Scatterings image

a) Image of a plasmid-coated particles (green) with foreign DNA that have been optically tweezed and inserted into a mammalian cancer cell. b) The same cell reveals the transfected gene material (bright green spots). c) Image b superimposed on image a.

Researchers in South Korea have announced successful high-precision optical insertion of a strand of DNA into a single cell without damaging nearby cells, a technique that may enable gene therapy and genetic engineering of single cells rather than groups of cells. The method uses femtosecond lasers and optical tweezers to precisely “transfect” a single cell (Biomed. Opt. Express 4, 1533). Optical transfection uses light to introduce foreign genes into living cells, in this case via optoporation—the generation of transient holes in cell membranes.

Yong-Gu Lee and colleagues at the Gwangju Institute of Science and Technology developed the method to have better control over cell transfection. Previous single-cell transfection methods such as microinjection risked damage to the cells and introduction of foreign substances and contamination into target cells.  In this new technique, a 75 mW near-infrared pulsed femtosecond laser at 800 nm punctures the membrane of a mammalian cancer cell at a single point, a second 1064 nm continuous-wave (CW) laser traps and inserts a plasmid-coated microparticle containing the DNA into the cell. A third CW laser at 685 nm monitors the location of the cell membrane while the trapping laser inserts the gene through the puncture.

The injected plasmid-coated microparticle fluoresces under UV excitation to produce a green fluorescent protein, which helps determine the exact location of the cell membrane and confirms successful transfection. Enabling such precision optoporation and transfection of a single cell in a group of similar cells means untreated cells may act as a control while confirming transfection in the treated cell—a breakthrough for controllable genetic therapy of cells.