The Fluorescent Polydiacetylene Liposome

Abstract

Development of efficient sensors utilizing conjugated polymer as sensing matrices has gained much attention among many research scientists.1-11 Especially, polydiacetylene (PDA)-based sensors for the detection of biologically important species have been intensively investigated due to the unique color changing properties upon stimulation.12-27 Closely packed and properly designed certain diacetylenes can undergo polymerization via 1,4-addition reaction to form an ene-yne alternated polymer chain upon UV irradiation with 254 nm as shown in Figure The resulting polydiacetylenes, if obtained under optimized conditions, appear to be intense blue color to the naked eyes. The blue-colored polydiacetylenes can be prepared in the form of liposomes in aqueous solutions or as thin films using Langmuir-Blodgett or Langmuir-Schaefer methods. The advantage of the nanostructured polydiacetylenes as biosensors comes from the fact that visible color change from blue to red occur in response to a variety of environmental pertur bations, such as temperature,36-39 pH,40 and ligand-receptor interactions.12-14,27 Many researchers have tried to understand the mechanism of the color transition. Although it is not clear, it has widely been accepted that color change is associated with a conformational change of polydiacetylene backbone. Accordingly, the polydiacetylenes in the blue form have extended conjugation of p-orbital in the main chain of the polymers. The conjugated p-orbitals undergo distortion by environmental stimuli, leading to partial twist (Ri functionalized alkyl chain, R2 alkyl chain)