# US 2014/0150887 A1 · Optofluidic tweezers

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- Number: US 2014/0150887 A1
- Document ID: US20140150887A1
- Status: Published application
- Kind: A1
- Application number: 14/123,316
- Filed: 2012-06-04
- Published: 2014-06-05
- Earliest claimed: 2011-06-03
- Assignees: Wayne State University
- Applicants: Wayne State University
- Inventors: Amar Basu; Gopakumar Kamalakshakurup
- Web page: https://patentgrep.com/patent/US20140150887A1

## CPC

- F17D 3/01: for controlling, signalling, or supervising the conveyance of a product
- B01L 3/50273: {characterised by the means or forces applied to move the fluids}
- B01L 3/502792: {for moving individual droplets on a plate, e.g. by locally altering surface tension}
- B01L 2400/0448: Marangoni flow; Thermocapillary effect
- Y10T 137/0391: Affecting flow by the addition of material or energy
- F17D: PIPE-LINE SYSTEMS; PIPE-LINES (pumps or compressors F04; fluid dynamics F15D; valves or the like F16K; pipes, laying pipes, supports, joints, branches, repairing, work on the entire line, accessories F16L; steam traps or the like F16T; fluid-pressure electric cables H01B9/06)
- B01L: CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

In a method of moving droplets, local heat is applied to a surface portion of a droplet for an amount of time sufficient to create a Marangoni flow in the droplet. Droplets are suspended in an emulsion in a carrier liquid on a substrate. A laser beam is used to move one of the droplets. the droplet consists of a first substance and a carrier liquid consists of a second substance that is not mixable with the first substance. The droplet is placed in the carrier liquid, and the mixture is emulsified. The emulsified mixture is placed on a substrate. Then the local heat is applied to the surface of the droplet. The first substance may include oil and the second substance may include water.

## Claims

### Claim 1

A method of moving droplets, the method comprising the following steps:
providing a droplet; and
applying local heat to a surface portion of the droplet for an amount of time sufficient to create a Marangoni flow in the droplet that causes the droplet to move toward the local heat.

### Claim 2 (depends on 1)

The method of claim 1, wherein Marangoni flow creates microvortices in the droplet causing the droplet to move.

### Claim 3 (depends on 1)

The method of claim 1, wherein the droplet consists of a first substance, further comprising the steps of:
providing a substrate suitable for holding a carrier liquid on a top surface;
providing a carrier liquid consisting of a second substance generally not mixable with the first substance;
placing the droplet in the carrier liquid; and
placing the carrier liquid with the droplet on the top surface of the substrate before applying the local heat.

### Claim 4 (depends on 3)

The method of claim 3, wherein the first substance is a gas.

### Claim 5 (depends on 3)

The method of claim 3, wherein the first and second substances are selected to have an interfacial tension negatively correlated to temperature.

### Claim 6 (depends on 3)

The method of claim 3, wherein the second substance is a polar liquid and the first substance is a substantially nonpolar fluid.

### Claim 7 (depends on 6)

The method of claim 6, wherein the first substance comprises oil.

### Claim 8 (depends on 6)

The method of claim 6, wherein the second substance comprises water.

### Claim 9 (depends on 6)

The method of claim 6, wherein the droplet is placed in the carrier liquid by creating an emulsion of the first substance in the second substance.

### Claim 10 (depends on 5)

The method of claim 5, wherein the substrate is transparent.

### Claim 11 (depends on 5)

The method of claim 5, wherein the heat is applied via a light beam originating under the substrate and propagating through the substrate and through the top surface of the substrate, the light beam comprising at least one wavelength for which the substrate and the carrier liquid are transparent.

### Claim 12 (depends on 11)

The method of claim 11, wherein the droplet is suspended in the carrier liquid and the local heat is applied until the droplet contacts the substrate.

### Claim 13 (depends on 11)

The method of claim 11, wherein the droplet perimeter has a center, wherein the light beam is directed at the surface portion of the droplet in a location outside the center and inside the perimeter of the projection and in a direction substantially perpendicular to the top surface of the substrate.

### Claim 14 (depends on 1)

The method of claim 1, wherein the local heat is applied by a laser generating a laser beam with a wavelength in the visible spectrum that is converted to heat upon contact with the droplet surface.

### Claim 15 (depends on 14)

The method of claim 14, wherein the local heat is applied by a diode laser.

### Claim 16 (depends on 14)

The method of claim 14, wherein the wavelength is between about 400 nm and about 500 nm.

### Claim 17 (depends on 14)

The method of claim 14, wherein the laser beam has a focal spot size of less than about 130 μm.

### Claim 18 (depends on 17)

The method of claim 17, wherein the focal spot size is smaller than about 70 μm.

### Claim 19 (depends on 18)

The method of claim 18, wherein the focal spot size is smaller than about 30 μm.