Faculty and Student Teams Program

Project Descriptions

Oak Ridge National Laboratory
Chemical Sciences Division

Development of Novel Substrates for Surface-Enhanced Raman Scattering

Requesting applications from science or engineering faculty members at institutions serving students underrepresented in science, engineering, mathematics and technology to work on the following projects at Oak Ridge National Laboratory (ORNL).

Project Description

In-situ characterization of radionuclides in ground water is essential to achieve shorter turn-around times for analytical results, which in turn would allow better control of waste contamination. Current techniques for monitoring and characterizing radionuclides rely primarily on liquid scintillation counting, ICP-MS, and some limited use of spectrofluorimetry, based on the fluorescence of radionuclide species under laser or UV excitation. These techniques often require chemical handling, for example, the use of scintillation cocktails in liquid scintillation counting, or complexing media such as phosphoric acids in order to enhance signals in fluorimetry. Furthermore, only fluorescent radionuclides (UO22+, Cm(III), Am(III)) can be detected by the last technique. Many environmentally-important radionuclides such as plutonium, neptunium, and technetium species have no strong fluorescence signals and therefore cannot be characterized via fluorescence spectroscopy. Additionally, it is difficult to perform remote analysis by ICP-MS and so it cannot completely eliminate safety concerns due to worker exposure.

Surface-enhanced Raman scattering (SERS) spectroscopy is a highly sensitive analytical technique developed in the early 1970’s that has been widely applied in organic and biological studies. It has much greater molecular selectivity than fluorescence or absorption spectroscopies. The SERS technique provides significant improvement over current analytical methods in reducing time of analysis, cost, and sample manipulation and it also has the advantage that it can be easily combined with fiberoptic instrumentation to perform in-situ sensing to gain information about the speciation of radionuclides under real environmental conditions. Thus, the SERS technique is an ideal tool for providing safe and efficient detection of radionuclides. The SERS technique is based on the enhancement of the Raman scattering of molecules adsorbed on or near metal colloid particles or metal surfaces with nanoscale roughness. One of the primary challenges of the application of SERS to detect radionuclides under real environmental conditions is the stability of the substrate. Because environmental samples are generally composed of a diverse mixture of chemical constituents, the SERS active metal substrates tend to deactivate when in contact with the chemical mixture for a long period of time as a result of decomposition and morphological changes to the silver particles. In our previous research, a silica sol-gel was used as a support matrix as well as a protective layer for the SERS active silver particles. However, the silver particles most responsible for signal enhancement are located at or near the surface of the silica sol-gel and remain in direct contact with the target molecules. Currently, we conduct research to develop a number of new sensitive SERS substrates that effectively address issues of selectivity and sensitivity. We will also further improve the developed SERS technique to provide methods with increased stability, selectivity and sensitivity to monitor and characterize the chemical speciation of radionuclides at trace levels. Thin dielectric metal oxide layers prepared by atomic layer deposition (ALD) techniques will be used to coat the SERS active metal substrates. The dielectric overlayer protects the metal substrates, thus greatly improving the stability of the substrates. Furthermore, by ALD techniques, ultra thin metal oxide layers can be prepared with atomic precision allowing the coated silver film to retain its SERS activity. The metal oxide layer itself also will provide an enrichment of actinide ions adsorbed to the substrate through a well established surface interaction, thus increasing the overall detection sensitivity. Finally, by imprinting chemicals into the overlayer that have a strong adsorption affinity toward actinyl ions, molecular recognition can be introduced into the SERS substrate, thereby improving selectivity and sensitivity.

Laboratory Contact: Dr. Sheng Dai, dais@ornl.gov

Applicants Responsibilities and Relationship to Project

Applicants will receive support under the Department of Energy Faculty Student Team Research Program (FaST) to work collaboratively with the project research team at the Laboratory for up to 10 weeks during the summer of 2008. The exact appointment period in the time frame of June to August will be scheduled by mutual agreement between the host divisions at Oak Ridge National Laboratory and the successful applicant. Faculty will be expected to identify students from their campuses to participate in the FaST program. The faculty member will provide some mentorship to students during the summer research activities. The faculty and students must participate as a group and serve their appointments concurrently. It is expected that the faculty member and the students become an integral part of the research team working on this project and that opportunities for continued collaboration may be identified.

Qualifications of Ideal Candidates

The ideal faculty candidate for this position has background and expertise to carry out self-directed research on development of SERS substrates. The candidate should have a background in chemistry with Ph. D. degree or related fields with experience in analytical chemistry.

Support and Financial Commitments

The successful candidate will receive a stipend based on the academic salary, travel expenses to and from the Laboratory, and a housing allowance. Students recommended by the faculty member for participation in the program will receive a stipend of $400/week for each week at the Laboratory, plus a housing allowance, and reimbursement for transportation expenses to and from the ORNL. Funds are provided for this program from the US Department of Energy, Office of Science in partnership with the National Science Foundation, from ORNL, and from other sources.

See Financial Information.