Enhancement of Luminescence from a Carbon Nanotube Aqueous Suspension at the Cysteine Doping: Influence of the Adsorbed Polymer

Abstract

We have studied the enhancement of the luminescence intensity from semiconducting carbon nanotubes with the adsorbed polymer (DNA) in an aqueous suspension due to the doping with amino acid cysteine. The intensity increase is caused by the presence of a thiol group in the cysteine structure, which allows a reduction of defects on the nanotube surface that quench the emission. It is observed that the initial nanotube/polymer weight ratio affects the dependence of the luminescence intensity on the cysteine concentration so that it is shifted toward greater concentrations in case of the 1 : 1 ratio comparing to the dependence obtained for a suspension with the 1 : 0.5 ratio. Such shift can be explained by a greater surface coverage with the polymer that restricts the access of cysteine molecules to nanotube defects. We have also noted that the obtained dependences vary for nanotubes with different chiralities, which can be attributed to different densities of a polymer coverage on their surfaces. K e y w o r d s: luminescence, exciton, cysteine, DNA, carbon nanotube, structure defect.