Dr. Xiaoguang Meng of the Center for Environmental Systems at Stevens Institute of Technology is developing an innovative approach for the detection of toxic chemicals by conducting extensive research in the field of Surface Enhanced Raman Scattering (SERS).
His experimental results demonstrate that SERS is a promising technique for quantitative, rapid on-site analysis of both arsenic and perchlorate chemicals.
Arsenic in Water Supplies
Did you know that arsenic-contaminated water affects the health of over 140 million people worldwide? According to a quote by Allan Smith from the University of California at Berkeley in an article on BBC news, "one in every ten people with high concentrations of arsenic in their water will die from it." Arsenic consumption leads to higher rates of some cancers, including tumors of the lung, bladder, skin and other lung conditions. Some of these effects show up decades after the first exposure.
This graphic illustrates global occurrences of arsenic in groundwater
This issue stems beyond drinking water. Especially in developing countries, food grown in contaminated soil can quickly spread disease throughout the population. For example, rice is typically grown in paddy fields; flooded with potentially contaminated water.
Identification is the key to improvement
The logical first and perhaps most important step is the capability to quickly and reliably determine the existence of arsenic in a particular water supply. The World Health Organization (W.H.O.) and the U.S. Environmental Protection Agency (E.P.A.) have set the maximum arsenic level of 10 parts-per billion (ppb) for drinking water. Baseline measurements enable researchers to highlight high risk areas, but until now the process has been overly expensive, cumbersome and slow. Communities suffering from illnesses need a rapid and accurate assessment that can be brought into the field and immediately put into use.
Enabling Rapid, On-Site Detection with SERS
SERS is a highly sensitive technique for the detection and identification of chemicals at trace levels (as small as a single molecule). According to Dr. Meng, "an extremely high enhancement factor for Raman Scattering is generated when analyte molecules are absorbed on nanostructured metal surfaces of mainly silver and gold."
Essentially, by transferring small samples of water onto a SERS active substrate (meaning a glass side with manufactured nanoparticles made of either gold or silver) and then recording the SERS spectra under a Raman spectrometer for a few minutes, Dr. Meng and his team can quickly detect the presence of arsenic. Only the portable Raman spectrometer and disposable sensor curvettes are required for analysis, making this a very cost-effective solution. According to Ph.D. Candidate Zhonghou Xu, "fundamental findings obtained in our research are especially valuable for the development of sensitive and reliable SERS methods for the rapid analysis of arsenic contaminated water."
Dr. Meng is also leading the charge towards using SERS results as a quantitative analytical tool. Traditionally, reproducibility was not possible due to the heterogeneous nature of the nanostructured SERS substrates. Now, however, by conducting an area scan, he can increase the reproducibility, thereby increasing the reliability and ease of use.
Perchlorate Detection and Quantification
Ammonia perchlorate is an inorganic compound made up of the salt of ammonia and perchloric acid. It is the driver behind the industrial production of perchloric acid. It is also commonly used as a solid propellant in rockets, missiles and fireworks.
According to the California Department of Toxic Substances Control, "Most perchlorate manufactured in the U.S. is used as an ingredient in solid fuel for rockets and missiles. In addition, perchlorate-based chemicals are used in the construction of highway safety flares, fireworks, pyrotechnics, explosives, common batteries and automobile restraint systems. Perchlorate contamination has been reported in at least 20 states and greatly impacts human health by interfering with iodide uptake into the thyroid gland. Perchlorate is becoming a serious threat to human health and water resources."
Perchlorate detection in the United States
If the damage to our health wasn't enough, consider this: Ammonia perchlorate is an oxidizer and the application of a fuel source could cause a deadly explosion. In fact, this scenario occurred in a huge industrial incident known as the PEPCON disaster, claiming two lives, injuring 372 people and causing an estimated $100 million worth of damage.
A Rapid Response
Detection of perchlorate is clearly a very important issue. Dr. Meng is again employing the use of SERS to develop a reliable platform for identification and quantification of energetic materials through the "optimization of the area scan and integration methods."
In a joint effort with Picatinny Arsenal, Professor Meng begins by preparing a "SERS substrate and forming Ag nanofilms on Cu foil which is then functioned with cysteamine." After successfully determining the optimal conditions for the area scan and integration methods, his team has fabricated a prototype scanner and developed a computer program which integrates SERS spectrum data. Upon completion of regularly scheduled progress reviews, Dr. Meng is hopeful that on site scanners, capable of providing real-time information, will be readily available in the field.
Dr. Jumin Hao holds a Ph.D. degree in Chemistry and is studying for another in Environmental Engineering. Dr. Hao has worked with Professor Meng for the past three years on the use of SERS techniques for detecting and remediating perchlorate contamination. Hao views the gains realized by the Stevens team as not only innovative, but as a potentially dramatic shift in the way communities detect pollutants. "The research coming out of the Center for Environmental Systems provides insights that will push the advancement of the entire field. Our preparation of Ag-Cu films is facile, controllable and reproducible, and as SERS substrates they are easy to store, transport and use on-site, making them very promising for being commercialized."
Impact on Communities
Few needs are more fundamental than clean drinking water and food supplies. Dr. Meng's passion is evident through his dedication to expanding the possibilities within toxic chemical analysis and detection.
By continuing to push the envelope and advance the study of SERS, he is leading the way in making dramatic improvements in the lives of millions of people and communities around the world while offering unique opportunities for collaboration and educational opportunities for his associates at Stevens. As Jumin Hao says of his time working with Professor Meng, "under his tutelage I have not only grown as a researcher through his expert professional knowledge, dedication, insights and personality, but also as a thinker and humanitarian. Upon graduating I fully intend on dedicating my career towards the detection and remediation of pollutants in water."
To learn how you can become involved in this important work, please visit the Center for Environmental Systems.
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