Nanoparticles capable of moving through the cell membrane usually do not penetrate deep into the cell. The membrane recognizes them as foreign elements and isolates them with the help of special membrane structures. Thanks to a special coating, new gold nanoparticles are able to penetrate the cell membrane without triggering protective mechanisms. This makes them promising carriers for delivering drugs or imaging agents inside the cell.
Only nanoparticles whose size does not exceed 5 nanometers can penetrate into the cell without hindrance, but particles with a larger surface area capable of simultaneously binding several large molecules have therapeutic and diagnostic value.
Researchers use various strategies to ensure the movement of larger particles through the membrane. Some coated the particles with peptides (short fragments of proteins), facilitating the penetration of particles into cells. Others used synthetic materials to get inside the cell using "brute force", for example, by opening pores as a result of electrostatic interactions. However, interference with the functioning of ion channels and the creation of pores in the membrane inevitably disrupts the work of the cell.
Scientists at the Massachusetts Institute of Technology, working under the leadership of Dr. Francesco Stellacci, coated gold nanoparticles with a diameter of 6 nm with alternating bands of hydrophobic and hydrophilic synthetic molecules, which mimics the ordered structure of proteins. The resulting structures were labeled with fluorescent dyes and their behavior was tested on mouse immune cells. Having penetrated through the membrane, the nanoparticles were distributed over the volume of the cytosol – the intracellular medium, without causing harm to the cell. It turned out that nanoparticles coated with similar molecules, but in an arbitrary order, trigger intracellular defense mechanisms that ensure their isolation inside membrane bubbles. The reasons for this phenomenon are currently unclear.
Compared to the peptides used for coating nanoparticles, synthetic molecules provide a number of advantages. The synthesis of such molecules in the laboratory is much easier and cheaper than the synthesis of peptides. In addition, peptide-coated nanoparticles tend to stick together and are unstable under certain conditions.
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