The Wong Lab

Single-molecule Force Studies


We have developed two techniques for measuring fluctuations, which overcome typical acquisition rate and frequency response limitations of instruments. The key concept is that motion blur can yield information about high-speed dynamics, even above the acquisition rate of an instrument.

  1. Blur-corrected equipartition and power spectrum trap calibration

  2. -Simple and accurate method for determining the spring constant of a harmonically confined particle (e.g. optically trapped bead).

  3. -Corrects for motion-blur effect, and uses blur information to quantify the diffusion coefficient of the particle

relevent group publications

W.P. Wong* and K. Halvorsen*, "Beyond the frame rate: Measuring high-frequency fluctuations with light intensity modulation," Optics Letters 34 (3), 277-279 (2009). [pdf]

W.P. Wong* and K. Halvorsen*, “The effect of integration time on fluctuation measurements: calibrating an optical trap in the presence of motion blur,” Optics Express 14 (25), 12517-12531 (2006). [pdf]

*contributed equally

Experimental example with an optically trapped bead: (left) blur-corrected and uncorrected spring constant measurements as a function of laser power;  (right) measured variance divided by true variance as a function of the dimensionless exposure time (exposure time divided by the trap relaxation time)

IMSA Figures:  (left) (a) impulse responses and (b) frequency filters for DC and oscillating light;  (right) experimental example: IMSA measurement of power spectra for optically trapped beads

  1. Intensity Modulation Spectral Analysis (IMSA)

  2. -By oscillating the signal source intensity, the power spectral density (PSD) can be determined at this frequency, even above the Nyquist limit

  3. -Overcomes acquisition rate and frequency response limitations of instruments, simply and inexpensively extending their effective dynamic range


Single-molecule Force Studies Group “SIMBA” presentation at the Rowland Institute at Harvard (2008). [Click to play video]../../../../Beyond_the_frame_rate_multimedia.html