Guanine quantum defects in carbon nanotubes for biosensing

Abstract

Fluorescent single wall carbon nanotubes (SWCNTs) are used as nanoscale biosensors in diverse applications. Selectivity is built in by non-covalent functionalization with polymers such as DNA. In general, fluorescence sensing with SWCNTs would benefit from covalent DNA-conjugation but it is not known how changes in conformational flexibility and photophysics affect the sensing mechanism. Recently, covalent functionalization was demonstrated by conjugating guanine bases of adsorbed DNA to the SWCNT surface as guanine quantum defects (g-defects). Here, we create guanine defects in (GT)10 coated SWCNTs (Gd-SWCNTs) and explore how this affects molecular sensing. We vary the defect densities, which shifts the E11 fluorescence emission by 55 nm to max = 1049 nm for the highest defect density. Furthermore, the difference between absorption maximum and emission maximum (Stokes shift) increases with increasing defect density by 0.87 nm per nm of absorption shift and up to 27 nm in total. Gd-SWCNTs represent sensitive sensors and increase their fluorescence >70 % in response to the important neurotransmitter dopamine and decrease 93 % in response to riboflavin. Additionally, cellular uptake of Gd-SWCNTs decreases. These results show how physiochemical properties alter with guanine defects and that Gd-SWCNTs constitute a versatile optical biosensor platform.

Stochastic Formation of Quantum Defects in Carbon Nanotubes

“…This approach can also be used directly for biosensing or conjugation of larger recognition motifs to create sensors for bacterial or viral motifs. 38,39 Diazonium chemistry also offers to conjugate more complex entities such as biomolecules. 40,41 It is useful to directly attach, for example, nanobodies or grow peptide chains on the SWCNT lattice, which expands the toolbox for many applications such as sensing with quantum defects.…”

Understanding the Molecular Assemblies of Single Walled Carbon Nanotubes and Tailoring their Photoluminescence for the Next-Generation Optical Nanosensors

“…126−129 Galonska and Kruss et al demonstrated enhanced sensitivity in detecting dopamine by using (GT) 10 -ssDNA-coated (6,5)-SWCNTs, specifically through covalent bonding that introduced guanine quantum defects. 130 Covalent sp 3 defects on carbon nanotubes (also called organic color centers) (6,5)-(GT) 15 were used in monitoring autophagy-associated lysosomal acidification in vivo and were designed to detect pH changes in the lysosomal environment of living cells and in vivo models. 131 The utilization of time-correlated single-photon counting techniques has provided insights into the photoluminescence lifetime of the E 11 * defect emission, demonstrating a notable extension compared to the lifetime of mobile excitons.…”

Near-Infrared Fluorescent Biosensors Based on Covalent DNA Anchors

“…47 As defect density depends on the RB concentration and the guanine content, one can pattern and tailor SWCNT surfaces. 40−42,47−49 Apart from the mechanistic and photophysical studies concerning this reaction, [40][41][42]47,48 as well as the signal observed upon the adsorption of small molecules, 49 this chemistry has up to our knowledge not been used for rational sensing.…”