Silica nanoparticles have a variety of interesting properties and thus a wide array of applications. They are strong, abrasive materials that can be used to polish silicon wafers. They are effective at reducing friction and as a result, are used to coat waxed floors and even railroad tracks. Their absorptive properties make them useful in papermaking as a drainage aid. They can serve as a binding agent in the manufacture of rubber, plastics, and concrete. Most notably, they are stable and non-toxic materials with innumerable applications in biomedicine.
Silica is an important component of an array of nanomaterial heterostructures with a wide range of interesting applications. Just a small sampling of these applications are described below.
Inorganic nanoparticles are useful for in vivo cell tracking due to their small sizes, high cellular uptake, and impedance mismatch with cells. A recent publication describes the use of NanoXact Silica Nanospheres as an ultrasound contrast agent to facilitate stem cell tracking in mice. The steps for cell labeling and nanoparticle integration are outlined in the report, using silica as a model system.
Mesoporous silica nanoparticles (MSNs) and hollow silica nanoparticles (HSNs) have garnered considerable attention for targeted drug delivery due to their uniquely large surface areas, easy surface modification, biocompatibility. The porous structures and surfaces can be engineered for targeting tissues and cells with unprecedented specificity and control. For more general information about nanomedicine, go to our course on Nanobiotechnology.
The pores and surface chemistries of mesoporous and hollow silica nanoparticles provide ideal sites for executing highly specific chemical transformations, offering increased efficiency and enhanced selectivity over other catalytic systems. The internal pores of these structures can be functionalized with catalyst, and the pore sizes tuned to offer exclusive entry to molecules participating in the catalytic process.
Silica coated plasmonic particles can be integrated into a much wider variety of matrices than unshelled particles. Silica coated silver and gold nanoparticles have been used to produce robust glazes and paints that can be applied to a wide variety of surfaces.
Silica coated silver nanoplates will change color in the presence of a liquid or high humidity. This is due to the transport of water and salts across the silica shell where the high curvature silver nanoplate edges will be selectively dissolved. When the silver plates dissolve, the plasmon resonant wavelength shifts resulting in a distinct color change. By adjusting the thickness of porosity of the silica shell, the rate of color change can be adjusted. This material is being investigated as a color indicator to signify when a wound dressing should be exchanged.
Silica shells are useful for embedding dyes or other specialized molecules near to the surfaces of metal nanoparticles. These nanomaterial architectures can be designed to enhance the spectroscopic signatures of plasmonic metal nanoparticles and increase the sensitivity of spectroscopic measurements such as fluorescence and Raman. For more information on this phenomenon, check out our course on Surface Enhanced Spectroscopy.
Functionalized silica can be used to bind DNA molecules as an effective method for DNA separation. By adjusting the ionic strength of the environment through manipulation of the pH and salt concentration, DNA fragments of various sizes can be selectively separated. This approach is especially valuable for binding DNA on microchips, where extracting DNA by other methods has proven challenging.
Silica shelled superparamagnetic nanoparticles combine the interesting properties of the core material with the enhanced stability offered by the shell material. Silica shells offer the additional benefits associated with their functionalized surfaces that facilitates binding to proteins or DNA molecules with an array of biomedical applications. Silica is a common component of columns used for biomolecular separation, thus magnetic silica particles have applications for separation in solution and microfluidic devices.
Additionally, a silica coating on magnetite particles can serve as an interface or spacer for attachment of a different material with interesting optical properties, such as a plasmonic metal or a fluorescent quantum dot that can couple to the magnetic nanoparticle core. For more information about interfacing silica with magnetic materials, visit this page about our Custom Magnetic Nanomaterials.
Silica nanoparticles are commonly used as standards for instrumental method development, including single-particle ICP-MS (SP-ICP-MS). Silica presents unique challenges for ICP-MS characterization due to high background at the m/z value of silicon's most abundant isotope (28Si).
Check out this Application Note to see how Perkin Elmer uses nanoComposix silica nanoparticles to overcome these challenges and analytically quantify Si content by SP-ICP-MS.