HOW TO STOP THE FLOW (ZERO FLOW) INSIDE A MICROFLUIDIC DEVICE WITH AN ELVEFLOW® MUX

SET-UP TIME : 20-25 MIN / DIFFICULTY : *****

Abstract

This application note describes how to generate a controlled flow inside a microfluidic chip and stop it completely (zero flow) by using an Elveflow® MUX and an Elveflow® pressure control instrument (OB1).

 

In order to provide a visual example of how to perform a zero flow, we are using fluorescent microspheres (sample) in poly-ethylene glycol (buffer medium).

First of all, we will fill the microfluidic system with the buffer medium. Once the full system is completely filled and the air bubbles have been removed, we will insert into the system a solution of the sample with the buffer medium with a syringe placed as a junction-T.

Please note that in order to ensure a good zero flow performance, the sample solution has to be miscible and of the same density as the buffer medium that fills the microfluidic system.

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Setup Diagram

This picture shows the microfluidic setup that will be used for this application note.

Microfluidic zero flow full setup

As often as possible avoid using soft tubing (like Tygon) which involves compliance and then increases the response time of the system.
If you’re not familiar with microfluidic tubings, you may read our dedicated tutorials.

The following diagram illustrates the complete chain of elements involved in this application note. You will need to assemble all these parts to set up your experiment:

Microfluidic zero flow diagramWith this set-up, it is possible to generate a positive flow, a negative flow and a zero flow inside the microfluidic chip:

Configurations-microfluidic-zero-flow

When injecting the sample into the microfluidic system a diffusion area is generated between the sample and the buffer medium. This area involves 5%-30% of the sample volume after 4 hours,  so it only represents a little sample loss:

Microfludic zero flow diffusion

Protocols

Using the Elveflow® smart interface to perform a zero flow:

Be sure that all the cables and tubing are well connected to your Elveflow devices (USB cable, 24V DC, etc).

Perform leakage tests and remove any air bubbles before starting your experiment to ensure a good flow regulation.
Knowing what fitting is best suited for your needs is a first step towards success. If you’re not familiar with microfluidic fittings, you may read our specific tutorials.

In order to monitor the pressure required to perform a zero flow, it is necessary to follow the next steps:

A) First of all it will be necessary to fill all the tubes with buffer medium and remove the air bubbles:

  • Step 1 – Open the Elveflow smart interface on the computer and select the OB1 (OB1Mix01 in the example case).
  • Step 2 – Back on the main window, set a pressure rate value in mbar (300 mbar in the example case) on the pertinent channel (channel 4 in the example case).
  • Step 3 -Now select the MUX (MUXP in the example case) and press the “on-off sequential” button to enable it.
    • On the first sequence (1/1), open the A1 and B2 valves by clicking on the corresponding circle buttons and set a time of 0,1 seconds. (This sequence will correspond to a positive flow inside the microfluidic device)
    • Press the “+” button on the right to add a new sequence (2/2). Open the A1 and A2 valves and set a time of 0,1 seconds. (This sequence will correspond to a zero flow)
  • Step 4 – Press the “Apply” button (you will hear the typical “clack clack” sound when the valves open and close). Select back the OB1 and press the “Apply” button to start the flow.

B) Once the filling is done and the bubbles are removed, it will be necessary to follow the next steps:

  • Step 1 – Press the “Stop” button to stop the flow. Then select again the MUX, press the “Stop” button and close all the valves.
  • Step 2 – To inject the sample, open the B1 and B2 valves and press “Apply” (this will allow the sample to enter through the tubing). Open the cap on the T-junction tool and inject the sample. Place the cap back when finish.
  • Step 3 - Open the A1 and B2 valves to move the sample from the point injected until the microfluidic device.
  • Step 4 – Select the OB1 and start the flow. Once the sample is placed inside the microfluidic device press the “Stop” button to stop the flow.
  • Step 5 – Select the MUX and press the sequential button “on”. The last sequential configuration remembered will appear.
    • On the first sequence (A1 and B2 valves open) increase the time to set a positive flow frequency.
    • Now increase the time of the second sequence (B1 and B2 valves open) to set a Zero flow frequency.
    • If needed, add a new sequence to set a negative flow frequency.
  • Step 6 – Press the “Apply” button. In the unlikely event that a little residual flow is observed, please check that the microfluidic system has no bubbles and no leakages.

Congratulations! You completely stopped the flow by using an Elveflow® OB1 and an Elveflow® MUX!

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