Biological membrane functions rely closely on the dynamic, fluidic nature of the membrane. Bio-membranes consist of various types of lipids and proteins. At physiological temperature, these molecules interact with each other and diffuse laterally in the membrane. Because of the complex composition of the system, membranes are thought to be heterogeneous at different length scales and timescales. Motions of individual molecules are also expected to be beyond simple Brownian diffusion. Numerical simulation has predicted anomalous diffusion of single lipid molecules in the membrane in the timescale of nanoseconds to microseconds. Experimentally, it has been challenging to measure single molecule diffusion at that small spatiotemporal scale. In this talk, I will present the recent advance of our ultrahigh-speed single-particle tracking (SPT) optical measurements. I will explain an imaging-based interferometric approach to detect scattering signal from single gold nanoparticles, as small as 20 nm in diameter. Using this method, we were able to track single 20 nm gold nanoparticles with a localization precision of 2 nm at ultrahigh-speed (up to 500,000 frames per second) [1]. By labeling small gold particles to membrane molecules, we investigate single molecule membrane dynamics at very small length scale (a few nanometers) and short timescale (a few microseconds). For example, we discovered the nanoscopic substructures of lipid bilayer membranes of liquid-ordered phase [2]. I will also show the recent high-resolution data measured on the plasma membranes of live cells. Finally, I will discuss the importance and our strategy of background correction for high-precision SPT [3]. The combination of scattering-based interferometric microscopy and proper background correction offers the opportunity to extend our understanding of single-molecule biophysics to a new spatiotemporal regime.

References

1. Lin YH, Chang WL, Hsieh CL, "Shot-noise limited localization of single 20 nm gold particles with nanometer spatial precision within microseconds," Optics Express 22(8), pp. 9159-9170 (2014).
2. Wu HM, Lin YH, Yen TC, Hsieh CL, "Nanoscopic substructures of raft-mimetic liquid-ordered membrane domains revealed by high-speed single-particle tracking," Scientific Reports 6:20542 (2016).

Cheng CY, Hsieh CL, "Background estimation and correction for high-precision localization microscopy," ACS Photonics, Article ASAP (2017).