Influence of sonication conditions and wrapping type on yield and fluorescent quality of noncovalently functionalized single-walled carbon nanotubes

As nanomaterials have become more accessible, nanoscale biosensor research has expanded to many useful applications. One such nanomaterial is the single-walled carbon nanotube (SWCNT), which fluoresces in the near-infrared biological window, making it ideal for in vivo applications. SWCNT can be suspended in water when non-covalently functionalized with an amphiphilic polymer or surfactant (e.g. ‘wrapped’); the suspended SWCNT can act as a simple optical probe or as a sensor by engineering the wrapping to have selective domains. The process of suspending nanotubes is typically achieved by sonication. While much application-focused research has been performed on SWCNT sensors and probes, little has been done to understand factors affecting SWCNT fluorescent quality after suspension. We explored effects of sonication power and duration on an array of nine potential wrappings including proteins, DNA, oligosaccharides, polysaccharides, synthetic polymers, and surfactant solutions. Optimal sonication conditions were found to vary on an individual wrapping basis. These trends may be used to predict optimal processing conditions to suspend SWCNT with maximal start fluorescence for various wrappings, improving dynamic range and sensitivity. These results also point to the need for control of sonication conditions in large scale synthesis to ensure tighter batch-to-batch reproducibility of nanotube sensors.