Preparation, characterization and fluorescent imaging of multi-walled carbon nanotube–porphyrin conjugate

Abstract

In order to track carbon nanotubes (CNTs) in vitro or in vivo, many technologies have already been applied. However, the potential toxic effects of technologies such as radio and quantum dot labeling are the major problems. Therefore, the need to search for a new kind of biocompatible material to label CNTs has become urgent. In this work, one kind of porphyrin derivative with a single amino group was synthesized and covalently conjugated to oxidized water-soluble multi-walled carbon nanotubes (MWCNTs). The physiochemical properties of the oxidized MWCNTs and the fluorescent characteristics of their conjugate were carefully investigated. The experimental results indicated that the carboxyl group was introduced to the oxidized MWCNTs, allowing reaction with the amino group of the porphyrin, while the tube-like structure was well retained. The conjugate of the amino porphyrin and the MWCNTs exhibited strong red fluorescence emissions at 670 nm and 730 nm when excited with the optimal excitation wavelength of 420 nm. An aqueous solution containing the conjugate was injected subcutaneously into mice and was then imaged in vivo and ex vivo. Results showed that the conjugate was mainly engulfed by macrophages under the skin, and most of the conjugates accumulated in subcutaneous connective mucosa and a small amount in the liver, over a long period.