Sensing with Chirality Pure near Infrared Fluorescent Carbon Nanotubes

Abstract

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 applications.

Quantum Defects in Fluorescent Carbon Nanotubes for Sensing and Mechanistic Studies

“…Such approaches are desired in biosensing because they are more robust and promise higher signal/noise ratios. 60 The dopamine response almost equals the average of the expected dopamine responses for two independent pSWCNT and dSWCNT samples, which further underlines that the presence of NO 2 -aryl units does not interfere with the overall DNA structure on the SWCNTs. Consequently, quantum defects are a useful tool to create spectrally encoded ratiometric sensors.…”

“…For most experiments, (GT) 10 -functionalized pristine CoMoCat-(6,5)-SWCNTs (from now on referred to as pSWCNTs) were used. Further purification 60 was used for experiments in which spectral congestion by other chiralities could cause a bias (see the Materials and Methods 49 ). Defects (NO 2 -aryl) were incorporated into (6,5)-SWCNTs by a reaction with diazonium salts (see the Materials and Methods for details).…”

Single-Chirality Near-Infrared Carbon Nanotube Sub-Cellular Imaging and FRET Probes

“…Although an increasing library of materials can be used to facilitate the isolation of SWCNTs, − ,, this work demonstrates that sorted SWCNT chiralities, originally encapsulated by one set of materials, can then be rewrapped with moieties that confer desired subcellular-targeting behavior. Regarding the resulting FRET probes, we believe that similar materials could be engineered to serve as reporters of molecular interactions in specific cellular compartments.…”

“…The resulting single-chirality/color nanotubes from ATPE, or any other separation technique, must then be derivatized in order to confer solubility and biological functionalities. To functionalize separated nanotubes, attempts to remove the original surfactant/wrapping often result in irreversible aggregation; surfactant exchange procedures have been most promising thus far. − …”

“…22 The resulting single-chirality/color nanotubes from ATPE, or any other separation technique, must then be derivatized in order to confer solubility and biological functionalities. To functionalize separated nanotubes, attempts to remove the original surfactant/wrapping often result in irreversible aggregation; surfactant exchange procedures 25 have been most promising thus far. 23−26 Herein, we developed single-chirality carbon nanotubebased optical probes to target subcellular locations to conduct multiplexed imaging in subcellular structures and to investigate internanotube FRET/EET in live cells.…”