Ultrasmall metal nanoclusters (MNCs) with high absorption-to-volume ratios for linear and non-linear optical applications have been developed at the University of Michigan. Metal nanoclusters (MNCs) are metal systems smaller than 2nm, and can be composed of various metals or alloys and formed in various shapes such as spheres, rods, and triangles.
Monolayered protected metal clusters (MPCs) are very small, stable, and water and organic solvent soluble forms of MNCs. MPCs are very different from known nanoparticles because of their physical, electronic and optical properties. For example, MPCs do not exhibit plasmonic effects common in metal nanoparticles, but demonstrate molecular-like behaviors such as emission. Further, MPCs exhibit 10x greater absorption-to-volume ratios (HA/V) compared to typical metal nanoculsters (10E+7/m vs. 10E+6/m).
Due to their high stability and low toxicity, HA/V metal nanoclusters (HA/V-MNCs) find applications in high efficiency photodynamic therapies. Given their small size, HA/V-MNCs in solution can enter cells; when the target cells are exposed to visible and near infrared excitation (400nm to 1600nm), the HA/V-MNCs generate singlet oxygen associated with type II photodynamic therapies. HA/V-MNCs exhibit 100x greater rates of singlet oxygen generation per cluster compared to regular MPCs. Due to their stability in solution and air, HA/V-MNCs can be used for ultra-thin coatings that demonstrate high photon absorption, or for coatings that protect underlying materials from photo damage. HA/V-MNCs exhibit non-linear properties whereby the absorption of photons increases non-linearly with excitation; these non-linear properties allow for low absorption or high transparency at lower light intensities (e.g., sun light), and high absorption or low transparency at high intensities (e.g., laser light). Concentration control of HA/V-MNCs can be leveraged for variable light transmission in applications ranging from windows to laser goggles. Due to the high stability and high absorption nature of HA/V-MNCs, they can be mixed with other materials that are not photo-stable (e.g., organic dyes) to provide additional stability.
- Photodynamic therapy using singlet oxygen generation
- Highly stable and durable photo-protective coatings
- Controlled light transmission through materials
- Laser excitation protection
- Highly stable
- Large absorption to volume ratios
- Increased rates of singlet generation