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Unexpected Changes in Functionality and Surface Coverage for Au Nanoparticle PEI Conjugates: Implications for Stability and Efficacy in Biological Systems.

Authors :
Cho TJ
Pettibone JM
Gorham JM
Nguyen TM
MacCuspie RI
Gigault J
Hackley VA
Source :
Langmuir : the ACS journal of surfaces and colloids [Langmuir] 2015 Jul 14; Vol. 31 (27), pp. 7673-83. Date of Electronic Publication: 2015 Jul 02.
Publication Year :
2015

Abstract

Cationic polyethylenimine conjugated gold nanoparticles (AuNP-PEI) are a widely studied vector for drug delivery and an effective probe for interrogating NP-cell interactions. However, an inconsistent body of literature currently exists regarding the reproducibility of physicochemical properties, colloidal stability, and efficacy for these species. To address this gap, we systematically examined the preparation, stability, and formation mechanism of PEI conjugates produced from citrate-capped AuNPs. We considered the dependence on relative molar mass, Mr, backbone conformation, and material source. The conjugation mechanism of Au-PEI was probed using attenuated total reflectance FTIR and X-ray photoelectron spectroscopy, revealing distinct fates for citrate when interacting with different PEI species. The differences in residual citrate, PEI properties, and sample preparation resulted in distinct products with differentiated stability. Overall, branched PEI (25 kDa) conjugates exhibited the greatest colloidal stability in all media tested. By contrast, linear PEI (25 kDa) induced agglomeration. Colloidal stability of the products was also observed to correlate with displaced citrate, which supports a glaring knowledge gap that has emerged regarding the role of this commonly used carboxylate species as a "place holder" for conjugation with ligands of broad functionalities. We observed an unexpected and previously unreported conversion of amine functional groups to quaternary ammonium species for 10 kDa branched conjugates. Results suggest that the AuNP surface catalyzes this conversion. The product is known to manifest distinct processes and uptake in biological systems compared to amines and may lead to unintentional toxicological consequences or decreased efficacy as delivery vectors. Overall, comprehensive physicochemical characterization (tandem spectroscopy methods combined with physical measurements) of the conjugation process provides a methodology for elucidating the contributing factors of colloidal stability and chemical functionality that likely influence the previously reported variations in conjugate properties and biological response models.

Details

Language :
English
ISSN :
1520-5827
Volume :
31
Issue :
27
Database :
MEDLINE
Journal :
Langmuir : the ACS journal of surfaces and colloids
Publication Type :
Academic Journal
Accession number :
26114747
Full Text :
https://doi.org/10.1021/acs.langmuir.5b01634