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submitted on 15.10.2020 and posted on 16.10.2020by Robert Nißler, Larissa Kurth,, Han Li, Alexander Spreinat, Ilyas Kuhlemann, Benjamin S. Flavel, Sebastian Kruss
Semiconducting single wall carbon nanotubes (SWCNTs) fluoresce in the near infrared (NIR) and the emission wavelength depends on their chirality (n,m). Interactions with the environment affect the fluorescence and can be tailored by functionalizing SWCNTs with biopolymers such as DNA, which is the basis for fluorescent biosensors. So far, such biosensors were mainly
assembled from mixtures of SWCNT chiralities with large spectral overlap, which affects sensitivity as well as selectivity and prevents multiplexed sensing. The main challenge to gain chirality pure sensors has been to combine approaches to isolate specific
SWCNTs and generic (bio)functionalization approaches. Here, we created chirality pure SWCNT-based NIR biosensors for important
analytes such as neurotransmitters and investigated the impact of SWCNT chirality/handedness as well as long-term stability and
sensitivity. For this purpose, we used aqueous two-phase extraction (ATPE) to gain chirality pure (6,5)-, (7,5)-, (9,4)- and (7,6)-
SWCNTs (emission at ~ 990, 1040, 1115 and 1130 nm). Exchange of the surfactant sodium deoxycholate (DOC) to specific singlestranded (ss)DNA sequences yielded monochiral sensors for small analytes (dopamine, riboflavin, ascorbic acid, pH). DOC used in
the separation process was completely removed because residues impaired sensing. The assembled monochiral sensors were up to 10
times brighter than their non-purified counterparts and the ssDNA sequence affected absolute fluorescence intensity as well as colloidal (long-term) stability and selectivity for the analytes. (GT)40-(6,5)-SWCNTs displayed the maximum fluorescence response to
the neurotransmitter dopamine (+140 %, Kd = 1.9 x10-7 M) and a long-term stability > 14 days. Furthermore, the specific ssDNA
sequences imparted selectivity to the analytes independent of SWCNT chirality and handedness of (+/-) (6,5)-SWCNTs. These
monochiral/single-color SWCNTs enabled ratiometric/multiplexed sensing of dopamine, riboflavin, H2O2 and pH. In summary, we
demonstrated the assembly, characteristics and potential of monochiral (single-color) SWCNTs for multiple NIR fluorescent sensing