Energy transfer with nanoparticles for in vitro diagnostics

In vitro diagnostics is an important application for nanoparticles in the life sciences and has attracted continuous research interest. While nanoparticles can be used as single luminescent probes, their unique photophysical properties provide many more advantages when they are combined with other nanoparticles or molecules to form energy transfer pairs. Energy transfer-based assays are homogeneous in nature and are often as simple as “mix and measure,” which has catalyzed their frequent use in clinical diagnostics. Most bioanalytical applications involve Förster resonance energy transfer (FRET), a distance-dependent nonradiative energy transfer from a donor to acceptor chromophore through dipole–dipole interaction. Nanosurface energy transfer (NSET) describes energy transfer to metal nanoparticles. Semiconductor quantum dots, upconversion nanoparticles, gold nanoparticles, and carbon dots are among the most applied nanoparticles in in vitro diagnostics and they have been largely explored in the analysis of disease-related nucleic acids, proteins, and small molecules. The utilizations of various nanoparticles with their intrinsic optical properties have changed the diagnostic horizon substantially by improving the assay simplicity, sensitivity, selectivity, robustness, and multiplexing capacity. In this chapter, we discuss the use of nanoparticles in energy transfer assays for in vitro diagnostics and show their strong potential for advancing the field beyond molecular fluorescent probes.