Ever since its discovery in 1928, the phenomenon of Raman Scattering has been used to determine key properties of both organic and inorganic materials. The technique is non-destructive, requires minimal sample preparation and provides easily identifiable, rapid results. Due to this, the past 20 years have seen a huge increase in the number of applications in Life Sciences that use Raman Spectroscopy and Raman Microscopy as the main tools for tissue and cell analysis.
In Raman Spectroscopy, samples are illuminated using monochromatic laser light causing photons to interact with the chemical bonds, and scatter differently based on vibrational, rotational and other modes of the system. The scattered light is composed of both elastically scattered photons (having the same wavelength as the incident laser light) and in-elastically scattered photons (having different wavelengths). This inelastic scatter is what is commonly known as the Raman Scatter. This scattered light is collected and filtered before being dispersed onto a detector, and then analyzed by computer software to produce a characteristic Raman spectrum for that substance. It gives us detailed information like structure, phase, temperature, crystallinity, polymorphism, intrinsic stress and strain and contamination.
Over the years, the advances in computer technology, increased sensitivity, automation of certain equipment and increased availability of different wavelengths of laser light has made it possible to analyze tissue at a very detailed level using Raman. It provides, for example, the imaging necessary to identify tumor margins in the brain - which is vital for accurate removal of brain tumors. This is achieved by a process known as Simulated Raman Scattering (SRS) Microscopy. As the progression of the tumor modifies the structure and molecular composition of the tissue, SRS microscopy enables the identification of the tumor margins down to a few cells. Scientists have been able to perform these experiments successfully on mice brains, and believe that this technology paves the way for non-destructive tumor removal subsequently in humans.
Raman also forms the basis of minute probes that can be used for measurements through an endoscope. Raman spectroscopy may also be used to identify bacteria at a species and strain level. This is especially important for point of care situations, where currently it takes several days to culture and identify pathogens. Another application of Raman that enables medical diagnosis has to do with laser trapping and cell sorting. Laser trapping refers to a laser's ability to 'trap' a dielectric particle, which provides it a stable position for Raman analysis. Sophistication of this method now allows trapping at a nanoscale level, and the ability to simultaneously trap the particle and measure its Raman signal. Cell sorting refers to the practice of sorting single cells in complex samples like biofilms, soils, sludge and tissue. Raman enables genomic sequencing that allows new microorganisms to be identified. Lastly, a recent experiment shows how a new chip for Surface Enhanced Raman Spectroscopy (SERS) can capture, identify and inactivate pathogenic bacteria and works effectively on human blood. This has massive potential in curing bacterial infections.
These examples represent just a few of the major applications in Biology that have been impacted by Raman. Organizations and research labs around the world are adapting this method each day to find new solutions for challenges in Life Sciences.
'Raman Spectroscopy and Microscopy: Solving Outstanding Problems in the Life Sciences'- articles, published Jan 2015 & March 2015- Biophotonics, Dr. Marinella G. Sandros & Dr. Fran Adar : Online Links- First Article,Second Article
Researchers have recently demonstrated how laser-excited photoluminescence of emeralds can determine their structural properties as well as their place of origin. The study, first published in The Journal of Gemology, aims to provide a clear methodology to gemologists on how to determine whether an emerald is natural or synthesized, as well as establish a natural emeralds' geological origin. Laserglow's LRS 532nm laser was used as an excitation source.
Previous methods of determining an emerald's origin are based on inclusion microscopy, FTIR and Raman Spectroscopy, and trace-element analysis by mass spectrometry. The new method based on laser-excited photoluminescence spectroscopy seeks to supplement these methods.
Emerald is a form of Beryl (naturally colorless) that has traces of Chromium ions. These ions then absorb light across the red-orange and blue-violet wavelength ranges, so emerald only transmits light in the green range- thereby giving it the characteristic green color. The presence of Chromium is what enables photoluminescence (PL) in emeralds. Laser-excited PL spectra shows that emerald displays 2 types of luminescence - one being broadband (peaking at about 710-720nm) and another being 2 narrow lines (appearing between 680 and 685nm). These 2 lines are called 'R lines', with the longer wavelength one called R1 and shorter, R2. The study shows the R lines in the PL spectra of various emerald samples can determine whether an emerald is originated from schist, or other rock types like shale or granite, or whether the stone was synthesized artificially in a lab.
For example, inclusion microscopy fails to distinguish between emeralds from Colombia (schist-origin) and those from Davdar in China (non-schist origin). However, the R1 line peaked at different wavelengths for both samples when using laser excited PL spectroscopy. Furthermore, the R1 peaks at slightly different wavelengths based on systematic mine-specific variations. This means, the origins of a stone can potentially be traced down right to the mine-level!
Laser-Assisted Surgery Tool Delivers Large Particles into 100,000 cells per min
Researchers at the University of California, Los Angeles (UCLA) have developed a Biophotonic Laser-Assisted Surgery Tool (BLAST) that can deliver nanoparticles, enzymes, antibodies, bacteria and other large particles into mammalian cells at 100,000 cells per minute. The delivery of such a large number of particles can help researchers understand the response of cells to external pathogens, the progression of diseases and the cell's defense mechanism against mutant mitochondrial DNA.
The BLAST system generates an array of bubbles that explode in response to laser pulsing. This causes microscopic fissures to appear on adjacent cell membranes through which particles may be delivered.
The device itself is a chip with micrometer-sized holes, each surrounded by a coating of titanium. Below the surface of the holes is the liquid that contains the particles (DNA, enzymes etc.) that need to be delivered to the cell. The pulsed laser light instantly heats up the titanium which causes the water surrounding the cell membranes to boil. The bubbles create fissures, thereby allowing the particles in the liquid to enter the cell membrane before it closes.
Not only does this method allow scientists to observe cell reaction to external particles or pathogens, it also allows them to examine the function of genes involved in the lifecycle of a pathogen. Dr. Michael Teitell- co-author of the study- believes that this method provides vital information on pathogen targets within the cell, which could lead to better drug development.