Instrument development for vibrational circular dichroism imaging

Abstract
Molecular chirality is at the heart of many chemical processes that determine life and drives significant research
in development and disease. All life has chiral asymmetry with naturally occurring molecules and long-range
assemblies being of distinct handedness. Many exogenous molecules, for example those useful as drugs, also
have a distinct enantiomeric dependence for their efficacy in benefiting human health. Thus, measurement of
molecular chirality is of critical importance across the medical sciences. Vibrational Circular Dichroism (VCD)
spectroscopy has emerged as a powerful platform for quantifying chirality and molecular structure. However,
imaging has not been demonstrated due to technological challenges. VCD measurements are largely of
homogeneous materials, neat or in solution and probed with sensitive Fourier transform infrared (FT-IR)
spectrometers. Microscopy would require ~105 reduction of the typical sensing volume and increase in speed
that would make imaging feasible. Instead of utilizing FT-IR spectroscopy, we built a custom quantum cascade
laser (QCL) microscope to demonstrate feasibility of a point scanning VCD instrument capable of acquiring
spectra rapidly across all fingerprint region wavelengths in both transflection and transmission configurations.
Moreover, for the first time, we also demonstrate the VCD imaging performance of our instrument for site-specific
chirality mapping of biological tissue samples. However, the feasibility data also point to several technological
and conceptual challenges that this project seeks to address in developing a practical prototype. The prototype
to be developed here, termed vibrational circular dichroism imaging microscope or VIM, aims to record chirality
from microscopically heterogeneous biomedical samples. We propose a design for VIM using a laser scanning
approach to minimize artifacts and maximize signal. Starting from a de novo design, we will use commercial and
custom optics, custom electronics for control and data management, and in-house software to develop the
prototype. Next, we model the VCD image formation process and develop the analytical methods for VIM. The
theoretical model developed here builds on our models of IR microscopy and will guide prototype development
while ultimately provide greater accuracy, precision and assurance to data recorded. Finally, we validate the
performance and broad utility of VIM using well-characterized samples. Together, the work will develop new
VCD imaging technology that opens capability to measure and research a wide variety of biological problems.

Grant Number: 5R01GM142172-04
NIH Institute/Center: NIH
Principal Investigator: Rohit Bhargava