1. Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843, United States
2. Institute of Physical Chemistry, Friedrich Schiller University Jena, Helmholtzweg 4, 07743 Jena, Germany
3. Merck & Company Inc., MRL, Analytical Research & Development, Boston, Massachusetts 02115, United States
4. Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843, United States