Cellular Uptake and Cytotoxicity of Gold Nanorods: Molecular Origin of Cytotoxicity and Surface Effects

Gold nanorods of different aspect ratios are prepared using the growth‐directing surfactant, cetyltrimethylammonium bromide (CTAB), which forms a bilayer on the gold nanorod surface. Toxicological assays of CTAB‐capped nanorod solutions with human colon carcinoma cells (HT‐29) reveal that the apparent cytotoxicity is caused by free CTAB in solution. Overcoating the nanorods with polymers substantially reduces cytotoxicity. The number of nanorods taken up per cell, for the different surface coatings, is quantitated by inductively coupled plasma mass spectrometry on washed cells; the number of nanorods per cell varies from 50 to 2300, depending on the surface chemistry. Serum proteins from the biological media, most likely bovine serum albumin, adsorb to gold nanorods, leading to all nanorod samples bearing the same effective charge, regardless of the initial nanorod surface charge. The results suggest that physiochemical surface properties of nanomaterials change substantially after coming into contact with biological media. Such changes should be taken into consideration when examining the biological properties or environmental impact of nanoparticles. Gold nanorods with different surface charges are prepared using a wet‐chemical method combined with layer‐by‐layer polyelectrolyte coating approaches (see image, scale bar = 100 nm). Toxicity studies using a human colon carcinoma cell line indicate similar toxicity profiles for both positively and negatively coated gold nanorods. Serum proteins from cell growth media adsorb onto nanorods, regardless of initial nanorod surface charge.