Towards Engineering Smart Nanosensors: Effects of Polymer Wrapping on Single-Walled Carbon Nanotube Photoluminescence

Polymer-wrapped single-walled carbon nanotubes (SWCNTs) have emerged as a new class of versatile optical sensors. The intrinsic near-infrared SWCNT fluorescence offers unparalleled advantages in sensitivity, tissue transparency, and photostability ideal for a breadth of sensing applications. The polymer provides the nanotube with molecular recognition capabilities necessary for selective sensing through a mechanism for modulating fluorescence. In this study, we develop a diffusion-based exciton model for helically wrapped SWCNTs that allows us to examine the effect of polymer morphology and photophysical contributions on SWCNT brightness. The model de-couples these contributions by accounting for polymer thickness, wrapping pitch, and optoelectronic exciton interactions. The quantum yield was found to increase with decreasing polymer thickness, wrapping pitch, and polymer quenching efficiency. Quenching efficiency was shown to have the strongest effect on quantum yield, with a 90% decrease in quenching efficiency increasing the quantum yield by up to 740% over the conditions tested. Photoluminescence measurements of DNA-wrapped SWCNTs, which serve as a model system for helical wrappings, were compared for different sequences of DNA with comparable wrapping thickness and pitch to examine the effects of polymer quenching efficiency. The highest quantum yields were observed for C₃₀, (AT)₁₅, and (GT)₁₅-wrapped SWCNTs, which were calculated to have polymer quenching efficiencies of 0.2%. Combined with ongoing efforts in characterizing polymer-analyte interactions, this model offers a powerful approach to realizing Specifically Modeled and Rationally Tailored (SMaRT) nanosensors with predetermined sequence-dependent brightness and selectivity.