Guanine Quantum Defects in Carbon Nanotubes for Biosensing

Fluorescent single-wall carbon nanotubes (SWCNTs) are used as nanoscale biosensors in diverse applications. Selectivity is built in by noncovalent functionalization with polymers such as DNA. 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 g-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 a lambda max of 1049 nm. Furthermore, the Stokes shift between absorption and emission maximum linearly increases with defect density by up to 27 nm. Gd-SWCNTs represent sensitive sensors and increase their fluorescence by >70% in response to the important neurotransmitter dopamine and decrease it by 93% in response to riboflavin. Additionally, the extent of cellular uptake of Gd-SWCNTs decreases. These results show how physiochemical properties change with g-defects and that Gd-SWCNTs constitute a versatile optical biosensor platform.

Automated summary

Fluorescent single-wall carbon nanotubes (SWCNTs) are used as nanoscale biosensors with selective sensing capability. By conjugating guanine bases of adsorbed DNA to the SWCNT surface, guanine quantum defects (g -defects) are created, resulting in a shift of fluorescence emission wavelength and an increase in sensitivity. Gd-SWCNTs show a >70% fluorescence increase in response to dopamine and a 93% decrease in response to riboflavin, indicating their potential as versatile optical biosensors. Cellular uptake of Gd-SWCNTs is also reduced with the presence of g-defects.