(Nanowerk Spotlight) Developing multifunctional nanomaterials has been a long-standing goal in the field of biomedical research. Over the years, scientists have explored various strategies to engineer nanostructures that can synergistically combine different properties to address complex medical challenges. However, achieving precise control over the composition, structure, and functionality of these nanomaterials has proven to be a formidable task.
Plasmonic nanostructures, in particular, have garnered significant attention due to their unique optical properties and potential applications in photothermal therapy and catalysis. These nanostructures can efficiently convert light into heat and generate reactive oxygen species, making them promising candidates for cancer treatment and antimicrobial applications. Nevertheless, the synthesis of plasmonic nanostructures with well-defined morphologies and multiple components remains a challenge.
Previous attempts to create multifunctional plasmonic nanostructures have often relied on complex synthesis methods, such as heterogeneous seed-mediated overgrowth, galvanic replacement, and ion exchange. While these approaches have yielded some success, they often lack the level of control and reproducibility needed for practical applications. Moreover, the resulting nanostructures may not possess the desired structural complexity and functionality required for effective biomedical interventions.
Recent advancements in nanomaterial synthesis and characterization techniques have opened up new possibilities for the rational design of multifunctional plasmonic nanostructures. The ability to precisely control the size, shape, and composition of these nanostructures has enabled researchers to fine-tune their optical and catalytic properties. Furthermore, the integration of plasmonic components with other functional materials, such as metal-organic frameworks and semiconductors, has expanded the range of applications for these nanostructures.
Schematic illustration of the synthetic route of the nanodart family and their applications for NIR-II-excited photothermal–catalytic synergetic cancer cell and tumor organoid ablation and antimicrobial effects. (Reprinted from DOI:10.1002/adfm.202405588, CC BY)
AgPd nanodarts are synthesized through a combination of galvanic replacement, co-reduction, and Ostwald ripening. By carefully controlling the reaction conditions, such as the amount of silver precursor, surfactant type, and pH value, the researchers were able to achieve a high yield of the desired nanodart structure. The morphological evolution of the nanodarts was thoroughly investigated, and a growth mechanism was proposed based on the experimental observations.
The AgPd nanodarts exhibit a remarkable set of properties that make them highly suitable for biomedical applications. First, the overgrowth of the AgPd nanoparticle on the gold nanobipyramid leads to a significant redshift of the plasmon resonance wavelength to the second near-infrared (NIR-II) region. This shift enables the nanodarts to efficiently absorb and convert light in the NIR-II window, which is highly desirable for deep tissue penetration and minimizing tissue damage.
Second, the AgPd nanodarts possess an outstanding photothermal conversion efficiency of 86.7% under 1064 nm laser irradiation. This efficiency surpasses that of many reported photothermal agents active in the NIR-II range, such as Au@Pd bimetallic nanoplates and nanorods. The high photothermal conversion efficiency makes the AgPd nanodarts a promising candidate for photothermal therapy, where the generated heat can be used to ablate cancer cells.
Third, the AgPd nanodarts exhibit a remarkable peroxidase-like activity, which enables them to catalyze the decomposition of hydrogen peroxide to produce highly toxic hydroxyl radicals. These reactive oxygen species can cause significant damage to cancer cells, leading to their apoptosis and necrosis. The combination of photothermal conversion and catalytic activity in a single nanostructure opens up the possibility of a synergistic approach to cancer treatment.
To demonstrate the potential of the AgPd nanodarts for biomedical applications, the researchers conducted a series of experiments on cancer cell ablation and antimicrobial wound treatment. They functionalized the nanodarts with folic acid to improve their biocompatibility and cancer cell targeting ability. The bare sharp tip of the gold nanobipyramid core also endowed the nanodarts with enhanced cell membrane penetration capabilities.
In vitro studies revealed that the folic acid-modified AgPd nanodarts could effectively ablate 4T1 cancer cells under NIR-II laser irradiation. Nearly 82% of the cancer cells were eliminated at a low nanodart concentration of 20 µg mL−1. Furthermore, the researchers cultured colorectal cancer patient-derived organoids to investigate the ablation ability of the nanodarts in a more clinically relevant model. Remarkably, nearly 70% of the organoids were killed by the nanodarts at a concentration of only 40 µg mL−1 under 10 minutes of laser irradiation, demonstrating their high efficiency in tumor treatment.
The researchers also explored the antimicrobial potential of the AgPd nanodarts by incorporating additional functional components. They successfully coated zeolitic imidazolate framework-8 (ZIF-8) and titanium dioxide (TiO2) selectively at the AgPd end of the nanodarts, resulting in AgPd@ZIF-8 and AgPd@TiO2 nanodarts, respectively. These modified nanodarts exhibited excellent antimicrobial activities against both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria, with minimum inhibitory concentrations in the range of 2-40 µg mL−1.
The combination of multiple antimicrobial elements in the AgPd@ZIF-8 nanodarts and the photo-generated reactive oxygen species from the AgPd@TiO2 nanodarts contributed to their superior antibacterial performance, highlighting their potential for disinfection and clinical wound healing applications.
The development of the AgPd nanodarts and their derivatives represents a significant advancement in the field of multifunctional plasmonic nanostructures. By selectively depositing AgPd nanoparticles at one end of gold nanobipyramids, the researchers have created a novel dart-like nanostructure with a unique set of properties. The combination of photothermal conversion, catalytic activity, and antimicrobial functionality in a single nanostructure opens up new avenues for cancer treatment and wound management.
The success of this research can be attributed to the careful design and precise control over the synthesis process, which enabled the formation of the desired nanodart structure with high yield and reproducibility. The systematic investigation of the growth mechanism and the exploration of the structure-property relationships provide valuable insights for the rational design of other multifunctional plasmonic nanostructures.
The AgPd nanodarts and their derivatives hold great promise for biomedical applications, particularly in the areas of cancer therapy and antimicrobial treatment. The high photothermal conversion efficiency and catalytic activity of the nanodarts make them highly effective for ablating cancer cells and generating reactive oxygen species. The incorporation of additional functional components, such as ZIF-8 and TiO2, further enhances their antimicrobial capabilities, making them suitable for disinfection and wound healing applications.
While the results presented in this study are highly encouraging, further research is needed to fully realize the potential of these multifunctional plasmonic nanostructures. The long-term stability, biocompatibility, and in vivo performance of the AgPd nanodarts and their derivatives need to be thoroughly investigated. Additionally, the scalability and cost-effectiveness of the synthesis process should be evaluated to determine the feasibility of their large-scale production and clinical translation.
The work by this team represents a significant step forward in the development of multifunctional plasmonic nanostructures for biomedical applications. The AgPd nanodarts and their derivatives demonstrate the power of rational design and precise control in creating nanostructures with tailored properties and functionalities. This research opens up new possibilities for the development of advanced nanomaterials that can address complex medical challenges, such as cancer treatment and antimicrobial resistance.
As the field of nanomedicine continues to evolve, the development of multifunctional plasmonic nanostructures like the AgPd nanodarts will play an increasingly important role. By combining multiple functionalities in a single nanostructure, these materials have the potential to revolutionize the way we diagnose, treat, and manage diseases. The continued exploration of novel synthesis strategies, the integration of diverse functional components, and the understanding of the underlying mechanisms will be crucial for unlocking the full potential of these nanostructures and bringing them closer to clinical applications.
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