Picturing Drugs With Raman Microscopes

On Friday, September 25th, Lucinda Buhs, Director, Division of Pharmaceutical Analysis, FDA, delivered a talk on "Raman Microscopic Imaging of Pharmaceuticals" for the Visualization Friday Forum.

Raman microscopic imaging is a spectroscopic technique that utilizes the concept of Raman

scattering of monochromatic light. It is based on the interaction of laser (monochromatic) light with vibrations of the lattice photons.

Using Raman microscope imaging, it is possible to determine the crystal structure of a tablet and determine the configuration of a particular drug in a tablet.

"So why did we select Raman spectroscopy?" asks Lucinda. "Raman spectroscopy exhibits extremely sharp features that are characteristic to a molecular structure. The Raman spectrum gives a series of intensity vs peak numbers(wave numbers) which are unique to each molecule. This way we can tell the difference between two samples. And we can even combine it with a third dimension called chemical spectrum"

Lucinda exhibited the images of a number of drug samples generated using Raman microscopy.

(Image adapted from the research paper: "Raman Chemical Imaging for Ingredient-specific Particle Size Characterization of Aqueous Suspension Nasal Spray Formulations: A Progress Report", by Lucinda Buhse et al.)

"Through this kind of imaging, we look at the distribution of a drug throughout the sample. Specifically, we also use chemical imaging and new infrared to look at the blending effect, i.e, how well do the drugs blend with other chemicals in the sample. We search for a uniform distribution, and if not, we immediately know that the drug wasn't mixed well."

Lucinda Buhse graduated with a PhD in Physical Chemistry from the University of California, Berkeley in 1986. She is also the sister of Rachael Brady, the founding director of the Visualization Technology Group at Duke University.

3D Cancer Detection

Biomedical engineers and cancer specialists at Duke have long been collaborating to discover ways to detect and treat cancer at all its stages. One of the recent major breakthroughs is the ability to observe and examine a live body tissue in three dimensions using a technique called Multi-photon microscopy.

According to researchers, more than 50% of all detected cancers arise in squamous epithelium, and if detected in a pre-invasive or pre-cancerous state, it can be treated relatively well.

The team led by Dr. Nirmala Ramanujam, Associate Professor of BME at Duke, has been studying optical spectroscopy, optical sectioning microscopy and photon migration techniques, and attempting to use them for characterizing and detecting biochemical and structural properties of various human tissues. According to Dr.Ramanujam, the multi-photon fluorescence microscopy—a technique enables doctors to "peer into the individual cells in a very non-invasive way to see how things change as early cancer progresses."

A multiphoton fluorescence microscope uses pulsed long wavelength laser light to excite fluorophores within a specimen. The fluorophore absorbs the energy from two long-wavelength photons that must arrive simultaneously in order to excite an electron into a higher energy state, from which it can decay, emitting a signal.

Another technique being explored by Ramanujam's group is called Ultraviolet-visible optical spectroscopy (UV-VIS). It is similar to fluorescence spectroscopy, in a way that fluorescence involves transitions from the excited state to the ground state, while absorption deals with electron transitions from the ground state to the excited state.

Dr. Ramanujam's current focus is on further researching and developing broad and effective techniques for clinical detection of cancer.