CN110125369B

CN110125369B - Method for preparing low-melting-point alloy electrode in micro-fluidic chip

Info

Publication number: CN110125369B
Application number: CN201910404684.4A
Authority: CN
Inventors: 常洪龙; 冯慧成; 杨东; 寻文鹏
Original assignee: Northwestern Polytechnical University
Current assignee: Northwestern Polytechnical University
Priority date: 2019-05-16
Filing date: 2019-05-16
Publication date: 2020-12-11
Anticipated expiration: 2039-05-16
Also published as: CN110125369A

Abstract

The invention discloses a method for preparing a low-melting-point alloy electrode in a microfluidic chip, which is used for solving the technical problem that the existing electrode preparation method is complex. Firstly, preparing a microfluidic chip comprising an electrode channel and a fluid channel; then, injecting the melted liquid low-melting-point alloy into an electrode channel under constant temperature and constant pressure, wherein the Laplace pressure is sharply increased under the action of surface tension because the tail end of the electrode channel is conical, so that the liquid alloy is prevented from continuously moving and is automatically stopped at the tail end of the electrode channel; finally, locally and rapidly cooling under constant pressure to ensure that the liquid alloy in the electrode channel is firstly solidified; the prepared low-melting-point alloy electrode is in contact with liquid in the fluid channel when in use, is a contact electrode, has excellent conductivity and is beneficial to generating a strong electric field in the microchannel. The electrode channel and the fluid channel are formed in one step, so that the alignment of the electrode and the channel is ensured, and the electrode preparation process is simplified.

Description

Method for preparing low-melting-point alloy electrode in micro-fluidic chip

Technical Field

The invention relates to an electrode preparation method, in particular to a method for preparing a low-melting-point alloy electrode in a microfluidic chip.

Background

The document "preparation of microfluidic chip 3D electrodes based on Ag-PDMS composite conductive materials, instrumentation techniques and sensors, 2017, 6, p 18-25" discloses a method for processing microfluidic chip 3D electrodes by using a composite material made of silver powder (Ag) and Polymethylsiloxane (PDMS). The method mixes silver powder and PDMS by combining an ultrasonic method and a mechanical mixing method to prepare the Ag-PDMS composite conductive material, and utilizes a soft lithography method to prepare the 3D electrode. The electrode prepared by the method disclosed by the document is formed by mixing an insulating material PDMS and silver powder, and relates to a complex manufacturing process, accurate alignment is required during bonding, and particularly, the resistivity (about 0.1 omega. m) of the Ag-PDMS composite material is far higher than that of a common metal electrode, so that a strong electric field cannot be generated in a microfluidic chip.

Disclosure of Invention

In order to overcome the defect that the existing electrode preparation method is complex, the invention provides a method for preparing a low-melting-point alloy electrode in a microfluidic chip. The method comprises the steps of firstly preparing a microfluidic chip comprising an electrode channel and a fluid channel; then, injecting the melted liquid low-melting-point alloy into an electrode channel under constant temperature and constant pressure, wherein the Laplace pressure is sharply increased under the action of surface tension because the tail end of the electrode channel is conical, so that the liquid alloy is prevented from continuously moving and is automatically stopped at the tail end of the electrode channel; finally, locally and rapidly cooling under constant pressure to ensure that the liquid alloy in the electrode channel is firstly solidified; the prepared low-melting-point alloy electrode is in contact with liquid in the fluid channel when in use, is a contact electrode, has excellent conductivity and is beneficial to generating a strong electric field in the microchannel. The electrode channel and the fluid channel are formed in one step, so that the alignment of the electrode and the channel is ensured, and the electrode preparation process is simplified.

The technical scheme adopted by the invention for solving the technical problems is as follows: a method for preparing a low-melting-point alloy electrode in a microfluidic chip is characterized by comprising the following steps:

step one, preparing a microfluidic chip comprising an electrode channel 1 and a fluid channel 2. The electrode channel 1 and the fluid channel 2 are integrally formed, so that the self-alignment of the alloy electrode is ensured; the end of the electrode channel 1 is tapered and communicated with the fluid channel 2; the included angle between the conical surface at the tail end of the electrode channel 1 and the wall surface of the fluid channel 2 is not more than 60 degrees, so that the Laplace pressure of the liquid alloy at the conical tail end is increased sharply to realize the self-stop of the liquid metal.

And step two, injecting the molten liquid low-melting-point alloy into the electrode channel 1 at constant temperature and constant pressure until the Laplace pressure is greater than the driving pressure and the self-stopping is generated. The contact angle of the low-melting-point alloy and the material of the microfluidic chip is more than 90 degrees so as to generate a hydrophobic effect. The driving pressure is kept constant and is larger than the laplace pressure of the liquid metal in the electrode channel 1 and smaller than the laplace pressure at the tapered end of the electrode channel 1, i.e. the liquid metal is ensured to flow in the electrode channel 1 until the end of the electrode channel is reached.

And step three, maintaining a constant pressure state, leading the liquid alloy in the electrode channel 1 to solidify firstly through local rapid cooling, and then solidifying the liquid metal in the external pipeline to ensure that the alloy electrode is filled in the whole electrode channel 1, and the prepared electrode is contacted with the solution in the fluid channel 2 in the using process.

The low-melting-point alloy is an alloy with a melting point not higher than the stable temperature of the material of the microfluidic chip.

The invention has the beneficial effects that: the method comprises the steps of firstly preparing a microfluidic chip comprising an electrode channel and a fluid channel; then, injecting the melted liquid low-melting-point alloy into an electrode channel under constant temperature and constant pressure, wherein the Laplace pressure is sharply increased under the action of surface tension because the tail end of the electrode channel is conical, so that the liquid alloy is prevented from continuously moving and is automatically stopped at the tail end of the electrode channel; finally, locally and rapidly cooling under constant pressure to ensure that the liquid alloy in the electrode channel is firstly solidified; the prepared low-melting-point alloy electrode is in contact with liquid in the fluid channel when in use, is a contact electrode, has excellent conductivity and is beneficial to generating a strong electric field in the microchannel. The electrode channel and the fluid channel are formed in one step, so that the alignment of the electrode and the channel is ensured, and the electrode preparation process is simplified.

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

Drawings

Fig. 1 is a schematic view and a partially enlarged view of a low melting point alloy electrode manufactured by the method for manufacturing a low melting point alloy electrode in a microfluidic chip according to the present invention.

FIG. 2 is a schematic diagram of the principle of preparing the low melting point alloy electrode by the method of the present invention.

In the figure, 1-electrode channel, 1-1-first electrode channel, 1-2-second electrode channel, 2-fluid channel, P₀Driving pressure, Δ P₁Laplace pressure, Δ P, of the molten liquid low-melting alloy in the electrode channel₂Laplace pressure of the molten liquid low-melting alloy at the tapered end of the electrode channel.

Detailed Description

The following examples refer to fig. 1-2.

The microfluidic chip for preparing the low-melting-point alloy electrode comprises an electrode channel 1 and a fluid channel 2, and is manufactured by using a Polymethylsiloxane (PDMS) soft lithography process, wherein a preferable specific preparation method comprises the following steps:

step one, photoetching. A silicon male mold is fabricated on a single-polished silicon wafer using photolithography.

And step two, casting PDMS. Mixing a monomer and a curing agent according to a ratio of 10: 1, removing bubbles in the mixed solution by using a vacuum box for vacuumizing, then casting the PDMS on a silicon male mold, and placing the silicon male mold in a constant temperature oven at 60 ℃ for baking for 5 hours to solidify the PDMS.

And step three, demolding and punching. The cured PDMS was demolded and punched at the inlet and outlet of the electrode channel 1 and the fluid channel 2 as tubing interfaces using a 0.7mm outer diameter punch.

And step three, bonding. And (3) treating PDMS by using a corona discharge instrument, bonding the PDMS with a glass slide, and then baking the PDMS in a 100 ℃ thermostat for 1 hour to obtain the complete microfluidic chip.

The microfluidic chip in this embodiment is prepared by a conventional PDMS soft lithography process, and the electrode channel 1 and the fluid channel 2 are integrally formed. Wherein the width of the fluid channel 2 is 30 μm, the width of the opening at the tail ends of the electrode channels 1-1 and 1-2 is 30 μm, and the included angle between the conical surface and the wall surface of the fluid channel 2 is 40 degrees. In order to ensure smooth flow of the liquid metal in the electrode channel 1, the width of the electrode channel 1 was 200 μm and the depth of all the channels was 30 μm. The preparation of the microfluidic chip is not limited to PDMS, and the microfluidic chip can be prepared by hot pressing PMMA or etching silicon or glass. The materials and methods of the microfluidic chip are not limited, but the microfluidic chip has two basic structural features: firstly, the electrode channel and the fluid channel are communicated with each other, namely, the contact between the electrode and the fluid is ensured; secondly, the front end of the electrode channel is tapered to play a role in hindering the liquid alloy and ensure the self-stop of the liquid alloy.

In this embodiment, the method for preparing the low melting point alloy electrode in the microfluidic chip is to inject the melted liquid tin-bismuth alloy into the electrode channel at a constant temperature and a constant pressure and solidify and mold the tin-bismuth alloy, and a preferred specific preparation method is as follows:

step one, injecting liquid alloy. The tin-bismuth alloy is melted to be in a liquid state by adopting a hot air blower and the state is kept, then a constant-voltage source is sequentially connected with a tin-bismuth alloy conveying pipeline and an electrode channel 1 of a microfluidic chip, the pressure of the constant-voltage source is set to be 30kPa, the constant-voltage source is kept for 5s, the liquid alloy rapidly flows in the electrode channel 1, fills the whole channel and automatically stops when reaching the tail end of the electrode channel 1 due to the fact that the Laplace pressure is sharply increased.

And step two, solidifying and forming the liquid alloy. And keeping the constant pressure state, and closing the air heater after the tin bismuth alloy is injected. Directly covering the ice block on the microfluidic chip, standing for 3min to rapidly cool and solidify the liquid tin-bismuth alloy in the electrode channel in the microfluidic chip, and then cooling and solidifying the tin-bismuth alloy in the conveying pipeline. The mode of local preferential cooling solidification avoids the solidification shrinkage phenomenon of the tin-bismuth alloy from generating holes in the electrode.

The Sn-Bi alloy used in this example had a melting point of 47 ℃ and a coefficient of thermal expansion of 25 ppm/DEG C. The low melting point alloy electrode material is not limited to tin-bismuth alloys, but should have two basic characteristics: firstly, the melting point of the low-melting-point alloy is lower than the stable temperature of the material of the microfluidic chip; and secondly, the contact angle between the low-melting-point alloy and the material of the microfluidic chip is larger than 90 degrees, so that a hydrophobic effect is generated.

Claims

1. A method for preparing a low-melting-point alloy electrode in a microfluidic chip is characterized by comprising the following steps of:

preparing a micro-fluidic chip comprising an electrode channel (1) and a fluid channel (2); the electrode channel (1) and the fluid channel (2) are integrally formed, so that the self-alignment of the alloy electrode is ensured; the tail end of the electrode channel (1) is tapered and is communicated with the fluid channel (2); the included angle between the conical surface at the tail end of the electrode channel (1) and the wall surface of the fluid channel (2) is not more than 60 degrees, so that the Laplace pressure of the liquid alloy at the conical tail end is rapidly increased to realize the self-stop of the liquid metal;

step two, injecting the molten liquid low-melting-point alloy into the electrode channel (1) at constant temperature and constant pressure until the Laplace pressure is greater than the driving pressure and the self-stop is generated; the contact angle between the low-melting-point alloy and the material of the microfluidic chip is more than 90 degrees so as to generate a hydrophobic effect; the driving pressure is kept constant, and the driving pressure is larger than the Laplace pressure of the liquid metal in the electrode channel (1) and smaller than the Laplace pressure at the conical end of the electrode channel (1), namely, the liquid metal is ensured to flow in the electrode channel (1) until the end of the electrode channel is reached;

and step three, maintaining a constant pressure state, leading the liquid alloy in the electrode channel (1) to solidify firstly through local rapid cooling, and then solidifying the liquid metal in the external pipeline to ensure that the alloy electrode is filled in the whole electrode channel (1), and the prepared electrode is contacted with the solution in the fluid channel (2) in the using process.

2. The method for preparing the low-melting-point alloy electrode in the microfluidic chip according to claim 1, wherein the method comprises the following steps: the low-melting-point alloy is an alloy with a melting point not higher than the stable temperature of the material of the microfluidic chip.