Colorimetric detection of aluminium ion based on conjugated polydiacetylene supramolecules

Abstract

Owing to their intriguing structural and optical properties, conjugated polydiacetylenes (PDAs) have received great attention from researchers. Unlike other conjugated polymers which require tedious multistep procedures to form water-compatible nanostructures, PDAs can be readily prepared in aqueous environment by a simple dispersion method. Thus, dropping an organic solution containing diacetylene (DA) monomers into water, followed by sonication yields self-assembled DA supramolecules, which can be readily polymerized by 254 nm UV light. The polymerized DA suspension displays, in general, an intense blue color (λmax: ca. 640 nm) and undergoes a colorimetric transition to red color (λmax: ca. 550 nm) upon environmental perturbations such as temperature change, mechanical stress and ligand-receptor interactions. The stimulus-induced blue-to-red color transition property of PDA has been applied for the detection of biologically, chemically and environmentally important target molecules. Accordingly, a variety of PDA-based sensor systems have been reported to detect influenza virus, E. coli, DNA, enzymes, ions, glucose, cyclodextrin etc. The detection of aluminium ion is significant due to its potential toxicity, and the correlation between aluminium ion and Alzheimer’s disease. Aluminium ion is abundantly found in nature in mineral form, and it is well known that aluminium ion causes drinking water contamination, which has harmful effects on human health. In recent times, several fluorometric and potentiometric aluminium ion selective sensors have been developed. However, these sensors have some limitations such as the need for additional fluorescence probes or matrix membranes. The motivation behind this work was to develop a PDAbased sensor system to detect aluminium ion in aqueous solution. We thought that if electron rich polar head groups which can coordinate aluminium ion, were introduced to a DA monomer, the resultant PDA supramolecules might undergo a colorimetric change upon exposure to the metal ion (Figure 1). The results described below suggest that the PDA derived from PCDA-EDEA can indeed be used as an aluminium ion specific chemosensor.