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.

In this work, we report a flexible film based on conjugated polyelectrolyte/silver nanocomposites with efficient antibacterial activity. A flexible poly(dimethylsiloxane) film served as a substrate for deposition of nanostructured silver. A light-activated antibacterial agent, based on the cationic conjugated polyelectrolyte poly({9,9-bis[6'-(N,N-trimethylamino)hexyl]-2,7-fluorenyleneethynylene}-alt-co-1,4-(2,5-dimethoxy)phenylene)dibromide (PFEMO) was self-assembled on the negatively charged substrate. By changing the thickness of the poly(l-lysine)/poly(acrylic acid) multilayers between the metal substrate and PFEMO, we obtained concomitant enhancement of PFEMO fluorescence, phosphorescence, and reactive oxygen species generation. These enhancements were induced by surface plasmon resonance effects of the Ag nanoparticles, which overlapped the PFEMO absorption band. Owing to the combination of enhanced bactericidal effects and good flexibility, these films have great potential for use as novel biomaterials for preventing bacterial infections.

Fluorescent gold nanoclusters with unique luminescence properties have drawn great attention in bioimaging. The gold nanoclusters with controlled multicolor fluorescence may benefit accurate fluorescence imaging. In this work, gold-nanoclusterengineered spiropyran ligands (AuNC-SP) were reported to achieve controlled dual-color imaging under single excitation. Through switching the Forster resonance energy transfer from the gold nanocluster segment to the open-ring state merocyanine by UV−vis irradiation, AuNC-SP possesses reversibly dual-color fluorescence. After AuNC-SP combined with chitosan to form AuNC-SP@CS nanoparticles, the steric protection of chitosan largely improved the oxidative stability of AuNC-SP upon UV irradiation. Moreover, the AuNC-SP@ CS could be internalized within cancer cells and released AuNC-SP that further underwent transportation into the nucleus. Thus, the AuNC-SP@CS exhibits excellent and reversible dual-color fluorescence to label not only the cytoplasm but also the nucleus. We envisage the AuNC-SP@CS as an ideal probe for fine subcellular assays in the cell interior.

In this paper, we report a novel organic fluorescent nanoparticle based on exciplexes for cell imaging. Through a reprecipitation method, we used a combination of 1,1-bis((di-4-tolylamino)phenyl) cyclohexane (TAPC) and 2,7-bis(diphenylphosphoryl)-9,9 0 -spirobi[fluorene] (SPPO13) to form nanoparticles. In the aggregated structures, TAPC and SPPO13 were forced into proximity that led to the corresponding exciplex formation. A red-shifted fluorescence emission with considerably longer fluorescence lifetimes ascribed to exciplex emission can be achieved. Along with the good stability and low cytotoxicity of organic nanoparticles, the prepared TAPC/SPPO13 exciplex nanoparticles were successfully applied in live cell imaging. These properties make TAPC/SPPO13 exciplex nanoparticles good candidates for cellular labeling and imaging materials.