Resonance energy transfer to gold nanoparticles: NSET defeats FRET

Gold nanoparticles (AuNPs) have been widely applied as highly efficient luminescence quenchers in combination with a large variety of donor fluorophores. While the application of such systems in optical biosensing has resulted in significant advances of biological, biochemical, and biophysical research, the underlying energy transfer mechanism has been much less investigated. In this review, we discuss the differences between Förster resonance energy transfer (FRET) and nanosurface energy transfer (NSET), give an overview of the literature concerning the assignment of FRET or NSET to AuNP-based luminescence quenching, show why the development of improved NSET models and their application to experimental data provided strong arguments in favor of the NSET formalism, and discuss applications of NSET in biosensing, molecular rulers, and molecular tension probes. Taking into account the existing literature, the NSET formalism, including size and wavelength-dependent issues, is superior to FRET theory for a general description of energy transfer to AuNPs.