Design of Magnetic Tweezers - University of California
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Transcript Design of Magnetic Tweezers - University of California
Group D
Mohammed Zuned Desai
Michael James Wong
Koji Hirota
Areio Hashemi
Background
Applications
Description
Objectives
Methodology
Fabrication
Results
Future Work
Gantt Chart
References
What are Magnetic Tweezers (MT)?
◦ Scientific instrument used for studying molecular
and cellular interactions
◦ Ability to apply known forces on paramagnetic
particles using a magnetic field gradient
◦ One of the most commonly used force spectroscopy
techniques
Atomic Force Microscopy
Optical Tweezers
They do not have problems of sample
heating and photodamage that effects
optical tweezers
Magnetic forces are orthogonal to biological
interactions
Offer the prospect of highly parallel singlemolecule measurements
◦ Hard to achieve with other single-molecule force
spectroscopy techniques
The magnet configurations are relatively easy to
assemble
Ideally suited for the study of DNA topology and topoisomerases
Study Molecular interactions
65pN to rupture bond between lectin and RBC membrane-bound
glycolipids.
60-130pN to extract beta2-integrins (CD18) from neutrophil
membrane in 1-4sec
100pN to extract integral glycoprotein from cell lipid bilayer (RBC
membrane)
165pN to rupture P-selectin bond with leukocyte-membranebound P-selectin glycoprotein ligand-1.
40-400pN to separate a pair of cell adhesion proteoglycan
molecules on marine sponge cell surfaces.
How do magnetic tweezers work?
Aspects:
• Two magnets
• Magnetic Field
• Magnetic Gradient
• Superparamagnetic
beads
• Surface Molecules
http://www.biotec.tu-dresden.de/cms/fileadmin/research/biophysics/practical_handouts/magnetictweezers.pdf
Design of Magnetic Tweezers
layer modified
with protein
• Experiment design: Working View
suspension of
microspheres
molecular layer
transparent
substrate
CCD
force
N
S
objective
mirror
layer modified
with ligands
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Dissociation of CA-sulfonamide
complexes:
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Beads and surfaces coated with Bovine
Carbonic anhydrase and sulfonamide inhibitor
F
F
beads
settle
magn. wash
@ 1 pN
time
°
°
°°
Negative Control:
No inhibitor on the surface
°
°
°
°
°
°
beads
settle
magn. wash
@ 1 pN
time
data collection
@ 12 pN
8
Calibrating design: Side View
Square capillary with
suspension of
microspheres
N
S
CCD
force
9
FM
Fd
Force calculations using Stoke’s
drag equation:
◦ Calibrate: Fd 6r
FM Fd Fg
Distance between the core of the
electromagnet and paramagnetic beads
Current flowing through the coil of the
magnet
Fg
Example:
◦ Time it takes bead to move vertically 0.5mm =
3.46s
◦ Velocity of bead (v) = 0.1445 mm/s
◦ Fluid’s viscosity (u)= 0.998 mPa s
◦ Radius of bead (r) = 1.5 um
◦ Drag Force = 4.07379 pN
force
Gravitational Force ~ 0.3 pN
10
Design and fabricate magnetic tweezers
that is capable of achieving forces up to
100pN
◦ Current design can achieve 2pN
◦ Consist of a single magnet
Introduce illumination for bright-field
transmission microscopy
Using Finite Element Method Magnetics
(FEMM) to predict the geometries of the
magnet and that will produce the largest
possible field gradients
Machine and assemble the design that will
produce the largest field gradients
Calibrate the magnet so it is ready for data
acquisition
Open source finite element analysis software package
for solving electromagnetic problems.
Good for processing:
◦
◦
◦
◦
2D planar and Axisymmetric problems
Magnet
Electrostatic
Heat and Current Flow
It is a simple, accurate, and low computational cost
freeware product, popular in science and engineering.
Reliability comparable to commercial software
Referenced in several Journals
Used by several reputable societies
IEEE Magnetics
UK and Japan Magnetics
A) Characteristics of Magnets
B) Double Magnet Runs
C) Core Material
D) Coil Manipulation
Core size
Tip shape
¼ inch
Test FEMM reliability
Core, Shape, and Angle
1.5 inch
Mu metal
Increasing the number of coils
Changing their location
Looking at how these
characteristics affect the magnetic
gradient
1/8 inch
Small vs Big Core
Coil
1.25 in
0.37 in
Iron
0.75 in
0.25 in
Core
Iron
1.5 in
0.5 in
Small core gave better uniform magnetic gradient
Magnetic field and Magnetic gradient
Tip Shape
θ
Angle
161.80
760
45.20
Arc Angle
300
450
600
900
Concave
300
450
600
900
Flat showed best results
Second best was tip with angle of 161.80
Length
Small: 0.01mm
Medium: 0.08mm
Large: 0.15
Whatever characteristics of single magnet we
don’t want to blindly assume are the same for
double magnets
◦ Ex: Flat small has better magnetic gradient but this
does not mean that Flat small gives better gradient
with double magnets so we run double magnets
Reliability of FEMM through comparison of
single and double results
A) Small double vs Big double
B) Small double with Shapes (tip, arc, concave)
C) Changing angle (600, 900,1800)
θ
1800 shows best results
2mm
θ = 150
θ = 450
θ = 600
Mu Metal vs Iron
Different tip shapes
Double vs Single
0.25 in
Mu
Metal
1.5 in
Angle
Tips
0.5 in
The Small Mu Metal flat magnet showed the
best results in single and double magnet runs
Testing to see how coil manipulation effects
the magnetic field
Increasing the number of coils
Location of the coil
A)
B)
C)
700
Magnet
Light
source
Stage
adjuster
DC
power
supply
Objective
lens
CCD
camera
Reflect
mirror
Overall Design
Stage
Stage
Stage
Manipulator
Magnet
Mirror
Objective:
Tested different tips
Parameters
Verify that flat tip shows the best results
Prove that the tip gives the largest magnetic field gradient
values at very short distances.
Flat
Cylinder
Tip
◦ Voltage: 3v, 6v, 12v
◦ Current: 0.1 Amps
◦ Distance:
0-.5mm (0.1mm increments)
.5-3.1mm (0.2mm increments)
Magnetometer
Probe
DC power supply
Tip
Scotch
Tape
Magnet
Adjustments
Knobs
1Gauss = 1 x 10-4 Tesla (B)
G vs Length
dG/dL vs Length
B vs Length
dB/dL vs Length
Finished experimenting on magnet
characteristics to obtain greatest magnetic
field gradient.
Fabricated majority of the device setup
Performed trial runs on single magnet with
different tips to verify certain trends
Ship final magnetic design with the material
to the Robert M. Hadley Company.
Locate homogeneous field
Experiment with horizontal distance with very small
increments
Capability: 100th of a mm
Start working with beads
◦ Velocity measurements
◦ Force measurements
Dr. Valentine Vullev
Dr. Sharad Gupta
Dr. Hyle Park
Dr. Jerome Schultz
Gokul Upadhyayula
Hong Xu
1) Neuman, Keri C, and Nagy, Attila. “Single-molecule force spectroscopy: optical
tweezers, magnetic tweezers and atomic force microscopy.” Nature Publishing
Group Vol. 5, NO. 6. June 2008.
2) Danilowicz, Claudia, Greefield, Derek and Prentiss, Mara. “Dissociation of
Ligand-Receptor Complexes Using Magnetic Tweezers.” Analytical Chemistry Vol.
77, No. 10. 15 May. 2005.
3) Humphries; David E., Hong; Seok-Cheol, Cozzarelli; Linda A., Pollard; Martin J.,
Cozzarelli; Nicholas R. “Hybrid magnet devices fro molecule manipulation and
small scale high gradient-field applications”. United States Patent and Trademark
Office, An Agency of The United States Department of Commerce.
<http://patft.uspto.gov>. January 6, 2009.
4) Ibrahim, George; Lu, Jyann-Tyng; Peterson, Katie; Vu, Andrew; Gupta, Dr.
Sharad; Vullev, Dr. Valentine. “Magnetic Tweezers for Measuring Forces.”
University of California Riverside. Bioengineering Senior Design June 2009.
5) Startracks Medical, “Serves Business, Education, Government and Medical
Facilities Worldside.” American Solution. Startracks.org, Inc. Copyright 2003.
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