Credit: © 2007 Nature

A wish list of features for any new biological imaging technique would almost certainly include the ability to produce images with subwavelength resolution, a light source that can be tuned over a wide range of frequencies or wavelengths, and compatibility with physiological conditions. By combining and improving a number of existing optical technologies, Peidong Yang, Jan Liphardt and colleagues1 at the University of California at Berkeley and the Lawrence Berkeley National Laboratory have developed a new optical probe that just might fit the bill.

The Berkeley team started by making a tunable nanowire laser from potassium niobate — a material that is well known for having nonlinear optical properties. Being able to tune the output of nanowire lasers significantly increases their usefulness, especially in subwavelength applications, which exploit the fact that the cross-sections of the nanowires are much smaller than the wavelengths used in many imaging experiments.

Yang and co-workers perform a 'nanowire scanning microscopy' experiment to demonstrate the potential of the nanowire lasers. Optical tweezers hold the nanowire in position while a piezoelectric stage moves a sample so that it is scanned by the laser radiation from the nanowire. The image is built up by measuring the amount of this radiation that is transmitted by the sample as a function of position. Measurements of line separations on a test sample performed by the nanowire scanning microscope agreed with those made using an atomic force microscope to within ˜10%.