Near-Field Infrared Microscopy

Shyamsunder Erramilli

The Erramilli group works on developing high-resolution infrared microscopy for studying biological systems. Images with spatial and temporal information add to our understanding of these systems. Vibrational spectroscopy is an exquisitely sensitive tool for studying the many biomolecular systems that exhibit characteristic “fingerprint” absorption bands. Combining this sensitivity with microscopy allows the imaging of living systems without using stains or labels. But conventional infrared microscopy is limited to poor spatial resolution set by the diffraction limit associated with the longer wavelengths involved. Scanning near-field infrared microscopy is used to break the diffraction limit without sacrificing the spectral sensitivity. A variety of bright infrared sources are used – broadband synchrotron radiation, free electron lasers, ultra fast tunable infrared lasers, and quantum cascade lasers.

Using this system, the first ever high-resolution underwater infrared images of single living cells have been obtained. Images of single fibroblasts at wavelengths at which proteins, nucleic acids, and lipids absorb suggest that cell motion is associated with complex topological changes in the membrane.

Currently, time-resolved methods taking advantage of a tunable 100-fs laser are being used to do “vibrational lifetime” imaging in the mid-infrared region of the spectrum.

Vibrational dynamics of biomolecular systems are studied using femtosecond single color and two color pump-probe methods, and photon echo studies. Ultrafast studies on anesthetic molecules like nitrous oxide are aimed at solving the long-standing biological physics problem of how anesthetics act.