Does Shape Matter? Bioeffects of Gold Nanomaterials in a Human Skin Cell Model Nicole M. Schaeublin, † Laura K. Braydich-Stolle, † Elizabeth I. Maurer, † Kyoungweon Park, ‡ Robert I. MacCuspie, § A. R. M. Nabiul Afrooz, ⊥ Richard A. Vaia, ‡ Navid B. Saleh, ⊥ and Saber M. Hussain* ,† Applied Biotechnology Branch, † Human Effectiveness Directorate, 711 Human Performance Wing, Air Force Research Laboratory, Wright-Patterson AFB, Dayton, Ohio 45431, United States ‡ Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Dayton, Ohio 45431, United States § Ceramics Division, Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States ⊥ Civil and Environmental Engineering, University of South Carolina, Columbia, South Carolina 29208, United States * S Supporting Information ABSTRACT: Gold nanomaterials (AuNMs) have distinctive electronic and optical properties, making them ideal candidates for biological, medical, and defense applications. Therefore, it is imperative to evaluate the potential biological impact of AuNMs before employing them in any application. This study investigates two AuNMs with different aspect ratios (AR) on mediation of biological responses in the human keratinocyte cell line (HaCaT) to model potential skin exposure to these AuNMs. The cellular responses were evaluated by cell viability, reactive oxygen species (ROS) generation, alteration in gene and protein expression, and inflammatory response. Gold nanospheres, nominally 20 nm in diameter and coated with mercaptopropane sulfonate (AuNS- MPS), formed agglomerates when dispersed in cell culture media, had a large fractal dimension (D f = 2.57 ± 0.4) (i.e., tightly bound and densely packed) and were found to be nontoxic even at the highest dose of 100 μg/mL. Highly uniform, 16.7 nm diameter, and 43.8 nm long polyethylene glycol-capped gold nanorods (AuNR-PEG) also formed agglomerates when dispersed into the cell culture media. However, the agglomerates had a smaller fractal dimension (D f = 1.28 ± 0.08) (i.e., loosely bound) and were found to be cytotoxic to the HaCaT cells, with a significant decrease in cell viability occurring at 25 μg/mL and higher. Moreover, AuNR- PEG caused significant ROS production and up-regulated several genes involved in cellular stress and toxicity. These results, combined with increased levels of inflammatory and apoptotic proteins, demonstrated that the AuNR-PEG induced apoptosis. Exposure to AuNS-MPS, however, did not show any of the detrimental effects observed from the AuNR-PEG. Therefore, we conclude that shape appears to play a key role in mediating the cellular response to AuNMs. 1. INTRODUCTION The unique physical and chemical properties of gold nanoma- terials (AuNMs) have led to their inclusion in extensive biological applications, including sensors, drug and gene delivery, photothermal therapy, and contrast agents for imaging. 1-5 Gold nanorods (AuNRs) are of specific interest because of their distinctive optical properties and their tunability toward distinct plasmon resonances in the visible and near infared (NIR) regions; e.g., NIR light passes harmlessly through biological tissues, whereas AuNRs absorb light in the NIR region, thus making them an excellent candidate for thermal therapy against cancer. 6-8 Electron oscillations, or surface plasmon resonances, along the transverse and longitudinal axes result in unique absorption or scattering which is tunable based on the length and diameter (aspect ratio) of the AuNR. Such advantages in optical properties encourage nanorod usage in the biological and medical applications, which necessitates understanding their effects on biological systems. One of the primary concerns for using AuNRs in biological and medical applications is cytotoxicity caused by the surface coating cetyltrimethylammonium bromide (CTAB), utilized in the synthesis process. CTAB is a cationic surfactant often used as a capping agent to control the size and the shape of AuNRs during synthesis. However, removal of CTAB causes loss of stability and induces unwanted aggregation or agglomeration to the AuNR suspensions. 9-12 Such challenges are overcome by functionalizing the AuNR surface with a polymer, such as Received: October 18, 2011 Revised: December 20, 2011 Published: January 13, 2012 Article pubs.acs.org/Langmuir © 2012 American Chemical Society 3248 dx.doi.org/10.1021/la204081m | Langmuir 2012, 28, 3248-3258