Engineered nanoparticles have increased in prominence for biological sensing (Zhang, Nat. Nanotechnol., 2013), imaging (Bonis-O’Donnell, Adv. Funct. Mater., 2017), and transgene delivery (Demirer, CEP, 2017) applications due to their distinctive optical and physical properties. In particular, semiconducting single-wall carbon nanotubes (SWCNTs) are a top candidate for nanosensor development owing to their photostability, biocompatibility, and emission in the near-infrared (nIR) region over which biological samples are optically transparent. Our lab has developed a platform for creating synthetic nanosensors based on the electrostatic pinning of biomimetic polymers, such as single-stranded DNA, onto SWCNTs. Modifying SWCNTs in this manner allows selective recognition of target molecules by the polymer and signal transduction by the nIR-emissive SWCNT, and thus the development of ‘synthetic antibodies’ (Bonifazi, Nat. Nanotechnol., 2017). When a target molecule binds and perturbs the local SWCNT electronic environment, the SWCNT fluorescence emission spectrum is modulated and hence provides a signal that can be harnessed for sensing purposes. These biological probes operate at spatiotemporal scales necessary to capture information on complex biological systems, such as neuromodulatory chemical signaling in the brain. Further, our lab has applied this SWCNT platform to demonstrate delivery of genetic cargo to mature plants (Demirer, Pre-print, 2017). The critical – and often overlooked – challenge with such novel tools is understanding the fundamental mechanisms of interaction between the nanoprobe and the system they are designed to query. When a nanoparticle enters a biological system, the surface becomes coated with proteins to form the ‘protein corona’. Binding of proteins to the nanoparticle not only affects the structure and function of the proteins, but has the added consequence of unpredictably re-defining the nanoparticle identity and potentially preventing the nanoparticle from carrying out its designated function.
To apply such probes in living biological systems, it is critical to understand: (i) what coats a nanoparticle upon exposure to a biological system, (ii) how this binding process occurs, and (iii) why these particular biomolecules coat the nanoparticle. My work develops and tests a novel view of protein corona formation around SWCNT-based dopamine nanosensors for applications in an unexplored system: cerebrospinal fluid (CSF) in the extracellular space of the brain. The method presented here involves (i) experimentally investigating protein corona composition, (ii) experimentally probing the thermodynamics and kinetics of protein binding, and (iii) modeling experimental results with the framework provided by colloid and surface science theory. Future work will apply this mechanistic understanding of the system to implement rational protein corona design for SWCNT-nanosensors. Specifically, pre-coating the nanosensors with strategically-engineered biomimetic polymers and/or proteins will create a designer corona to carry out specific tasks.
Quantifying the composition, driving forces of formation, and timescales upon which the nanoparticle corona forms will establish parameters for the design and implementation of dopamine SWCNT-nanosensors to study the innumerable complexities of the brain. Moreover, the generalizable nature of the system developed herein will provide a ubiquitous platform for validation of the numerous nanoscale probes currently in development or in use to probe complex biological systems.