Prospects of fluorescent single-chirality carbon nanotube-based biosensors

Semiconducting single-wall carbon nanotubes (SWCNTs) fluoresce in the near-infrared (NIR), and the emission wavelength depends on their structure (chirality). Interactions with other molecules affect their fluorescence, which has successfully been used for SWCNT-based molecular sensors. So far, most such sensors are assembled from crude mixtures of different SWCNT chiralities, which causes polydisperse sensor responses as well as spectral congestion and limits their performance. The advent of chirality-pure SWCNTs is about to overcome this limitation and paves the way for the next generation of biosensors. Here, we discuss the first examples of chirality-pure SWCNT-based fluorescent biosensors. We introduce routes to such sensors via aqueous two-phase extraction-assisted purification of SWCNTs and highlight the critical interplay between purification and surface modification procedures. Applications include the NIR detection and imaging of neurotransmitters, reactive oxygen species, lipids, bacterial motives, and plant metabolites. Most importantly, we outline a path toward how such monodisperse (chirality-pure) sensors will enable advanced multiplexed sensing with enhanced bioanalytical performance.