The unique optoelectronic properties of single-walled carbon nanotubes (SWCNTs) motivate their use as next-generation optical sensors. The intrinsic SWCNT near-infrared fluorescence offers many advantages in terms of bio-transparency, sensitivity, and photo-stability. Characteristics required for in vivo continuous sensing, such as selectivity, biocompatibility, and solubility, can be tuned by suspending SWCNTs with biomolecules such as single-stranded DNA (ssDNA). Despite the ubiquitous use of DNA-wrapped SWCNTs for a variety of in vivo sensing applications, their behaviour in the presence of varying concentrations of the different ions present in biological media has yet to be studied.

In this work, we present a systematic exploration of the effects of various cations and anions on the fluorescence of ssDNA-wrapped SWCNTs. The presence of multivalent cations was found to induce fluorescence shifting of near-infrared fluorescence through the transient formation of a metastable state. The incorporation of artificial oligonucleotides, or xeno nucleic acids, was shown to mitigate the effects of ion-induced conformal drift through improved conformational resiliency. The synthetic biology approach presented herein offers a powerful demonstration for enhancing sensor selectivity and stability while enabling a previously unexplored space for engineering oligonucleotide-based SWCNT sensors.