PEG-DHLA Ligand Engineering for Water-Dispersible and Protein-Stable Quantum Dots
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Abstract
Quantum dots (QDs) are fluorescent nanomaterials useful for biosensing and immunoassays owing to their high photoluminescence efficiency, narrow emission spectra, and excellent photostability. However, high-quality QDs are generally stabilized with hydrophobic ligands, which limits their direct use in aqueous and protein-containing biological environments. Therefore, surface modification is required to improve water dispersibility and colloidal stability while preserving the optical properties of QDs and reducing nonspecific adsorption. In this study, various core-type QDs were rendered water-dispersible using dihydrolipoic acid-functionalized poly(ethylene glycol) (PEG-DHLA) ligands, and the effects of PEG chain length on ligand exchange, dispersion stability, and optical properties were evaluated. The dispersion behavior of PEG-DHLA-coated QDs depended on both QD core size and PEG chain length, and shorter PEG-DHLA ligands were more favorable for the phase transfer of relatively small QDs. After ligand exchange, Cd-based red-emitting QDs retained over 80% absolute photoluminescence quantum yield in water, indicating that the PEG-DHLA coating effectively preserved their high emission properties. In addition, PEG-DHLA-coated QDs maintained their dispersibility and photoluminescence in albumin-containing buffer without noticeable aggregation. Furthermore, nonspecific adsorption was evaluated on albumin-coated PDMS surfaces by comparing the residual fluorescence after QD introduction and washing. The residual signal was observed to be low, indicating reduced nonspecific adsorption to protein-coated surfaces. These results show that PEG-DHLA-based surface modification can simultaneously improve QD stability and low-adsorption properties in aqueous media and protein-rich interfaces. Overall, PEG-DHLA-coated QDs have potential as bright, stable, and low-background fluorescent nanoprobes for solution-based biosensing and surface-based immunoassays.
