Conventional liquid crystal (LC)-based sensors for detecting metal ions usually apply a molecular probe for target recognition and an amphiphilic molecule for LC alignment, which makes LC-based sensors require additional pre-mixing procedures such that they are not suitable for in-situ monitoring. In this work, we applied an amphiphilic molecule, i.e., N-dodecyl-ethane-1,2-diamine (NN12C) as the molecular probes in LC-based sensors for detecting aluminum ions (Al3+). At the LC/aqueous interface, NN12C is protonated and aligns at the interface to cause the homeotropic orientation of LC. The binding of Al3+ and the amino groups of NN12C changed the amphiphilicity of NN12C and disrupted the orientation of LC, resulting into a dark-to-bright transition of LC images. Based on this mechanism, the lowest detectable concentration of Al3+ was 8 μM with the detection range from 8 to 25 μM. Moreover, we demonstrated that this sensor can detect aluminum ions in drinking water. This work provides a strategy to develop the LC-based sensors to detect metal ions with simplified operating procedures.
