Ionophore-based optical nanosensors incorporating hydrophobic carbon dots and a pH-sensitive quencher dye for sodium detection.

Nanosensors present a biological monitoring method that is biocompatible, reversible, and nano-scale, and they offer many advantages over traditional organic indicators. Typical ionophore-based nanosensors incorporate nile-blue derivative pH indicators but suffer from photobleaching while quantum dot alternatives pose a potential toxicity risk. In order to address this challenge, sodium selective nanosensors containing carbon dots and a pH-sensitive quencher molecule were developed based on an ion-exchange theory and a decoupled recognition element from the pH indicator. Carbon dots were synthesized and integrated into nanosensors containing a pH-indicator, an analyte-binding ligand (ionophore), and a charge-balancing additive. These nanosensors are ion-selective against potassium (selectivity coefficient of 0.4) and lithium (selectivity coefficient of 0.9). Reversible nanosensor response to sodium is also demonstrated. The carbon dot nanosensors are resistant to changes in optical properties for at least 12 h and display stable selectivity to physiologically-relevant sodium (alpha = 0.5 of 200 mM NaCl) for a minimum of 6 days.

Effects of metal mining effluent on Atlantic salmon (Salmo salar) and slimy sculpin (Cottus cognatus): using artificial streams to assess existing effects and predict future consequences.

In the summer of 2000, the effects of metal mine discharge on fish growth and exercise performance were assessed at a Zn-Pb-Cu mine in New Brunswick, Canada. Juvenile Atlantic salmon (Salmo salar) were exposed to 0%, 20%, and 80% treated metal mine effluent in a mobile, fish-only artificial stream system. Fish were fed commercial salmon pellets throughout the study. Young-of-the-year slimy sculpins (Cottus cognatus) were exposed to the same treatments in a multitrophic level, modular artificial stream system or mesocosm, in which the fish were dependent on seeded algae and invertebrates for nutrition. Treatment concentrations were chosen to represent existing discharge dilutions (80%) and a scenario of reduced effluent discharge (20%) as predicted upon mine closure (scheduled for 2008). Al, Ba, B, Fe, Mn, Sr, Tl, Ti, and Zn increased in a concentration-dependent fashion across the three treatments. Salmon body burdens of Ba, Cd, Li, Cu, Mn, Se, Sr, and Zn were increased in the 80% treatment, while Tl increased across all treatment levels. Mortalities and depressions in growth in both fish species paralleled treatment concentrations (80%>20%>0%). Salmon liver weight was significantly greater in fish exposed to 20% and 80% effluent in a concentration-dependent fashion. Exercise performance in fish, as assessed by the ability to recover from forced exercise, showed little effect of treatment. The contamination of the receiving environment by mine discharges has led to loss of fish, making it impossible to study the system in situ. However, the use of the artificial stream systems enabled us to assess effects of present conditions on fish, as well as the potential impacts of mine reclamation. The 20% discharge predicted following mine reclamation is potentially favourable for the reinstitution of native fishes into the system.