General principles

Particle tracking microrheology may mean two different methods. One is single particle tracking technique, where the particle acts as a probe to investigate the rheology of the matrix. Another is general particle tracking microrheology where the ensemble of many particles itself is investigated. The particle tracking methods considered here involve the use of optical microscope. DWS which involve laser light scattering is not considered here. In DWS the MSD is not directly tracked but calculated from g₂(t)-1.

The detailed principles of optical and video microscopy were reviewed. Thierry Savin’s PhD dissertation (MIT, 2006) is a good source of information.

Microscope

An inverted microscope with fluorescent, live cell, time-lapse imaging, high-speed multi-fluorescence optical sectioning, polarization contrast and DIC, micromanipulation, etc. is favorable. Oil immersion objectives are required to correctly resolve Brownian colloidal particles.

• Leica DM IRB, now obsolete. Current suggestion: DMI4000 B — +86-20-87320225
• Olympus IX71 — 86-20-61227171
• Zeiss Axio Observer — 020-87755770*123 — RMB50万 13802758186

60X oil immersion type objective lens (Olympus, Japan) with numerical aperture of 1.40, while 500 nm probe particles were observed using 100X oil immersion type objective lens with numerical aperture of 1.42¹.

CCD/CMOS

Cooling reduces the array’s dark current, improving the sensitivity of the CCD to low light intensities, even for ultraviolet and visible wavelengths. Professional observatories often cool their detectors with liquid nitrogen to reduce the dark current, and therefore the thermal noise, to negligible levels². Magnification is characterized by nm per pixel. Generaly hundreds of nm per pixel can achieved, which yields spatial resolutions of tens of nm, well below the optical resolution of ~250 nm.

• Phantom v9, 20fps~500fps, 2e3 frames USD38000 — 13609003283谢先生
• ImageSource DMK 21AU04 — 上海英诚图像

Cells/Chambers

• Grace Bio-Labs CoverWell series

• Linkam CSS450 Optical Rheology Systems
• 安立佳2003年专利《便携式温控锥板剪切池》（CN200310115944.5）

Software

How to know which in the current frame is the particle in the last frame?

Calculation of: MSD, PDF

Routines here³.