CN111307714B - Droplet control chip based on optical flow control thermal capillary micro-flow vortex and control method thereof - Google Patents

Droplet control chip based on optical flow control thermal capillary micro-flow vortex and control method thereof Download PDF

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CN111307714B
CN111307714B CN202010142481.5A CN202010142481A CN111307714B CN 111307714 B CN111307714 B CN 111307714B CN 202010142481 A CN202010142481 A CN 202010142481A CN 111307714 B CN111307714 B CN 111307714B
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channel
droplet
particles
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CN111307714A (en
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邢晓波
黄建林
陈伊琳
罗芳婧
李瑶
水玲玲
杨剑鑫
周瑞雪
吴家隐
何浩培
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South China Normal University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L3/00—Containers or dishes for laboratory use, e.g. laboratory glassware; Droppers
    • B01L3/56—Labware specially adapted for transferring fluids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L2200/00—Solutions for specific problems relating to chemical or physical laboratory apparatus
    • B01L2200/06—Fluid handling related problems
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L2200/00—Solutions for specific problems relating to chemical or physical laboratory apparatus
    • B01L2200/06—Fluid handling related problems
    • B01L2200/061—Counting droplets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L2200/00—Solutions for specific problems relating to chemical or physical laboratory apparatus
    • B01L2200/06—Fluid handling related problems
    • B01L2200/0678—Facilitating or initiating evaporation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L2200/00—Solutions for specific problems relating to chemical or physical laboratory apparatus
    • B01L2200/12—Specific details about manufacturing devices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L2300/00—Additional constructional details
    • B01L2300/08—Geometry, shape and general structure
    • B01L2300/0832—Geometry, shape and general structure cylindrical, tube shaped
    • B01L2300/0838—Capillaries
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L2300/00—Additional constructional details
    • B01L2300/18—Means for temperature control
    • B01L2300/1861—Means for temperature control using radiation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L2400/00—Moving or stopping fluids
    • B01L2400/04—Moving fluids with specific forces or mechanical means
    • B01L2400/0403—Moving fluids with specific forces or mechanical means specific forces
    • B01L2400/0415—Moving fluids with specific forces or mechanical means specific forces electrical forces, e.g. electrokinetic
    • B01L2400/0427—Electrowetting

Abstract

The invention discloses a droplet control chip based on optical flow control thermal capillary micro-flow vortex and a droplet control method thereof. The droplet manipulation chip includes: a substrate; the microfluidic channel is arranged in the substrate and is used for accommodating two immiscible liquids; the photothermal waveguide is movably arranged on the substrate and comprises an optical signal input end and an excitation end, wherein the optical signal input end is used for accessing an optical signal, and the excitation end is used for exciting one of the liquids in the microfluidic channel to form a bipolar light flow control thermal capillary microfluidic vortex. The microfluidic chip has the advantages of simple structure, simple and easy manufacturing method and low cost, can be used for fusing, capturing and releasing picoliter liquid drops in immiscible carrier oil and selectively wrapping micron objects, and has higher convenience and feasibility, low requirements on external conditions, small sample pollution and very high adjustable characteristics.

Description

Droplet control chip based on optical flow control thermal capillary micro-flow vortex and control method thereof
Technical Field
The invention belongs to the technical field of optical flow control, and particularly relates to a droplet control chip of optical flow control thermal capillary vortex and a droplet control method thereof.
Background
Droplet generation and controlled fusion are increasingly important in biochemical reactions, medical diagnostics, and environmental sciences. The micro-droplets have the characteristics of high monodispersity, small volume and the like, and are widely applied to the fields of chemical detection, biomedical engineering, environmental monitoring and the like. As a novel biochemical analysis method, the droplet microfluidic technology has the advantages of less reagent consumption, high transmission efficiency, high reaction speed and the like, and has wide application prospects in the aspects of drug encapsulation, single cell monitoring, disease treatment, biological imaging, enhanced sensing and the like. Prior to this time, important droplet manipulation techniques have been developed to achieve a variety of manipulations, including droplet generation, movement, fusion, mixing, particle encapsulation. Unlike electrowetting on media (EWOD) and magnetic manipulation techniques, in microfluidic chips the hydrodynamic manipulation of droplets in the continuous phase is independent of the pH, ionic concentration, conductivity and dielectric constant of the droplets; meanwhile, the pollution of the sample caused by physical attachment can be avoided.
Max et al propose a pure water flow dynamic method which realizes high-throughput single cell encapsulation of picoliter droplets and self-sorting of the droplets. However, most passive techniques for single particle packing in droplets are performed randomly and are determined by poisson statistics, and therefore deterministic particle packing cannot be guaranteed. Inertial vortexing has so far overcome the inherent limitations of poisson statistics, providing size-selective packing and separation of rare particles in a single microfluidic device. In conclusion, the liquid drop manipulation through the pure water flow mechanics method or the inertial vortex has the advantages of simple manufacture, high stability, high flux and the like. Heretofore, few studies have been reported on droplet generation and selective encapsulation at low loading particle concentration based on microfluidic vortex in a system, and therefore, how to combine optical and hydrodynamic forces to realize size selective manipulation of droplets is a technical problem to be solved urgently in the art.
Disclosure of Invention
(I) technical problems to be solved by the invention
The invention solves the technical problems that: how to use the optofluidic thermocapillary microfluidic vortex to carry out size selective manipulation on liquid drops, such as liquid drop generation, fusion and encapsulation.
(II) the technical scheme adopted by the invention
In order to solve the technical problems, the invention adopts the following technical scheme:
a droplet manipulation chip based on optofluidic thermocapillary microfluidic vortexing, the droplet manipulation chip comprising:
a substrate;
the microfluidic channel is arranged in the substrate and is used for accommodating two immiscible liquids;
the photothermal waveguide is movably arranged on the substrate and comprises an optical signal input end and an excitation end, wherein the optical signal input end is used for accessing an optical signal, and the excitation end is used for exciting one of the liquids in the microfluidic channel to form a bipolar light flow control thermal capillary microfluidic vortex.
Preferably, the microfluidic channel comprises a first channel and a second channel which are communicated with each other; the substrate is provided with a first injection port and a first discharge port, the first injection port is communicated with the first channel and is used for injecting liquid into the first channel, and the first discharge port is communicated with the first channel and is used for discharging the liquid in the first channel.
Preferably, a second injection port and a second discharge port are arranged on the substrate, the second injection port is communicated with the second channel and is used for injecting liquid into the second channel, and the second discharge port is communicated with the second channel and is used for discharging the liquid in the second channel.
Preferably, the excitation end comprises a tapered optical fiber and a graphene oxide layer coated outside the tapered optical fiber.
The invention also discloses a control method of the droplet control chip based on the optical flow control thermal capillary micro-flow vortex, which comprises the following steps:
sequentially injecting a first liquid and a second liquid into the microfluidic channel, wherein the first liquid and the second liquid are insoluble with each other, the density of the first liquid is higher than that of the second liquid, and the first liquid contains particles;
moving the photothermal waveguide such that the excitation end is in the second liquid and proximate to the interface of the first liquid and the second liquid;
and connecting an optical signal by using the optical signal input end, so that the excitation end generates a light flow control thermal capillary micro-flow vortex in the second liquid, and drives a part of the first liquid and the particles in the first liquid into the second liquid to form the droplets encapsulating the particles.
Preferably, the first liquid is an aqueous solution comprising particles of various sizes and the second liquid is a silicone oil.
Preferably, the manipulation method further comprises:
and sequentially inputting optical signals with different powers into the optical signal input end to sequentially form liquid drops encapsulating particles with different sizes.
Preferably, the manipulation method further comprises:
the vertical distance between the interface between the second liquid and the air and the excitation end is sequentially adjusted to sequentially form droplets encapsulating particles of different sizes.
Preferably, the manipulation method further comprises: after the droplet of encapsulated particles is formed, the optical signal is input continuously until the droplet of encapsulated particles is released from the optofluidic thermocapillary microfluidic vortex.
(III) advantageous effects
The invention discloses a droplet control chip based on optical flow control hot capillary microfluidic vortex and a droplet control method thereof, and compared with the prior art, the droplet control chip has the following advantages and beneficial effects:
(1) Has higher convenience and feasibility. Compared with the traditional pure water flow power method, the method has the advantages that the optical signals emitted by the optical fiber laser are coupled into the photothermal waveguide, the bipolar optofluidic micro-flow vortex excited by the photothermal waveguide is used as the micro-motor to selectively control the size of the liquid drop, an injection pump and a valve are not required to be externally connected, and the liquid drop can be controlled more conveniently, flexibly and tunably.
(2) The requirement on external conditions is low, and the sample pollution is small. Unlike electrowetting technology and magnetic force control technology, the photothermal waveguide has small volume, high mobility and other features, and may be integrated with microfluidic chip easily in narrower and compact space. In the micro-fluidic chip, the fluid mechanics control of the liquid drop in the continuous phase is independent of the pH value, the ion concentration, the conductivity and the dielectric constant of the liquid drop; meanwhile, the pollution of the sample caused by physical adhesion can be avoided.
(3) The preparation method is simple and easy to implement, and the cost is low. The photo-thermal waveguide used in the invention is formed by integrating graphene oxide and superfine optical fibers and is prepared by a liquid drop method. The graphene oxide is prepared by an improved Hummers method, the tapered optical fiber is prepared by a single-mode optical fiber through a flame heating method, complex machine equipment is not needed, and the preparation is simple and easy to implement.
(4) Has high adjustability. Compared with the traditional passive liquid drop control method, the performance of the optical flow control hot capillary micro-flow vortex utilized by the invention can be controlled by the input optical power, the viscosity coefficient of liquid and the boundary condition of a micro-channel, and the invention has strong adjustability.
Drawings
Fig. 1 is a schematic structural diagram of a droplet manipulation chip based on optofluidic thermocapillary microfluidic vortexing according to a first embodiment of the present invention;
FIG. 2 is a diagram of a droplet fusion process for generating a target droplet in a bipolar optofluidic thermocapillary microfluidic vortex according to a first embodiment of the present invention;
FIG. 3a is a simulated distribution plot of temperature in the free interface region at 40mW optical power with the photothermal waveguide center at a (0, 0) point in the oil;
FIG. 3b is a simulated distribution plot of flow velocity in the free interface region at an optical power of 40mW when the photothermal waveguide is centered at a (0, 0) point in the oil;
fig. 4 is a flowchart of a droplet manipulation chip based on optofluidic thermocapillary microfluidic vortexing according to a second embodiment of the present invention;
FIG. 5a shows the excitation end under different optical powersX component (V) of ambient flow velocity x ) Schematic diagram of the change situation;
FIG. 5b is a schematic diagram of the diameter distribution and the microscope of the droplets produced when the optical power is 60 mW;
fig. 5c is a microscope image of the droplet fusion and release process in vortex 2 between t1=0 and t1=14 s;
FIG. 6a is a microscope image of the fusion and release process of water-in-oil droplets in a bipolar optofluidic thermocapillary microfluidic vortex at optical powers of 20mW, 30mW, 40mW, 50mW, 60mW and 70mW, respectively;
FIG. 6b is a microscope image of the process of fusion of oil-in-water droplets in a bipolar optofluidic thermocapillary microfluidic vortex at optical powers of 60mW, 50mW, 40mW, 30mW and 20mW, respectively;
FIG. 7a is a schematic illustration of particle size selective encapsulation during droplet fusion;
fig. 7b is a microscope image of bipolar optofluidic thermocapillary microfluidic vortex-induced PS particle size selective encapsulation.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.
Example one
As shown in fig. 1, a droplet manipulation chip based on optofluidic thermocapillary microfluidic vortex according to an embodiment of the present invention includes a substrate 10, a microfluidic channel 20 and a photothermal waveguide 30, wherein the microfluidic channel 20 is disposed in the substrate 10 and is used for accommodating two immiscible liquids; the photothermal waveguide 30 is movably disposed on the substrate 10 and includes an optical signal input terminal 31 and an excitation terminal 32, the optical signal input terminal 31 is used for receiving an optical signal, and the excitation terminal 32 is used for exciting to form a bipolar optoflow control thermocapillary microfluidic vortex in one of the liquids in the microfluidic channel 20.
Specifically, the microfluidic channel 20 includes a first channel 21 and a second channel 22 that are communicated with each other, and the first channel 21 and the second channel 22 are perpendicular to each other, that is, the microfluidic channel 20 is a T-shaped channel. As a preferred embodiment, the first channel 21 and the second channel 22 are both rectangular channels. Further, the substrate 10 is provided with a first inlet 11 and a first outlet 12, the first inlet 11 is communicated with the first channel 21 and is used for injecting liquid into the first channel 21, and the first outlet 12 is communicated with the first channel 21 and is used for discharging the liquid in the first channel 21. Further, a second injection port 13 and a second discharge port 14 are disposed on the substrate 10, the second injection port 13 is communicated with the second channel 22 and is used for injecting the liquid into the second channel 22, and the second discharge port 14 is communicated with the second channel 22 and is used for discharging the liquid in the second channel 221. Further, a through hole 15 is formed in the side wall of the first channel 21, the photo-thermal waveguide 30 penetrates through the through hole 15, wherein the optical signal input end 31 is located outside the first channel 21, the excitation end 32 is located in the first channel 21, the through hole 15 comprises a plurality of array-type circular small holes which are arranged from top to bottom, the interval between each small hole is 1mm, the aperture of each circular small hole is larger than the diameter of the photo-thermal waveguide 30, and therefore the photo-thermal waveguide 30 can penetrate through different circular small holes in the actual use process, and the relative height of the photo-thermal waveguide 30 can be adjusted conveniently.
As a preferred embodiment, the excitation end 32 of the photothermal waveguide 30 includes a tapered optical fiber and a graphene oxide layer coated outside the tapered optical fiber. When the optical signal input end 24 is connected and coupled with an optical signal, the graphene oxide layer 23 is used for limiting and absorbing light energy, and the photothermal waveguide 30 can be used as a heater, and can excite the bipolar optofluidic-controlled thermocapillary microfluidic vortex due to the temperature gradient and the surface tension gradient; the optofluidic thermocapillary microfluidic vortex 31 can be used as a micro-motor, and can perform operations such as size selective generation, fusion, particle wrapping and the like on liquid drops, and fig. 2 shows a dynamic process diagram of liquid drop generation, fusion and release in the optofluidic thermocapillary microfluidic vortex. As a preferred embodiment, the tapered waveguide is preferably formed by heating and drawing a silica fiber, the material of the tapered waveguide may further include other waveguide materials, such as silicon nitride, sapphire, a polymer with a melting point greater than 100 degrees celsius, and the like, and the preparation method thereof may also be a chemical etching method, and these materials and preparation methods are common technical means in the art and are not described herein again.
The principle of generation of droplets by optofluidic thermocapillary microfluidic vortexing was analyzed as follows: the invention is based on that the photothermal waveguide 30 is used as a heater excitation system to generate thermal capillary convection and buoyancy convection, thereby generating the fusion of picoliter liquid drops with controllable size and the selective wrapping of micron targets. In a preferred embodiment, the first liquid is an aqueous solution, the second liquid is silicon oil, and the excitation end 32 of the photothermal waveguide 30 is disposed at different positions of the gas-oil system, so that the thermocapillary convection and the buoyancy convection are simultaneously excited and generate acting force on the liquid in the system. The force is divided into two parts: one is the buoyancy generated by the buoyancy convection, which causes the water at the bottom to flow toward the excitation end 32 and the water layer to generate upward convection; the other is that under the action of thermocapillary convection, thermocapillary shear stress is applied on a horizontal plane, and the liquid can be driven to flow in the horizontal plane direction. As shown in fig. 3a and 3b, when the center of the excitation end 32 is located in the silicone oil, its coordinates are (0, 0), the black bars inside the ellipse represent the excitation end 32, and when the optical power is 40mW, the temperature and flow rate are simulated distribution profiles in the free interface area (1 mm × 0.73 mm), and the black arrows represent the direction and magnitude of the flow rate. Under the influence of forces in two different directions, water-in-oil droplets with a volume of picoliters can be generated. The magnitude of the acting force is related to the relative strength of the thermocapillary convection and the buoyancy convection, the relative position of the photothermal waveguide and the water-oil interface, the optical power and other conditions. Therefore, the size of the droplets in this embodiment can be adjusted by adjusting the above conditions.
The droplet control chip based on the optofluidic thermocapillary microfluidic vortex provided by the embodiment has the advantages of simple structure, simple and easy manufacturing method, low cost, capability of efficiently and flexibly generating liquid droplets with picoliter volumes by utilizing the photothermal waveguide, and capability of controlling the size and the shape of the generated liquid droplets. The disclosed droplet manipulation chip can be incorporated as a stand-alone device or as a module in any suitable microfluidic system recognized in the art. In some embodiments, a droplet manipulation chip based on optofluidic thermocapillary microfluidic vortexing may form one element on a chip with multiple functions.
Example two
As shown in fig. 4, the second embodiment of the present invention provides a droplet manipulation chip based on optofluidic thermocapillary microfluidic vortexing, and the method includes the following steps:
step S10: a first liquid and a second liquid are sequentially injected into the microfluidic channel 20, wherein the first liquid and the second liquid are immiscible with each other, and the density of the first liquid is higher than that of the second liquid, and the first liquid contains particles.
Specifically, the first liquid is preferably an aqueous solution, and the second liquid is preferably a silicone oil. Wherein an aqueous solution is injected from the first injection port 11 so that the aqueous solution enters the first passage 21 and the second passage 22; the silicone oil is injected from the second injection port 13 so that the silicone oil enters the second passage 22, wherein the aqueous solution is pure water containing particles of various sizes, and the water-oil interface position is controlled by controlling the volume ratio of the oil phase and the water phase due to the low surface tension and the low density of the silicone oil. Further, the first injection port 11 may be connected to a liquid storage tank, and when the liquid is evaporated due to the heating of the photo-thermal waveguide, the liquid may be automatically supplemented to reduce human resources.
Step S20: the photothermal waveguide 30 is moved so that the excitation end 32 is located in the second liquid and near the interface of the first liquid and the second liquid.
Specifically, the position of the photothermal waveguide 30 may be adjusted by means of a three-dimensional adjustment frame such that the excitation end 32 is located in the second liquid and close to the interface of the first liquid and the second liquid, wherein the distance from the excitation end 32 to the interface is controlled to be about 5 mm. The specific adjustment process is the prior art and is not described herein.
Step S30: an optical signal is input by the optical signal input end 31, so that the excitation end 32 generates a light-flow control thermal capillary micro-flow vortex in the second liquid, and drives a part of the first liquid and particles in the first liquid into the second liquid to form droplets encapsulating the particles.
Specifically, as shown in FIGS. 3a and 3b, when the excitation end 32 is againstNear the interface of the first liquid and the second liquid, the major axis (a) on the left side of the elliptic isotherm 1 ) Is compressed. Due to the significant reduction in flow rate of vortices 1 and 3 caused by the larger ellipticity (b/a) of the isotherm, the bipolar axisymmetric optoflow-controlled thermo-capillary microfluidic vortices (vortices 2 and 4) dominate. At this time, a large temperature gradient is generated at the gas-liquid interface, and a stable bipolar optofluidic thermocapillary microfluidic vortex is generated under the action of the temperature gradient and the surface tension gradient.
In experiments, the rotation radius of the particles in the hot capillary vortex is regularly reduced along with the increase of the size of the particles, and the rotation radius is in negative correlation with the mass according to the kinematics law, and when the mass of the particles is the same, the rotation radius is the same, and the larger the mass of the particles is, the smaller the rotation radius is. For the same mass of particles and droplets, the rotation radius of the particles and the droplets are the same, and the density of the particles is greater than that of the droplets, so that the volume of the particles is smaller than that of the droplets with the same mass, and when the particles and the droplets with the same mass rotate in a vortex with the same rotation radius, the collision probability of the particles and the droplets with the same mass is very high, and the droplets are encapsulated by the particles. The size of the particles to be encapsulated can be effectively adjusted by adjusting the size of the generated droplets, so that the selective encapsulation of the particle size is realized.
According to the first embodiment, the power of the optical signal and the relative strength of the thermocapillary convection and the buoyancy convection can be adjusted to generate different sizes of droplets. Further description is made below in these two respects, respectively.
First from an optical power perspective. As shown in fig. 5a, the x-component of the flow velocity of the thermo-capillary vortex around the excitation end increases with increasing optical power and the flow velocity at the center of the vortex remains 0. As the vortex flow rate increases, the droplet experiences a greater gradient lift and moment, and the equation of motion for the rotating droplet is described as:
Figure BDA0002399561650000081
wherein, f L Rho, U and W are dimensionlessLift coefficient, fluid density, maximum fluid velocity, and channel width. m, v d And r is the mass, velocity and orbital radius of rotation of the droplet, respectively. From the equation, it is known that an increase in the vortex flow velocity results in a smaller radius of rotation of the droplets and a shorter distance between the rotating droplets, resulting in a greater probability of collision and fusion efficiency. As shown in fig. 2, the droplets are continuously rotational fused and then released after the threshold is reached. When the optical power was 60mW, as shown in FIG. 5b, the diameter of the droplets generated in the vortex was gradually increased until release, as shown in FIG. 5c, at t 1 =0 to t 1 Between =14s, droplets merge and release in vortex 2.
In order to prove that the diameter thresholds of the droplets obtained under different optical powers have corresponding relation with the increase of the optical power, 20mW, 30mW, 40mW, 50mW, 60mW and 70mW optical powers are selected in a proper optical power interval, and the different diameter thresholds of the droplets generated under the corresponding optical powers are obtained. As shown in FIG. 6a, droplets having threshold diameters of 17.6 μm, 31.2 μm, 52.8 μm, 61.6 μm, 76.8 μm and 84.8 μm, respectively, were sequentially generated at the center of the vortex when the powers were 20mW, 30mW, 40mW, 50mW, 60mW and 70mW, respectively. Meanwhile, in order to be able to verify the reliability of the above threshold diameter, the optical power, which had reached 70mW, was reduced stepwise to 20mW, and the corresponding drop threshold diameter obtained at the above optical power was obtained. Droplets with threshold diameters of 78.4 μm, 64.8 μm, 52 μm, 29.6 μm and 17.6 μm were generated in sequence at the center of the vortex at powers of 60mW, 50mW, 40mW, 30mW and 20mW, respectively. The above results of the threshold diameters are sufficient to indicate that in the case of increasing and decreasing the optical power, droplets of different threshold diameters are always generated and finally released at the corresponding optical power, which is sufficient to indicate that the size of the droplets generated in the thermal capillary vortex can be adjusted by the optical power.
Illustratively, the aqueous solution contained two different sized particles, 10 μm and 800nm polystyrene Particles (PS), respectively, at a concentration of 5.0X 10 3 mu.L/L. To clearly observe the encapsulation process, the ratio of 10 μm and 800nm polystyrene particles in the channel was 1The particle rotation radius is large.
As shown in FIG. 7a and FIG. 7b, an optical signal with an optical power of 40mW was applied at t 2 =0, 30 μm droplets are generated in the vortex and move along a certain rotational trajectory. It was also found that 10 μm polystyrene particles also rotated along a similar trajectory. At t 2 (ii) a shear gradient lift force (F) exerted on the particle when the radius of rotation of the particle is almost equal to the radius of rotation of the droplet at 1s L ) Overcoming the water-oil interfacial tension. Thus, 10 μm particles pass through the oil-water interface into the internal phase, and the particles are then encapsulated by the droplets. At t 2 When =2s, the droplet encapsulating the particle continues to rotate and merge with the surrounding droplets to form a droplet having a diameter of 42 μm, in which case the radius of rotation of the 10 μm polystyrene particle is slightly smaller than the radius of rotation of the droplet, so that the particle is encapsulated in the droplet and does not detach. However, the radius of rotation of 800nm polystyrene particles is larger than the radius of the droplets, and thus it is difficult to wrap them in the droplets. At t 2 And =3s, the droplet of encapsulated particles is released from the vortex. The results show that size selective packing of particles with a diameter of 10 μm can be achieved in a hot capillary vortex, which is suitable for application in the separation and packing of rare particles. It is also known from the above analysis that droplets of different sizes can be generated by selecting lasers with different optical powers to be passed through, thereby encapsulating particles of different sizes.
Second, in terms of the relative strength of thermocapillary convection and buoyancy convection, the thermocapillary strength relative to buoyancy can be controlled by the perpendicular distance of the photothermal waveguide from the gas-liquid interface. On the surface of the system, due to the action of temperature gradient, the mass density of the oil is reduced, and the oil is pushed away from the photo-thermal waveguide to a low-temperature region; simultaneously, water flows to the photothermal waveguide at the bottom, and flows in buoyancy F B The water layer generates upward convection, and generates bipolar optofluidic thermal capillary microfluidic vortex under the drive of surface tension gradient. The oil flows from the photothermal waveguide to the peripheral region in the y-direction, circulates in the peripheral region, and then returns to the photothermal waveguide. Due to the application of thermal capillary shear stress in the horizontal plane, water droplets in the oil are generated with a volume of picoliters. Due to the photo-thermal waveguide being arranged on the free surface of the water-in-oil emulsionThe temperature gradient of the gas-liquid interface is larger than that of the interior of the liquid, so that stable thermocapillary convection is generated, and meanwhile, buoyancy convection is weakened. By adjusting the relative heights of the excitation ends, buoyancy convection currents with different sizes are generated, so that liquid drops with different sizes are generated, and particles with different sizes are encapsulated.
Further, the control method further comprises the following steps:
step S40: after the droplets of the encapsulated particles are formed, the input optical signal is stopped and a surfactant is added to the second liquid to collect the droplets of the encapsulated particles.
Specifically, when the solution contains particles of various sizes, droplets of different sizes are generated by one of the two methods, and after the droplets encapsulate the particles, the input optical signal can be stopped, thereby stopping the vortex, and then 2% surfactant can be added to the second liquid, i.e., silicone oil, to collect the droplets encapsulating the particles, thereby achieving the purpose of screening the particles of different sizes.
In another embodiment of course, the optical signal is input continuously after the droplet of encapsulated particles is formed until the droplet of encapsulated particles is released from the optofluidic thermocapillary microfluidic vortex. Experimental process shows that when the light signal is input continuously after the liquid drops encapsulate the particles, the liquid drops encapsulating the particles can rotate in the vortex for a period of time until the liquid drops are released from the vortex, and therefore the purpose of screening the particles with different sizes can be achieved.
The operation method of the droplet control chip based on the optical flow control thermal capillary microfluidic vortex provided by the second embodiment is simple and easy to implement, low in cost, and capable of accurately, efficiently and flexibly selectively encapsulating particles with different sizes by controlling the sizes of the generated droplets, so that the purpose of screening the particles is achieved.
Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents, and that such changes and modifications are intended to be within the scope of the invention.

Claims (7)

1. A control method of a droplet control chip based on a light flow control thermal capillary micro-fluidic vortex is characterized in that the droplet control chip comprises:
a substrate (10);
a microfluidic channel (20) disposed in the substrate (10) for containing two immiscible liquids;
a photothermal waveguide (30) movably disposed on the substrate (10) and comprising an optical signal input (31) and an excitation end (32), the optical signal input (31) for receiving an optical signal, the excitation end (32) for being disposed in one of the liquids and proximate to an interface of the two liquids and for exciting a bipolar optoflow-controlled thermocapillary microfluidic vortex in the one of the liquids in the microfluidic channel (20) to form a droplet encapsulating the particle;
the control method comprises the following steps:
sequentially injecting a first liquid and a second liquid into the microfluidic channel (20), wherein the first liquid and the second liquid are immiscible, and the density of the first liquid is higher than that of the second liquid, and the first liquid contains particles;
moving the photothermal waveguide (30) such that the excitation end (32) is located in the second liquid and proximate to the interface of the first and second liquids;
accessing an optical signal by using the optical signal input end (31) to enable the excitation end (32) to generate optofluidic thermocapillary microfluidic vortex in the second liquid and drive a part of the first liquid and the particles in the first liquid into the second liquid to form liquid drops encapsulating the particles;
sequentially inputting optical signals of different powers into the optical signal input end (31) to sequentially form droplets encapsulating particles of different sizes, or sequentially adjusting a vertical distance between an interface between a second liquid and air and the excitation end (32) to sequentially form droplets encapsulating particles of different sizes.
2. The manipulation method according to claim 1, wherein the microfluidic channel (20) comprises a first channel (21) and a second channel (22) which are in communication; the substrate (10) is provided with a first injection port (11) and a first discharge port (12), the first injection port (11) is communicated with the first channel (21) and is used for injecting liquid into the first channel (21), and the first discharge port (12) is communicated with the first channel (21) and is used for discharging the liquid in the first channel (21).
3. The manipulation method according to claim 2, wherein a second injection port (13) and a second discharge port (14) are provided on the substrate (10), the second injection port (13) communicating with the second channel (22) and being used for injecting the liquid into the second channel (22), and the second discharge port (14) communicating with the second channel (22) and being used for discharging the liquid in the second channel (22).
4. The manipulation method according to any one of claims 1 to 3, wherein the excitation end (32) comprises a tapered optical fiber and a graphene oxide layer coated on the tapered optical fiber.
5. The manipulation method of claim 4, wherein the first liquid is an aqueous solution comprising particles of multiple sizes and the second liquid is a silicone oil.
6. The steering method according to claim 5, further comprising:
stopping the input optical signal after the droplet of encapsulated particles is formed;
a surfactant is added to the second liquid to collect droplets of the encapsulated particles.
7. The steering method according to claim 6, further comprising:
after the droplet of encapsulated particles is formed, the optical signal is input continuously until the droplet of encapsulated particles is released from the optofluidic thermocapillary microfluidic vortex.
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