We introduce a method for detecting and tracking small particles in a solution near a surface. The method is based on blocking the backreflected illumination beam in an objective-type total internal reflection microscope, leaving unhindered the light scattered by the particles and resulting in dark-field illumination. Using this method, we tracked the motion of 60-nm polystyrene beads with a signal-to-noise ratio of 6 and detected 20-nm gold particles with a signal-to-noise ratio of 5. We illustrate the method’s use by following the Brownian motion of small beads attached by short DNA tethers to a substrate.
© 2001 Optical Society of America
(110.0180) Imaging systems : Microscopy
(120.1880) Instrumentation, measurement, and metrology : Detection
(120.5820) Instrumentation, measurement, and metrology : Scattering measurements
(290.5850) Scattering : Scattering, particles
Ido Braslavsky, Roee Amit, B. M. Jaffar Ali, Opher Gileadi, Amos Oppenheim, and Joel Stavans, "Objective-Type Dark-Field Illumination for Scattering from Microbeads," Appl. Opt. 40, 5650-5657 (2001)