Tailored Carbon Nanotube-Based Fluorescent Sensors for Cellular Metabolites

Abstract

Single-walled carbon nanotubes (SWCNTs) are an emerging building block for nanoscale sensors and labels because of their unique photophysical properties. Semiconducting SWCNTs fluoresce in the tissue transparency near infrared (nIR) window (840 – 1650 nm) and do not bleach. Due to their 1D nature small perturbations in their environment strongly affect their fluorescence. The major challenges in using SWCNTS for sensing is on the one side their purification and on the other side a tailored surface chemistry for molecular recognition and photophysical signal transduction. Cellular metabolites such as first messengers are important biomolecules used by cells to exchange both energy and information but up to day there are many such molecules for which no sensors exist. DNA is a versatile macromolecule to functionalize and solubilize SWCNTs. Furthermore, DNA acts as a conformational quantum yield switch, which makes it a good candidate to impart signal transduction. However, different sensing strategies are known, but general recognition capabilities need to be further explored. Here, we present three different approaches with DNA to tailor SWCNT surface chemistry and detect biologically important metabolites.Firstly, we tuned the sensitivity of ssDNA/SWCNTs against the neurotransmitter dopamine and different plant polyphenols by changing systematically the DNA sequence. In a more rational approach, we engineered DNA strands conjugated to small peptide sequences. In order to enable a ratio-specific linkage, we determined the amount of bound DNA on the SWCNT surface, which was further observed to play an important role in maintaining colloidal stability of the modified ssDNA/SWCNT conjugates. Finally, aptamer-based approaches were used to combine stable surface modification with target selective binding.For all these approaches we demonstrated via nIR-fluorescence spectroscopy and nIR-fluorescence microscopy that tailoring these nanosensors resulted in an increased specificity against their targets, ranging from small chemical communication compounds (dopamine, H2O2) to cell wall components and secreted enzymes.