With the potential wide uses of nanoparticles such as carbon nanotubes in biomedical applications, and the growing concerns of nanotoxicity of these engineered nanoparticles, the importance of nanoparticle–protein interactions cannot be stressed enough. In this study, we use both experimental and theoretical approaches, including atomic force microscope images, fluorescence spectroscopy, CD, SDS-PAGE, and molecular dynamics simulations, to investigate the interactions of single-wall carbon nanotubes (SWCNTs) with human serum proteins, and find a competitive binding of these proteins with different adsorption capacity and packing modes. The π - π stacking interactions between SWCNTs and aromatic residues (Trp, Phe, Tyr) are found to play a critical role in determining their adsorption capacity. Additional cellular cytotoxicity assays, with human acute monocytic leukemia cell line and human umbilical vein endothelial cells, reveal that the competitive bindings of blood proteins on the SWCNT surface can greatly alter their cellular interaction pathways and result in much reduced cytotoxicity for these protein-coated SWCNTs, according to their respective adsorption capacity. These findings have shed light toward the design of safe carbon nanotube nanomaterials by comprehensive preconsideration of their interactions with human serum proteins.

Upon shearing a microscale lithographically defined graphite mesa, the sheared section retracts spontaneously to minimize interface energy. Here, we demonstrate a sixfold symmetry of the self-retraction and provide a first experimental estimate of the frictional force involved, as direct evidence that the self-retraction is due to superlubricity, where ultralow friction occurs between incommensurate surfaces. The effect is remarkable because it occurs reproducibly under ambient conditions and over a contact area of up to 10\ifmmode\times\else\texttimes\fi{}10\,\,$\mu${}m2, more than 7 orders of magnitude larger than previous scanning-probe-based studies of superlubricity in graphite. By analyzing the sheared interface, we show how the grain structure of highly oriented pyrolitic graphite determines the probability of self-retraction. Our results demonstrate that such self-retraction provides a novel probe of superlubricity, and the robustness of the phenomenon opens the way for practical applications of superlubricity in micromechanical systems.

CD44/CD24 and ALDH1 are widely used cancer stem cell (CSC) markers in breast cancer. However, their expression is not always consistent even in the same subtype of breast cancer. Systematic comparison of their functions is still lacking. We investigated the expression of CD44, CD24 and ALDH1 in different subtypes of breast cancer cells, and explored their relationship with cancer progression. We defined a parameter CD44/CD24 ratio to present the expression level of CD44 and CD24 and found that high CD44/CD24 ratio and ALDH1⁺ are both indicators for cancer malignancy, but play different functions during tumor progression. High CD44/CD24 ratio is more related to cell proliferation and tumorigenesis, which is confirmed by mammosphere formation and tumorigenesis in xenotransplanted mice. ALDH1⁺ is a stronger indicator for cell migration and tumor metastasis. Suppression of CD44 and ALDH1 by siRNA led to decreased tumorigenicity and cell migration capacity. The combination of high CD44/CD24 ratio and ALDH1⁺ would be a more reliable way to characterize CSCs. Moreover, both high CD44/CD24 ratio and ALDH1⁺ were conserved during metastasis, from the primary tumors to the circulating tumor cells (CTCs) and the distant metastases, suggesting the significant value of these CSC markers in assisting cancer detection, prognostic evaluation, and even cancer therapeutics.