In-Brain Multiphoton Imaging of Vaterite Cargoes Loaded with Carbon Dots.

Biocompatible fluorescent agents are key contributors to the theranostic paradigm by enabling real-time in vivo imaging. This study explores the optical properties of phenylenediamine carbon dots (CDs) and demonstrates their potential for fluorescence imaging in cells and brain blood vessels. The nonlinear absorption cross-section of the CDs was measured and achieved values near 50 Goeppert-Mayer (GM) units with efficient excitation in the 775-895 nm spectral range. Mesoporous vaterite nanoparticles were loaded with CDs to examine the possibility of a biocompatible imaging platform. Efficient one- and two-photon imaging of the CD-vaterite composites uptaken by diverse cells was demonstrated. For an in vivo scenario, CD-vaterite composites were injected into the bloodstream of a mouse, and their flow was monitored within the blood vessels of the brain through a cranial window. These results show the potential of the platform for high-brightness biocompatible imaging with the potential for both sensing and simultaneous drug delivery.

Thermo-optics of gilded hollow-core fibers.

Hollow core fibers, supporting waveguiding in a void, open a room of opportunities for numerous applications owing to an extended light-matter interaction distance and relatively high optical confinement. Decorating an inner capillary with functional materials allows tailoring the fiber's optical properties further and turns the structure into a functional device. Here, we functionalize an anti-resonant hollow-core fiber with 18 nm-size gold nanoparticles, approaching a uniform 45% surface coverage along 10 s of centimeters along its inner capillary. Owing to a moderately low overlap between the fundamental mode and the gold layer, the fiber maintains its high transmission properties; nevertheless, the entire structure experiences considerable heating, which is observed and quantified with the aid of a thermal camera. The hollow core and the surrounding capillary are subsequently filled with ethanol and thermo-optical heating is demonstrated. We also show that at moderate laser intensities, the liquid inside the fiber begins to boil and, as a result, the optical guiding is destroyed. The gilded hollow core fiber and its high thermal-optical responsivity suggest considering the structure as an efficient optically driven catalytic reactor in applications where either small reaction volumes or remote control over a process are demanded.