Greg J. Sommer, Ph.D.

Biosystems Research and Development Department

Robert Meagher photo

Research Interests:

My research interests involve developing lab-on-a-chip technology for biological diagnostic applications. I am part of a team investigating chip-based approaches for processing and analyzing human samples for traces of disease biomarkers and evidence of toxin exposure. Our goal is the development of a rapid, portable, sensitive, and inexpensive tool with deployment applications including clinical environments, border patrol stations, and bioterrorism scenarios.

Projects at Sandia

Parallel Botulinum Neurotoxin/A Immuno- and Enzyme Activity Assays
Botulinum neurotoxin (BoNT) is the most toxic substance known, with a human lethal dose of ~1 ng/kg. The current gold standard diagnostic is the mouse bioassay, a > 4 day test in which laboratory mice are infected with sample and observed for signs of botulism. We are configuring the RapiDx portable medical diagnostic to conduct electrophoretic immunoassays for the presence of both the heavy chain and light chain of the toxin, as well as a parallel enzymatic activity assay to quantify the potency of toxin present. In pursuit of this assay I am developing methods for achieving isolated regions of sample incubation and SDS denaturation on-chip prior to separation.

Microscale Immobilized pH Gradients (µIPG’s) We have developed a robust technique for generating on-chip polymer gradients, in particular microscale immobilized pH gradients (µIPG’s) for rapid and high resolution isoelectric focusing. Precise amphoteric monomer gradients are established via diffusion and immobilized following photopolymerization, resulting in a well-defined pH gradient. We have achieved rapid (< 20 minutes) and high resolution (ΔpI ~ 0.040) focusing across 6 mm-long µIPG’s.

Microscale Pore Limit Electrophoresis (µPLE) To demonstrate another on-chip separation method, the same fabrication technique used to generate µIPG’s was adapted to instead establish and polymerize polyacrylamide porosity gradients. This allows proteins to be fractionated based on their size by electrophoretically driving them toward their effective pore limit – the pore size at which migration is essentially halted. The method also lends itself to sample enrichment due to the stacking phenomenon achieved with decreasing analyte mobility. Concentration factors > 40,000 were easily achieved.

Peer Reviewed Publications:

G.J. Sommer, A.K. Singh, A.V. Hatch. “Enrichment and Fractionation of Proteins via Microscale Pore Limit Electrophoresis” Lab on a Chip 9, 2729-2737 (2009) Pubmed
G.J. Sommer and A.V. Hatch. “IEF in Microfluidic Devices” Electrophoresis 30, 742-757 (2009). Invited Review. Pubmed
G.J. Sommer, A.K. Singh, A.V. Hatch. “On-Chip Isoelectric Focusing Using Photopolymerized Immobilized pH Gradients” Analytical Chemistry 80, 3327-3333 (2008) Pubmed
G.J. Sommer, S.M. Kim, R.J. Littrell, E.F. Hasselbrink. “Theoretical and Numerical Analysis of Temperature Gradient Focusing via Joule Heating” Lab on a Chip 7, 898-907 (2007) Pubmed
S.M. Kim*, G.J. Sommer*, M.A. Burns, E.F. Hasselbrink. “Low-Power Concentration and Separation Using Temperature Gradient Focusing via Joule Heating” Analytical Chemistry 78, 8028-8035 (2006) Pubmed

Book Chapters:

G.J. Sommer, D.S. Chang, A. Jain, S.M. Langelier, J. Park, M. Rhee, F. Wang, R.I. Zeitoun, M.A. Burns. “Introduction to Microfluidics” in Microfluidics for Biological Applications. Springer Science, New York, NY. Ed. Wei-Cheng Tian and Erin Finehout. (2008)

Appointments:

2008 – Present: Postdoctoral Research Scientist, Sandia National Laboratories, Livermore, CA

Education:

2006-2008: Ph.D. Mechanical Engineering, University of Michigan, Ann Arbor, MI
2004-2005: M.S. Mechanical Engineering, University of Michigan, Ann Arbor, MI
2000-2004: B.S. Mechanical Engineering, Iowa State University, Ames, IA

Contact Information:

Dr. Greg J. Sommer
Biosystems Research & Development Department
Sandia National Laboratories
PO Box 969, MS 9292
Livermore, CA 94551-0969

gsommer@sandia.gov
phone: 925-294-2692
fax: 925-294-3020