The antimicrobial effects of silver have been known for over a century with the first known use traced back to the Greeks and Romans, who increased the potability of water by storing it in silver vessels. Recent research has demonstrated that silver ions are an effective antimicrobial yet have a low toxicity for humans, making silver an attractive component in wound dressings, packaging materials, and anti-fouling surface coatings. The antimicrobial efficacy of the silver source depends on the rate and duration of silver ion release, which can be modulated by selecting the size, shape, and surface coating of the added silver. NanoComposix provides precisely sized and shaped, highly purified silver nanomaterials with tailorable surface coatings that can be used for antimicrobial research studies or incorporated into devices and products.

Nanomaterial Selection Criteria

When silver nanoparticles are exposed to water and oxygen, the surface slowly dissolves releasing silver ions:

The choice of nanoparticle depends on the desired release rate for the target antimicrobial application.  The rate at which silver ions are released depends on the concentration, size, shape, and aggregation state of the silver nanoparticles, as well as environmental factors such as pH and temperature.   When selecting a nanoparticle it is important to take into account the potential effects that nanomaterial size, shape and surface may have:

  • Size and Aggregation State - The ion release rate from different sizes of spherical silver nanoparticles has been widely studied, and there is a significant dependence on the size of the particle. For a given mass of silver nanoparticles, as the particle diameter decreases there is a increase in the total surface area, and a corresponding increase in the ion release rate. If particles become destabilized in solution, or cluster when incorporated into a substrate, the available surface area and ion release rate will decrease.
  • Shape – Non-spherical silver nanoparticles (e.g. spheres, rods, or plates) have different crystal facets exposed to the surrounding environment. The different facets will dissolve at different rates, resulting in shape-specific ion release rates.
  • Surface Coating – Different molecules absorbed to the surface of the nanoparticles will modulate the dissolution rate. For example, the encapsulation of a silver nanoparticle with a porous silica shell will slow but not eliminate the dissolution of the central silver nanoparticle.

We have measured the silver ion release rate from different sizes and shapes of our nanoparticles, using Inductively Coupled Plasma Mass Spectroscopy (ICP-MS), which allows the silver ion concentration to be determined with accuracy at the parts per billion level. As expected given the criteria described above, smaller (10 nm diameter) silver nanoparticles exhibited a significantly higher ion release rate and final ion concentration in solution than larger (110 nm diameter) particles. Anisotropic silver nanoplates had significantly different ion release rates than spherical particles. Large silver nanoplates, with an average diameter of 150 nm, had nearly the same silver concentration profile over time as the 10 nm spherical silver particles, and the 35 nm-diameter plates exhibited silver ion concentrations nearly twice as high as the smaller silver spheres.

Silver ion release as a function of time, for silver spheres and nanoplates of different sizes.  The same mass of silver is used in each samples.

Available Nanomaterials

At nanoComposix, we fabricate precisely sized and shaped, extensively purified, highly characterized silver nanomaterials with a variety of sizes, shapes, and surfaces. For research purposes, our BioPure product line provides sterile and endotoxin-free materials with narrow size and shape distributions. The BioPure line we produce is subjected to a rigorous washing and purification process to remove excess residual synthesis precursors that are used in the wet synthesis process ensuring that an observed antimicrobial response can be correlated to the nanoparticles themselves rather than reactants used during fabrication. As larger quantities of materials become necessary for product integration, our Econix line provides lower-cost materials at larger volumes.

Silfuze Antimicrobial Additive

NanoComposix has recently developed Silfuze, a silver and zinc particle additive for integration into protective coatings.  The additive is water based and has excellent long term performance for biostatic protection of surfaces (>99.99% protection after 2 year accelerated aging of coating for MRSA, p. aeruginosa, acinetobacter baumannii, and enterbacter cloacae).  In a separate study, >99.4% of MRSA was killed after a 1 hour contact time.  The Silfuze additive is optically clear in transparent coatings and is easily integrated into paints, varnishes, and other protective finishes.  The mean particle size is >100 nm so it is not classified as a nanomaterial under European REACH regulations, eliminating the need for any additional labeling requirements.  

Characterization & Integration Services

Characterization of nanoparticles before, during, and after introduction into the test system provides critical information that can be used to understand the interaction of the system with the nanoparticles. However, once nanoparticles are exposed to a hetergeneous and complex environmental or biological system, it is difficult to determine the state of the nanoparticles. At nanoComposix we utilize a wide variety of characterization techniques to monitor the state of nanoparticles over time and provide both data and characterization methods for each of our products.

NanoComposix has experience attaching silver nanoparticles to a variety of textiles and can engineer nanoparticle surfaces that are compatible with a variety of aqueous and organic solvents, fluoropolymers, epoxies, and other polymers. For more information, please contact us.