The Wong Lab

Single-molecule Force Studies


Our optical tweezers system incorporates high-resolution 3D particle tracking with active feedback for longterm stability, to enable the measurement of both forward and reverse molecular transitions, and near-equilibrium phenomena.

Horizontal Mode

... for “far-from-equilibrium” studies

(e.g. bond rupture, protein unfolding)

Vertical Mode

... for “near-equilibrium” studies

(e.g. bond formation, protein refolding)

  1. High-speed 1D tracking

  2. -Real-time video tracking and edge-detection

  3. -~2 nm resolution@ 2500 samples/s

  1. High-resolution 3D tracking

  2. -Reflection Interference Contrast Microscopy

  3. -~0.2 nm (z), ~1 nm (x-y) resolution @ 200 samples/s

  4. -Absolute distance measurement ideal for small (nm) distances

3D tracking example: bead positions for short spectrin tether with  planar slice (inset)

  1. Active feedback for high-repeatability

  2. -Feedback loops for touch control, force application, and bead alignment

  1. Active feedback for high-stability

  2. -Continuous autofocus system corrects for slow drift

  3. -long-term stability:  1-2 nm in trap height, 10 fN in force

relevent group publications

V. Heinrich*, W.P. Wong*, K. Halvorsen, and E. Evans, “Imaging biomolecular interactions by fast three-dimensional tracking of laser-confined carrier particles,” Langmuir 24, 1194-1203 (2008). [pdf]

K. Halvorsen, “Probing weak single-molecule interactions: development and demonstration of a new instrument,” Ph. D Thesis (advisor: E. Evans), Department of Biomedical Engineering, Boston University, USA (2007). [pdf]

W.P. Wong, “Exploring single-molecule interactions through 3D optical trapping and tracking: from thermal noise to protein refolding,” Ph. D Thesis (advisors: D.R. Nelson and E. Evans), Department of Physics, Harvard University, USA (2006). [pdf]

W.P. Wong, V. Heinrich, and E. Evans, “Exploring reaction pathways of single-molecule interactions through the manipulation and tracking of a potential-confined microsphere in three dimensions,” Mat. Res. Soc. Symp. Proc. 790, P5.1.1-P5.1.12 (2004). [pdf]

*contributed equally