(410c) A Spin-Coated Hydrogel Platform Enables Accurate Investigation of Immobilized Individual Single-Walled Carbon Nanotubes

Semiconducting single-walled carbon nanotubes (SWCNTs) have recently been utilized extensively as near-infrared sensors (NIR) due to their unique optical properties. Commonly, SWCNTs have been employed to detect target analytes in the solution-phase via modulations in emission intensity and/or wavelength. It is desirable to lower the limit of detection for these sensors by attempting single molecule detection using isolated SWCNTs adhered to a surface. Conventional methods of SWCNT immobilization, such as adherence to rough glass surfaces adversely affect SWCNT fluorescence. Here, we have designed a novel spin coated hydrogel platform using thin layers of alginate that mitigates SWCNT interactions with the surrounding environment, recapitulating fluorescence properties from similar solution-based sensors. The hydrogel platform is also remarkably stable, allowing for accurate spectral measurements of individual SWCNTs before and after addition of various analytes. DNA-functionalized (6,5)-SWCNTs deposited on a glass coverslip displayed an average wavelength red-shift of 3.4 nm when compared to the solution-phase, while in contrast the hydrogel platform statistically matched emission wavelength values. By looking at the width of emission wavelength histograms, the heterogeneity of SWCNTs on glass coverslips was determined to be greater by a factor of 3 when compared to SWCNTs in the hydrogel platform. Upon addition of a model analyte in calcium chloride, the DNA-SWCNTs in the hydrogel platform showed a smaller wavelength red-shift and almost no aggregation when compared to the solution-phase. Using SWCNTs with different functionalizations (DNA or surfactant) and longer than the diffraction limit of light, we show that a glass coverslip can induce spectral heterogeneity along the length of a single SWCNT. Our hydrogel platform is shown to significantly reduce the spectral heterogeneity of long SWCNTs in the hydrogel platform. Finally, we show the heterogenous spectral response on a single long SWCNT after the addition of calcium chloride.