Biocompatibility of gold nanoparticles in retinal pigment epithelial cell line Bedia Begüm Karakoçak a,b,1 , Ramesh Raliya a,1 , Josh T. Davis b,c , Sanmathi Chavalmane a , Wei-Ning Wang a,d , Nathan Ravi a,b,c, ⁎, Pratim Biswas a, ⁎⁎ a Aerosol and Air Quality Research Laboratory, Dept. of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO, USA b Department of Ophthalmology and Visual Sciences, Washington University in St. Louis, St. Louis, MO, USA c Veterans Affairs Medical Center, St. Louis, MO, USA d Department of Mechanical and Nuclear Engineering, Virginia Commonwealth University, Richmond, VA, USA abstract article info Article history: Received 23 July 2016 Accepted 30 August 2016 Available online 04 September 2016 Gold nanoparticles (Au NPs) have been tested as targeted delivery agents because of their high chemical stability and surface plasmon properties. Here, we investigated the biocompatibility of Au spheres (5-, 10-, 20-, 30-, 50-. and 100-nm), cubes (50-nm), and rods (10 × 90 nm) on a retinal pigment epithelial (ARPE-19) cell line. The le- thal dose for killing 50% of the cells (LD 50 ) was evaluated using an MTT (3-[4, 5 dimethyl-thiazoly-2-yl] 2-5 diphenyl tetrazolium bromide) assay. At and above LD 50 , based on mass concentrations, the confluent cell layer began to detach, as shown by real-time measurements of electric impedance. We found that the biocompat- ibility of spheres improved with increasing nanoparticle size. The Au rods were less biocompatible than 10-nm spheres. Confocal microscopy showed that cubic (50-nm) and spherical NPs (50- and 100-nm) neither had cyto- toxic effects nor entered cells. Lethal doses for internalized spherical NPs, which were toxic, were recalculated based on surface area (LD 50,A ) concentrations. Indeed, when biocompatibility was expressed as the surface area concentration of NPs, the curve was independent of size. The LD 50,A of Au nanospheres was 23 cm 2 /ml. Our findings demonstrate that the sole modulation of the surface area would make it possible to use Au NPs for therapeutic purposes. © 2016 Published by Elsevier Ltd. Keywords: Biocompatibility Retina Cytotoxicity Gold nanoparticles Electrical impedance Surface area 1. Introduction Materials at the nanometer scale have a large surface area to mass ratio, which gives them novel properties that differ markedly from those of other material properties with corresponding bulk sizes. Recent advances in the synthesis and biomolecular functionalization of engineered nanoparticles have led to a dramatic expansion of their po- tential biomedical applications, including their use as nanoprobes (Leduc et al., 2013), nanosensors (Swierczewska et al., 2012) and in bioimaging (Peng et al., 2006; Ruiz-Ederra et al., 2005), photothermal therapy (Ryu et al., 2012), gene therapy (Raju et al., 2011; Shestopalov et al., 2002), targeted drug delivery, and tissue engineering (Austin et al., 2015; Kompella et al., 2013; Naha et al., 2015; Parveen et al., 2012). Specifically, gold nanoparticles (Au NPs) are being used because of their intrinsic characteristics, such as high chemical stability, suitable surface functionalization, and unique surface plasmon properties (Diebold and Calonge, 2010; Parveen et al., 2012). Researchers have attempted nanoparticle-mediated drug and gene delivery to tissues of the eye, including the retina, to treat major eye dis- eases such as age-related macular degeneration and diabetes-related retinopathy (Jin Hyoung et al., 2011; Joris et al., 2013; Li et al., 2012a; Ngwa et al., 2012a; Ngwa et al., 2012b). Moreover, intravitreal injection of Au NPs has been investigated for retinal imaging and inhibition of an- giogenesis to prevent macular degeneration (Farjo and Ma, 2010; Jeong Hun et al., 2009). Au NPs have been shown to be promising agents for enhanced delivery of anti-VEGF antibody or other antiangiogenic agents to specific sites in the eye (Diebold and Calonge, 2010; Hayashi et al., 2009a; Jeong Hun et al., 2009). Currently, intravitreal and topical routes are most commonly used (Hayashi et al., 2009b). The use of intravitreal injection of nanoparticles depends on the safety of the particles (Biswas and Wu, 2005; Diebold and Calonge, 2010; Kompella et al., 2013). Therefore, safety concerns necessitate a better understanding of the potential toxicity hazards of novel mate- rials. One method of measuring toxicity is to examine cellular viability (Abe and Saito, 1999) by determining the lethal dose concentration (LD 50 ), the dose required to kill 50% of the cells. Lethal doses of selected Toxicology in Vitro 37 (2016) 61–69 ⁎ Correspondence to: N. Ravi, Department of Ophthalmology and Visual Sciences, Washington University in St. Louis, St. Louis, MO, USA. ⁎⁎ Corresponding author. E-mail addresses: ravi@vision.wustl.edu (N. Ravi), pbiswas@wustl.edu (P. Biswas). 1 Equal contribution. http://dx.doi.org/10.1016/j.tiv.2016.08.013 0887-2333/© 2016 Published by Elsevier Ltd. Contents lists available at ScienceDirect Toxicology in Vitro journal homepage: www.elsevier.com/locate/toxinvit