But University of Illinois researchers have come up with a way to sequence DNA in real time. The technique uses a nanoscale pore in an ultrathin membrane capacitor. The pore has two ring-electrode collars. It turns out individual base pairs of a DNA molecule have different dielectric constants, or electrical resistivities. These can induce unique voltage changes in the electrodes as the DNA moves through the pore. Should these electrical "signatures" be associated with specific base pairs, biologists could discriminate among them quickly and inexpensively.

The researchers used electron beam decomposition and sputtering to make the 0.34-nm-wide pores in MOS capacitor membranes less than 40-nm thick. Ions are created when the membrane is immersed in an electrolyte with a dc voltage across it. DNA molecules are also ionic and therefore attracted to the pore and forced through it. Molecules transiting the pore induce a measurable voltage change at the ring electrodes.

Sensitivity and bandwidth of the device aren't yet sufficient for practical devices though results are promising, say researchers.