Optimally Designed Nanoshell and Matryoshka-Nanoshell as a Plasmonic-Enhanced Fluorescence Probe

Nanoshell and Matryoshka-nanoshell constructs are rationally optimized utilizing the finite-difference time-domain method to design probes with enhanced fluorescence. Through the systematical investigation of interactions between the spontaneous emission of a single emitter and a metal-based nanostructure, the plasmonic-enhanced fluorescence is found maximal for certain morphologies that balance two competitive factors: field enhancement and quantum efficiency. For instance, key parameters such as the emitter’s position, its orientation, and the spectral overlaps between molecular bands and plasmon resonance are investigated to fully understand the complete behavior of the system. In the case of metal nanoshells, it is shown that the molecular fluorescence is differently enhanced inside or outside the shell. In that of Matryoshka-nanoshells that consist of concentric gold core and shell, the construct appears as an exceptionally promising probe especially when the fluorophore lies within the gap layer. Indeed, the strong coupling between the adjacent core and shell allows electromagnetic excitation to be squeezed within the gap, so resulting in giant fluorescence and photostability. Such a construct opens a way for still increasing the sensitivity of fluorescence detection, which is promising for almost all biological imaging applications.