Oak Ridge Lab develops microscope with a chemical lens

09 Jul 2020

Noninvasive instrument allows researchers to capture bio-images with ultrashort laser pulses.

Researchers at Oak Ridge National Laboratory, Oak Ridge, TN, US, have built a new type microscope that provides a “chemical lens” for viewing biological systems including cell membranes and biofilms. They say the tool could advance the understanding of complex biological interactions, such as those between microbes and plants.

The noninvasive instrument, described in Optics Letters, allows researchers to capture images using ultrashort laser pulses.

The intense pulses illuminate large areas of a sample, generating wavelengths that allow detection of different chemical species. This approach can rapidly produce images over a wide field of view with chemical details.

“Because we can generate the whole image all in the same single image, we are able to study changes in space and in time,” commented ORNL researcher Dr. Benjamin Doughty.

Dr. Doughty’s work revolves around two major themes: understanding the molecular origins of chemical selectivity at interfaces, using nonlinear optical methods to probe orientation and dynamics; and developing new tools to probe complex living biosystems.

He added, “Unlike common bioimaging techniques that can destroy or disturb samples, this label-free tool can be used on unaltered, living cells. The microscope is made with commonly available components, which may accelerate its implementation.”

Optics Letters abstract

The paper's abstract states: “Wide-field coherent anti-Stokes Raman scattering (CARS) microscopy offers an attractive means for the rapid and simultaneous acquisition of vibrationally-resolved images across a large field of view. A major challenge in the implementation lies in how to achieve sufficiently strong excitation fields necessary to drive the third-order optical responses over the large focal region.

“Here, we report a new wide-field CARS microscope enabled by a total internal reflection excitation scheme using a femtosecond Ti:Sapphire oscillator to generate pump and broadband near-infrared Stokes pulses.

“The spectrally broad Stokes pulse, in combination with its inherent chirp, offers not only access to a wide range of Raman modes spanning ~1000 to ~3500cm^-1 but also a straightforward means to select vibrational transitions within this range by simply varying the time delay between the pulses.

“The capabilities of this wide-field CARS microscope were validated by acquiring high-quality CARS images from the model and complex biological samples on conventional microscope coverslips.”