CN111637032A - Photothermal Micropump Based on Capillary Fiber - Google Patents

Abstract

The invention provides a photothermal micropump based on a capillary fiber. It is characterized in that the photothermal micropump is composed of a micro-processed annular core capillary fiber and a light source. The annular optical fiber core is thinned by heating and melting until the capillary hole of the optical fiber is sealed to form a solid light wave channel, thus becoming an optical interface connecting with an external light source. The outlet of the pump is also the inlet of the chip microfluidics. A microfluidic liquid inlet is prepared by using femtosecond drilling technology in the part near the fused end of the capillary fiber. The microfluidic channels within the fluidic chip are connected. The capillary fiber photothermal micropump that can be used in a microfluidic chip is simple to prepare, has good consistency, is convenient for chip connection, convenient and quick to connect with a light source, and is suitable for large-scale mass production.

Description

Photothermal Micropump Based on Capillary Fiber

(1) Technical field

The invention relates to a photothermal micropump based on a capillary fiber, which is convenient for connection with a microfluidic chip, and can also replace large-scale sampling equipment such as a micro-injection pump and a micro-fluidic peristaltic pump in the micro-scale operation of micro-fluid. The control chip provides a convenient method for peripheral control equipment for high-throughput analysis and detection in the fields of chemistry, biology, medicine, etc., and belongs to the technical field of optofluidics.

(2) Background technology

Microfluidics (Microfluidics or Lab-on-a-chip) refers to systems that process or manipulate tiny fluids using microchannels of tens or hundreds of microns. After decades of development, microfluidic technology has become an emerging interdisciplinary subject involving chemistry, fluid physics, optics, microelectronics, new materials, biology and biomedical engineering. Due to the small size of the sample in the microfluidic chip, the short detection optical path, the optical detector with high sensitivity, fast response time, and low power consumption, and new detection methods are very important for the practical development of microfluidic technology, and whether it is Biological testing, drug testing, chemical analysis, environmental monitoring, more and more systems require micro-leveling of liquids. In addition to the chip as the main technical integration unit in the microfluidic system, many other peripheral devices are also required, such as sampling equipment, fluid drive control equipment, temperature control and detection control units. The chip unit is connected to complete the functional requirements.

The existing microfluidic chips combined with optical fibers and their applications include: optical fiber microfluidic electrophoresis chips [Su Bo et al., Development of optical fiber microfluidic electrophoresis chips. Measurement and Control Technology, 2005, 24(11): 5-8], the chip realizes the fabrication of microfluidic channels and optical fiber channels with different depths on polydimethylsiloxane (PDMS), so that the optical fiber and the microfluidic The control channel can be easily aligned. Another is the embedded optical fiber microfluidic chip [Jin Yonglong et al., preparation of embedded optical fiber microfluidic device based on excimer laser processing technology. China Laser, 2008, 35(11): 1821-1824], the preparation method is to use a 248nm KrF excimer laser to perform micromachining on a polymethyl methacrylate (PMMA) substrate to build a chip structure, and embed the etched A single-mode fiber with a diameter of 35 μm is used to form an embedded fiber-type chip. Both of these are realized by traditional microfluidic chips combined with optical fibers. In addition, special optical fibers with air holes can also be used as part of the chip microchannels. For example, the hollow optical channels of hollow photonic crystal fibers can be directly used as microchannels. Flow Matter Channel [Jiang Chao, Precision fabrication of microfluidic fiber devices with femtosecond laser pulses and their applications. Laser Journal, 2009, 30(5): 6-8]. The working principle of this microfluidic measurement device is based on the direct interaction of the optical field transmitted in the optical fiber with the microfluidic matter, thereby changing the properties of the light wave in the optical fiber. There are also micro-processing of optical fibers through some processing technologies, and the functions of microfluidic chips are achieved. For example, microfluidic channels parallel to the core can also be fabricated in single-mode fibers by femtosecond laser-assisted processing, thus creating a new type of fiber-optic microfluidic device that can be applied to liquid refractive index sensing. , Femtosecond laser fabrication of fiber-optic microfluidic devices and liquid refractive index sensing. Harbin Institute of Technology, 2013; Sun Huihui, Femtosecond laser fabrication and temperature-salt sensing properties of Mach-Zed interference microcavities in optical fibers. Harbin Institute of Technology, 2015], this microfluidic device has the characteristics of high temperature resistance, and the liquid flows inside the microfluidic channel to avoid the contact between the measured liquid and the outside world, and has strong anti-interference ability. Patent CN106582903 proposes a microfluidic chip of photothermal waveguide. The photothermal waveguide is immersed in the bottom of the microfluidic chamber of the cuboid, and the length, width and height of the microfluidic chamber are fixed. The surface of the optical waveguide is coated with nanomaterials with thermal conductivity. There is a positive correlation between flow intensity and optical power.

In the above-mentioned microfluidic systems related to optical waveguides, the injection liquid often needs to be driven, controlled, or various operations are performed, and the photothermal effect characteristics in the optical fiber are not used. In the above microfluidic systems, the injection method still needs to be connected to a micropump, such as a peristaltic pump or a large volume peripheral device such as a microfluidic injector.

Micropump is an important part of microfluidic system, its main function is to transmit and distribute liquid flow, which can be divided into mechanical micropump and non-mechanical micropump. Mechanical micropumps rely on mechanical moving parts to transmit and control microfluidics, while non-mechanical micropumps rely on various physical actions or effects to convert certain non-mechanical energy into kinetic energy of microfluidics to realize the drive of microfluidics. Mechanical micro-pumps mainly include piezoelectric, electrostatic, electromagnetic, pneumatic and other driving methods. Such micro-pumps usually have complex manufacturing processes, high cost, high power consumption, poor long-term reliability, and difficult to integrate. Non-mechanical micropumps mainly include electroosmotic, surface tension, magnetic fluid and thermal bubble driving methods. Such micropumps have certain advantages in manufacturing process and reliability, and there will be no long-term working conditions of mechanical micropumps. However, such micropumps require complex driving circuits or devices. These additional components often increase the complexity of the system and reduce the portability of the system, thus limiting the application of microfluidic systems.

In order to further improve the integration and miniaturization of the microfluidic chip and overcome the above shortcomings and deficiencies in the advanced technology, the present invention provides a photothermal micropump based on a capillary fiber, which can be used for microfluidic control. The capillary fiber photothermal micropump of the chip is simple to prepare, has good consistency, is convenient for chip connection, avoids optical alignment and adjustment in the case of separation, and is suitable for large-scale mass production.

(3) Contents of the invention

The purpose of the present invention is to provide a photothermal micropump that can replace the large-scale sample injection equipment in the periphery of the microfluidic chip when operating a small amount of liquid at the micrometer scale.

The object of the present invention is achieved in this way:

A capillary fiber-based photothermal micropump. Its main feature is that the micropump is fabricated and processed by the annular core capillary fiber shown in FIG. 1 . One end of the capillary fiber is heated and shrunk, so that the capillary hole is collapsed and closed to form a solid light wave channel 2-1, thereby becoming an optical interface interconnected with an external energy light source, and the unprocessed other end is an open channel port 2- 2. This is both the outlet of the micropump and the inlet of the chip microfluidics. The side femtosecond punching technology is used on the outer surface of the optical fiber near the melting end, and a micro-porous channel inlet for micro-fluidic substances is fabricated, which is used as the inlet 2-3 of the micro-fluidic liquid, as shown in Figure 2.

In order to realize the function of the micropump in the microfluidic chip, the core collapsed into a solid light wave channel is connected to an external light source. When the capillary fiber is injected with light energy, the light propagates along the annular core, and when the air hole in the fiber is filled When the liquid is in liquid, the inner wall of the fiber core is in full contact with the liquid, and the light energy is converted into heat energy absorbed by the liquid and then converted into molecular kinetic energy to push the liquid forward. After the heated liquid is rapidly pushed into the microchannel of the microfluidic chip, the pressure in the micropump cavity is reduced and is lower than the external atmospheric pressure, and the liquid outside the photothermal micropump enters through the etched microfluidic material microporous channel. into the cavity of the micropump, so that only the liquid to be tested is added to the microfluidic chip, and no additional peripheral equipment is required.

The specific principles are as follows:

As we all know, light is a kind of electromagnetic wave. The light energy provided by the light source connected to the photothermal micropump is the electromagnetic wave, and it is radiated through the surface of the annular core. When the energy of the light source is stronger, the temperature of the core will be higher, and the radioactive energy will be higher. Therefore, the micropump transfers heat from a high temperature object (fiber core) to a low temperature object (microfluidic liquid) in the form of electromagnetic waves.

So how is the microfluidic liquid pushed into the microfluidic channel of the chip? It can be simply understood that two convective heat transfer phenomena occur simultaneously in the micropump, which increases the intramolecular energy in the microfluidic liquid and accelerates the movement, which promotes the microfluidic liquid in the micropump cavity to be pushed into the microfluidic channel of the chip. This phenomenon occurs. The first kind of convective heat transfer phenomenon is: the heat transfer mode of the fluid heated by the high temperature object (the inner wall surface of the annular core) to the low temperature object (the liquid in the center of the micropump) is convective heat transfer. If the fluid on the surface of the object is static , then the surface of the object and the fluid will also transfer heat through thermal conduction, that is to say, convective heat transfer is based on heat conduction and the flow of fluid (ie, convection). The second convective heat transfer phenomenon is: the heat transfer mode between the heated microfluidic liquid in the capillary fiber photothermal micropump cavity and the slightly lower temperature microfluidic liquid that has entered the chip microfluidic channel belongs to convective heat transfer. , and when the fluid is heated up, the density of the liquid changes, and convection occurs, resulting in the phenomenon of free convection.

那么局部热流密度

与温差的关系可用牛顿冷却定律来表示，If the light intensity injected into the photothermal micropump is constant and the energy is stable, it is assumed that the core temperature of the capillary fiber is T ₁ , the surface area is A, and a fluid with temperature T ₂ flows around, because there is a temperature difference between the surface of the fiber core and the fluid , so there is convective heat transfer. The fluid on the surface of the optical fiber core has the same temperature as the surface of the optical fiber core because it is in contact with the optical fiber core. In addition, the temperature of the fluid far enough away from the optical fiber core is T ₂ . Near the optical fiber core, there are changes in temperature and flow rate boundary layer. Assuming the area is dA(m ² ), the heat transfer is

Then the local heat flux density

The relationship with the temperature difference can be expressed by Newton's law of cooling,

q=h(T ₁ -T ₂ ) (1)

Among them, h(W/(m ² gK)) is the heat transfer coefficient. The heat transfer coefficient is different from the thermal conductivity. The thermal conductivity is the inherent physical property of the material, and the heat transfer coefficient changes with the flow state of the fluid.

In addition, when the microfluidic liquid is in contact with the annular core, a thin layer of thermal fluid with a sharp change in temperature from the fiber core temperature to the liquid temperature will be formed around the inner wall of the fiber core, which is called the temperature boundary layer. Similarly, when there is liquid flowing When , the fluid will adhere to the fiber core, and the surface of the fiber core will form a thin flow layer that changes sharply from zero velocity, called the velocity boundary layer (as shown in Figure 3). And the faster the fluid flow around the core, the thicker the boundary layer thickness.

It can be seen that the thermal conductivity equation can be derived from the Fourier law and the energy conservation equation, and the following thermal equilibrium exists within the Δt(s) time interval:

(The amount of change in thermodynamic energy)=[(heat introduced into the micro-element body)-(heat exported from the micro-element body)]+(heat generated in the micro-element body)×Δt(s) (2)

In the microfluidic liquid environment in the micropump capillary, the situation where the fluid is surrounded by a solid wall is a classic in-tube flow.

So the thermal conductivity equation of the cylindrical coordinate system is:

是微元体内单位时间、单位体积的发热量。In the formula, the thermal conductivity k is a constant, r is the radius of the cylinder, ρ(kg/m ³ ) is the density of the object, c(J/(kg·K)) is the specific heat, in addition,

It is the calorific value per unit time and unit volume in the microelement.

Considering that the photothermal micropump proposed in this invention is mainly used in the field of microfluidic chips, the micropump structure and the microfluidic channel of the chip are both in the order of microns, so the Reynolds number is low, and the liquid flow is laminar flow. A brief analysis is made when the photothermal micropump cavity is a circular tube structure.

First, the Reynolds number is low, the flow is laminar, and the temperature difference between the fiber core and the fluid is small. Correspondingly, the physical properties such as fluid viscosity, thermal conductivity and specific heat are fixed, and the influence of internal heat generation and buoyancy caused by viscous friction can also be ignored. The fully developed temperature field achieved in the downstream of the flow (at the open liquid outlet of the low-beam thermal micropump) is shown in Fig. 4(a), and there is a temperature field in the exact same distribution form, whose coordinate origin is taken as the micropump at the center of the cavity channel. For the intracavity flow, the difference between the inner surface temperature T1 of the fiber core and the average temperature T2 _of the _microfluid is selected as the reference temperature difference. The average fluid temperature represents the fluid temperature within the selected flow channel section and is defined by:

When the difference between the inner surface temperature of the fiber core and the average temperature of the microfluid is selected as the reference temperature difference, the temperature distribution of the fully developed temperature field can be described by the following expression

The dimensionless independent variable η is defined as η=r/R in the cylindrical coordinate system.

Correspondingly, the fully developed temperature field can be interpreted as the temperature field in which the heat transfer coefficient does not change with the axis coordinate x, which can be obtained from equation (5),

First consider the condition of equal wall heat flux. At this time, for the fully developed temperature field, since q and h are constant, from Newton's law of cooling q=h(T ₁ -T ₂ ), it can be known that the temperature difference (T ₁ -T ₂ ) is also constant, so, By fully developing the temperature field as Eq. (6), we can get

That is, as shown in Fig. 4(b), for a fully developed temperature field under the condition of constant wall heat flux density, as the fluid flows downstream, the temperature of the fluid at the runner cross-section rises with a constant temperature difference.

The photothermal micropump device can be further combined with the traditional microfluidic chip, and the micropore channel of the microfluidic substance corresponds to the position of the injection port outside the chip. The flowing liquid will be sucked into the micropump cavity through the microporous inlet channel without external force, and will play a role in boosting the liquid in the chip. The liquid discharge port at the other end of the micropump can be connected with the microfluidic chip used, which can completely replace the sampling equipment such as the microfluidic syringe pump in the microfluidic chip system.

In order to further expand the structure of the fluid inlet of the capillary fiber photothermal micropump, the micropump can be expanded into a micropump device with a plurality of microfluidic substance microporous inlet channel structures, which is characterized by adding microfluidics on the side of the hollow annular core capillary fiber. The number m of the material micropore inlet channels (m>1, m is an integer), each micropore can be used as an inlet of the microfluid, so that the purpose of increasing the liquid flow per unit time can be achieved.

Further, in the photothermal micropump based on the capillary fiber, the photothermal micropump can adjust the propulsion speed and propulsion amount of the microfluidic liquid into the microchannel of the chip by changing the magnitude of the injected light energy. When the number of micropores is constant, the greater the light energy, the greater the speed of the micropump to the liquid, and vice versa.

Further, in the photothermal micropump based on the capillary fiber, the microfluidic material microporous inlet channel contained in the micropump can be of various sizes and shapes, according to the length of the micropump and the sample injection requirements. The required size and shape of micropores are prepared by the second punching technology, such as circular micropores, square micropores, oval micropores, rectangular micropores, etc., as shown in Figure 5.

In practical applications, the appropriate micropump should be selected according to the specific system requirements. Micropumps are widely used in microsensors, microbiology, chemical analysis, and various occasions involving microfluidic transport. At present, the micropump has been greatly developed, the structure forms and principles are rich and diverse, and the stability has also been greatly improved. In order to further improve the integration and miniaturization of the microfluidic chip and overcome the above shortcomings and deficiencies in the advanced technology, the present invention provides a photothermal micropump based on a capillary fiber, which can be used for microfluidic control. The capillary fiber photothermal micropump of the chip is simple to prepare, has good consistency, is convenient for chip connection, avoids optical alignment and adjustment in the case of separation, and is suitable for large-scale mass production. It can also replace large-scale sampling equipment such as microfluidic syringe pumps in micro-scale operation of trace liquids, providing an excellent research and application platform for high-throughput chemical, biological, and medical analysis and detection, and for microfluidic chips in chemistry, biology, and medicine. Peripheral control equipment for high-throughput analysis and detection in medicine and other fields provides a convenient method.

(4) Description of drawings

Figure 1(a) is a cross-sectional structural diagram of a capillary optical fiber; (b) is a real cross-sectional view of a capillary optical fiber, including an air hole 1-1, a core 1-2 and a cladding 1-3.

Figure 2 is a schematic diagram of a capillary fiber photothermal micropump.

Figure 3. Schematic diagram of the boundary layer in the case of convective heat transfer.

Fig. 4 is (a) fully developed temperature field and (b) temperature change of circular tube-type micropump cavity under the condition of constant wall heat flux density.

Fig. 5 is a schematic diagram of a capillary fiber-optic photothermal micropump with a plurality of microfluidic substance microporous inlet channel structures, including a light wave channel 2-1, an open channel port 2-2 and a microfluidic liquid inlet port 2-3.

FIG. 6 is a schematic structural diagram of a microfluidic chip with a capillary fiber photothermal micropump structure embedded therein.

(5) Specific implementation methods

The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

Figure 1 shows a cross-sectional view of a capillary fiber, which consists of a thin layer, a ring-shaped core with a slightly higher refractive index than the cladding material, and an air hole structure that allows access to microfluidics.

Figure 2 shows that one end of the capillary fiber is heated and shrunk, so that the capillary hole is collapsed and closed to form a solid light wave channel 2-1, thereby becoming an optical interface interconnected with an external energy light source, and the unprocessed other end is open Type channel port 2-2, which is both the outlet of the micropump and the inlet of the chip microfluidics. At the outer surface of the optical fiber near the melting end, femtosecond drilling technology is used on the side to manufacture a microporous channel inlet for microfluidic substances, which is used as an inlet for microfluidic liquids 2-3.

Without loss of generality, we describe the specific implementation steps and implementation methods of the present invention in detail with the specific example of the capillary fiber-optic photothermal micropump with one circular microfluidic micropore inlet shown in FIG. 6 .

(1) First, take a section of the capillary optical fiber shown in FIG. 1, remove the coating layer for use.

(2) Then, one end is melted and collapsed by heating, so that one end is completely closed. At this time, the closed inner wall waveguide layer of the annular core fiber will form a circular solid optical waveguide 6-1.

(3) Next, use femtosecond laser etching technology to etch a circular micro-hole on the surface of the vertical optical fiber near the closed end of the optical fiber, which is used as the inlet 6-3 for the microfluidic liquid to be injected, and the open end of the optical fiber is used as the inlet 6-3. The discharge port 6-2 is connected with the microfluidic chip.

(4) The final collapsed solid optical waveguide is connected to the light source, and the photodynamic force is used as the liquid driving force to complete the function realization of the microfluidic chip.

(5) A liquid to be tested is added to the liquid storage tank 6-4 outside the chip, and the liquid is pushed into the chip channel through the micropore discharge port, replacing the traditional large peripheral syringe pump to realize the function of the sampling device, and the waste liquid It is drained from the drain hole 6-5 outside the chip.

Since different liquids have different absorption rates for light sources with different wavelengths, the flow rate and flow rate of microfluidic substances can be adjusted according to the function of the chip according to the wavelength of the connected light source and the absorption rate of the liquid to be measured.

In this embodiment, the number m of microfluidic material micropore channels of the capillary fiber-based photothermal micropump is one, and the shape of the micropore is circular. Similarly, the number of micropores can also be expanded to multiple (m> 1, m is an integer), the shape can also be extended to square, oval, rectangle, etc. These changes in quantity, shape, and size will affect the test index of the micropump, which requires specific parameter design according to the functional requirements of the chip in specific practical applications.

Claims (5)

1. A photo-thermal micro pump based on capillary optical fiber. The micro-pump is mainly characterized in that the micro-pump is manufactured and processed by a ring-core capillary optical fiber. One end of the capillary optical fiber is heated and fused to enable the capillary hole to be collapsed and closed to form a solid light wave channel 2-1, so that an optical interface which is connected with an external energy light source is formed, and the other unprocessed end of the capillary optical fiber is an open channel port 2-2 which is a liquid discharge port of the micro pump and an inlet of chip microfluid. And a micro-flow substance micro-pore channel inlet is processed and manufactured at the outer surface of the optical fiber near the fusion end by adopting a side femtosecond punching technology and is used as an inlet 2-3 of micro-flow liquid.

2. The capillary-fiber based photothermal micropump of claim 1. The photo-thermal micropump can be a micropump device with a structure of a plurality of micro-flow substance micro-pore inlet channels, and is characterized in that the number m (m is greater than 1, m is an integer) of the micro-flow substance micro-pore channels on the surface of a capillary optical fiber, and a plurality of micro-pores can be used as inlet ports of micro-flow liquid.

3. The capillary-fiber based photothermal micropump of claim 1. The photo-thermal micropump can adjust the propelling speed and propelling amount of the microfluidic liquid entering the chip microchannel by changing 2-1 of the injected light energy.

4. The capillary-fiber based photothermal micropump of claim 2. The micro-fluid substance micro-pore inlet channel of the photo-thermal micro-pump can be in various sizes and shapes, and the required size and shape of micro-pores, such as round micro-pores, square micro-pores, oval micro-pores, rectangular micro-pores and the like, can be prepared by the femtosecond punching technology according to the length of the micro-pump and the sample introduction requirement.

5. A photo-thermal micro pump based on capillary optical fiber. The photothermal micropump device is mainly characterized in that the photothermal micropump device can be further combined with a traditional microfluidic chip, can be integrated into the chip and embedded into a microgroove in the chip for use, and completely replaces peripheral sample inlet equipment such as a microfluidic injection pump and the like in a microfluidic chip system.

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