The intrinsic band-gap photoluminescence (fluorescence) of single-walled carbon nanotubes (SWCNTs) exhibits exceptional photostability, narrow bandwidth, near-infrared (nIR) tissue-penetrating emission, and microenvironmental sensitivity, which potentiates their usage in a variety of biomedical imaging applications. Amphiphilic bio-polymers, such as single-stranded DNA, were found capable of singly-dispersing SWCNTs, enabling photoluminescence in aqueous solutions. A DNA sequence-dependent scheme for SWCNT species (chirality) separation has been observed with DNA-SWCNT binding strengths that were highly correlated. Using all-atom replica exchange molecular dynamics simulations (REMD), equilibrium structures confirmed that a variety of novel DNA secondary structures were forming when confined to the cylindrical surface of the SWCNT in a DNA-sequence and SWCNT-chirality-dependent fashion.
In cellular applications, DNA-encapsulated SWCNTs were found to enter primary mammalian endothelial cells by means of an energy-dependent endocytosis mechanism and remain in the endosomal pathway. A novel spectral imaging approach was able to spatially resolve over a dozen chiralities of single SWCNTs in live cells, in excised mouse tissue, and in live zebrafish. Additionally, in the endosomes of live cells, the SWCNT’s ability to sense perturbations in its microenvironment, via modulations in emission intensity and peak center wavelength, was exploited as a non-destructive and long-term monitoring nIR optical reporter. Again using REMD simulation, there was observed correspondence between the optical signals of the SWCNT and the nanostructured analytes and solvent molecules.
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