Department of Physics




Courses Taught

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2362 New Physics Bldg.

1012 New Physics Bldg.

University of Florida
P.O. Box 118440
Gainesville FL 32611-8440

tel. 352-392-4716
fax 352-392-7709

Office hours
see course webpage

Hagen Laboratory Research

In our laboratory we study the dynamics of biological systems. Areas of interest include protein conformational dynamics and folding, which we have studied using time-resolved laser fluorescence and absorption spectroscopy. More recently we have been studying dynamics of gene regulatory systems. We are particularly interested in the dynamics of bacterial quorum sensing. Quorum sensing is a mechanism by which bacteria communicate with each other and detect their own population density through the exchange of chemical signals. We are using microfluidic devices to control and manipulate bacterial environments so that we can study the ways that bacteria use quorum sensing to probe and respond to their local environment. The diagram at upper left is a rough schematic of the quorum sensing gene regulatory network of Vibrio fischeri, a bioluminescent (light-emitting) marine bacterium that lives in symbiosis with several fish and squid species. This network controls the luminescence output of the bacterium, in response to levels of chemical signals (red symbols) received from other bacteria.

The microscopy images at left show individual V.fischeri cells as illuminated by an external light source (Dark Field, left) and by their own natural luminescent emission (Luminescence,right).

The figure below shows the more complex quorum sensing network that regulates genetic competence in the oral bacterium Streptococcus mutans. Using microfluidic devices to study the behavior of this network at the level of individual cells, we have found that very small changes in the environmental conditions can cause the behavior of this network to switch from a simple "rheostat"-like (unimodal) activation to a fully bimodal or bistable behavior: The dynamics of the network are exquisitely sensitive to the cell's environment.

Finally, the movie below shows an intriguing spreading behavior of a droplet of liquid containing the soil bacterium Sinorhizobium meliloti that has been deposited onto a moist surface. In this curious collective behavior the bacteria use quorum sensing to activate and harness entropic (thermophysical) forces in their environment. These forces generate complex patterns of cellular aggregation and spreading. .

Graduate Students | Undergraduates | Equipment | Contact

Graduate Students

  • Minjun Son | PhD 2014 | Microfluidic devices for studying genetic competence in Streptococcus mutans| Publications
  • Gabriel Dilanji | PhD 2014 | Autoinducer signalling and diffusion in Sinorhizobia | Publications
  • Jessica Langebrake | PhD 2013 (Mathematics and Physics) | Reaction Diffusion Equations in Biological Systems: Marine Protected Areas and Quorum Sensing | Publications
  • Pablo Delfino Pérez | PhD 2011 | Stochasticity in Quorum Sensing: lux Expression in Vibrio fischeri at the Single Cell Level | Publications
  • Ranjani Narayanan | PhD 2009 | Title: Time-Resolved Laser Spectroscopic Studies of Rate-Limiting Events in Protein Folding and Binding | Publications
  • Omjoy K. Ganesh | PhD 2008 | Title: Intrinsic Disorder In Proteins: Folding of the Yeast Proteinase Inhibitor IA3 | Publications
  • Dana E. Doucet | MS 2006 | Loop formation in unfolded polypeptides | Publications
  • Suzette A. Pabit | PhD 2004 | Title: Fast Dynamics in Protein Folding: Time-Resolved Fluorescence and Absorbance Studies of Polypeptide Reconfigurations | Publications
  • Linlin Qiu | PhD 2003| Title: Laser Induced Temperature Jump Investigations of Fast Protein Folding Dynamics| Publications
  • Priiyank Shukla | MS 2005 | Laser temperature-jump studies of peptide folding

Undergraduate Students

  • Lab Alumni: Lauren McLeod9 | Dylan Billiodeaux | Addie J. Barron (REU 2014) | Suzanne Helfrich | Matthew DeFurio | Dylan Wolfgram | Joel T. Weiss8 (BS 2011) | Jonathan H. Young7 (BS 2009) | Leslie Pelakh (BS expected 2011) | Juan Jaspe (BS 2006) | Elaine L. Johnson2(BS 2009) | Christian Pecora (REU) | Adam Hunnell4 (REU) | Geoff Gordon | Ki Park1 | Michelle (Planicka) Neeley3 (REU) | Kimberly Ferraro | James E. Crooks| Lawrence Dunn5 (REU) | Rachel West10 (REU) | Caleb Carswell | Erik Sjolander | Melissa R. Sarantos6 | Rupika Madhavan2 (REU) (BS 2013) | (incomplete listing)
  • Notes: 1. MD University of Florida, Fellow in Cardiology; 2. Teach for America; 3. MS 2009, Medical Physics, University of Tennessee; 4. PhD Physics, Case Western Reserve; 5. PhD Physics, University of Texas - Austin; 6. PhD 2006, Biomedical Engineering, UC Davis; 7. Graduate student in applied mathematics, University of Texas - Austin; 8. Currently a PhD student in physics, Cornell University; 9. 2012 Barry M. Goldwater Scholar and currently a PhD student in physics at Cornell University; 10. Economist, Volpe National Transportation Systems Center.

Major Equipment

Contact Information

  • Tel. 352-392-4716 | Email: sjhagen at ufl dot edu
  • Physical Address: Room 1012 NPB (Physics Building), University of Florida, Corner of Museum Rd & Lemerand Drive, Gainesville FL 32611-8440
  • Shipping Address: Physics Department, University of Florida, B100 Physics Building, PO Box 118440, Corner of MuseumRd & Lemerand Drive, Gainesville FL 32611-8440



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