High sensitivity near-infrared imaging of fluorescent nanosensors

Biochemical processes are fast and occur on small length scales, which makes them difficult to measure. Optical nanosensors based on single-wall carbon nanotubes (SWCNTs) are able to capture such dynamics. They fluoresce in the near-infrared (NIR, 850 3 1700 nm) tissue transparency window and the emission wavelength depends on their chirality. However, NIR imaging requires specialized and cooled InGaAs cameras with low resolution because the quantum yield of normal Si-based cameras rapidly decreases in the NIR. Here, we developed an efficient one-step phase separation approach to isolate monochiral (6,4)-SWCNTs (880 nm emission) from mixed SWCNT samples. It enabled us to image them in the NIR with highresolution standard Si-based cameras (>50 x more pixels). (6,4)-SWCNTs modified with (GT)10-ssDNA become highly sensitive for the important neurotransmitter dopamine. These sensors are 1.7-fold brighter and 7.5 x more sensitive and allow fast imaging (< 50 ms). They enable high-resolution imaging of dopamine release from cells. Thus, the assembly of biosensors from (6,4)-SWCNTs combines the advantages of nanosensors working in the NIR with the sensitivity of (Si-based) cameras and enables broad usage of these nanomaterials.