1. Research School of Engineering, College of Engineering and Computer Science; Australia National University; North Road Canberra ACT 2601 Australia
2. John Curtin School of Medical Research; Australian National University; Garran Road Canberra ACT 2601 Australia
3. Australia- EMBL Node in Single Molecule Science, School of Medical Sciences; University of New South Wales; Sydney NSW 2052 Australia
4. Australia Research Council Centre of Excellence in Advanced Molecular Imaging; University of New South Wales; Australia
5. Wellman Center for Photomedicine, Massachusetts General Hospital; Harvard Medical School, Boston; Massachusetts 02114 USA
6. Australia Research Council Centre of Excellence in Advanced Molecular Imaging; Australian National University; Australia