Optical cavity design enables enhanced sensing of distinct versions of chiral molecules

Chiral molecules are the building blocks for some of the most important substances to life on earth, and the study of the handedness of chiral molecules is a crucial task in chemistry, biology, and pharmacology.

The left- and right-handed chiral molecules are mirror images of one another, and a technique called circular dichroism (CD) is used to tell the two apart. However, the CD signal produced using existing methods tend to be very weak and there is a need to amplify the signal for detection, especially for samples with low molecular concentrations and/or short measurement times.

Scott et al. propose a simplified design of optical cavities for enhancing vibrational CD, in an effort to bring the signal over the detection threshold of typical spectrometers. The proposed design largely avoids the switching of handedness of the circularly polarized light during reflections off the internal walls in ordinary optical cavities. According to numerical calculations, this design can resonantly enhance the vibrational CD signal by up to three orders of magnitude.

“While in typical devices the light passes only once through the solution of chiral molecules, we use a cavity filled with the solution,” said author Ivan Fernandez-Corbaton. “This allows light to bounce back and forth several times inside the cavity, hence picking up more of the difference as it goes.”

Next, the researchers plan to test the proposed cavity design in experiments that would show large signal enhancements. This design could be used as a steppingstone towards applications on future lab-on-a-chip devices which in turn will play a crucial role in drug development efforts.

Source: “On enhanced sensing of chiral molecules in optical cavities,” by Philip Scott, Xavier Garcia-Santiago, Dominik Beutel, Carsten Rockstuhl, Martin Wegener, and Ivan Fernandez-Corbaton, Applied Physics Reviews (2020). The article can be accessed at https://doi.org/10.1063/5.0025006 .