Polyacrylic acid coating of highly luminescent CdS nanocrystals for biological labeling applications

Surface coating of highly luminescent CdS nanocrystals by polyacrylic acid was demonstrated. The method proceeded in 2 steps, (i) modification of the CdS surface by alkyl molecules and (ii) polyacrylic acid coating of the surface modified CdS. Attachment of alkyl ammonium on the CdS surface induced a phase transfer reaction from an aqueous to a non-polar phase with a yield of ∼100%. Investigating alkyl molecules with various functional groups revealed that the alkyl molecules, possessing the cation moiety, such as amine or ammonium salt, can electrostatically interact with the CdS surface. The PL of the uncoated nanocrystals was almost entirely quenched in the pH range of ∼7, while the polyacrylic acid coated nanocrystals exhibited moderate PL intensity. This PL intensity was preserved for at least several days, facilitating biological labeling application under a neutral condition.

We demonstrate the methods to coat photoluminescent CdS nanoparticles by polyacrylic acid. The coated nanocrystals maintained photoluminescence intensity even in neutral pH for at least several days.Figure optionsDownload as PowerPoint slide