Amine-functionalized polydiacetylene demonstrated a specific color response to an aminoglycosidic anti-biotic such as neomycin. This phenomenon is very interesting because the presented system lacks any specif-ic interacting binding site and possesses only amine functional groups. The effect of functional groups in polydiacetylene system was characterized, and the substrate effects were also characterized for other amino-glycosidic antibiotics. The system consisting of amine-functionalized polydiacetylene and neomycin only showed the color change at a 10 $\mu$ M concentration of neomycin; at 1 $\mu$ M of neomycin it could be detected using fluorescence. The results from zeta potential measurements and pH variations revealed color response to be the result of interaction between the vesicle and neomycin. The strength of the interaction depended on the number of amine functional groups in the polydiacetylene that are in contact with one neomycin mole-cule.
In the next study the noble vesicular system of polydiacetylene showed a red shift by two kinds of detect-ing systems. One of the systems involves absorption of target materials from outer side of the vesicle, and the other system involves the permeation through the vesicular layers from within the vesicle. The chromatic mixed vesicles of N-(2-aminoethyl)pentacosa-10,12-diynamide (AEPCDA) and dimethyldioctadecylammo-nium chloride (DODAC) were fabricated by sonication, followed by polymerization by UV irradiation. The stability of monomeric vesicles was observed to increase with polymerization of the vesicles. Methotrexate was used as a target material. The polymerized mixed vesicles having a blue color were exposed to a concen-tration gradient of methotrexate, and a red shift was observed indicating the adsorption of methotrexate on the polydiacetylene bilayer. In order to check the chromatic change by the permeation of methotrexate, we separated the vesicle portion, which contained methotrexate inside the vesicle, and checked chromatic change during the permeation of methotrexate through the vesicle. The red shift apparently indicates the dis-turbance in the bilayer induced by the permeation of methotrexate. The maximum contrast of color ap-peared at the equal molar ratio of AEPCDA and DODAC, indicating that the formation of flexible and de-formable vesicular layers is important for red shift. Therefore, it is hypothesized that the system can be appli-cable for chromatic detection of the permeation of methotrexate through the polydiacetylene layer.
In the next study the thermal chromatic sensitivity of polydiacetylenes (PDAs) with 10,12-pentacosadiynoic acid (PCDA) derivatives, which have a hydroxyl group (HEEPCDA) and an amine group (APPCDA), were investigated using $D_2O$ and $H_2O$ as solvents. The vesicle solution with polymerized HEEPCDA exhibited a reversible chromatic response during the heating and cooling cycle in $D_2O$, but not in $H_2O$. On the other hand, the vesicle solution with the polymerized APPCDA exhibited a reversible chromatic response in $H_2O$ during the heating and cooling cycle, but the color of the solution did not change much in $D_2O$. The critical vesicle con-centration of HEEPCDA was lower in $D_2O$ than in $H_2O$, and the chromatic sensitivity of the polymerized vesi-cles to temperature was slower in $D_2O$ than in $H_2O$. We think that it is due to $D_2O$ being a more highly struc-tured solvent than $H_2O$ with the hydrogen bonding in $D_2O$ stronger than that in $H_2O$.