Single-chirality single-wall carbon nanotubes for electrochemical biosensing†

Single-wall carbon nanotubes (SWCNTs) exhibit versatile optoelectronic properties closely linked to their structural characteristics, such as chiral angles and diameters. Given this, they are promising materials for biosensors. However, in studies investigating SWCNT-based electrochemical biosensors, raw soot has been mostly used. Soot typically contains a mixture of different chiralities, metallic compounds, and various impurities from the synthesis process. As a result, this mixture significantly limits the reproducibility and precision of SWCNT-based sensors. To ensure consistent sensor performance, we employed an aqueous two-phase extraction (ATPE) technique to purify and sort single-chirality SWCNTs—specifically, semiconducting (6,5) SWCNTs and metallic (6,6) SWCNTs. In addition, we used multiple fabrication methods to ensure that only pure-chirality SWCNTs were deposited onto the electrodes. Our findings emphasise the importance of using surfactant-free systems when investigating the influence of chirality on the electrochemical behaviour of SWCNTs. By using monochiral SWCNTs, we achieved precise control over their concentration and density, allowing us to assess their electrochemical properties accurately. Our results reveal that the adsorption-controlled process of the inner sphere redox probe occurs on (6,5) SWCNTs, while a diffusion-controlled process is observed on (6,6) SWCNTs. These findings provide valuable insights that will enhance the performance of SWCNT-based electrochemical biosensors.