Team D
Mohammed Zuned Desai
Areio Barzan Hashemi
Koji Hirota
Michael James Wong

 Exerts magnetic forces to determine mechanical properties of molecules, proteins, chemical bonds
 Advantages



The magnet configurations are relatively easy to assemble
Magnetic forces are orthogonal to biological interactions
Offer the prospect for massively parallel single-molecule measurements
Figure 1: Illustration of Magnetic Tweezers, adapted from http://www.nature.com/nature/journal/v421/n6921/images/n ature01405-f2.0.jpg

Magnet(s)
Light Source
PDMS Wells Containing Sample
10x Objective
Lens
Stage layer modified with protein force
Mirror
Figure 2: Diagram of setup of magnetic tweezers
CCD Camera layer modified with ligands
Figure 3: Animation of how magnetic tweezers work


 What do these forces depend on?
F
M
 m

B
 The force on the paramagnetic beads depend on the
F
M
Force Calculations:
F d
F g

Magnet
• What do we mean by magnetic field gradient ?
• Want to achieve a high gradient
• For the same distance we want a constant change in gradient
Figure 4: Diagram demonstrating the definition of homogeneous gradient
0.2 mm
0.2 mm
0.2 mm
Sample attached to paramagnetic beads
B = 800G
B = 700G
B = 620G
B = 560G

 Main goal is to focus on attaining forces with the Magnetic
Tweezers for single-molecule measurements (e.g. 5 – 100 pN):


Design producing the highest gradient
Achieving force higher than
1.5pN (previous group)
 Calibrating the selected design
Figure 5 and 6: Setup of last years senior design group taken at different angles.

 To maximize the magnetic gradient
 Build the stronger magnet(s) with materials
 Geometry shape and position
 Using FEMM (Finite Element Method Magnetics)
Figure 8: Double Magnet FEMM Design
Figure 9: Single Magnet FEMM Design



Using FEMM simulation program
 Choose the materials
 Design the core including length, diameter and shape
Outcome
CORE


Steel
127mm (5 in.) core length


6.35mm (0.25 in.) core diameter
Flat Shape
COIL
 30 Gauge Copper wire



2500 coil turns
91.44mm (3.6 in.) coil length
15.49mm (0.61 in.) coil diameter
Figure 11: Picture of the magnet (coil and core)

•
From the literature research and FEMM simulation, this design of double magnets should exert higher magnetic gradient
Figure 10: Drawing of final double magnet design


Single Magnet  Double magnets
 Up to 5.9 pN  Up to 3.5 pN
Inverse relationship of strength of magnetic field over distance
Figure 12: Close up picture of single magnet design Figure 13: Close up picture of double magnet design

 Measure magnetic gradient over distance
 Graphs to be linear
 Magnetic gradient is decreasing at a constant rate
 Compare magnetic gradient within working distance (2mm)


Single Magnet: 148.43 G/mm
Double Magnet: 120.56 G/mm
Figure 14 and 15: Comparison of the gradient results for the single magnet and double magnet

Light Source
Magnet
1mm Capillary Tube With Paramagnetic
Beads
Light Source
Stage
10x Objective Lens
Magnets
1mm Capillary Tube With Paramagnetic
Beads
Stage
10x Objective Lens
CCD Camera
Figure 16: Calibration setup for the single magnet
CCD Camera
Figure 17: Calibration setup for the double magnet

Adjustable Stage
Magnet(s)
CCD Camera
10x Objective Lens
Sample Stage with
Capillary Tube
LED Light Source
Power Supply
Figure 7: Picture of the setup of our final design

1) Zero apparatus
 Have the tip of the magnet close to the capillary tube
2)Inject beads into the capillary tube
3)Turn on the power source
4) Note time it takes for the bead to travel 0.5mm
Light Source
Magnet
1mm Capillary Tube With Paramagnetic
Beads
Stage
10x Objective Lens
CCD Camera

F d
F
M
F g
 Force calculations using Stoke’s drag equation:
F  m  B
 Calibrate:

 Distance between the core of the electromagnet and paramagnetic beads
 F d
 
6
 r
 
F
M
Gravitational Force ~ 0.3 pN

F d

F g force
 Example:





Time it takes bead to move vertically 0.5mm = 9.4s
Velocity of bead (v) = 0.054 mm/s
Fluid’s viscosity (u)= 3.63 mPa s (40% Glycerol Solution)
Radius of bead (r) = 1.5 um
Net Force (F m
) = 5.91 pN
15
Figure 18: Animation of forces acting on the bead

1mm
0.75mm
0.5mm
0.25mm
0mm
Video 1 : Sample video of beads moving for the calibration process

3V Results
Single Magnet Calibration
Force at 1mm: 1.02pN
Force at 2mm: 0.98pN
Double Magnet Calibration
Force at 1mm: 0.76pN
Force at 2mm: 0.73pN
6V Results
Single Magnet Calibration
Force at 1mm: 2.23pN
Force at 2mm: 1.85pN
Double Magnet Calibration
Force at 1mm: 1.44pN
Force at 2mm: 1.20pN
Figure 19 and 20: Caparison of the forces the single and double magnet could achieve using 3V and 6V

12V Results
Single Magnet Calibration
Force at 1mm: 5.91pN
Force at 2mm: 4.84pN
Double Magnet Calibration
Force at 1mm: 3.52pN
Force at 2mm: 3.18pN
Figure 21: Caparison of the forces the single and double magnet could achieve using 12V
We are mainly concerned about the 12V measurements
The results show that the single magnet can achieve higher forces than the double magnet

 We accomplished our objectives:
1) We were able to design and build a pair of magnetic tweezers that can achieve over 1.5pN

Single magnet magnetic tweezers can achieve
3.94times more force than old design

Double magnet magnetic tweezers can achieve
2.35times more force than old design
2) Successfully able to calibrate both magnetic setups




F  m  B m = magnetic moment in a superparamagnetic bead
B = magnetic field in Tesla
B  K 
0 nI
I = amperes n = turns per meter
K = permeability

0
= magnetic constant
Permeability of steel = 100
Permeability of Mu Metal = 20,000

 Mu Metal
 Nickel-iron alloy


Permeability


Ability to support magnetism
200 times than that of steel
Heat treatment


Reduces amount of oxygen in metal
Gains back permeability that was lost

 Heat Conduction
 Thermoelectric Cooling
 Peltier Cells
 Liquid Cooling System
 Water Blocks

 Stage
 Holds PDMS wells and tube
 Repeatable parameters
 Detachable
 Fitted to optics table or microscope if needed

 Dr. Valentine Vullev
 Dr. Sharad Gupta
 Dr. Hyle Park
 Dr. Jerome Schultz
 Gokul Upadhyayula
 Hong Xu







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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.
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