Self-assembly of silver nanoclusters and phthalic acid into hollow tubes as a superior sensor for Fe3+

Abstract Supramolecular self-assembly is a noncovalent bond-based method to build complex ordered aggregates with specific functions. However, self-assembly based on metal nanoclusters (NCs) has been rarely studied because of the poor water solubility and silent fluorescence in a single-molecular state of metal NCs. Here, water-soluble silver NCs (NH4)9[Ag9(mba)9] (Ag9-NCs, H2mna = 2-mercaptonicotinic acid) were synthesized with phthalic acid (PA) to form hydrogels using the self-assembly strategy. Due to the formation of hydrogen bonds, hollow tubes appear in the hydrogel. For comparison, isophthalic acid (IPA) and terephthalic acid (TPA) are selected to self-assemble with Ag9-NCs in aqueous solutions. The result shows that only PA can form a strong phosphorescent hydrogel due to the ligand-to-metal charge transfer (LMCT) and ligand-metal-metal charge transfer (LMMCT). In addition, the hydrogel is used as an excellent sensor for Fe3+, and the detection limit, which is defined as the change of 10% of fluorescence intensity, is 0.611 μM. This work shows that a hydrogel was successfully prepared using a supramolecular self-assembly strategy and will become a candidate in the fields of biological sciences and sensors.