Optimizing Dialysis Experiments to Functionalize Single Walled Carbon Nanotubes for Optical Biosensors

Single-walled carbon nanotubes (SWCNTs) have unique optical properties that are sensitive to changes in the local environment. This makes them an attractive candidate for sensitive fluorescent biosensors. Existing biosensors using SWCNTs utilize single or small chirality systems. This involves many processing steps, which makes it expensive. Therefore, it is significant to select a specific chirality from a SWCNT suspension without separation. Various surfactants have been used to form stable suspensions of SWCNTs in different solvents. Surfactant structure around the nanotube plays an important role in stability of SWCNTs. Our work examines the properties of SWCNTs to create a glucose sensor that is exclusively detected on a specific chirality in a mixture of different chiralities. We achieve this via use of a selective co-surfactant environment and ligand functionalization.

In this work, we are using dialysis to control the concentrations of surfactants and ligands in a solution to target specific (n,m) species in solution. Our group has previously utilized co-surfactant solution approach to separate (6,5) species at a very specific ratio of sodium dodecyl sulphate (SDS)/sodium deoxycholate (DOC). We have also demonstrated that the adsorption number of SDS on SWCNTs can be calculated by examining the changes in the critical micelle concentration. Using this prior knowledge, we have optimized the conditions of dialysis to selectively target (7,6) or (8,3) chirality in a solution by titrating a specific co-surfactant ratio that changes the fluorescent spectra and by determining the relative abundance of each chirality using deconvolution analysis. Following dialysis, the selected chirality is functionalized with a ligand, which is observed in the fluorescence spectra as a peak quenching at the specific chirality wavelength. The specific chirality is further characterized by fitting a kinetic model to the response of each surfactant and ligand. Upon addition of the analyte, the responding quench or recovery at that wavelength is directly correlated to the concentration. This methodology has shown that selective chirality functionalization to detect an analyte can be done without any previous varying separation techniques.

In this poster, we highlight the role of dialysis and the significance of buffer concentrations in achieving sensing on a single chirality.