Del Pino provides a review article on the relevant parameters and some of the most promising applications resulting from the interactions between electromagnetic (EM) fields and nanoparticles. This review focuses on EM-active nanoparticles, which upon coupling with light or magnetic fields can provide highly useful responses, such as photoluminescence, nanoheating, energy or charge transfer, magnetic resonance, optoacoustic signal, etc. Several examples of bio-functional materials (that is, functionalized nanoparticles towards bio-applications) and corresponding applications in therapy, bioimaging, and biosensing are given. A significant part of this review discusses how current synthetic methods allow for tailoring the coupling and response of materials toward EM fields. Indeed, this topic connects very well with the report of Fujimoto et al. on the use of titanium oxide powder, localized on the tip of a quartz optical fiber, as a medium for transduction of optical energy emitted from a 980 nm semiconductor laser into heat. The authors propose high-power tip-functionalized semiconductor lasers with emission within the NIR window (also called biological window) as an alternative surgical tool for the clinic. By means of this interesting approach, extremely high temperatures can be produced at the tip of the fiber, which may find very useful applications in surgical procedures such as drilling holes in bone.