1. LifeFoundry, Inc. Champaign, IL 61820, USA
2. Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
3. Biosensor National Special Laboratory, Key Laboratory for Biomedical Engineering of Education Ministry, Department of Biomedical Engineering, Zhejiang University, Hangzhou 310027, P.R. China
4. Centre for Nano Optics, University of Southern Denmark, Campusvej 55, DK-5230 Odense, Denmark