Nanoplasmonic Upconverting Nanoparticles as Orientation Sensors for Single Particle Microscopy

Area of Science:

• Nanotechnology
• Biophysics
• Materials Science

Background:

• Anisotropic nanoparticles exhibit unique optical properties.
• Upconverting nanoparticles (UCNPs) convert near-infrared light to visible light.
• Plasmonic effects can enhance nanoparticle luminescence.

Purpose of the Study:

• To investigate the influence of nanoparticle shape and orientation on fluorescence intensity.
• To explore the use of nanoplasmonic upconverting nanoparticles (NP-UCNPs) for detecting rotational motion.
• To characterize the effect of a gold shell on NP-UCNP optical properties.

Main Methods:

• Fabrication of anisotropic NP-UCNPs with gold shells.
• Measurement of fluorescence intensity as a function of particle orientation and excitation light polarization.
• Single-particle tracking in solution to determine rotational diffusivity.

Main Results:

• Fluorescence intensity showed a three-fold difference between flat and on-edge orientations.
• Intensity varied sinusoidally with excitation light polarization (Imax/Imin ratio up to 2.02).
• Orientation dependence and intensity ratios were influenced by the gold shell.

Conclusions:

• The anisotropic shape and plasmonic shell enable orientation-dependent fluorescence.
• NP-UCNPs can serve as sensitive probes for rotational motion of coupled biomolecules.
• Real-time tracking of single NP-UCNP rotational motion in solution was achieved.