Nature Nanotech. 8, 946–951 (2013)

Passing molecules, including DNA, through nanopores in membranes is an active area in sensor research, as it allows sensitive detection of chemicals and molecules. However, it is not simple to control the passage of molecules through pores, because of the range of forces involved. Now, Nicolas Di Fiori and colleagues from the USA and Israel claim that tightly focusing low-power, visible laser light on a pore can assist with controlling the flow through the pore. They show that such light can be used to manipulate the surface charge on solid-state pores, and hence affect electro-osmotic flow through them. For example, light can be used to reduce the translocation speeds of double-stranded DNA and small globular proteins by one and two orders of magnitude, respectively. The effect is also reversible. The researchers consider pores with diameters from 4 nm to 20 nm in a silicon nitride membrane. The team used a green (532 nm) laser diode with just a few milliwatts of power; this is strong enough to induce the desired effect, but small enough that any thermal effects are insignificant and can be neglected. A common problem with nanopore devices is that the pores can become blocked; the researchers show that illumination with 5 mW of laser light can also be used to unclog blocked pores.