banner USF Home College of Arts & Sciences OASIS myUSF USF A-Z Index

USF Home > College of Arts and Sciences > Chemistry Department

Theresa  Evans-Nguyen

Theresa Evans-Nguyen

Theresa Evans-Nguyen
Assistant Professor

Contact

Office: SCA 416
Phone: 813/974-9633
Lab: SCA 421-423
Email:

Links

Education

B.S., Chemistry, The College of William & Mary, Williamsburg, VA, 2000
Ph.D., Analytical Chemistry, The University of North Carolina, Chapel Hill, NC, 2005
Postdoctoral Fellow, The Johns Hopkins University, School of Medicine, Baltimore, MD, 2005-2009

Research

My long-term research goals focus on the advanced development of chemical sensing technologies, particularly with respect to mass spectrometry (MS) instrumentation. I have applications interests in space, biomedical, and defense sectors which all make use of mass spectrometry. In the field of space applications, I am interested in improving chemical resolution analyses using robust, low power, digital electronics for ion trap mass analyzers. This work speaks to planetary science goals including the search for earth-like habitats. For biomedical applications, my interests include high spatial resolution chemical imaging for broadband analyses of cellular systems. Current MS imaging instruments are limited in speed and sensitivity which can be mitigated by elegant integration of optical methods including extraordinary optical transmission. Alternatively, in-vacuum ion chemistry can possibly be leveraged to enrich certain analytes involved in specific cellular pathways. Finally, defense applications leveraging MS analyses include chemical warfare agent detection, pathogen identification, and radiological/nuclear isotopic characterization which may be conceived into various challenging analytical problems.

My current funded research involves MS technology development for radio-nuclear forensic applications. We currently have a program involving portable mass spectrometry development. The project concept depicted in Figure 1, involves the separate development of three individual aspects of MS instrumentation, namely: ambient ionization sources, differential mobility spectrometry filtering, and low power high resolution mass analysis. The DMS application incorporates classical ion mobility measurements into engineering models in COMSOL and SIMION. We initially investigated separation of inorganic constituents from molecular explosives and quickly thereafter focused on the potential for atomic ion separation. We modified DMS electronics and mechanically integrated a home-built DMS sensor to a commercial MS system (Agilent 6230 TOF) to successfully demonstrate the separation of near neighbor elements for radionuclide analogs. With the DMS methods we were thus able to separate the stable isotope of cobalt-59 from the nickel interferent. Such separation is not possible in the mass spectrometer and otherwise requires lengthy sample preparation.

DTRA portable mass spectrometer

Figure 1: DTRA Portable Mass Spectrometer Development for On-Site Forensic Analysis of Post-Detonation Debris

For the MS portion, we have incorporated digital electronics with commercial components to develop frequency scanning methods with the potential for low power operation as well as targeted high resolution analysis. The ultimate goal of this work is towards the rapid forensic assessment of the inorganic make-up in post-detonation radiological debris analysis. This requires sufficient targeted identification of radiological elements such as cobalt-60, cesium-137, and strontium-90 be positively made in the presence of isobaric interferences (oxides, hydroxides, and near neighbor isotopes). High resolution MS analysis in the field would be highly valuable to reducing the timeline for forensic investigation. We independently developed a continuous injection method which allowed us to enhance detection efficiency. Leveraging the digital scanning electronics, we have also investigated high resolution analysis by careful implementation of various waveforms to achieve a potential mass resolution of 20,000. The potential impact of this work is the ability to distinguish species with mass differences as little as 0.0004 Da, roughly the mass of an electron, to characterize forensic debris with incredibly high accuracy.

Digital electronics block diagram

Figure 2: Digital electronics block diagram for low power quadrupolar frequency scanning. (Submitted to NASA)

We recently began integration of some of these individual development projects such as fitting the DMS sensor with various ambient ionization sources to determine their suitability for field deployment. Thus far, we have incorporated nano-spray ionization and DART metastable ionization. Additionally we began the design of interfacing methods for the DMS to the digital ion trap for consideration of the vacuum system requirements for effective hybrid DMS-MS/MS analysis.

A few smaller scale targeted analytical measurements address our lab’s interests in biomedical applications as well, usually involving small molecules (<1000Da). These include carcinogenic heterocyclic aromatic amines and their metabolites for clinical studies, products of biological function to validate engineered microfluidic devices, and sugar moiety LC based assays to quantify production yields. These projects speak to the lab’s evolving interest in biologically relevant applications of mass spectrometry in across the wide field of biotechnology.

Graduate Students

Ifeoluwa Ayodeji, Victoria Izumi, Iman (Seyedmahmoudreza) Keshavarz, Linxia Song, Timothy Vazquez, Sinduri Vuppala