Engineering bright sub-10-nm upconverting nanocrystals for single-molecule imaging

Area of Science:

• Nanotechnology
• Biophysics
• Materials Science

Background:

• Single-molecule imaging requires luminescent probes with high photostability, brightness, and continuous emission.
• Lanthanide-doped upconverting nanoparticles offer advantages like photostability and near-infrared excitation but face brightness limitations.
• Existing upconverting nanoparticles have tradeoffs between brightness and size, with surface effects poorly understood at small scales.

Purpose of the Study:

• To develop highly bright, small upconverting nanoparticles for advanced single-molecule microscopy.
• To investigate the factors limiting brightness in upconverting nanoparticles, particularly at the nanoscale.
• To understand the role of surface effects and excitation power on nanocrystal luminescence.

Main Methods:

• Synthesis of upconverting nanoparticles with diameters under 10 nm.
• Single-particle imaging and advanced characterization techniques.
• Theoretical modeling to analyze energy transfer and surface effects.

Main Results:

• Developed upconverting nanoparticles over an order of magnitude brighter than existing ones under single-particle conditions.
• Visualized single upconverting nanoparticles as small as 4.8 nm, comparable to fluorescent proteins.
• Identified critical surface effects at diameters under 20 nm and demonstrated that excitation fluence alters brightness determinants.

Conclusions:

• Novel, small upconverting nanoparticles significantly enhance single-molecule imaging capabilities.
• Surface effects and excitation power are crucial for optimizing nanoparticle brightness at the single-molecule level.
• The brightest probes for single-molecule excitation may exhibit low luminescence in ensemble measurements.