1. Design of Magnetic Tweezers
Team D
Mohammed Zuned Desai
Areio Barzan Hashemi
Koji Hirota
Michael James Wong

2. Magnetic Tweezers
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
Frame better, what last years group had ( better field stregnth and gradiest)
Improve the magnet (better coiling)
Improve the configuration (the whole two magnet and machinging the tip)
1st show how twe are implemented into the larger setup
Figure 1: Illustration of Magnetic Tweezers, adapted from

3. How do Magnetic Tweezers Work?
Magnet(s)
Stage
PDMS Wells Containing Sample
10x Objective Lens
CCD Camera
Light Source
Mirror
layer modified
with protein
force
Magnetic tweezers is essentially and inverted microscope (with the objective on the bottom), and a magnet on top.
We have a CCD camera in order to observe the interactions between protein-ligand complexes, where proteins are coated on the super paramagnetic beads and glass surface is coated with the ligand
By turning on the electromagnet, we can exert specific force on these beads.
At small forces, beads that did not complex with the surfaces are washed
And at higher forces, we are able to observe the dissociation of the protein-ligand complex
-remover caplirry put slide with holes
Incorporate the force and calibrations (paramagentic beads and force felt by beads are equal to m del b)
layer modified
with ligands
Figure 2: Diagram of setup of magnetic tweezers
Figure 3: Animation of how magnetic tweezers work 3

4. How Magnetic Tweezers Work?
What do these forces depend on?
The force on the paramagnetic beads depend on the magnetic moment and the magnetic field gradient ( )
To achieve higher forces we either increase or m
Force Calculations:
-**Later on we will calculate the force by on obtaining the rersulting terminal velocity which is a resultant of del B FM Fd Fg

5. Magnetic Field Gradient
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
0.2 mm
B = 800G
B = 700G
B = 620G
B = 560G
Figure 4: Diagram demonstrating the definition of homogeneous gradient
Gauss
Need arieos equ
Show how ma
-this is del b
Sample attached to paramagnetic beads

6. Objectives
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
Improve the magnetic gradient
Figure 5 and 6: Setup of last years senior design group taken at different angles.

7. High Magnetic Gradient
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

8. Single Magnet 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)

9. Double Magnets Design
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

10. Magnetic Tweezers Setup
Single Magnet
Up to 5.9 pN
Double magnets
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

11. Measuring Magnetic Gradient by Gaussmeter
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: G/mm
Double Magnet: G/mm
Mike is
Figure 14 and 15: Comparison of the gradient results for the single magnet and double magnet

12. Calibration Process: Setup
**-How is the capillary tube related to the first layered slide.
-Previous used a slide with pdms, this slide uses capillary tube with beads resting on the surface due to gravity. We need to do this calibration so that we know what forces are exerted at certain distances.
Only for calibration so don’t need coat
-camera location side=calibration, bottom=pdms
Figure 16: Calibration setup for the single magnet
Figure 17: Calibration setup for the double magnet

13. Actual Setup 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

14. Calibration Process 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

15. Calibrating Magnetic Tweezers
Force calculations using Stoke’s drag equation:
Calibrate:
Distance between the core of the electromagnet and paramagnetic beads
Gravitational Force ~ 0.3 pN
Example:
Time it takes bead to move vertically 0.5mm = 9.4s
Velocity of bead (v) = mm/s
Fluid’s viscosity (u)= 3.63 mPa s (40% Glycerol Solution)
Radius of bead (r) = 1.5 um
Net Force (Fm) = 5.91 pN FM Fd Fg
To use magnetic tweezers, we need to calibrate two parameter:
First, the distance between the core of the electromagent and the force exerted on the paramagnetic beads… and
Second, relation between the current flowing through the coil of the electromagnet and the force exerted on the beads
We can do this by using stoke’s law
Once we let the beads settle and then apply a certain voltage at a specific magnet height, we can determine the drag force.
We can determine the terminal velocity by measuring the time it takes the bead to move vertically for a certain distance
By plugging in the velocity, fluid’s viscosity and radius of the bead, we can determine the drag force.
By measuring the time it takes the beads to move down in the absence of external force, we calculated the gravitational force to be ~0.3pN
-need duplicate simplified slide in the beginning
-Increase the Force not FIED…
Remember the force equation of a solonoid, increase the force want del cross b to be as higest possible (we want the highest gradient which inturn implies the highest velocity)
***Velcity that we obtain is a resultant of the gradient acting on the bead
force 15
Figure 18: Animation of forces acting on the bead 15

16. Sample Calibration Video
1mm
0.75mm
0.5mm
Constant velocity questions
2 mega pixels
0.25mm
0mm
Video 1 : Sample video of beads moving for the calibration process

17. Calibration Results 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
-** Interested in 0.2mm because that is the working distance of the pdms slides.
Figure 19 and 20: Caparison of the forces the single and double magnet could achieve using 3V and 6V

18. Calibration Results 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
-**By increasing the votlage we increase the current from (0 to 0.4A) which leads to an increase in the force
As you increase the voltage you increase the current (which increase the force) (the field depends on the current)
2mm, bc of wells
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

19. Conclusion 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

20. Future Work
m = magnetic moment in a superparamagnetic bead B = magnetic field in Tesla I = amperes n = turns per meter K = permeability = magnetic constant Permeability of steel = 100 Permeability of Mu Metal = 20,000

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

22. Future Work Heat Conduction Thermoelectric Cooling
Peltier Cells
Liquid Cooling System
Water Blocks

23. Future Work Stage Holds PDMS wells and tube Repeatable parameters
Detachable
Fitted to optics table or microscope if needed

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

25. References
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 May
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. < 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 <
6) Janshoff A, Neitzert M, Oberdorfer Y, Fuchs H. Force spectroscopy of molecular systems-single molecule spectroscopy of polymers and biomolecules. Angew Chem Int Ed 2000;39:

26. Questions