With their bright, photostable fluorescence, semiconductor quantum dots show promise as alternatives to organic dyes for biological labeling. Questions about their potential cytotoxicity, however, remain unanswered. While cytotoxicity of bulk cadmium selenide (CdSe) is well documented, a number of groups have suggested that CdSe QDs are cytocompatible, at least with some immortalized cell lines. Using primary hepatocytes as a liver model, we found that CdSe-core QDs were indeed acutely toxic under certain conditions. Specifically, we found that the cytotoxicity of QDs was modulated by processing parameters during synthesis, exposure to ultraviolet light, and surface coatings. Our data further suggests that cytotoxicity correlates with the liberation of free Cd ions due to deterioration of the CdSe lattice. When appropriately coated, CdSe-core QDs can be rendered non-toxic and used to track cell migration and reorganization . Our results inform design criteria for the use of QDs in vitro and especially in vivo where deterioration over time may occur.

time. This might be a promising antimicrobial coating for a wide range of materials for biomedical or daily-life applications. ExperimentalPEI (MW 5000 g/mol) was purchased from Hyperpolymers (Freiburg, Germany). All other chemicals, if not stated otherwise, were from Fluka and used without further purification. One gram of PEI was suspended in 50 mL acetone and the mixture was cooled to 0 C . Methacryloyl chloride (0.83 mL dissolved in 35 mL acetone) was added dropwise to the stirred suspension within 20 min. After 30 min at 0 C, 150 mL of methanol and 20.4 mL of HEA were added to give a clear solution. The solvents were removed under reduced pressure, the PEI-MA/HEA stock solution was further diluted with HEA to control the PEI content, and 1 mg of the photoinitiator Irgacure 651 (Ciba) was dissolved in 1 mL of the solution. 20 lL of the this mixture was spread on a commercial glass slide previously modified with methacryloyloxy-propyltrimethoxysilane using a standard procedure [20]. The slide was then covered with another glass slide, previously coated with a polypropylene film. The liquid layer between the two slides was UV cured in the UV reactor Heraflash from Heraeus-Kulzer (Hanau, Germany) for 180 s to give a transparent film. The films were then washed with water/methanol/triethylamine (TEA) (1:1:1 v/v/v), water/methanol (1:1 v/v), and water, than immersed in a solution of 250 mg AgNO 3 in 8 mL water for 30 s, washed with water, and finally added to 50 mL of an aqueous solution of ascorbic acid (10 mg mL ±1 ). The modification of the films with PEG was performed as follows: The samples were washed with the water/methanol/TEA mixture, methanol, and acetone, then immersed into a solution of 2 g cyanuric chloride in 10 mL acetone at room temperature overnight, rinsed with acetone and chloroform, and finally left in a solution of 2 g O-2-aminoethyl-O¢-methoxy polyethylene glycol (MW 5000 g/ mol) in 10 mL chloroform for 24 h at room temperature. Prior to use the films were thoroughly rinsed with chloroform and immersed in a large amount of water for at least 24 h.UV-vis measurements were carried out with the photospectrometer Lambda 11 from Perkin Elmer. AFM images were recorded with a Nanoscope III scanning probe microscope using Si cantilevers with a fundamental resonance frequency of around 200 kHz. TEM measurements were carried out using a LEO 912 transmission electron microscope applying an acceleration voltage of 120 kV. The silver content was determined using the flame-atom absorption spectrometer Vario 6 from Analytik-Jena-AG (Jena, Germany).The bacterial susceptibility measurement was carried out according to a modified procedure described earlier [21]. S. aureus (ATCC 25123) cells were cultivated by adding 100 lL of a suspension of the bacterial cells in PBS (10 11 cells/mL) to 50 mL of a standard growth medium from Merck and incubating it under shaking at 37 C for 6 h. The bacterial suspension was then centrifuged at 2750 rpm for 10 min, the cells were washed twice with PBS, pH 7.0, re-suspended in...

Nanoparticle-based diagnostics and therapeutics hold great promise because multiple functions can be built into the particles. One such function is an ability to home to specific sites in the body. We describe here biomimetic particles that not only home to tumors, but also amplify their own homing. The system is based on a peptide that recognizes clotted plasma proteins and selectively homes to tumors, where it binds to vessel walls and tumor stroma. Iron oxide nanoparticles and liposomes coated with this tumorhoming peptide accumulate in tumor vessels, where they induce additional local clotting, thereby producing new binding sites for more particles. The system mimics platelets, which also circulate freely but accumulate at a diseased site and amplify their own accumulation at that site. The self-amplifying homing is a novel function for nanoparticles. The clotting-based amplification greatly enhances tumor imaging, and the addition of a drug carrier function to the particles is envisioned.clotting ͉ liver ͉ peptide ͉ tumor targeting ͉ iron oxide