processes to destroy microorganisms. The concentration of the released substances changes spatially and temporally and is a biochemical fingerprint of the biological state. However, such biologically relevant processes occur on temporal (ms) and spatial (nm) scales that are difficult to access using established methods. [3] For example, electrochemical methods, such as amperometry or voltammetry, lack the required spatial resolution determined by the number of electrodes and are invasive as the microelectrodes penetrate the tissue. [4] On the other hand, optical methods provide often only indirect information, for example, by labeling cellular components [5,6] or suffering from photobleaching. [7] In this context, nanomaterials, such as single-wall carbon nanotubes (SWCNTs), have emerged as promising building blocks to capture these dynamics. [3,8] In addition to a high surface-to-volume ratio that makes them sensitive to single-molecule detection, [9][10][11][12] their surface can be chemically tailored. [13][14][15][16][17] Thus, SWCNTs have already been used for several bioimaging studies [18,19] and the detection of numerous analytes such as reactive oxygen species, [20][21][22][23] small molecules like nitroaromatics [24,25] or neurotransmitters, [26,27] proteins, [28][29][30] sugars, [31] enzymes, [32] or bacteria. [33] Due to their fluorescence in the near-infrared (NIR, 850-1700 nm), which shows no bleaching or blinking, they represent stable fluorophores, whose emission falls within the biological transparency window. [34] Here, Biochemical processes are fast and occur on small-length scales, which makes them difficult to measure. Optical nanosensors based on singlewall carbon nanotubes (SWCNTs) are able to capture such dynamics. They fluoresce in the near-infrared (NIR, 850-1700 nm) tissue transparency window and the emission wavelength depends on their chirality. However, NIR imaging requires specialized indium gallium arsenide (InGaAs) cameras with a typically low resolution because the quantum yield of normal Si-based cameras rapidly decreases in the NIR. Here, an efficient one-step phase separation approach to isolate monochiral (6,4)-SWCNTs (880 nm emission) from mixed SWCNT samples is developed. It enables imaging them in the NIR with high-resolution standard Si-based cameras (>50× more pixels). (6,4)-SWCNTs modified with (GT) 10 -ssDNA become highly sensitive to the important neurotransmitter dopamine. These sensors are 1.7× brighter and 7.5× 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.
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.
The molecules released by cells are a fingerprint of their current state. Methods that measure them with high spatial and temporal resolution would provide valuable insights into cell physiology and diseases. Here, we develop a nanosensor coating that transforms standard cell culture materials/dishes into “Smart Slides” capable of optically monitoring biochemical efflux from cells. For this purpose, we use single wall carbon nanotubes (SWCNTs) that are fluorescent in the beneficial near-infrared (NIR, 850 – 1700 nm) window. They are chemically tailored to detect the neurotransmitter dopamine by a change in fluorescence intensity. These nanosensors are spin-coated on glass substrates and we show that such sensor layers can be sterilized by UV light and can be stored in dry condition or buffer for at least 6 weeks. We also identify the optimal sensor density to maximize sensitivity. Finally, we use these materials to image dopamine release from neuronal cells cultivated on top in the presence of various psychotropic substances, which represents a system to test pharmaceuticals for neurological or neurodegenerative diseases. Therefore, Smart Slides are a powerful tool to monitor cellular processes in cell culture systems.
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