Dr. Pappas’s group focuses their efforts on the interface between cell science and analytical chemistry.  Dr. Pappas is currently developing novel analytical methods to study intact cells, cell digests, and tissue aggregates using spectroscopic and immunochemical techniques.  The majority of the group’s research is geared toward clinical analysis as well as medical testing in remote areas.  Some of the current projects in the Pappas group are listed below:

Cellular Chromatography.  Recent advances in chemical instrumentation have improved the state-of-the-art in biomedical analysis.  Indeed, these two fields have been closely intertwined as the information content of chemical analysis has allowed a host of scientists in other fields to advance their studies.  Dr. Pappas is actively developing methods of so-called cellular chromatography, where cells are regarded as analytes – rather than a living vessel containing analyte – and are separated based on physical and chemical properties.  Much like a traditional chemical separation, cells can be separated, isolated, and analyzed from crude samples (such as human blood) with minimal sample preparation.  These chromatographic methods can serve as the analysis itself or can be integrated into other systems such as lab-on-a-chip devices, which currently can require extensive sample preparation for cells.

Single-Molecule Sorting.  Single-molecule detection has reached the utmost sensitivity in solution.  Using fluorescent probes, it is possible to detect single molecules in capillaries, hydrodynamic flow, or optically defined volumes, but no additional analyses are possible.  Dr. Pappas’s group intends to merge the well-known concepts of fluorescence-activated cell sorting to develop methods to first detect, then sort, single molecules.  Single molecule sorting can allow for molecular enrichment of rare samples or allow additional analyses – Raman spectroscopy, mass spectrometry, etc. – to occur after detection.

Cell Digest and Separation.  Dr. Pappas is working toward methods of selecting individual cells undergoing chemical reactions and digesting the single cell for chromatographic or mass spectrometric analysis.  Individual cells can be selected under a microscope, stimulated chemically, and then digested for analysis.  The cell digest studies can be directly integrated with single-molecule sorting or other analyses.

Remote Medical Testing.  Flow cytometry has become the benchmark technique for measuring blood cells in a variety of medical testing.  Flow cytometry is used extensively in AIDS monitoring and for noninvasive prenatal testing, as well as immunological testing.  While flow cytometry is a powerful and well-established technique, Dr. Pappas’s group hopes to create instrumentation that can perform on par with some flow cytometers for a fraction of the size, cost, complexity, and reagent volume.  Ideal devices would provide autonomous blood testing with minimal sample preparation for deployment to remote areas where access to medical equipment is limited.  Such locations include developing nations, rural areas, military settings (battlefields, submarines) and space flight.

 Selected Publications

• "Evaluation of the Paratrend Multi-parameter Sensor for Potential Utilization in Long-Duration Automated Cell Culture Monitoring", Hwang, E.Y.; Pappas, D.; Jeevarajan, A.S.; Anderson, M.M. Biomedical Microdevices 2004, 6, 241-249.

• "Velocity-selective Imaging Using a Cesium Resonance Fluorescence Imaging Monochromator", Pixley, N.C.; Correll, T.L.; Pappas, D.; Smith, B.W.; Winefordner, J.D. Optics Communications 2003, 219(1-6), 27-31.

• "Detection of Mie Scatter Using a Resonance Fluorescence Monochromator", Pappas, D.; Correll, T.L.; Pixley, N.C.; Smith, B.W.; Winefordner, J.D.  Appl. Spectrosc. 2002, 56(9), 1237-1240.

• "Sub-Doppler Spectral Resolution and Improved Sensitivity in a Cesium Resonance Fluorescence Imaging Monochromator", Pixley, N.C.; Pappas, D.; Correll, T.L.; Smith, B.W.; Winefordner, J.D.  Appl. Spectrosc. 2002, 56(6), 677-681.

• "Sub-Doppler Photon Detection in a Tunable Resonance Fluorescence Monochromator", Pixley, N.C.; Correll, T.L.; Pappas, D.;  Matveev, O.I.; Smith, B.W.; Winefordner, J.D.  Optics Letters 2001, 26(24), 1946-1948.

• "Resonance Radiation Diffusion in Atomic Vapor Imaging", Pappas, D.; Pixley, N.C.; Smith, B.W.; Winefordner, J.D. Spectrochimica Acta Part B 2001, 56, 1761-1767.

• "A Cesium Resonance Fluorescence Imaging Monochromator", Pappas, D.; Pixley, N.C.; Matveev, O.I.; Smith, B.W.; Winefordner, J.D. Optics Communications 2001, 191, 263-269.