1. University of Pennsylvania School of Dental Medicine, 240 South 40th Street, Philadelphia, PA 19104-6030, USA;
2. University of Pennsylvania, School of Arts and Sciences, Department of Mechanical Engineering and Applied Mechanics, Philadelphia, PA 19104-6315, USA;
3. OraSure Technologies, Inc., 220 East First St., Bethlehem, PA 18015, USA; and
4. Leiden University Medical Center, Wassenaarseweg 72, 2333 AL Leiden, The Netherlands;