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MOLECULAR SENSING
A universal receptor
Complexes made of carbon nanotubes and polymers can potentially be used to selectively detect almost any molecule.
Davide Bonifazi
a
Starting from the lock and key model proposed by Emil Fischer at the end of the nineteenth century,
and more recently through the work of Charles Pedersen, Donald Cram and Jean-Marie Lehn on supramolecular chemistry, chemists have conceptualized the principles of molecular recognition and exploited the specicity of articial hostguest interactions1. A tremendous degree of control over the use of non-covalent bonds has been achieved and a plethora of functional molecular architectures have been reported in both materials science and biochemistry. Interfacing these self-assembled architectures with living systems could lead to non-invasive technologies for therapeutic and diagnostic applications2.
Of particular interest are hybrid complexes of carbon nanotubes and polymers in which the polymeric component exhibitsa strong affinity for a specic biologically relevant guest molecule. This affinity can lead to the formation of a hostguest complex that can be sensed through a change in the optoelectronic propertiesof the carbon nanotube framework35.
Writing in Nature Nanotechnology, Michael Strano and co-workers at the Massachusetts Institute of Technology now report single-walled carbon nanotubes wrapped with polymers that can function as molecular sensors, despite the fact that the polymer has no predened recognition motifs towards the targeted substrate6.
The recognition of a molecule of interest exclusively occurs as a result of the chemical perturbation of the nanotube polymer complex.
The polymeric unit is composedof a central polar backbone either polyethylene glycol or a dextran-bearing boronic acid that is terminated withtwo hydrophobic tails acting as the anchor termini for adsorption on the carbon nanotube. This conguration forces the central hydrophilic backbone to adopt loop-like structures that protrude into the surrounding aqueous environment (Fig.1a, step i). Depending on the chemical nature of both the anchoring groups and the polymer backbone, the looped cavities control the diusion of the analyte molecules within
the hybrid, mediating adsorption at the graphitic interface. By monitoring either the intensity or the shi of the near-infrared emission peaks of...