Li et al. Nanoscale Res Lett 2011, 6:29 http://www.nanoscalereslett.com/content/6/1/29 collected by centrifugation at 1,000 g for 5 min. Then, the supernatant solutions were discarded. The pellets were resuspended with PBS to eliminate the effect of medium in the fluorescence detection. And the cell sus- pension was detected on a Leica TCS SP2 (Leica). In the control experiments, only daunorubicin or PLA/ Au nanocomposites were injected for relevant cellular incubation. The freshly prepared cell culture was dropped on a strictly cleaned glass plate immediately before the measurement. The excitation wavelength of fluorescence was 480 nm. All the optical measurements were carried out at room temperature (20 ± 2°C). Results and Discussion AFM Study of PLA/Au Nanocomposites Conjugated with Daunorubicin As shown in Figures 1 and 2, the AFM images of PLA nanofibers, Au nanoparticles and the blending of the PLA/Au nanocomposites with daunorubicin demon- strate that upon blending of daunorubicin with the PLA/Au nanocomposites, some relatively large nano- spheres appear at PLA chains. It is observed that there was a discernible substrate under the spherical particles, which is at the same level as the pure PLA nanofiber, the average height of which is about 1.5 ± 0.05 nm. Meanwhile, relevant measurements show that the aver- age height of the conjugated nanocomplexes was (26 ± 0.62) nm, and the average outer diameter of spherical nanoparticles was (22 ± 0.55) nm. It is apparent that the Au nanoparticles and the drug molecules could self- assemble or pack together to form the spherical particles on poly(lactic acid) nanofibers, as shown in Figure 2. The rational behind this could be attributed to the fact that daunorubicin is positively charged while the relative surface of nano PLA/Au polymer nanofibers is nega- tively charged in pH 7.2 PBS solution. Thus, Page 3 of 8 daunorubicin could be readily self-assembled onto the surface of PLA/Au nanocomposites through electrostatic interaction and other non-covalent binding. Since the PLA nanofiber has a very high continuous surface area, it has attracted a great deal of attention in fabricating continuous ultrafine fibers or fibrous struc- tures for various polymers, with typical examples includ- ing engineering plastics, biopolymers and polymer blends [32,33]. From the specific nanostructure of the PLA nanofibers and the relevant nanocomposites observed in above AFM study, it is evident that the anticancer drug daunorubicin could be readily self- assembled on the surface of the new PLA/Au nanocom- posites, which could be utilized as a new promising carrier for nanomedicine in cancer treatment. Fluorescence Imaging of Intracellular Drug Delivery in Leukemia Cancer Cells Based on the above observations, the PLA/Au nanocom- posites have been further explored as a new potential drug carrier for efficient drug delivery. Initially, the microscopy images of leukemia cancer cells in the absence and presence of PLA/Au nanocomposites have been investigated by optical microscopy. As shown in Figure 3, it is observed that the drug-sensitive leukemia cancer cells K562 and drug-resistant leukemia cancer cells K562/AO2 had the good morphology in the nega- tive control. While K562 cells were cultured with DNR conjugated with PLA/Au nanocomposites, significant morphological changes were detected and more cell death occurred than that of cells treated with DNR alone. In comparison, there were no any morphological changes for drug-resistant leukemia cells K562/AO2 after treated with DNR alone because of the relevant multidrug resistance, as shown in Figure 3b and 3d. After the cells were treated by DNR conjugated with Figure 1 Typical AFM images of a Au nanoparticles, and b PLA nanofiber.