Transcript Slide 1

Particle/Surface Interactions Investigated with TIRM
L. Schaffner, G. Brügger, J. Ríčka, and M.Frenz
Dept. of Biomedical Photonics, Institute of Applied Physics, University of Bern
Evanescent Wave Illumination/TIRM
• total internal reflection (TIRM) when angle of incidence qi higher than
critical angle qc → “evanescent wave” is generated
• Intensity of evanescent wave gets exponentially weaker with increasing
distance to surface and particles scatter light proportional to this intensity
→ evanescent wave illuminates only particles very close to the surface
→ possible to determine particle/surface separation by particle brightness
Optical Tweezers
• particles with refractive index higher than surrounding medium can be trapped with a
gaussian laser beam
• depending on beam shape, particles will be trapped around focus or pushed away
Possible Measurements
• observation of ad- and desorption of single particles to
surface → deposition statistics, particle counting [1]
• total fluorescence signal → determination of surface mass
density of fluorescence marked molecules [2]
• interaction between single particle (trapped by optical
tweezers) and surface, intensity of scattered light contains
information about weak repulsive and attractive forces →
interaction potential can be restored [3]
Selected Measurements
• particle adsorption on different
surfaces
• glass Supported Phospholipid
Bilayer (SPB) encourages
particle adsorption
• protein adsorption onto glass
• adsorbed amount can be
determined absolutely from
subsequent flushing at the end
of the experiment
• single particle pushed by
optical trap against glass
• fluctuations due to Brownian
motion allow determination of
interaction potential
References
1.
L. Schaffner et al., “Surfactant mediated adsorption of negatively charged latex particles to a cellulose surface”, Colloids and Surfaces A: Physicochem. Eng. Aspects 286 (2006), 39–50
2.
V. Hlady, D. R. Reinecke, J. D. Andrade, “Fluorescence of Adsorbed Protein Layers”, Journal of Colloid and Interface Science 111 (1986), 555-569
3.
Dennis C. Prieve, “Measurement of colloidal forces with TIRM”, Advances in Colloid and Interface Science 82 (1999), 93-125