Next, we wanted to find out how G d -SWCNTs perform in cellular environments. Incubation of SWCNTs in cell culture medium (see materials section) led to a significant change in fluorescence intensity in pristine SWCNTs whereas the change in G d -SWCNTs fluorescence intensity change was very low (Figure ). This indicates increased stability in such complex environments. It is also interesting to study if the change in DNA flexibility affects the interaction with cells e,g. the cell membrane. For DNA-SWCNTs it is known that they are able to pass cell membranes and accumulate inside the cells . Depending on the intended application, this is either wanted (gene delivery) or a problem (extracellular sensing). To test if membrane interaction of DNA-SWCNTs is changed by g-defects, we incubated HeLa cells for one hour with 1 nM SWCNT solutions of After incubation, the cells were washed with IMDM to remove free SWCNTs in solution and imaged in a NIR fluorescence microscopy setup to localize single SWCNTs. This incubation protocol is consistent with the paint methodology recently used for dopamine detection (AndromeDA). We found strong single NIR-fluorescence signals inside cells incubated with pristine SWCNTs. For cells incubated with G d -SWCNTs, NIR fluorescence colocalized rather with the cell membranes than with the cytosol (Figure ). This observation was quantified by comparing the SWCNT signals and the boundaries outer membranes of healthy cells from the brightfield image and automated identification of SWCNT signals inside the cell. Indeed, G d -SWCNTs were found significantly fewer inside cells than pristine SWCNTs (Figure ). These results show that the uptake probability decreases and membrane passage is affected by the covalent chemistry. For applications of SWCNTs e.g. as sensors it is desirable to have precise control of the interaction between them and the biological system. The altered cellular uptake observed in G d -SWCNTs is such a control mechanism and allows to influence localization of SWCNTs more precisely. G d -SWCNT applications in biological contexts, e.g. for neurotransmitter detection or as cellular delivery vehicles could profit from this additional layer of control. Our studies leave it open whether an active or inactive uptake mechanism is affected by g-defects . In some cases, G d -SWCNTs were still able to enter cells. Therefore, it is likely that not all mechanisms are affected and physisorption onto the outer cell membrane still takes place.