Nano Emitters and Innate Immunity: The Role of Surfactants and Bio-Coronas in Myeloperoxidase-catalyzed Oxidation of Pristine Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) are experimentally utilized in in-vivo imaging and photothermal cancer therapy for their unique physicochemical and electronic properties. For these applications, pristine carbon nanotubes are often modified by polymer surfactant coatings to improve their bio-compatibility, adding more complexity to their recognition and biodegradation by immuno-competent cells. Here, we investigate the oxidative degradation of SWCNTs catalyzed by neutrophil myeloperoxidase (MPO) using bandgap near-infrared (NIR) photoluminescence and Raman spectroscopy. Our results show diameter-dependence at the initial stages of the oxidative degradation of sodium cholate-, DNA-, and albumin-coated SWCNTs, but not phosphatidylserine-coated SWCNTs. Moreover, sodium deoxycholate- and phospholipid-polyethylene glycol coated SWCNTs were not oxidized under the same reaction conditions, indicating that surfactant can greatly impact the biodegradability of nanomaterial. Our data also revealed that possible binding between MPO and surfactant coated-SWCNTs was unfavorable, suggesting that oxidation is likely caused by hypochlorite generated through halogenation cycle of free MPO, and not MPO bound to SWCNTs surface. Identification of SWCNT diameters and coatings that retain NIR fluorescence during the interactions with the components of innate immune system is important for their applications in in-vivo imaging.