Current flow of single-walled carbon nanotubes upon the encapsulation of beta-carotene by using conducting probe atomic force microscopy.
Beta-carotene was inserted into single-walled carbon nanotubes (SWCNTs) by using the encapsulation method in a solution phase, and the energy transfer process was studied under irradiation of visible light. The encapsulation of beta-carotene inside SWCNTs was confirmed by ultraviolet (UV)/visible (Vis) and near-IR (N-IR) spectroscopy, and the stability of encapsulated beta-carotene was also confirmed by a UV irradiation experiment. The N-IR absorption spectrum revealed that the beta-carotene donated electrons to the SWCNTs upon encapsulation. We measured current flow through SWCNT bundles by using conducting probe atomic force microscopy (CP-AFM) while the samples were irradiated by green light (532 nm) and red light (650 nm). The current changed with the irradiation of 532 nm light, where the beta-carotene has its own absorption, but not with the irradiation of 650 nm light. From these results, we concluded that the encapsulated beta-carotene inside SWCNTs efficiently absorbed 532 nm light and excited electrons of beta-carotene might be transferred to the SWCNTs like an energy transfer process. Our conclusion was consistent with a previously suggested energy transfer theory between beta-carotene and SWCNTs.