Article updated on 21 May 2020
To address the wide range of problems affecting our environment, it is crucial for climate scientists to have the tools necessary to accurately detect, measure, and analyze the chemicals that are often the sources of most ecological issues.
Although numerous microscopy tools have been used for these purposes, they are often limited in their detection capabilities and capacity to distinguish between different chemical classes.
Over the past ten years, Raman spectroscopy has emerged as a highly precise and unique tool capable of overcoming these common limitations of traditional microscopy techniques in order to evaluate some of the most significant substances affecting the health of this planet.
Measuring Aerosol Particles
The small size of most aerosol particle contaminants can prevent environmental analysts from accurately identifying individual particles, especially when their diffraction limit is below 350 nanometers.
Atmospheric aerosol particles have the potential to adversely affect the environment through various mechanisms, some of which include the scattering and absorbing of solar radiation, as well as mimicking the actions of cloud condensation and ice nuclei to modify natural precipitation and cloud properties.
To further complicate matters, atmospheric aerosol particles can contain up to thousands of different chemical species from different sources and different atmospheric ages. Therefore, it is imperative for environmentalists to be capable of quantifying these impacts by analyzing the various physicochemical properties of aerosols.
To address these critical concerns, researchers have often turned to Raman spectroscopy to characterize the properties of aerosol particles. Raman spectroscopy has been used to characterize many different types of particles, the specific compounds present within the aerosol particles, hygroscopic properties, phase separations, heterogeneous reactions, ice nucleation, and acidity.
The minimal sample preparation required for Raman spectroscopy, combined with its non-destructive analysis under ambient temperature and relative humidity (RH) conditions has proven to be especially useful for aerosol particle characterization.
Surface Enhanced Raman Spectroscopy (SERS) and the Environment
Although Raman spectroscopy alone has proven to be useful for the analysis of aerosol particles, it is limited in its ability to distinguish between particles that are smaller than 1 micrometer (µm) in size. Another limitation of this analytical technique is attributed to its inability to determine different chemical species within the particles when present in lower concentrations.
In an effort to improve the limit of detection for low concentration chemical species, researchers have turned to surface enhanced Raman spectroscopy (SERS). SERS enhances weak Raman signals by exciting electrons in metallic substrates in order to create interactions with localized surface plasmon resonances (LSPRs).
To date, SERS has been used for biosensors, chemical warfare agents, and in conjunction with spectroelectrochemistry, as well being used in many other applications. When applied for the analysis of atmospheric aerosol particles, SERS has demonstrated its ability to accurately detect particles as small as 150 nm in size, as well as their chemical composition and mixing state.
The widespread pollution of microplastics within our environment has continued to raise concerns on the damage these contaminants can inflict on all living organisms. Raman spectroscopy has demonstrated its ability to accurately detect microplastics as small as 20 µm. Furthermore, when Raman microscopy is used in conjunction with advanced detectors and spectrum processing devices, researchers have been able to achieve enhanced signal quality.
References and Further Reading
- Tirella, P. N., Craig, R. L., Tubbs, D. B., Olson, N. E., Lei, Z., & Ault, A. P. (2018). Extending surface enhanced Raman spectroscopy (SERS) of atmospheric aerosol particles to the accumulation mode (150-800 nm). Environmental Scientific Processes Impacts 20; 1570-1580. DOI: 10.1039/C8EM00276B.
- Sharma, B., Frontiera, R. R., Henry, A., Ringe, E., & Van Duyne, R. P. (2012). SERS: Materials, applications, and the future. Materials Today 15(1-2); 16-25. DOI: 10.1016/S1369-7021(12)70017-2.
- Araújo, Catarina & Nolasco, Mariela & Ribeiro, António & Ribeiro Claro, Paulo. (2018). Identification of microplastics using Raman spectroscopy: Latest developments and future prospects. Water Research, 142. DOI: 10.1016/j.watres.2018.05.060.