Thin layer of silica enables golden nanoparticles “to shine” brighter

Scientists from the Immanuel Kant Baltic Federal University found out that gold nanoparticles, covered by thin layer of silica, disperse light better than those that have thick “coat”. Such nanoparticles are used as a system of targeted delivery of drugs, and the intense dispersion of light enables to keep track of their movement in organism with the help of special devices. The results were published in the magazine Nanomaterials. The research is made on the base of Kovalevskaya North-West Centre of Mathematical Research of the Immanuel Kant Baltic Federal University.

The targeted delivery of drugs actively develops in modern medicine. This approach consists in the transferring drugs with the help of special carriers exactly to definite place, for example, to tumor. It enables to avoid damaging and ruining of the healthy cells and tissues.

One of the possible systems of drug delivery is gold nanoparticles, to which the drug molecules are attached. This construction is covered by special shell, that protects drug from the early release. Besides this, antibodies, protein molecules, targeting particles to the proper place, are attached to it.

For creating the shells of such particles people use silica, compound that is identical to sand in its chemical composition. These shells turn out to be very convenient because they are stable and safe for people, and also because their thickness can be easily and very precisely controlled. Until now scientists were mainly interested what size and form must the nanoparticles on the base of gold have, in order to deliver drugs more effectively, however, the optical characteristics of such constructions deserve less attention. By this, if the particles are able to disperse light of a certain diapason falling on them well, they can be tracked with the help of special devices, and that means, the delivery of drugs can be controlled. The ability to disperse light in many ways depend upon tension of electrical field around the particles, so it is obvious from its parameters which particles will “shine” better.

Scientists from the Immanuel Kant Baltic Federal University mathematically modelled the parameters of the electrical field, that is created by three types of structures – gold nanoparticles without shell, particles covered by the layer of silica, and also empty silica capsule. By this the authors studied the shells of different thickness – from 2 to 20 nanometers (parameters, not exceeding the size of the smallest viral particles).

It turned out that the biggest tension of the electrical field appeared around the particles covered by 20 nanometer layer of silica. The tension around them exceeded the parameters characteristic for free gold nanoparticles in 2.5 times. This leads to the fact that tightly “dressed” particles were worse at dispersing light. The thin covering about 2-5 nanometers, on the contrary, strengthened the dispersion, and due to this, the particles were detected by laser illumination more easily.

“Our research showed that the effect of the silica shell is contradictory: of it is thin, it increases the light dispersion by the particles, if it is thick, it makes it worse. This enables to define, that in the first case the particles can be tracked more easily, and therefore they are more perspective as a system of drug delivery. In the future we plan to study other physical characteristics of gold nanoparticles covered by layers of silica of various thickness”, – tells Andrey Zyubin, PhD, Immanuel Kant Baltic Federal University Research & Education Center “Fundamental and Applied Photonics. Nanophotonics”.