(100d) Protein Detection with Peptoid-Functionalized Carbon Nanotube Optical Sensors

A limitation to real-time imaging of metabolites and proteins has been the selective detection of biomolecules that have no naturally-occurring or stable molecular recognition counterparts.¹ We present developments in the design of synthetic near-infrared fluorescent nanosensors based on the fluorescence modulation of single-walled carbon nanotubes (SWNT) with select sequences of surface-adsorbed N-substituted glycine peptoid polymers.² We assess the stability of the peptoid-SWNT nanosensor candidates under variable ionic strengths, solution composition, protease exposure, and cell-compatible conditions, and find that the stability of peptoid-SWNTs depends on the composition and length of the peptoid polymer. We identify a peptoid-SWNT assembly that can detect lectin protein wheat germ agglutinin (WGA) with a sensitivity comparable to the concentration of serum proteins. To demonstrate the retention of nanosensor-bound protein activity, we show that WGA bound to the nanosensor produces an additional fluorescent signal modulation upon exposure to the lectin’s target sugars, suggesting the lectin protein remains active and selectively binds its target sugars through ternary molecular recognition interactions relayed to the nanosensor. Additionally, we demonstrate that peptoid-SWNT assemblies present a generic platform for protein detection, by demonstrating extension of peptoid-SWNTs for detection of additional protein analytes. Our results inform design considerations for developing synthetic molecular recognition elements by assembling peptoid polymers on SWNTs, and also demonstrate these assemblies can serve as optical nanosensors for lectin proteins and their target sugars. Together, these data suggest peptoid sequences can be assembled with SWNTs to serve as versatile optical probes to detect proteins and their molecular substrates.

1) Landry, M. P., ... Chio, L., et al. Single-molecule detection of protein efflux from microorganisms using fluorescent single-walled carbon nanotube sensor arrays. Nature Nanotechnology (2017). doi:10.1038/nnano.2016.284

2) Chio, L., Del Bonis-O’Donnell, J.T., Kline, M.A., Kim, J.H., McFarlane, I.R., Zuckermann, N., Landry, M.P. Electrostatic-Assemblies of Single-Walled Carbon Nanotubes and Sequence-Tunable Peptoid Polymers Detect a Lectin Protein and its Target Sugars. Nano Letters, (2019) DOI: 10.1021/acs.nanolett.8b04955