Carbon Nanotube Sensor Passivation Mitigates Inflammatory Response in Microglia

Abstract

Non-covalent functionalization of single-walled carbon nanotubes (SWCNTs) has enabled advances in biomolecule imaging. In particular, modification of SWCNTs with select sequences of single-stranded DNA (ssDNA) produces near infrared optically active sensors for neurotransmitters such as dopamine, enabling high spatiotemporally resolved optical recording of synaptic and extrasynaptic signaling. However, the carbon lattice surface of SWCNT induces activation of the innate immune system, leading to an inflammatory response. Activation of microglia, the brain’s resident immune cells, is of particular relevance to imaging neuromodulation. Here, we show that non-covalent ssDNA-SWCNT nanosensor passivation with a PEGylated phospholipid can mitigate microglial activation while maintaining the nanosensor’s response towards dopamine. To do so, we screen a candidate library of PEGylated biomolecules, nonionic surfactants, and block copolymers against their ability to mitigate the microglial immune response as measured by transcriptomic analysis. We find that PEGylated phospholipids are capable of adsorption to ssDNA-SWCNTs without significant ssDNA displacement, with moderate reduction in nonspecific protein adsorption. These trends are recapitulated by a reduction in inflammatory response of SIM-A9 microglial cells, marked by lowered expression of cytokines CXCL2 and IL-6, mitigated morphological change, and decreased cytotoxicity. Taken together, these results suggest noncovalent passivation improves biocompatibility of DNA-SWNCT nanosensors and provides the groundwork for implementing similar passivation methods for other optical probes of this class.