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nIR Fluorescence Properties of Functionalized Carbon Nanotubes


Nanostructured carbon nanomaterials have gained a lot of interest since last years, particularly the unique optoelectronic properties of single-walled carbon nanotubes (SWCNTs) such as their excitonic fluorescence (see Fig. 1) in the near-infrared (nIR) region have attracted a lot of interest. These properties make SWCNT versatile building blocks for applications in biosensing, imaging and even drug delivery or photodynamic therapy. [1]

We are interested in using SWCNTs as near-infrared optical sensors to detect biomolecules. [1-3] These sensors are powerful tools e.g. to image release of neurotransmitters from cells. [4] To use these highly hydrophobic nanomaterial for the sensing of (bio) molecules, the functionalization of their surface is crucial. [5]

This is commonly achieved via ultrasonic “wrapping” with small synthetic DNA sequences. Recently, we also showed, that it is possible to use barrel-forming peptides to achieve a colloidal aqueous solution of SWCNTs. [6]

Experimental set-up

To characterize these functionalized SWCNTs, we routinely employ near-infrared (nIR) fluorescence spectroscopy using the Kymera-193i-B2 spectrograph equipped with an iDus InGaAs DU491A-1.7 nIR detector array. The samples are excited with a Cobolt 561 nm laser.

Figure 1: (a) Single-walled carbon nanotubes (SWCNT) can be considered as rolled up sheets of graphene. (b) Density of electronic states diagram of semiconducting SWCNTs and transitions E11 and E22 between van-Hove singularities leading to different absorbance and fluorescence spectra depending on the chiral index (m,n). (c) nIR fluorescence spectra of SWCNTs of different chirality (n,m) [1],[2].


Fig. 2 shows the absorption and fluorescence spectra of DNA-wrapped carbon nanotubes. In this particular study, we tested the sensing capabilities of these special SWCNT-DNA conjugates for the neurotransmitter dopamine and the competitive selectivity for its structural analogues epinephrine and norepinephrine.

The spectra in the range between 800 nm – 1200 nm clearly show that the (GT)10 DNA sequence leads to a high fluorescence increase for dopamine, whereas (nor-)epinephrine only induces a slight increase. Thus, these sensors can be used for the detection of dopamine in the presence of equimolar amounts of epinephrine or norepinephrine. [4]


We successfully used the Kymera-193i spectrograph and the iDus InGaAs 491 nIR detector to acquire nIR fluorescence spectra of functionalized carbon nanotubes. [5-8] They act as sensors for biomolecules and we quantified quantum yield changes after the addition of neurotransmitters. These findings lead to a better understanding of carbon nanotube photophysics and sensors of high selectivity/sensitivity for promising biomedical applications.

Figure 2, Absorbance and fluorescence spectra of DNA-wrapped SWCNTs. (a) vis-nIR absorbance spectrum of DNA-wrapped SWCNTs. (b,c,d) nIRfluorescence spectra of (GT)10 functionalized SWCNTs excited at 560nm before and after the addition of 100 nM dopamine (b), epinephrine (c) and norepinephrine (d).[7]


  1. Kruss, A. J. Hilmer, J. Zhang, N. F. Reuel, B. Mu, M. S. Strano, Adv. Drug Deliv. Rev. 2013, 65, 1933–1950.
  2. Mann, Florian A., Meyer, D., Mischke, S., Kruss, Bunsenmagazin 2017, 19, 228–237.
  3. Elena Polo, Sebastian Kruss: Nanosensors for Neurotransmitters, Analytical and Bioanalytical Chemistry 2016, 408: 2727. doi: 10.1007/s00216-015-9160-x.
  4. Sebastian Kruss, Daniel Salem, Lela Vukovic, Barbara Lima, Emma Vander Ende, Ed Boyden, Michael Strano: High resolution imaging of cellular dopamine efflux using nanosensor arrays, PNAS 2017, 114(8), 1789-1794, DOI: 10.1073/pnas.1613541114.
  5. Elena Polo, Sebastian Kruss: Impact of Redox-Active Molecules on the Fluorescence of Polymer-Wrapped Carbon Nanotubes, Journal of Physical Chemistry C 2016, 120(5), 3061-3070, DOI:10.1021/acs.jpcc.5b12183.
  6. A. Mann, J. Horlebein, N. F. Meyer, D. Meyer, F. Thomas, S. Kruss, Chem. - A Eur. J. 2018, 24, 12241–12245.
  7. A. Mann, N. Herrmann, D. Meyer, S. Kruss, Sensors (Switzerland) 2017, 17, DOI 10.3390/s17071521.
  8. Elena Polo, Tadeusz T. Nitka, Elsa Neubert, Luise Erpenbeck, Lela Vukovic, Sebastian Kruss: Control of integrin affinity by confining RGD peptides on fluorescent carbon nanotubes, ACS Applied Materials & Interfaces 2018, 10(21),17693-17703, DOI: 10.1021/acsami.8b04373.

Date: September 2018

Author: F. Mann, S. Kruss, Institute of Physical Chemistry, Göttingen University

Category: Application Note

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