Quantum Defects Engineered in Chirality Pure Single-Wall Carbon Nanotubes for Enabling Ratiometric Sensing of Insulin

The Corona Phase Molecular Recognition (CoPhMoRe) method employs fluorescent semiconducting single-wall carbon nanotubes (SWCNTs) wrapped with heteropolymers composed of hydrophobic and hydrophilic groups, thereby creating binding sites on the surface for specific analytes. The C₁₆ PEG2K Ceramide heteropolymer corona phase of SWCNTs allows selective binding and fluorescent detection of the hormone insulin. Herein, we incorporate quantum defects into the pristine structure of fluorescent SWCNTs to enable ratiometric sensing of analytes with insulin as a test case. SWCNTs are wrapped with C₁₆ PEG2K Ceramide and subjected to UV irradiation in the presence of 5-iodoracil, inducing sp³ defects within the sp² hybridized carbon atom network of the SWCNTs. This modification results in the emergence of a new emission feature (E₁₁^*) alongside the intrinsic E₁₁ emission. Additionally, we scaled up a method for the isolation of single-chirality SWCNTs, which enhances the efficacy of CoPhMoRe by considerably simplifying the fluorescence spectrum and background emission of the sensor. Our observations show that insulin quenches the fluorescence of such sensors composed of chirality-sorted SWCNTs by an average of 20% more than that of sensors made from unsorted SWCNTs. The use of sorted SWCNTs also significantly improves the fabrication of ratiometric insulin sensors by enabling precise modulation of the E₁₁^*/E₁₁ ratio. To quantify the ratiometric sensor response, a new set of metrics is introduced, including the spectral shift and intensity of the E₁₁ and E₁₁^* emission features, along with their ratio. Based on these metrics, our findings suggest that a minimum E₁₁^*/E₁₁ ratio of 3 is recommended for the transformation of a standard nanosensor into a ratiometric nanosensor via the incorporation of quantum defects into the pristine structure of a single-chirality SWCNT. The results herein underscore new, chemically enabled methods of improving CoPhMoRe sensors by the induction of quantum defects and use of chirality sorted SWCNTs.