Transcript Слайд 1 - Eventry

Light microscopy
for real-time characterization of
colloids and nanoparticles
Ivan V. Fedosov,
Saratov State University, Saratov, Russia
Boris N. Khlebtsov,
Institute. of Biochemistry and Physiology of Plants and
Microorganisms of RAS, Saratov, Russia
Valery V. Tuchin,
Saratov State University, Saratov, Russia
Introduction
Brownian motion is a random motion of small particles suspended in a
fluid. It results from collisions of particles with fluid molecules. Brownian
motion can be described in terms of probability distribution function (PDF)
of particle displacements. Root mean square displacement of a particle
due to its Brownian motion characterizes fluid temperature and viscosity
as well as hydraulic diameter of particle. The center of distribution
characterizes the effect of external forces like gravitation, Stokes drag
force or light pressure force on a particle.
One way to estimate a (PDF) of small particle displacements is based on
tracking of the particle position with a microscope. Digital image
processing allows for simultaneous tracking of a large number of particles
over microscope field of view to provide reliable characteristic of a colloid.
Earlier we reported the method for characterization of nanoparticles and
colloids based on automated tracking of nanoparticles.
Goal of our current work is to perform real time measurements of PDF of
nanoparticle displacements to study non stationary effects of light to heat
conversion enabled with noble metal colloids.
Statistical particle tracking
Frame 1
Frame 2
Brownian
particles
Mismatches
Detection of
particle positions
through image
series
Calculation of all possible
displacements of each
particle
Model for particle displacement PDF
is biased normal distribution:
 (x  c x )2 

p(x )  bx  ax exp 
2


2 x


D

2
2 t
Vx 
cx
t
Calculation histogram of
displacements
Diffusion coefficient:
kT
particle diameter;
D
temperature;
3d p
fluid viscosity
Mean displacement:
velocity of regular movement
Guasto J.S., Huang P., Breuer K.S., Exp. Fluids. (2006) V. 41. p.869 .
Parallel acquisition & processing
1 – creating a memory location for image series; 2 – acquisition of image series with
CMOS camera; 3 – particle detection; 4 – SPTV binning; 5 – circular buffer to average
displacements over several series; 6 – PDF model fit; 7 – calculation of temperature,
size etc.; 8, 9 – visualization of contour map and vector plot; 10 – updating of results
time series; 11 – updating of preview monitor.
The software was developed using
National Instruments LabVIEW 8.5 Professional Development System
Graphical user interface
Graphical user interface designed for widescreen digital display provides easy access
to all controls and indicators for easy monitoring and adjustment of acquisition and
processing.
Laser induced heating of colloids
Heating with 532 nm laser
532 nm
laser beam
14 m in diameter
532 nm light is not
visible here because it is
blocked with a filter
introduced into optical
path of microscope
Glass cell
Colloid
20 m
Illumination with 473 nm
Polystyrene nanospheres
Polystyrene nanospheres of 100 nm in diameter suspended in distilled water.
Concentration of 5 x 1010 particles/ml. Because of their extremely small absorption
cross section polystyrene nanospheres are not impact laser induced heating. Only
moderate rise of temperature caused by absorption of laser light in water is
observed.
Polystyrene nanospheres & 15nm colloid gold
Mix of 100 nm polystyrene nanospheres and 15 nm colloid gold particles. Concentration
of each fraction is 5 x 1010 particles/ml. Scattering cross section of 15 nm gold particles
is small and camera detects only polystyrene spheres which acts as temperature
sensors.
Polystyrene nanospheres & 25nm colloid gold
Mix of 100 nm polystyrene nanospheres and 25 nm colloid gold particles. Concentration
of each fraction is 5 x 1010 particles/ml. Absorption cross section of 25 nm gold particles
is about 3 times larger than that of 15 nm particles. Therefore 3 time less power of
laser beam is needed to reach the same local temperature as in previous case.
Conclusion
We had developed software for real-time characterization of colloids by
means of statistical tracking of particle images. Optimized algorithms of
data processing ensure refresh rate up to 1 measurement per second.
The software makes it possible to measure temperature, particle size,
concentration, fluid viscosity and flow velocity in various monodisperse
colloid systems containing small particles suspended in a fluid.
Acknowledgements
This work is supported through the grants:
•
“Photonics4Life” EU Seventh Framework Program No224014
•
CRDF REC-006/SA-006-00
•
CRDF BRHE RUXO-006-SR-06/BP1M06
•
RF №1.4.06
•
RNP.2.1.1.4473
•
NSh-208.2008.2
•
RFBR 08-02-00399-a
Thank You!
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