CN111637032A

CN111637032A - Photo-thermal micropump based on capillary optical fiber

Info

Publication number: CN111637032A
Application number: CN202010276476.3A
Authority: CN
Inventors: 苑婷婷; 张晓彤; 苑立波
Original assignee: Guilin University of Electronic Technology
Current assignee: Guilin University of Electronic Technology
Priority date: 2020-04-10
Filing date: 2020-04-10
Publication date: 2020-09-08

Abstract

The invention provides a photo-thermal micro pump based on a capillary optical fiber. The photo-thermal micropump is characterized by consisting of a section of micro-processed annular core capillary optical fiber and a light source. The annular optical fiber core is heated, fused and thinned until capillary holes of the optical fiber are sealed to form a solid optical wave channel, so that the optical fiber core becomes an optical interface which is connected with an external light source, and the unprocessed other end is an open channel port which is an outlet of a micro pump and an inlet of chip microfluid. The near-fused part of the capillary optical fiber is processed by femtosecond punching to prepare a microfluidic liquid inlet corresponding to the position of the sample inlet outside the chip, and the liquid outlet at the other end is connected with the microfluidic channel inside the microfluidic chip. The capillary optical fiber photo-thermal micropump capable of being used for the microfluidic chip is simple to prepare, good in consistency, convenient for chip connection, convenient and fast to connect with a light source and suitable for large-scale mass production.

Description

Photo-thermal micropump based on capillary optical fiber

(I) technical field

The invention relates to a photo-thermal micro pump based on capillary optical fibers, which is convenient to connect with a micro-fluidic chip, can replace a micro injection pump, a micro-fluidic peristaltic pump and other large-size sample feeding equipment in micro-scale operation micro liquid, provides a convenient method for the micro-fluidic chip to be used as peripheral control equipment for high-throughput analysis and detection in the fields of chemistry, biology, medicine and the like, and belongs to the technical field of optical flow control.

(II) background of the invention

Microfluidic technology (Microfluidics or Lab-on-a-chip) refers to systems that process or manipulate tiny fluids using microchannels of tens or hundreds of microns. Microfluidic technology has developed over decades and has become an emerging interdiscipline of chemistry, fluid physics, optics, microelectronics, new materials, biology, and biomedical engineering. Because the sample in the micro-fluidic chip is small in volume, the detection optical path is short, the sensitivity is high, the response time is fast, the power consumption is low, the optical detector and the novel detection method are very important for the practical development of the micro-fluidic technology, and no matter biological detection, drug testing, chemical analysis and environmental monitoring are carried out, more and more systems needing micro-upgrading of liquid are needed. Besides the chip as a main technology integration unit, the microfluidic system also needs a lot of other peripheral devices, such as a sample introduction device, a fluid driving control device, a temperature control and detection control unit, and the like, and the devices are further connected with microfluidic chip units with different purposes to complete the functional requirements.

Microfluidic chips combined with optical fibers and applications exist today including: optical fiber type microfluidic electrophoresis chip [ Subo et al ], development of optical fiber type microfluidic electrophoresis chip. Measurement and control technology, 2005, 24 (11): 5-8, the chip realizes that microfluidic channels and optical fiber channels with different depths are manufactured on Polydimethylsiloxane (PDMS), so that the optical fibers can be conveniently aligned with the microfluidic channels. And the other is the preparation of the embedded optical fiber type micro-fluidic device based on the excimer laser processing technology, such as the embedded optical fiber type micro-fluidic chip (Jinyonglong). Chinese laser, 2008, 35 (11): 1821-1824, the preparation method comprises micromachining on a polymethyl methacrylate (PMMA) substrate with 248nm KrF excimer laser to construct a chip structure, and embedding etched single-mode optical fiber with diameter of 35 μm to form an embedded optical fiber type chip. The two types are realized by combining the traditional microfluidic chip with the optical fiber, in addition, a special optical fiber with an air hole can be used as a part of a chip micro-channel, for example, a hollow optical channel of a hollow photonic crystal optical fiber is directly used as a microfluidic substance channel (Jiangtao), and a microfluidic optical fiber device is precisely manufactured by femtosecond laser pulses and application thereof. Laser journal, 2009, 30 (5): 6-8. The working principle of the microfluidic measuring device is based on the fact that an optical field transmitted in an optical fiber directly interacts with microfluidic substances, and therefore the characteristics of light waves in the optical fiber are changed. The micro-processing of the optical fiber is also carried out by certain processing technologies, so as to achieve the function of the micro-fluidic chip. For example, a micro-flow channel parallel to the fiber core can be processed in a single-mode fiber by using a femtosecond laser assisted processing method, so that a novel fiber microfluidic device (Lixiang) capable of being applied to liquid refractive index sensing, femtosecond laser preparation of the fiber microfluidic device and liquid refractive index sensing are manufactured. Harbin university of industry, 2013; sun comet, the femtosecond laser preparation of the Mach Zehnder interference microcavity in the optical fiber and the temperature and salt sensing characteristics. Harbin industrial university, 2015), this kind of microfluid device has high temperature resistant characteristic, and liquid flows in miniflow channel, avoids being surveyed liquid and external contact, has very strong interference killing feature. Patent CN106582903 proposes a microfluidic chip of a photothermal waveguide, in which the photothermal waveguide is immersed in the bottom of a rectangular parallelepiped microfluidic chamber, the length, width and height of the microfluidic chamber are fixed, the surface of the optical waveguide is coated with a nano material with thermal conductivity, and the fluid flow strength and the optical power have a positive correlation.

In the microfluidic systems related to the optical waveguide, the sample injection liquid is often driven, controlled or operated in various ways, and is not used and has photothermal effect in the optical fiber. In the microfluidic system, the sample introduction mode still needs to be connected with a micropump, such as a peristaltic pump or a microfluidic injector and other large-volume peripheral equipment.

Micropumps are important components in microfluidic systems, and their main functions are to transport and distribute fluid, which can be divided into mechanical micropumps and non-mechanical micropumps. The mechanical micropump transfers and controls microfluid by means of mechanical moving parts, while the non-mechanical micropump converts certain non-mechanical energy into kinetic energy of the microfluid by means of various physical actions or effects, so as to drive the microfluid. Mechanical micropumps mainly adopt piezoelectric, electrostatic, electromagnetic and pneumatic driving modes, and the like, and generally have the disadvantages of complex manufacturing process, high cost, high power consumption, poor reliability in long-term operation and difficulty in integration. The non-mechanical micropump mainly has driving modes such as an electroosmosis mode, a surface tension mode, a magnetofluid mode and a thermal bubble mode, and the micropump has certain advantages in the aspects of manufacturing process and reliability, and the problems of membrane deformation, fatigue and the like under the long-term working condition of the mechanical micropump cannot occur.

In order to further improve the integration level and miniaturization of the microfluidic chip and overcome the defects and shortcomings in the advanced technology, the invention provides the photo-thermal micropump based on the capillary optical fiber.

Disclosure of the invention

The invention aims to provide a photo-thermal micropump which can replace large-size sample feeding equipment at the periphery of a microfluidic chip when micro-liquid is operated at a micron scale.

The purpose of the invention is realized as follows:

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 shown in figure 1. 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 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 an outlet of a micro pump and an inlet of chip microfluid. A micro-flow substance micro-pore channel inlet is processed and manufactured at the outer surface of the optical fiber near the melting end by adopting a side femtosecond punching technology and is used as an inlet 2-3 of micro-flow liquid, as shown in figure 2.

In order to realize the function of a micro pump in the micro-fluidic chip, a fiber core collapsed into a solid light wave channel is connected with an external light source, when the capillary optical fiber is injected with light energy, the light propagates along the annular core, when an air hole in the optical fiber is filled with liquid, the inner wall of the fiber core of the optical fiber is fully contacted with the liquid, the light energy is converted into heat energy absorbed by the liquid and further converted into molecular kinetic energy, and the liquid is pushed to advance. After the heated liquid is rapidly pushed into the micro-channel of the micro-fluidic chip, the pressure in the cavity of the micro-pump is reduced and is less than the external atmospheric pressure, and the liquid outside the photo-thermal micro-pump enters the cavity of the micro-pump through the etched micro-fluidic substance micro-pore channel, so that the liquid to be measured only needs to be added outside the micro-fluidic chip, and other peripheral equipment does not need to be additionally connected.

The specific principle is as follows:

as is known, light is one kind of electromagnetic waves, light energy provided by a light source connected with the photothermal micro pump is the electromagnetic waves, the electromagnetic waves are emitted through the surface of an annular core, and as the inner wall of a fiber core is in direct contact with micro-flow liquid, the electromagnetic waves are transmitted in the fiber core and reach the micro-flow liquid again to be converted into internal energy, and when the energy of the light source is stronger, the temperature of the fiber core is higher, and the radioactive energy is higher. The micropump transfers heat from a high temperature object (fiber core) to a low temperature object (microfluidic liquid) in the form of electromagnetic waves.

How is the microfluidic liquid pushed into the microfluidic channels of the chip? The micro-pump can be simply understood as the phenomenon that two convection heat transfer phenomena occur in the micro-pump at the same time, so that the molecular internal energy in the micro-fluid liquid is increased, the movement is accelerated, and the micro-fluid liquid in the cavity of the micro-pump is promoted to be pushed into a micro-fluid channel of the chip. The first phenomenon of convective heat transfer is: the heat transfer mode of the fluid after the high-temperature object (inner wall surface of the annular core) is heated to move to the low-temperature object (central liquid of the micro pump) is convection heat transfer, and if the fluid on the surface of the object is static, heat can be transferred between the surface of the object and the fluid through heat conduction, that is, the convection heat transfer is heat transfer based on heat conduction and fluid flow (i.e. convection). The second phenomenon of convective heat transfer is: the heat transfer mode between the micro-flow liquid heated in the capillary optical fiber photo-thermal micro-pump cavity and the micro-flow liquid with slightly low temperature entering the micro-flow channel of the chip belongs to convection heat transfer, and the liquid density is changed after the temperature of the fluid is raised, so that convection is generated, and the free convection phenomenon is generated.

If the light intensity injected into the photo-thermal micropump is constant and the energy is stable, the temperature of the fiber core of the capillary fiber is assumed to be T₁Surface area A, ambient temperature T₂Because of the temperature difference between the fiber core surface and the fluid, convective heat transfer occurs. The fluid at the surface of the optical fiber core is at the same temperature as the surface of the optical fiber core due to contact with the optical fiber core, and the temperature of the fluid at a sufficient distance from the optical fiber core is T₂A boundary layer in which temperature and flow velocity change exists near the optical fiber core. Assuming an area of dA (m)²) The heat transfer amount is

Then local heat flux density

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

q＝h(T₁-T₂) (1)

wherein h (W/(m)²gK)) is a heat transfer coefficient, which is different from a thermal conductivity, which is an inherent physical property of a substance, and which changes with the flow state of a fluid.

In addition, when the micro-flow liquid contacts the annular core, a thin layer of thermal fluid with a temperature changing sharply from the temperature of the optical fiber core to the temperature of the liquid is formed around the inner wall of the optical fiber core, which is called a temperature boundary layer, and similarly, when the liquid flows, the fluid is attached to the optical fiber core, and a thin layer of flow with a sharp change from zero speed is formed on the surface of the optical fiber core, which is called a speed boundary layer (as shown in fig. 3). And the faster the fluid flow velocity around the core, the thicker the boundary layer thickness.

It is known that the thermal conductivity equation can be derived from fourier law and energy conservation equation, and that the following thermal equilibrium exists during the Δ t(s) time interval:

(amount of change in thermodynamic energy) ([ (amount of heat introduced into the micelle) - (amount of heat derived from the micelle) ] + (amount of heat generated in the micelle) × Δ t(s) (2)

In the environment of microfluidic liquid in the capillary of the micropump, the case where the fluid is surrounded by solid walls is the classical flow in the tube.

The thermal conductance equation of the cylindrical coordinate system is:

wherein the thermal conductivity k is constant, r is the radius of the cylinder, ρ (kg/m)³) C (J/(kg. K)) is specific heat, and further,

is the calorific value per unit time and unit volume in the infinitesimal body.

Considering that the photothermal micropump provided by the invention is mainly applied to the field of microfluidic chips, the micropump structure and the chip microfluidic channel are both in micron order, so that the Reynolds number is low, the liquid flow is laminar flow, and the analysis is briefly performed below when the photothermal micropump cavity is in a circular tube structure.

First, when the reynolds number is low, the flow is laminar, and the temperature difference between the fiber core and the fluid is small. Accordingly, the physical property values such as the viscosity, the thermal conductivity and the specific heat of the fluid are fixed values, and the influence of the internal heat generation and the buoyancy of the fluid caused by viscous friction is also negligible. The fully developed temperature field achieved downstream of the flow (near the photo-thermal micropump open liquid outlet) is that of the exact same distribution with the origin of coordinates taken at the center of the micropump chamber channel as shown in fig. 4 (a). For intracavity flow, the temperature T of the inner surface of the optical fiber core is selected₁And the average temperature T of the microfluid₂The difference is used as a reference temperature difference. The average temperature of the fluid represents the temperature of the fluid within the selected flow channel cross-section, defined by the following equation:

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

Wherein the dimensionless argument η is defined as η R/R in the cylindrical coordinate system.

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

first, consider the conditions of equal wall surface heat flux density, and then for a fully developed temperature field, q and h are constant, so that the newton's law of cooling q is equal to h (T)₁-T₂) The temperature difference (T) can be known₁-T₂) And also, then, by fully developing the temperature field as in equation (6)

That is, as shown in fig. 4(b), with respect to a sufficiently developed temperature field under the equal wall surface heat flux density condition, the temperature of the fluid at the flow path cross section increases by a constant temperature difference as the fluid flows downstream.

The photo-thermal micropump device can be combined with a traditional micro-fluidic chip in a near step, the micro-fluidic substance micro-pore channel corresponds to the position of an external sample inlet of the chip, and when the photo-thermal micropump injects light energy, micro-fluidic liquid to be detected outside the chip can be sucked into a micropump cavity through the micro-pore inlet channel without external force, and the micro-fluidic liquid to be detected in the chip can be boosted to push the liquid in the chip. The other end of the micro pump has a liquid outlet connected to the micro flow control chip and may be used in replacing micro flow injection pump and other sample introducing equipment.

In order to further expand the structure of the fluid inlet of the capillary fiber photo-thermal micropump, the micropump can be expanded into a micropump device with a structure of a plurality of micro-fluidic substance micro-pore inlet channels, and the micropump is characterized in that the number m (m is more than 1, m is an integer) of the micro-fluidic substance micro-pore inlet channels is increased on the side surface of the hollow annular core capillary fiber, and each micro-pore can be used as an inlet port of micro-fluid, so that the aim of increasing the liquid flow in unit time can be fulfilled.

Further, the photo-thermal micro-pump based on the capillary optical fiber can adjust the propelling speed and the propelling amount of the micro-fluid liquid entering the micro-channel of the chip by changing the injected light energy. When the number of the micropores is fixed, the larger the light energy is, the larger the propelling speed of the micro pump to the liquid is, and vice versa.

Further, the micro-fluidic substance micro-pore inlet channel contained in the micro-pump can be in various sizes and shapes, and the required micro-pore size and shape, such as a round micro-pore, a square micro-pore, an oval micro-pore, a rectangular micro-pore and the like, can be prepared by the femtosecond punching technology according to the length of the micro-pump and the sample injection requirement, as shown in fig. 5.

In practical applications, the micro pump is selected according to specific system requirements. Micropumps find wide application in microsensors, microbiology, chemical analysis, and various applications involving microfluidic transport. At present, the micropump has been greatly developed, the structural form and principle are rich and various, and the stability is also greatly improved. In order to further improve the integration level and miniaturization of the microfluidic chip and overcome the defects and shortcomings in the advanced technology, the invention provides the photo-thermal micropump based on the capillary optical fiber. And large-size sample injection equipment such as a micro-flow injection pump and the like can be replaced in micro-scale operation micro-liquid, an excellent research and application platform is provided for high-throughput analysis and detection of chemistry, biology and medicine, and a convenient method is provided for peripheral control equipment for high-throughput analysis and detection of a micro-fluidic chip in the fields of chemistry, biology, medicine and the like.

(IV) description of the drawings

FIG. 1(a) is a cross-sectional view of a capillary optical fiber; (b) the capillary fiber section real object diagram comprises air holes 1-1, a fiber core 1-2 and a cladding 1-3.

FIG. 2 is a schematic view of a capillary fiber optic photothermal micro pump.

FIG. 3 is a schematic diagram of the boundary layer in the case of convective heat transfer.

Fig. 4 shows (a) a fully developed temperature field and (b) a change in temperature of the circular tube-shaped micro-pump chamber under the condition of the equal wall surface heat flux density.

FIG. 5 is a schematic diagram of a capillary fiber optic photothermal micropump having 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 view of a microfluidic chip structure with a capillary fiber photo-thermal micro-pump structure embedded therein.

(V) detailed description of the preferred embodiments

The invention is further illustrated with reference to the following figures and specific examples.

Fig. 1 shows a cross-section of a capillary fiber consisting of a thin layer, an annular core with a refractive index slightly higher than the cladding material, and an air hole structure that allows access to the microfluid.

Fig. 2 shows that one end of the capillary fiber is heated and fused to collapse and close the capillary hole to form a solid light wave channel 2-1, thereby becoming an optical interface for interconnecting with an external energy light source, and the other unprocessed end is an open channel port 2-2, which is the outlet of the micro pump and the inlet of the chip micro fluid. 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.

Without loss of generality, the specific implementation steps and implementation method of the present invention are described in detail by referring to the specific embodiment of the capillary fiber optic photothermal micro pump with 1 circular microfluidic micro-hole inlet shown in fig. 6.

(1) First, a section of the capillary optical fiber shown in FIG. 1 is taken, and the coating layer is removed for use.

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

(3) And then, etching 1 round micropore close to the closed end of the optical fiber and vertical to the surface of the optical fiber by adopting a femtosecond laser etching technology to serve as an inlet 6-3 of the micro-fluid liquid to be injected, and connecting the open part at the other end of the optical fiber to serve as an outlet 6-2 with the micro-fluid chip.

(4) And finally, the collapsed solid optical waveguide is connected with a light source, and the function of the microfluidic chip is realized by taking photodynamic as a liquid driving force.

(5) A liquid to be tested is added into a liquid storage pool 6-4 outside the chip, the liquid is pushed into a chip channel through a micropore discharge port to replace a traditional peripheral large injection pump to realize the function of a sample injection device, and waste liquid is discharged from a liquid discharge hole 6-5 outside the chip.

Because different liquids have different absorptions to different wavelength light sources, the flow rate and the flow of the microfluidic substance can be adjusted according to the functional requirements of the chip by combining the connected light source wavelength and the absorptance of the liquid to be measured.

In this embodiment, the number m of the micro-fluidic substance micro-pore channels of the photo-thermal micro-pump based on the capillary optical fiber is one, the shape of the micro-pore is circular, similarly, the number of the micro-pores can be expanded to be a plurality (m is greater than 1, m is an integer), and the shape can be expanded to be square, oval, rectangular and the like. These changes in number, shape, and size all affect the testing criteria of the micro pump, which requires specific parameter design according to the functional requirements of the chip in specific practical applications.

Claims

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.