FULL PAPER © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 3433 wileyonlinelibrary.com (RAFT) is particularly well suited to syn- thesize sulfur-end-functionalized polymers due to the use of thiocarbonate RAFT chain transfer agents (CTAs). [4] It is known that size, shape, and surface chemistry of goldNP affect their uptake by living cells. [5] However, few have been reported on whether altering the hydro- philic-to-hydrophobic ratio of a polymer coating can affect cellular interaction. In this paper we report on goldNP decorated with a series of polymers that differ in their hydrophilic-to-hydrophobic comonomer ratio and investi- gate how the latter affects cellular uptake. In addition, we devel- oped a novel flow cytometry method for label-free investigation of goldNP-cell interaction. This methodology is then used to investigate the different parameters that affect the interaction of the goldNP and in vitro cultured cells. 2. Results and Discussion Copolymers composed of the hydrophilic 2-hydroxyethylacrylate (HEA) and the hydrophobic methoxyethylacrylate (MEA) were obtained by RAFT in an automated parallel synthesis robot to minimize batch-to-batch variation. [6] Polymers with a theo- retical degree of polymerization (DP; monomer to CTA ratio) of 100 and HEA:MEA ratios of 100:0, 80:20, 60:40, 50:50, 40:60, and 20:80, respectively, were synthesized according to Scheme 1. For clarity of presentation these polymers will fur- ther on be denoted as HEA x MEA y ( x and y represent HEA and MEA to CTA ratio, respectively). Polymerization was stopped at a conversion of approximately 65% to ensure good chain end- fidelity of the polymers and Table S1, Supporting Information, summarizes their properties. In all cases linear first order poly- merization kinetics (Figure S1, Supporting Information) were observed and good control over the polymerizations was fur- ther evidenced by dispersities below 1.3. As reported earlier by Hoogenboom et al., copolymers of HEA and MEA have an ideal random monomer distribution [7] which was confirmed in our present study. The polymers HEA 40 MEA 60 and HEA 20 MEA 80 appeared to by insoluble in water at room temperature or above and were not included in further experiments. 13 nm (size measured by transmission electron micro- scopy (TEM)) citrate-stabilized goldNP were synthesized by the Tailoring Cellular Uptake of Gold Nanoparticles Via the Hydrophilic-to-Hydrophobic Ratio of their (Co)polymer Coating Zhiyue Zhang, Katleen Van Steendam, Samarendra Maji, Lieve Balcaen, Yulia Anoshkina, Qilu Zhang, Glenn Vanluchene, Riet De Rycke, Frank Van Haecke, Dieter Deforce, Richard Hoogenboom,* and Bruno G. De Geest* It is demonstrated how cellular uptake and protein corona of (co)polymer- coated gold nanoparticles can be altered by the hydrophilic-to-hydrophobic comonomer ratio. A novel, label-free flow cytometry strategy is developed to investigate particle uptake. These findings offer insight in the design and analysis of hybrid nanomaterials for interfacing with biological systems. DOI: 10.1002/adfm.201500904 Z. Zhang, Dr. K. Van Steendam, Prof. D. Deforce, Prof. B. De Geest Department of Pharmaceutics Ghent University 9000 Ghent, Belgium E-mail: br.degeest@ugent.be Dr. S. Maji, Dr. Q. Zhang, G. Vanluchene, Prof. R. Hoogenboom Supramolecular Chemistry Group Department of Organic and Macromolecular Chemistry Ghent University 9000 Ghent, Belgium E-mail: richard.hoogenboom@ugent.be Dr. L. Balcaen, Y. Anoshkina, Prof. F. Van Haecke Department of Analytical Chemistry Ghent University 9000 Ghent, Belgium R. De Rijcke Department of Biomedical Molecular Biology Ghent University 9000 Ghent, and Inflammation Research Center VIB, 9052 Zwijnaarde, Belgium 1. Introduction The design of engineered nanoparticles that can interact with living cells and tissues is important for many biomedical appli- cations, including imaging, diagnostics, and drug delivery. [1] Gold nanoparticles (goldNP) have attracted major interest due to their chemical stability, cytocompatibility, and their tunable optical and electronic properties. [2] Furthermore, (quasi) cova- lent surface functionalization of metallic gold is straightforward using sulfur-containing compounds that form self-assembled monolayers. [3] Polymer-decoration of goldNP is attractive to modulate the goldNP properties and to render them colloidally stable in complex media. To produce polymer-decorated goldNP, reversible addition fragment chain-transfer polymerization Adv. Funct. Mater. 2015, 25, 3433–3439 www.afm-journal.de www.MaterialsViews.com