Forget dancing angels, a research team from the National Institute of Standards and Technology (NIST) and the University of Colorado (CU) has shown how to detect and monitor the tiny amount of light reflected directly off the needle point of an atomic force microscope probe, and in so doing has demonstrated a 100-fold improvement in the stability of the instrument's measurements under ambient conditions. Their recently reported work* potentially affects a broad range of research from nanomanufacturing to biology, where sensitive, atomic-scale measurements must be made at room temperature in liquids.

Atomic force microscopes (AFMs) are one of the workhorse tools of nanotechnology. AFMs have a sharp, pointed probe fixed to one end of a diving-board-like cantilever. As the probe is scanned across a sample, atomic-scale forces tug at the probe tip, deflecting the cantilever. By reflecting a laser beam from the top of the cantilever, researchers can sense changes in the force and build up a nanoscale topographic image of the sample. The instruments are terrifically versatile—in various configurations they can image electrostatic forces, chemical bonds, magnetic forces and other atomic-scale interactions.

While extremely sensitive to atomic-scale features, AFMs also are extremely sensitive to interference from acoustic noise, temperature shifts and vibration, among other factors. This makes it difficult or impossible either to hold the probe in one place to observe the specimen under it over time (useful for studying the dynamics of proteins) or to move the probe away and return to exactly the same spot (potentially useful for nanoscale manufacturing). "At this scale, it's like trying to hold a pen and draw on a sheet of paper while riding in a jeep," observes NIST physicist Thomas Perkins.

A few instruments in specialized labs, including some at NIST, solve this problem by operating at extremely cold temperatures in ultra-high vacuums and in heavily isolated environments, but those options aren't available for the vast majority of AFMs, particularly those used in bioscience laboratories where the specimen often must be immersed in a fluid.