Colorimetric sensors of ultraviolet-C light using diacetylene-zinc(II)-zinc oxide nanocomposites with tunable sensitivity

Polydiacetylene (PDA) material-based colorimetric sensors have been devised for monitoring ultraviolet-C (UVC) light. However, it is rather difficult to systematically control their sensitivity. This work introduces an easy and inexpensive approach for developing diacetylene/zinc(II)/zinc oxide (DA/Zn²⁺/ZnO) nanocomposites as colorimetric sensors of UVC light. Here, we demonstrate the ability to tune the sensitivity of the nanocomposites to UVC light by varying different parameters including ZnO ratio, ZnO size, and alkyl chain length of DA monomers. We have found that the increase of ZnO ratio significantly enhances the UVC sensitivity. Furthermore, the color transition from blue to purple upon prolonged exposure to UVC light can be controlled by adjusting the ZnO ratio. Interestingly, the use of ZnO quantum dots with a diameter of 3.8 nm drastically increases the sensitivity to UVC light. The adjustment in DA alkyl chain length also enables fine-tuning of sensitivity. The shortening of the alkyl chain length at the tail and headgroup position strongly influences the color-transition behaviors of the nanocomposites upon increasing the UVC irradiation time. Two different types of UVC sensors can be fabricated including flexible film and hydrogel bead sensors. These sensors exhibit a color transition from yellow to green to red as UVC exposure increases from 0 to 16.4 J/cm².