The Impact of Covalent Functionalization on Single-Walled Carbon Nanotube Biosensor Fluorescence and Function

Abstract

Single-walled carbon nanotubes (SWCNTs) are advantageous signal transduction elements for biological imaging and sensing due to their notable fluorescence in the near-infrared (NIR) region with minimal light absorbance by water or scattering by tissue (1). Recently, exciting developments in SWCNT surface chemistry have shown the retention and improvement of fluorescence intensity in SWCNTs after covalent surface functionalization (2). These chemistries provide chemical handles for specific attachment of molecules of interest to the SWCNT surface while keeping the intrinsic SWCNT NIR fluorescence intact for bioimaging and sensing applications. However, despite their unperturbed fluorescence, it is unclear whether functionalized SWCNTs maintain their ability for molecular sensing, which necessitates a modulation in SWCNT fluorescence provided by the molecular recognition of a noncovalently surface-adsorbed polymer. We compare the photophysical properties of functionalized SWCNTs to their pristine counterparts, and show SWCNT optical properties remain available for sensing applications, however with noted attenuation of fluorescence modulation between certain surface coating and analyte pairs. Molecular recognition provided by phospholipid SWCNT surface coatings maintain their ability to detect molecular analytes such as fibrinogen and insulin. Conversely, DNA oligonucleotide surface coatings under-perform for molecular recognition of dopamine compared to sensors constructed from pristine SWCNTs. We also discuss the use of covalent handles to tune the intrinsic properties of the SWCNT surface for use as biological tools. Lastly, we explore the application of covalently functionalized SWCNTs as dual-functional nanoparticles with both targeting and sensing capabilities. Our work establishes the potential advantages and drawbacks of covalent SWCNT functionalization, despite preservation of SWCNT fluorescence, and implications for applications in molecular sensing.(1) Bonis-O’Donnell, J. T. D.; Page, R. H.; Beyene, A. G.; Tindall, E. G.; McFarlane, I. R.; Landry, M. P. Dual Near-Infrared Two-Photon Microscopy for Deep-Tissue Dopamine Nanosensor Imaging. Adv. Funct. Mater. 2017, 27 (39), 1–10.(2) Setaro, A.; Adeli, M.; Glaeske, M.; Przyrembel, D.; Bisswanger, T.; Gordeev, G.; Maschietto, F.; Faghani, A.; Paulus, B.; Weinelt, M.; et al. Preserving π-Conjugation in Covalently Functionalized Carbon Nanotubes for Optoelectronic Applications. Nat. Commun. 2017, 8, 1–7.