(114g) Utilizing Unique Thermodynamic Equilibria of Co-Surfactant States Around Nanotubes for Optical Biosensors

The unique optical properties of single walled carbon nanotubes (SWCNTs) make them a suitable candidate for biosensing applications. Although difficulty in separating monochiral fractions has limited their use as fluorescent sensors, surfactants offer a convenient and scalable approach towards suspending nanotubes in solvents. Surfactant structure around the nanotube plays an important role in stability and separation of (n,m) species. The presence of thermodynamically stable co-surfactants states enables selective coating of species in solution. Our group has previously utilized co-surfactant solution approach to elute (6,5) species at a very specific ratio of sodium dodecyl sulphate (SDS)/sodium deoxycholate (DOC). This idea was used to selectively target other chiralities and obtain high concentration monochiral in the nanotube solution.

Here, we present a new method of utilizing this thermodynamic equilibria for selectively eluting a mixture of chiralities and attaching ligands on them without separating monochiral fractions. Adsorption of added surfactant leads to reorganization of the surfactant shell around nanotube which leads to solvatochromatic shifts that can be probed through optical spectroscopy. Difference in surfactant binding strength can be used to protect chiralities against further coating using addition of controlled ratios of co-surfactant solutions to nanotubes. We investigated the role of covalent and non-covalent functionalization to the nanotube surface for obtaining best biosensing responses. This led to study the role of different ligands for functionalizing different chiralities for simultaneous detection of analytes in solution. This approach provides a unique way of using SWCNTs as biosensors by selectively functionalizing different chiralities without obtaining monochiral fractions.