Cytotoxicity assessment of silica-based nanosized contrast agents for ultrasound molecular imaging

Nanosized contrast agents for medical imaging are being increasingly studied because of their potential for direct and selective targeting of diseased cells located in the extravascular compartment. Recently, our research group has experimentally investigated the echogenicity of silica nanospheres (SiNSs), potentially useful for tumor targeting purposes, demonstrating their contrast enhancement power on conventional ultrasound (US) images in a wide range of sizes and concentrations. In the present work, we evaluated the "in vitro" cytotoxicity of SiNSs at variable concentration in human cervical cancer cell line (HeLa). Toxicity of SiNSs with diameter in our investigated range (160-330 nm) had never been previously quantified, although this is the most promising size interval for US targeted imaging. Our reported results indicated a SiNS concentration range which does not cause appreciable decrements in cell survival, being therefore safely exploitable for contrast-enhanced US imaging.