Tirlapur and König pierced a cell membrane with a Ti:sapphire laser, allowing DNA delivery through the resulting hole – a process known as transfection. This hole quickly closed up, and the implanted cell and the new DNA appeared to be undamaged by the process.

The researchers say that this is a better method than conventional cell-perforation techniques. For instance, electroperforation cannot target individual cells, while mechanical or chemical techniques can damage either the cell or the foreign DNA.

Nanosecond laser pulses from a frequency-tripled Nd:YAG source have also been tried, but according to the researchers, this technique damages the cells beyond repair.

The femtosecond pulses were focused at the cell membrane using a high-numerical-aperture objective lens. The target cells were exposed to the 50-100 mW average power beam for 16 ms during transfection.

Having implanted the foreign DNA into the target cells, Tirlapur and König used the same set-up to study the success of the transfer. To do this, they tagged the foreign genes with green fluorescent protein. The Ti:sapphire source then generated two-photon fluorescence images of the cell expressing this protein.

The researchers say that irrespective of the type of cell implanted with foreign DNA, the femtosecond laser method worked each time. They add that the high level of selectivity prevented transfection into any neighbouring cells, and claim that there are "no detrimental effects on growth and division, and virtually no cell death".

In gene therapy, a cell which lacks a certain gene is fixed by implanting foreign DNA that can express the missing gene. Though potentially revolutionary, the technique is also highly controversial.