Ultraefficient Cap-Exchange Protocol To Compact Biofunctional Quantum Dots for Sensitive Ratiometric Biosensing and...

Area of Science:

• Nanotechnology
• Bioconjugation
• Quantum Dot Chemistry

Background:

• Hydrophobic quantum dots (QDs) require surface modification for biological applications.
• Existing cap-exchange methods often demand high ligand ratios and can compromise QD properties.
• Stable, biocompatible QDs are crucial for advanced bioimaging and sensing.

Purpose of the Study:

• To develop an ultraefficient cap-exchange protocol (UCEP) for preparing stable, water-dispersible quantum dots.
• To demonstrate the utility of UCEP-modified QDs in sensitive protein detection and cellular imaging.
• To reduce the ligand-to-QD ratio required for effective surface functionalization.

Main Methods:

• Developed an ultraefficient cap-exchange protocol (UCEP) using lipoic acid (LA)-based ligands and tris(2-carboxylethyl phosphine) for in situ reduction.
• Prepared compact, bright, and stable quantum dots with low hydrodynamic radii (< 4.5 nm) and high fluorescence retention (> 90%).
• Utilized UCEP-modified QDs for conjugation with His8-tagged Affimers and biotinylation for protein detection and cellular imaging.

Main Results:

• Achieved water-dispersible quantum dots at ligand:QD molar ratios 20-200 fold lower than literature methods.
• Demonstrated resistance to nonspecific protein adsorption and stability in high-salt biological buffers (2 M NaCl).
• Enabled rapid, ratiometric detection of target proteins (Affimer target protein down to 10 pM, neutravidin down to 5 pM) using QD-sensitized FRET and biotinylated QDs.

Conclusions:

• The UCEP offers a highly efficient and convenient method for producing high-quality quantum dots for biological applications.
• UCEP-derived quantum dots are suitable for sensitive ratiometric biosensing and fluorescence imaging of cancer cells.
• This protocol significantly advances the use of quantum dots in bioconjugation and diagnostics.