Zwitterionic Stealth Dye-Loaded Polymer Nanoparticles for Intracellular Imaging

Area of Science:

• Nanotechnology
• Biomedical Engineering
• Polymer Science

Background:

• Intracellular applications of fluorescent nanoparticles (NPs) are hindered by molecular crowding and cellular complexity.
• Developing ultrasmall, bright, and noninteracting (stealth) NPs is crucial for effective intracellular use.
• Achieving stealth behavior requires the thinnest possible hydrophilic shell.

Purpose of the Study:

• To develop a one-step method for preparing ultrasmall, bright, and stealthy fluorescent NPs.
• To implement stealth behavior using a zwitterionic (ZI) methacrylate-based copolymer.
• To enable advanced intracellular applications like single-particle tracking and biosensing.

Main Methods:

• Preparation of dye-loaded polymer NPs via nanoprecipitation of a zwitterionic copolymer with a rhodamine B derivative and a hydrophobic counterion.
• Characterization of NP size, brightness, and stability in physiological conditions.
• Assessment of protein adsorption resistance using fluorescence correlation spectroscopy.
• Microinjection into living cells and single-particle tracking to evaluate intracellular diffusion.

Main Results:

• Ultrasmall NPs (<15 nm) were achieved with 10 mol % ZI groups in the polymer.
• NPs demonstrated stability in physiological salt conditions and resistance to protein adsorption.
• ZI polymer NPs spread throughout the cytosol after microinjection.
• Single-particle tracking revealed up to four times faster diffusion of ZI NPs compared to PEGylated NPs.

Conclusions:

• The developed zwitterionic polymer NPs offer a promising solution for intracellular imaging and sensing.
• Their small size, brightness, and stealth properties facilitate efficient cytosolic spreading and diffusion.
• These NPs are suitable for advanced intracellular single-particle tracking and biosensing applications.