Scientists have performed a delicate surgical operation on a single living cell, using a needle that is just a few billionths of a metre wide.
The needle can be seen in yellow as it enters the cell (orange)
They claim the procedure could be used to manipulate embryonic stem cells intended for use in medical treatment.
This "nano-needle" was used together with an atomic force microscope (AFM) to penetrate the membrane of a cell to a depth of one or two micrometres.
The Japanese team will outline details in a future issue of Nano-Letters.
"The cells used were on the micrometre scale but we adjusted the procedure for the nanometre scale using an AFM," co-author Noriyuki Nakamura told the BBC News website.
In order to manipulate cells, scientists currently use tiny injectors called micro-capillaries to introduce molecules such as proteins, peptides and genetic material into cells.
But the shape of these micro-capillaries and a lack of accuracy in controlling them often results in fatal damage to the cell.
Dr Nakamura, of the National Institute of Advanced Industrial Science and Technology (AIST), and colleagues used an AFM because it is able to see ongoing physiological processes in cells at high resolution.
They sharpened the tip of the microscope's pyramid-shaped probe tool - which can be used either to modify or break through cell surfaces - into a needle that was just 200-300 nanometres in diameter.
Finally, they experimented with the technique on human cells, measuring the forces as the nano-needle penetrated their interiors.
Tour de force
The needles used much less force to penetrate the cell than a conventional AFM probe, causing less damage and deformation to the cell.
In one experiment, on a human embryonic kidney cell, the scientists managed to insert the needle accurately into the cell's nucleus, which contains its genetic material.
"To the best of our knowledge, the results demonstrated for the first time that solid material was inserted into a nucleus of such a small living cell with highly accurate positioning," the team writes in Nano-Letters.
The needles are sharpened to make them ultra-thin
The researchers say the technique could provide a versatile apparatus for surgery on living cells.
"We can inject metabolic inhibitors into cells through a nano-needle allowing it to be accepted by the cell's metabolic pathways," said Dr Nakamura. "This cell surgery allows us to modify the cell's functions."
Dr Nakamura aims to use the technique on embryonic stem cells. It could be used to control the cells' differentiation - the process by which cells become, say, heart, kidney or liver cells - and how they proliferate - or divide.