(45h) Length Selective Delivery and Altered Subcellular Processing of Protein Stabilized Single Wall Carbon Nanotubes

Single wall carbon nanotubes (SWCNTs) are increasingly being investigated for biomedical imaging, sensing, and drug delivery.  Selective cellular delivery and preservation of inherent SWCNT properties within cells are crucial for the realization of SWCNTs as safe and effective biomaterials. SWCNT uptake and subsequent intracellular trafficking are dictated by the cellular entry mechanism.  Specialized immune cells known as macrophages are capable of two size dependent entry mechanisms, endocytosis and phagocytosis.  To determine how SWCNT entry via these mechanisms affects cellular uptake and subcellular distribution, we created SWCNT dispersions with three different lengths ranging from nm to μm.  In order to maintain SWCNT optical properties and promote cellular uptake into macrophages, we noncovalently dispersed SWCNTs with bovine serum albumin.  Using Raman spectroscopy, we quantify cellular uptake as well as track the intracellular state of the SWCNTs as a function of SWCNT length in macrophages.  We find that bulk uptake in cells increases with decreasing SWCNT length.  We also observe smaller, more numerous endosomes as SWCNT length decreases, suggesting that increased bulk uptake is driven by efficient entry and processing via endocytosis.  Highly concentrated intracellular regions of SWCNTs are observed in phase dense endosomes which correlate with changes in SWCNT properties observed via Raman spectroscopy.  SWCNTs in these regions were found to be less isolated and more aggregated resulting in disruption of SWCNT properties including reduced NIR fluorescence intensity and suggesting the removal of the protein dispersing agent.  Similar SWCNT property changes are not observed in fibroblasts treated with equal length SWCNTs at the same concentration.  Longer SWCNTs forced to enter through phagocytosis remain relatively isolated with preserved SWCNT properties compared to their shorter counterparts.  We hypothesize that aggregation of SWCNTs within macrophages but not fibroblasts may facilitate the retention of SWCNTs within macrophages.  Further, the greater individualization of SWCNTs in fibroblasts may promote their release from the cell over time which could have useful implications for cell based delivery systems.