Integrative Self‐Assembly of Graphene Quantum Dots and Biopolymers into a Versatile Biosensing Toolkit

Hybrid self‐assembly has become a reliable approach to synthesize soft materials with multiple levels of structural complexity and synergistic functionality. In this work, photoluminescent graphene quantum dots (GQDs, 2–5 nm) are used for the first time as molecule‐like building blocks to construct self‐assembled hybrid materials for label‐free biosensors. Ionic self‐assembly of disc‐shaped GQDs and charged biopolymers is found to generate a series of hierarchical structures that exhibit aggregation‐induced fluorescence quenching of the GQDs and change the protein/polypeptide secondary structure. The integration of GQDs and biopolymers via self‐assembly offers a flexible toolkit for the design of label‐free biosensors in which the GQDs serve as a fluorescent probe and the biopolymers provide biological function. The versatility of this approach is demonstrated in the detection of glycosaminoglycans (GAGs), pH, and proteases using three strategies: 1) competitive binding of GAGs to biopolymers, 2) pH‐responsive structural changes of polypeptides, and 3) enzymatic hydrolysis of the protein backbone, respectively. It is anticipated that the integrative self‐assembly of biomolecules and GQDs will open up new avenues for the design of multifunctional biomaterials with combined optoelectronic properties and biological applications.