The ever-expanding optics of single-molecules and nanoparticles.

This article explores the shift in chemical physics research towards studying single molecules and nanoparticles instead of bulk samples. Advancements in experimental techniques, such as single-molecule absorption and fluorescence spectroscopy, have made this shift possible. The article discusses various observations made through single-molecule spectroscopy, as well as theoretical considerations and applications in biology, materials science, and nanophotonics. It provides a summary of studies conducted using single-molecule spectroscopy in different disciplinary categories, demonstrating its interdisciplinary nature. The article concludes by discussing the challenges and future directions in the field, including integrating particle tracking with time-dependent spectroscopy and actively manipulating nanoscale objects. [Extracted from the article]