Ratiometric imaging of catecholamine neurotransmitters with nanosensors

Neurotransmitters are important signaling molecules in the brain and relevant in many diseases. Measuring them with high spatial and temporal resolution in biological systems is challenging. Here, we develop a ratiometric fluorescent sensor/probe for catecholamine neurotransmitters based on near-infrared (NIR) semiconducting single wall carbon nanotubes (SWCNTs). Phenylboronic acid (PBA)-based quantum defects are incorporated into them to interact selectively with catechol moieties. These PBA-SWCNTs are further modified with polyethylene glycol phospholipids (PEG-PL) for biocompatibility. Catecholamines including dopamine do not affect the intrinsic E11 fluorescence (990 nm) of these (PEG-PL-PBA-SWCNT) sensors. In contrast, the defect-related E11* emission (1130 nm) decreases by up to 35%. Furthermore, this dual-functionalization allows tuning selectivity by changing the charge of the PEG-polymer. These sensors are not taken up by cells, which is beneficial for extracellular imaging and they are functional in brain slices. In summary, we use dual-functionalization of SWCNTs to create a ratiometric biosensor for dopamine.