Ligand-protected gold nanoclusters (AuNCs) show promise for high performance in biological applications, such as imaging and therapeutics. The assembly of AuNCs with biological macromolecules represents a simple but effective approach to fine-tuning of material functionalities. Thus, these materials might enable intracellular applications of AuNCs. Herein, we prepared a new AuNC-based nanometric system through a self-assembly approach mediated by hydrophobic and electrostatic effects. We show that hydrophobic and electrostatic effects between fluorescent AuNCs with protamine and hyaluronic acid contribute to the formation of small nanocomposites with acceptable colloidal stability. More importantly, the AuNC-decorated nanocomposites show assembly enhanced emission and singlet oxygen generation. In vitro experiments showed that our nanocomposites labeled specific cells by targeting CD44 and induced cell death by producing singlet oxygen. Hence, our AuNC-decorated nanocomposites show great potential as theranostic fluorescent nanomaterials.

Fluorescent gold nanoclusters (AuNCs) have drawn considerable research interest owing to their unique emission properties. However, the environment surrounding the NC greatly influences its luminous behavior. In this work, a novel nanocomposite based on AuNCs with bright fluorescence and high biocompatibility was prepared. In this nanocomposite, mesoporous silica nanospheres provided a mesoporous framework, which helped to template the formation of ultrasmall AuNCs and also prevented their aggregation in different solutions. These nanocomposites emitted stable fluorescence even in complex biological environments. After the self-assembly of folic acid-conjugated poly(l-lysine), the presence of folic acid on the nanocomposites guaranteed a good recognition in folate receptor (FR)-positive cells, improving detection selectivity. Cellular experiments demonstrated that the nanocomposites had good dispersity in the physiological environment and could be internalized by FR-positive cancer cells, resulting in bright fluorescence. We believe that this research provides a simple approach to the fabrication of stable fluorescent AuNC nanocomposites, which show good compatibility with complex biological systems and great potential for applications in biological imaging and cell detection.

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