Russian researchers have developed a new type of composite nanoparticles, which successfully deliver porphyrines (for combating cancer) to target tissues. Luminescence can enhance photodynamic effect and helps control distribution of nanoparticles in living tissues.

Photodynamic therapy is a cancer fighting technique, based upon the same principle as chemotherapy, but with a “bit” of physics. Some substances, known as photosensitizers, are affected by light of a certain wavelength in a way that they launch photochemical reactions in surrounding solution. For instance, they help oxygen molecules to convert to energetically excited (singlet) state. These excited oxygen molecules destroy neighboring molecules, such as organic ones, for example. All this multiplies the amount of free radicals in the solution, which is fatal for a living cell.

When a photosensitizer has selective affinity to cells that should be killed, like cancer cells, it can be used for treatment. However, in order for photosensitizer to work, a damaged tissue should be exposed to light – modern medicine uses lasers for this purpose. Main principle of photodynamic therapy was discovered in Germany between 19 and 20 century. Researchers worked with acridine orange dye and noticed that this dye’s solution, exposed to light with wavelength inside absorption range of this substance, kills infusorians. Without exposure to light, acridine solution was harmless to these animals.

Today photodynamic therapy is a powerful tool for treating cancer, lymphoid tumors, and some bacteria-induced infections, especially when pathogens are drug-resistant. Most often it is used for treating skin, because it is the most easily exposed to light body part.

Photodynamic therapy has many advantages, however, there exist technical difficulties, connected with this technique. Many chemical substances, which are nice photosensitizers, are not soluble in water due to their chemical properties. And our organism contains large amount of water, being a water solution. In order to facilitate traveling of an active agent with blood and its penetration into tissues its molecules are placed in carrier particles. These particles should be very small, smaller than a bacterial cell – in other words, they should be nanoparticles.

Researchers from the Institute of Biochemistry and Physiology of Plants and Microorganisms (Russian academy of sciences), Saratov State University and Moscow State Academy of Fine Chemical Technology developed a new type of composite nanoparticles, in which silver and gold body is covered with a porous silicon shell. These particles are like small viruses – 40 nanometers in size. They are perfect carriers for porphyrines, very important photosensitizers. Moreover, these particles often become luminescent, when exposed to visible light.

Luminescence helps to control nanoparticles’ distribution in living tissues and can enhance photodynamic effect, when a correct distance between metal body and molecules of an active ingredient is chose, thus making therapy even more successful.

Source: Science & Technologies

Anna Kizilova