostecki, Xiaozhou Zhang Jinxin Pei, Daniel B.Stubing, Heike Ebendorff-Heidepriem, Andrew D.Abel

Dual Sensor for Cd(II) and Ca(II): Selective Nanoliter-Scale Sensing of Metal Ions

The first selective, dual sensor for Ca²⁺ and Cd²⁺ capable of detection at 100 pM concentrations was designed and synthesized. The experimental observations made for the MC-cation complexes and the selectivity of compounds <b>1</b> and <b>2</b> with Ca²⁺ and Cd²⁺ ions were further explored using density functional theory. A first step toward a nanoliter-scale dip sensor for the dual sensing of Ca²⁺ and Cd²⁺ was demonstrated using microstructured optical fiber as the sensing platform which is important for ion sensing in confined spaces such as the medium surrounding cell clusters. In addition, this system displays picomolar sensitivity for these ions, with an added ability to reproducibly turn ion-binding on/off

Microstructured Optical Fibers and Live Cells: A Water-Soluble, Photochromic Zinc Sensor

A new biologically compatible Zn­(II) sensor was fabricated by embedding a Zn­(II) sensing spiropyran within the surface of a liposome derived from Escherichia coli lipids (<b>LSP2</b>). Solution-based experiments with increasing Zn­(II) concentrations show improved aqueous solubility and sensitivity compared to the isolated spiropyran molecule (<b>SP2</b>). <b>LSP2</b> is capable of sensing Zn­(II) efflux from dying cells with preliminary data indicating that sensing is localized near the surface membrane of HEK 293 cells. Finally, <b>LSP2</b> is suitable for development into a nanoliter-scale dip-sensor for Zn­(II) using microstructured optical fiber as the sensing platform to detect Zn­(II) in the range of 100 ρM with minimal photobleaching. Existing spiropyran based sensing molecules can thus be made biologically compatible, with an ability to operate with improved sensitivity using nanoscale liquid sample volumes. This work represents the first instance where photochromic spiropyran molecules and liposomes are combined to create a new and multifunctional sensing entity for Zn­(II)

Microstructured optical fibers and live cells: a water-soluble, photochromic zinc sensor

A new biologically compatible Zn(II) sensor was fabricated by embedding a Zn(II) sensing spiropyran within the surface of a liposome derived from Escherichia coli lipids (LSP2). Solution-based experiments with increasing Zn(II) concentrations show improved aqueous solubility and sensitivity compared to the isolated spiropyran molecule (SP2). LSP2 is capable of sensing Zn(II) efflux from dying cells with preliminary data indicating that sensing is localized near the surface membrane of HEK 293 cells. Finally, LSP2 is suitable for development into a nanoliter-scale dip-sensor for Zn(II) using microstructured optical fiber as the sensing platform to detect Zn(II) in the range of 100 ρM with minimal photobleaching. Existing spiropyran based sensing molecules can thus be made biologically compatible, with an ability to operate with improved sensitivity using nanoscale liquid sample volumes. This work represents the first instance where photochromic spiropyran molecules and liposomes are combined to create a new and multifunctional sensing entity for Zn(II).Sabrina Heng, Christopher A. McDevitt, Andrew D. Abell, Daniel B Stubing, Jonathan J. Whittall, Jeremy G. Thompson, Timothy K Engler, Tanya M. Monr