Recent advances in NIR-II emitting nanomaterials: design and biomedical applications of lanthanide complexes and functionalized mesoporous silica nanoparticles (MSNs).

The second near-infrared (NIR-II, 1000-1700 nm) region has gained significant attention due to its superior tissue penetration depth, reduced photon scattering, and minimal autofluorescence compared to the first near-infrared (NIR-I, 700-900 nm) window. These advantages make NIR-II an ideal spectral range for bioimaging, photothermal therapy (PTT), and photodynamic therapy (PDT). Various nanomaterials, including metal-based complexes, organic dyes, and carbon-based materials, have been engineered to serve as efficient NIR-II agents for enhanced biomedical applications. Among these, mesoporous silica nanoparticles (MSNs) have emerged as versatile nanoplatforms due to their tunable porosity, high surface area, and biocompatibility. MSNs can be modified with different functional materials, such as luminescent coordination complexes, organic dyes, and metal nanoclusters, to optimize photothermal conversion efficiency and imaging capabilities. Their ability to encapsulate therapeutic agents further enables controlled drug delivery and combinational cancer therapies. Additionally, hybrid MSN systems incorporating nanocarbon materials (, fullerenes, carbon nanotubes) and metal nanoparticles have been explored to enhance stability and bioavailability. Despite their promising potential, challenges such as long-term biocompatibility, clearance mechanisms, and precise targeting remain key hurdles in clinical translation. Future research should focus on overcoming these limitations by developing next-generation MSN-based nanocomposites, such as MSN-graphene oxide, MSN-fullerenes, MSN-carbon nanotubes, MSN-quantum dots, and MSN-metal nanoparticles. These advancements will pave the way for improved therapeutic efficacy and broader biomedical applications.