Single molecule detection ( LAMDA-P )

3D Micromanufacturing Lab.School of MechatronicsGwangju Institute of Science and Technology 3D Micromanufacturing Lab.School of MechatronicsGwangju Institute of Science and Technology

Single molecule detection (LAMDA-P)

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Conventional optical trapping using a tightly focused beam is not suitable for trapping particles that are smaller

than the diffraction limit because of the increasing need of the incident laser power that could produce perma-

nent thermal damages.

One of the current solutions to this problem is to intensify the local field enhancement by using nanoplasmonic

structures without increasing the laser power.

Nanoplasmonic tweezers can be used to trap various small molecules.

Surface plasmon resonance (SPR) is the collective oscillation of electrons in a solid or liquid stimulated

by incident light.

The resonance condition is established when the frequency of light photons matches the natural frequency

of surface electrons oscillating against the restoring force of positive nuclei.

SPR in nanometer-sized structures is called localized surface plasmon resonance (LSPR).

Nanoplasmonic tweezers

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1. Prepare PDMS microchamber

① Preparation of PDMS mixture

② Removal of PDMS vapor

③ Spin coating PDMS mixture

④ Solidification of PDMS film

2. Prepare specimen

3. Implementation of tapping single molecule experiment

Content: experiment procedure

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• Electric scale• Hot plate• Desiccator• PDMS materials• Spin coater• Disposable gloves

• Disposable pipet• Tweezers• Mixture plate• Dish

Composition to make PDMS microchamber

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1. Turn on and set the scale to “0”.

Preparation of PDMS mixture

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2. Put the plate on the electronic scale and set the scale to “0” again.


3. Pour Sylgard A/B in the plate at the ratio of 10:1. Total amount is set 10 g.

Preparation of PDMS mixture cont.

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4. Mix Sylgard A/B well to make PDMS mixture for about 2 min..


When mixing PDMS mixture, the vapor is created. If the vapor is not removed, the quality is de-

creased. Firstly, put the plate including PDMS mixture in the desiccator and turn on the vacuum

pump. Amount of PDMS mixture should be less than 10 g. If not, the mixture will be overflowed

from the plate. After removing the vapor, turn off the vacuum pump.

Removal of PDMS vapor

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1. When spin coating, the plate is stained with the solutions. These solutions are not re-

moved from the plate easily due to high viscosity. That’s why the plate and chuck of

spin coater should be covered by aluminum foil, before spin coating.

Spin coating PDMS mixture

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2. After setting the program, put the plate on the chuck.

Spin coating PDMS mixture cont.

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3. For fixation of the plate, press “vacuum” button to give vacuum.


4. Pour the prepared PDMS mixture on the substrate adequately. At this moment, make

sure that the vapor should not be created. Start to spin coating by pressing “start” but-

ton. After finishing spin coating, turn off vacuum and main power.


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When spin coating, the thickness of PDMS film is defined by rpm and time. Please refer

following graph to make PDMS microchamber you want.


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Move the plate thinly coated by PDMS mixture to the hot plate. To solidify the PDMS

mixture, apply heat for 10 min. at 120 °C.

Solidification of PDMS film

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2. Prepare specimen



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Nanoholes can be fabricated by focused ion beam (FIB) from NNFC in KAIST.

To confirm the efficiency of plasmonic phenomenon at which size of hole, fabricate var-

ious different size (210 ~ 450 nm) of hole on the gold plate.

Nanoholes fabrication on the gold plate

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Prepare PDMS substrate, DNA solution and gold plate.

1. Make the chamber on the PDMS substrate by cutter.

2. Pour the DNA solution in the PDMS microchamber.

3. Put the gold plate on the substrate

Prepare specimen

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2. Prepare specimen



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1. The trapping experiment is implemented in LAMDA-H system.

2. Put the specimen on the sample stage and turn on the all instruments.

3. Operate HOT and Lab VIEW program.

4. Find the fabricated nanoholes by controlling motorized stage.

Preparation of trapping experiment

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1. If you find nanoholes, turn on the laser .

2. Laser focus is exactly located on the target nanohole by controlling piezo stage.

3. The exact position can be confirmed by APD signal.

4. Increased the scattering signal up to maximum as you can by controlling the piezo stage

at vicinity of the target nanohole. If done, you’re ready to measure the trapping signal.

Measurement of trapping signal by APD

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5. Turn off the laser and set the storage path.

6. Most of area is covered by gold (metal) excluding holes. When the laser is emitted, heat

absorption problem is happened by gold plate. The absorption vaporizes the medium in-

cluding DNA molecules. However, the medium influences on the laser scattering. That’s

why scattering signal should be measured within 2 min., after turning on the laser.

Measurement of trapping signal by APD cont.

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After the laser is turned on, the scattering signal rises up to line B and then rises for the

second time to line A. Afterwards, the measurement oscillates only between the two

lines. We can deduce that the higher value at line A is due to the increased signal by

trapping the DNA. If measuring time is increased by maintaining the quantity of

medium in experiment environment.

Analysis of measured trapping signal

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Documents

Single molecule detection ( LAMDA-P )