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Single-walled carbon nanotubes (SWCNTs) are versatile near infrared (NIR) fluorescent building blocks for biosensors. Their surface is chemically tailored to respond to analytes by a change in fluorescence. However, intensity-based signals are easily affected by external factors such as sample movements. Here, we demonstrate fluorescence lifetime imaging microscopy (FLIM) of SWCNT-based sensors in the NIR. We tailor a confocal laser scanning microscope (CLSM) for NIR signals (> 800 nm) and employ time correlated single photon counting of (GT) 10 -DNA functionalized SWCNTs. They act as sensors for the important neurotransmitter dopamine. Their fluorescence lifetime (> 900 nm) decays biexponentially and the longer lifetime component (370 ps) increases by up to 25 % with dopamine concentration. These sensors serve as paint to cover cells and report extracellular dopamine in 3D via FLIM. Therefore, we demonstrate the potential of fluorescence lifetime as a readout of SWCNT-based NIR sensors.

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 E 11 fluorescence emission by 55 nm to a λmax 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.

Fluorescent single wall carbon nanotubes (SWCNTs) are used as nanoscale biosensors in diverse applications. Selectivity is built in by non-covalent functionalization with polymers such as DNA. In general, fluorescence sensing with SWCNTs would benefit from covalent DNA-conjugation but it is not known how changes in conformational flexibility and photophysics affect the sensing mechanism. 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 guanine 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 max = 1049 nm for the highest defect density. Furthermore, the difference between absorption maximum and emission maximum (Stokes shift) increases with increasing defect density by 0.87 nm per nm of absorption shift and up to 27 nm in total. Gd-SWCNTs represent sensitive sensors and increase their fluorescence >70 % in response to the important neurotransmitter dopamine and decrease 93 % in response to riboflavin. Additionally, cellular uptake of Gd-SWCNTs decreases. These results show how physiochemical properties alter with guanine defects and that Gd-SWCNTs constitute a versatile optical biosensor platform.

No abstract

Single wall carbon nanotubes (SWCNTs) are versatile building blocks for biosensors. Their near infrared (NIR) fluorescence enables detection of biomolecules in the optical tissue transparency window. The fluorescence intensity of SWCNTs changes in response to an analyte and this interaction can be chemical tailored by the surface chemistry. However, optical signals based on intensity are affected by external factors such as sample movement or fluctuations in excitation light. Here, we demonstrate fluorescence lifetime imaging microscopy (FLIM) of SWCNT-based sensors in the NIR as calibration-free method. For this purpose, we tailored a confocal laser scanning microscope (CLSM) for NIR signals (>800 nm) and employed time correlated single photon counting (TCSPC). (GT)10-DNA functionalized SWCNTs are then used as sensors because they increase their fluorescence (995 nm) in response to the important neurotransmitter dopamine. Their fluorescence lifetime (> 900 nm) follows a biexponential decay and the longer lifetime component (370 ps) changes with dopamine concentration. It increases by up to 25 % with detection limits in the nM range. These sensors serve as paint to cover cells and report extracellular dopamine in 3D via FLIM. We therefore show the potential of using fluorescence lifetime in combination with confocal microscopy as readout for SWCNT-based sensors.

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Einwandige Kohlenstoffnanoröhren (singlewalled carbon nanotubes, SWCNTs) sind vielseitig einsetzbare Bausteine für Biosensoren, die im nahen Infrarot (NIR) fluoreszieren. Ihre Oberfläche kann chemisch so modifiziert werden, dass sie auf Analyten mit einer Veränderung ihrer Fluoreszenz reagieren. Intensitätsbasierte Signale werden jedoch leicht durch äußere Faktoren wie Bewegungen der Probe beeinflusst. Hier zeigen wir Fluoreszenz-Lebensdauer Mikroskopie (fluorescence lifetime imaging microscopy, FLIM) von SWCNT-basierten Sensoren im NIR. Dafür wurde ein konfokales Laser-Scanning-Mikroskop (CLSM) für NIR-Signale (> 800 nm) angepasst und zeitkorrelierte Einzelphotonenzählung von (GT) 10 -DNA-funktionalisierten SWCNTs verwendet. (GT) 10 -SWCNTs fungieren als Sensoren für den wichtigen Neurotransmitter Dopamin. Ihre Fluoreszenzlebensdauer (> 900 nm) fällt biexponentiell ab, wobei die längere Lebensdauerkomponente (370 ps) mit steigender Dopaminkonzentration um bis zu 25 % ansteigt. Mit diesen Sensoren können Zellen beschichtet werden, um extrazelluläres Dopamin in 3D mittels FLIM zu messen. Wir demonstrieren damit das Potenzial der Fluoreszenzlebensdauer als Messgröße für SWCNT-basierte NIR-Sensoren.