AFM-IR designer: Rohit Bhargava and colleagues have developed a new chemical imaging technique. (Courtesy: L Brian Stauffer, University of Illinois at Urbana-Champaign)
A new closed-loop microscopy technique that can detect chemical compositions at the nanoscale and at high sensitivity has been unveiled by Rohit Bhargava and colleagues at the Beckman Institute for Advanced Science and Technology at the University of Illinois. Their design relies on a piezoelectric material that responds to the voltages produced when a sample is probed by a cantilever. Their approach could enable researchers to precisely measure the spectra of a wide range of nanomaterials, including molecular-scale biological samples.
Based on atomic force microscopy (AFM), AFM-IR involves firing an infrared (IR) laser at a sample, then measuring the resulting thermal expansion using the sharp cantilever tip of an AFM. This is a very useful measurement because the thermal response of a material is characteristic of its chemical composition.
AFM-IR is now widely used to study the spectra of nanomaterials, but still faces a major challenge in dealing with unknown sources of vibrational noise in the cantilever, which can overwhelm the signal. This had been addressed by placing samples on specialized substrates or using specialized sample preparation methods – but these solutions tend to limit the versatility of the technique.
