PHYS 671 |
| Molecular detection using near-infrared light between 0.9 and 1.3 eV has important biomedical applications because of greater tissue penetration and reduced autofluorescent background in thick tissue or whole-blood media. Carbon nanotubes have a tunable near-infrared emission that responds to changes in the local dielectric function but otherwise remains stable to permanent photobleaching. In this work, we report the synthesis and successful testing of solution-phase, near-infrared sensors, with beta-D-glucose sensing as a model system, using single-walled carbon nanotubes that modulate their emission in response to the adsorption of specific biomolecules. The optical transition energies of single-walled carbon nanotubes (SWNT) are influenced by the local environment created by solvents or other adsorbed molecules. We analyze the emission energies of SWNT photoluminescence (PL) in various dielectric media, and elucidate a 1/R^4 scaling of the transition polarizability from a classical solvatochromic formalism. This solvatochromic shift is shown to vary inversely with the square of the of the transition energy, as predicted by theory and ab-initio calculations. SWNT band-gap fluorescence undergoes a red shift when an encapsulating 30-nucleotide oligomer is exposed to counter ions that screen the charged backbone. The transition is thermodynamically identical for DNA on and off the nanotube, except that the propagation length of the former is shorter by five-sixths. The magnitude of the energy shift is described by using an effective medium model and the DNA geometry on the nanotube sidewall. We demonstrate the detection of the B-Z change in whole blood, tissue, and from within living mammalian cells. |
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Nanostructured Materials
8:20 AM-12:00 PM, Thursday, April 10, 2008 Morial Convention Center -- Rm. 338/339, Oral
Division of Physical Chemistry |