Quantum Dot Biofunctionalization

We have shown the efficacy of Quantum Dots (qdots), nano-scale fluorescent particles made of semi-conductive material, as versatile biologically functional research tools. This functionality depends upon a series of chemical transformations that produce stable, aqueous, biomolecule-bound qdots with high quantum yield. We utilize the metal binding and chelating properties of the amino acid histidine to displace hydrophobic surface ligands and to phase-transfer qdots from organic to aqueous media. The intermediate binding strength of histidine to qdot surface facilitates its exchange with a variety of strongly binding thiolated biomolecules. Ligand profiles are subsequently characterized via FTIR, NMR, and gel electrophoresis. Negatively-charged aqueous qdots are shown to be taken-up and contained within phospholipid liposomes formed via several different protocols. Flexible liposome synthetic procedures allow intercalation of a number of moieties into liposomal membranes, including hydrophobic dyes and hydrophobic qdots. Possible implications for cellular delivery are discusse

A standardized and reproducible method to measure decision-making in mice.

Abstract Progress in neuroscience is hindered by poor reproducibility of mouse behavior. Here we show that in a visual decision making task, reproducibility can be achieved by automating the training protocol and by standardizing experimental hardware, software, and procedures. We trained 101 mice in this task across seven laboratories at six different research institutions in three countries, and obtained 3 million mouse choices. In trained mice, variability in behavior between labs was indistinguishable from variability within labs. Psychometric curves showed no significant differences in visual threshold, bias, or lapse rates across labs. Moreover, mice across laboratories adopted similar strategies when stimulus location had asymmetrical probability that changed over time. We provide detailed instructions and open-source tools to set up and implement our method in other laboratories. These results establish a new standard for reproducibility of rodent behavior and provide accessible tools for the study of decision making in mice

Zn(Sn,Ge)N2 : a new double nitride tunable semiconductor family for LED and solar devices

National audienc

Prospective analysis of optoelectronic properties of ZnSnN2 for future tandem solar cells

International audienc

Prospective analysis of optoelectronic properties of ZnSnN2 for future tandem solar cells

International audienc

Cenozoic weathering of fluvial terraces and emergence of biogeographic boundaries in Central Amazonia

International audienceThe study of paleofluvial dynamics is crucial to understand the role of rivers as biogeographic boundaries in Amazonia during the Cenozoic. In central Amazonia, Mesozoic and Cenozoic fluvial deposits - Alter do Chão, Iranduba and Novo Remanso Formations - host supergene iron oxides and record changes in the distribution of flooded and non-flooded (upland) environments. Geochronological data on these deposits are still scarce to constrain past landscape changes. Therefore, in this study we investigate iron oxides precipitated within weathering profiles developed on ancient fluvial terraces to access the interplay between flooded and non-flooded environments in central Amazonia. We aimed to trace the history of abandonment of alluvial plains and the subsequent weathering of lowland sediment deposits during the Cenozoic. We identified at least two main periods of iron oxide precipitation: (1) one starting before ~42 Ma and ending at ~18 Ma; and (2) a well-defined humid and weathering prone phase between ~8 and 1 Ma. Dominant goethite precipitation marks a major climatic shift towards more humid conditions from ~3 Ma. The increase in water discharge of the Negro and Solimões rivers possibly promoted fluvial incision and conversion of floodplains into long-lasting upland terrains as indicated by the development of lateritic weathering profiles. This major phase of upland expansion corroborates upland birds phylogenetic data, which indicate the emergence of a major biogeographic barrier in central Amazonia during late Pliocene/Pleistocene

Standardized and reproducible measurement of decision-making in mice.

Progress in science requires standardized assays whose results can be readily shared, compared, and reproduced across laboratories. Reproducibility, however, has been a concern in neuroscience, particularly for measurements of mouse behavior. Here, we show that a standardized task to probe decision-making in mice produces reproducible results across multiple laboratories. We adopted a task for head-fixed mice that assays perceptual and value-based decision making, and we standardized training protocol and experimental hardware, software, and procedures. We trained 140 mice across seven laboratories in three countries, and we collected 5 million mouse choices into a publicly available database. Learning speed was variable across mice and laboratories, but once training was complete there were no significant differences in behavior across laboratories. Mice in different laboratories adopted similar reliance on visual stimuli, on past successes and failures, and on estimates of stimulus prior probability to guide their choices. These results reveal that a complex mouse behavior can be reproduced across multiple laboratories. They establish a standard for reproducible rodent behavior, and provide an unprecedented dataset and open-access tools to study decision-making in mice. More generally, they indicate a path toward achieving reproducibility in neuroscience through collaborative open-science approaches