1. © Imperial College LondonPage 1 Detecting gold nanoparticles in electron microscope images John Cupitt, Exp. Med. & Tox. 16 November 2009

2. © Imperial College LondonPage 2 Technique Use gold nanoparticles to label receptors, signalling proteins and lipids Use up to three particle sizes to label different features Image sections of cell membrane with transmission electron microscopy Particle positions reveal information about membrane function

3. © Imperial College LondonPage 3 TEM imaging of cell membrane fragments Then fix lightly, label with gold particles, fix securely, stain, dry and image with TEM

4. © Imperial College LondonPage 4 Problem Gold nanoparticles are in the 3 – 15nm range, as few as 100 atoms Image sections of cell membrane ~2000nm across containing several hundred particles Particles therefore appear rather small: 4 - 12 pixels across Standard blob detectors are designed for larger features and have poor accuracy at this scale Only 50% accuracy with most systems

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9. © Imperial College LondonPage 9 Characteristics Approximately Gaussian profile 7 – 13 pixels across Approximately circular Among the darkest objects in the image

10. © Imperial College LondonPage 10 Our new detector Gaussian ring divided into octants, convolve with each octant, take minimum response, compare to centre average

11. © Imperial College LondonPage 11 Results On the test image, with a little tuning, we get 99+% accuracy Searching the whole 2,500 x 2,500 pixel image takes about 2 seconds Need to test on more images, add some better tuning

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14. © Imperial College LondonPage 14 Credits Nicolas Robidoux, Department of Mathematics and Computer Science, Laurentian University, designed the detector with help from Chantal Racette, an undergraduate student The NIH/NIGMS Center for the Spatiotemporal Modeling of Cell Signaling provided images and the gold standard, as well as funding for Chantal Racette's work.