Rational Assembly of Polymer–Metal Coordination Hierarchical Superstructures for Azathioprine-Responsive Electrodes in Biological Samples

The sustainable self-assembly of small molecules into a superstructure is of prevalent interest for particle engineering and its applications. Herein, a ligand–metal cross-linking chemistry strategy is developed for the design of molybdenum–polydopamine (Mo–Px) coordination flowers and their electrochemical sensing performance. The morphology of Mo–Px can be easily tuned by adding surfactants such as cetyltrimethylammonium bromide (CTAB) and sodium lauryl sulfate (SLS). This coordination polymerization is a rapid, single-step approach to producing functional materials and offers excellent control over the formation of flower-shaped superstructures. The devised Mo–Px (namely, x = H2O, CTAB, SLS) superstructures were applied as electrode materials to study the electrocatalytic activity of azathioprine (AP). Having the advantages of a hierarchical superstructure, including a great electroactive surface area, rapid electron transfer, interconnected nanosheet-based architectures, and Mo doping, the as-obtained Mo–PSLS served as a high-performance electrocatalyst in a AP sensor and unveiled great sensitivity (6.13 μA μM–1 cm–2), a low detection limit (3.5 nM), and good operational stability. Additionally, a Mo–PSLS-modified electrode was successfully utilized to monitor the AP concentration in actual rat blood serum samples with satisfactory recovery results. This work paves the way for the design of ligand–metal coordination complex superstructures for electrocatalyst-based applications.