Time-Gated FRET Nanoprobes for Autofluorescence-Free Long-Term In Vivo Imaging of Developing Zebrafish

The zebrafish is an important vertebrate model for disease, drug discovery, toxicity, embryogenesis, and neuroscience. In vivo fluorescence microscopy can reveal cellular and subcellular details down to the molecular level with fluorescent proteins (FPs) currently the main tool for zebrafish imaging. However, long maturation times, low brightness, photobleaching, broad emission spectra, and sample autofluorescence are disadvantages that cannot be easily overcome by FPs. Here, a bright and photostable terbium-to-quantum dot (QD) Förster resonance energy transfer (FRET) nanoprobe with narrow and tunable emission bands for intracellular in vivo imaging is presented. The long photoluminescence (PL) lifetime enables time-gated (TG) detection without autofluorescence background. Intracellular four-color multiplexing with a single excitation wavelength and in situ assembly and FRET to mCherry demonstrate the versatility of the TG-FRET nanoprobes and the possibility of in vivo bioconjugation to FPs and combined nanoprobe-FP FRET sensing. Upon injection at the one-cell stage, FRET nanoprobes can be imaged in developing zebrafish embryos over seven days with toxicity similar to injected RNA and strongly improved signal-to-background ratios compared to non-TG imaging. This work provides a strategy for advancing in vivo fluorescence imaging applications beyond the capabilities of FPs.     

Numerical and experimental study of the microstructural evolution and the properties of joints welded on rebars using the GMAW process

This paper is a study of CA-50 rebars from SAE steel grade 1026. This study was carried out in order to improve the control of the mechanical properties of welded joints. Knowing certain variables are very important when it comes to finding the ideal welding parameters and the respective microstructural results, and consequently for the mechanical properties of welded joints. In order to carry out this study, a study of the material as received was carried out in order to establish a solid basis for comparison. The material was welded using argon as the shielding gas with 20% carbon dioxide. The wire used was copper-covered ER70S-6, and the welded joints were lap joints. The temperature was monitored using thermocouples for two different heat inputs. A numerical computer code was developed to simulate the phenomena that occur during the process (temperature gradient, phase transformations and heat transfer). The welded joints did not introduce martensite as a brittle phase, the weld metal had a dendritic structure, the heat-affected zone (HAZ) had two different zones with different grain sizes. All of this was due to the temperature gradient, which also led to different characteristics in the weld bead, HAZ, phases formed and different grain sizes.