Active Feedback Provides Sub-Nanometer Resolution

Two back illuminated Andor EMCCD cameras have been instrumental in helping Steven Chu, a Nobel laureate and Energy Secretary for the United States of America, redraw the boundaries of optical microscopy.

One of the cameras was an Andor DU860, which is capable of acquiring images at 500 frames per second; the other was a highly sensitive DU897 model that can capture individual photons from single fluorescence emitters.

By developing an active feedback system, Chu and his team were able to repeatedly place the centroid of a single fluorescent molecule image anywhere on either of the camera’s CCD arrays and measure its position with sub-pixel accuracy. This means, that in conjunction with additional optical beams to stabilise the microscopy system, the traditional errors caused by non-uniformity of chip manufacture can be reduced to subnanometre scale.

As a result, the team were able to develop a two colour, single molecule imaging system, which achieved image resolutions with an order of magnitude greater than the current best super resolution techniques (5nm).

Gaining the ability to resolve single molecules at this level has significant implications for biological research, where it should allow the structure of large, multi-subunit complexes to be analysed at the single molecule level.

Chu and his colleagues are planning to harness the new technique to learn more about the human RNA polymerase II system, which initiates the transcription of DNA, and the molecular mechanisms controlling cell-to-cell adhesion processes. The resolving power of this new super resolution technique may also be of great use in guiding the design of new photometric imaging systems in scientific fields such as nanometrology, atomic physics and astronomy