For more than a decade, DNA and oligonucleotides of single-strand DNA (ssDNA) have studied as agents for dispersing single-walled carbon nanotubes (SWCNT), with the goals of potential biomedical applications and the selective sorting of specific (n,m) structures from as-produced inhomogeneous mixtures. We have recently discovered that SWCNTs suspended by ssDNA oligos in water show rather strong quenching from dissolved molecular oxygen. In many cases dissolved oxygen in equilibrium with 1 atm partial pressure of O₂ decreases the SWCNT fluorescence intensity by a factor of two, and for some systems the quenching factor is two in air-saturated solutions and reaches three under 1 atm of pure O₂. We find that the quenching depends on (n,m) species and ssDNA sequence, in addition to some other experimental parameters. The effect varies smoothly with dissolved oxygen concentration and is fully reversible on purging with other gases such as argon or nitrogen. The quenching effect appears and disappears on a sub-second time scale.

An important finding is that the extent of oxygen quenching correlates with the apparent affinity between the DNA oligo and the SWCNT species. Combinations thought to give strong coating show weak quenching, possibly because of reduced exposure of the nanotube surface to the surrounding solution. Thus, this effect can provide a simple way to identify special affinities just by measuring fluorescence changes when dissolved oxygen is displaced by inert gases. To help understand the mechanism of the quenching effect and its potential value in other applications, we have studied a variety ssDNA oligos, including those containing only one nucleotide. We have also studied the effect with other dispersing agents and surfactants, quantified the dependence of quenching on oxygen concentration, analyzed fluorescence spectral shifts caused by dissolved oxygen, and explored the quenching effect in solid nanotube films and in solutions modified by addition of polymers and other chemicals. We will present the results of those experiments and our proposed mechanism for the effect.