Aqueous quantum dots with high fluorescence, colloidal stability and biocompatibility encapsulated by an amphiphilic fluorine copolymer

Abstract

Quantum dots (QDs) encapsulated by amphiphilic fluorine copolymers have shown great promise as molecular probes for bio-imaging. Here, a series of amphiphilic fluorine copolymers, methoxypolyethylene glycols-block-poly (2-(diethylamino)ethyl methacrylate)-block-poly (2,2,3,4,4,4-hexafluorobutyl methacrylate) (OmAnFp), were successfully coated on the surface of semi conductive quantum dots (QDs) to overcome their stability issues in aqueous solution. The hydrodynamic diameters (Dh,DLS) of these OmAnFp encapsulated QDs (OmAnFp@QDs) can be tuned between 40 nm and 61 nm by choosing amphiphilic fluorine copolymers with different hydrophobic portions. The obtained OmAnFp@QDs colloids are found stable over a wide pH range (4.0–12.0) with no sign of aggregation. In the pH range of 4.0–7.0, the repulsion of block O and cationic block A on OmAnFp@QDs contributes to the colloids’ stability in aqueous solution. The protonation of block A also leads to the decrease of Dh,DLS from 61 to 51 nm and the enhancement of the transmittance of O113A11F19@QDs solution from 78% to 92%. In the pH range from 8.0 to 12.0, the repulsion between the strong hydrated block O makes OmAnFp@QDs nanoparticles stable with deprotonated hydrophobic block A. The fluorescent quantum yield properties of QDs are well preserved in OmAnFp@QDs aqueous solution due to the protection of block F wrapping tightly around the QDs cores. The photoluminescence quantum yield (PL QY) is found reserved better under basic conditions due to the co-encapsulation of hydrophobic block A. The PL intensity of OmAnFp@QDs in 400 mM NaCl solution changes only slightly. Block O and F in the polymer offer OmAnFp@QDs with good biocompatibility and low levels of nonspecific binding to bovine serum albumin proteins (BSA). These advantages render OmAnFp@QDs an attractive candidate as ideal fluorescent probes in advanced biomedical imaging studies.