Nanoparticles that can penetrate a cell without causing overt disruption are described online this week in Nature Materials. When covered with two different kinds of molecules in a \\\\\\\'striped\\\\\\\' arrangement, these nanoparticles can pass directly through the highly protective barrier of the cell membrane without creating holes leading to cell death. This mechanism could be used to deliver biologically active molecules into the cell for therapeutic purposes.
Although some biomolecules can directly pass through cell membranes, for some time there has been controversy surrounding the possibility of a similar mechanism occurring for synthetic particles of a similar size. Usually, the uptake of synthetic objects into the cell results in them reaching only a limited area within small compartments rather than the main fluid section, called the cytosol, of the cell. Objects, such as positively charged nanoparticles, also create small transient holes that disrupt the membrane in the process and can cause cell death.
Francesco Stellacci and colleagues show that gold nanoparticles can penetrate the cell membrane without causing disruption, and reach the cytosol if the particles are coated with both negatively charged and hydrophobic ligands arranged in an alternating ‘striped’ fashion. If these ligands are arranged in a random way, but in the same ratio, on the nanoparticles, the particles can not directly pass through the membrane.