How to maintain Cellix's microfluidic Flow Sensor


Introduction

Flow Sensors for Microfluidic Pumps are designed to provide accurate and pulse-free flow rates for microfluidic applications. Flow sensors for Cellix's microfluidic pumps enable active feedback and PID control. They are ideal for microfluidic applications, where accurate and stable flow rate delivery is required resulting in superior performance. Our flow sensors are compatible with our ExiGo, UniGo and 4U microfluidic pumps.


How to handle the Flow Sensor?

Cellix's microfluidic flow sensors are highly sensitive measurement devices that should be properly handled and cleaned to ensure long term high performance. Improper cleaning (or no cleaning) may leave deposits on the internal flow channel wall that can cause measurement deviations. This should be avoided by cleaning the sensor after usage and especially before storing the sensor for longer periods.

This blog will guide you through the general cleaning protocol for Cellix’s microfluidic flow sensors and advise you on which cleaning agents to use depending on the liquid media samples you are working with.

We recommend this cleaning protocol after every use and before storing your flow sensor.

Below are some things to keep in mind for general handling of the Flow Sensor :

  • Do not allow the sensor to dry with media in the capillary tube without flushing clean first. Also try to avoid letting the filled sensor sit for extended periods (depending on your liquid).

  • Before storing the sensor, always drain the fluid, flush with cleaning agent, blow out, and dry the capillary. Sensor plugs should be installed for storage. The cleaning agent (detergent, solvent, etc.) should be chosen for its effectiveness in removing the liquid media, and compatibility with borosilicate glass.

  • In general we recommend finishing any cleaning with an acetone and/or IPA flush before letting the sensor dry out and closing it for storage. The advantage of using clean IPA is that it evaporates without residue (in contrast to acetone, for example).

  • Before storing the flow sensor, always drain the fluid:

  1. This is done easily by connecting an empty syringe and pushing air through the flow sensor. We recommend a 1mL syringe for 1.5, 7 and 80uL/min flow sensors; and a 5mL syringe for 1mL/min flow sensors.

  2. Once there are no liquid droplets emerging from the tubing, the tubing may be disconnected, and the plugs provided should be installed on the fluidic ports for storage.

Finally, Never try to clean the flow sensor by mechanical means and never put any rigid or sharp objects inside the flow sensor.


What is the cleaning procedure for the Flow Sensor?

Working with Multiple Liquids

Switching between multiple liquids can leave transient deposits in the form of liquid layers inside the glass capillary. This is especially common for insoluble liquids, but can happen even with miscible liquid combinations. For example, when IPA is followed by water in a sensor without drying in between, large offsets can be observed for hours after switching to water.

If possible, dedicate a separate sensor for each different liquid to be measured. If not possible, use caution when switching media and clean properly.


Working with Water

When working with water it is recommended to not let the sensor dry out. All salts and minerals in the water will deposit on the glass and are difficult to remove. Although salt solutions are particularly prone to problems, even clean water can still contain enough dissolved minerals to form a deposition layer. Flush with DI water on a regular basis to prevent build- up. If you still encounter problems, occasionally flush the sensor with slightly acidic cleaning agents.

When working with non-DI water, especially when organic materials (sugars, proteins etc.) are present, microorganisms often grow on the walls of the glass capillary and form an organic film that can be difficult to remove. Flush on a regular basis with solvents such as acetone, ethanol, methanol or IPA, or with cleaning detergents to remove organic films.


Working with Oils

When working with oil it is recommended to not let the sensor dry out. Edible oils can become rancid, dry out or simply change their composition over time and leave sticky films on the wall of the capillary. This will typically happen if the sensor is only drained after usage but not properly cleaned. Then the oil film on the capillary wall becomes a constant deposition and will be more difficult to clean than right after emptying the sensor. These films might not be dissolved by oil anymore and cause measurement deviations.

Flush with solvents such as acetone, methanol, ethanol, IPA, etc or cleaning detergents on a regular basis to remove oil films.


Working with Silicone Oils

When working with silicone oil it is recommended to not let the sensor dry out. Silicone oils can be cleaned out using acetone or special cleaners. Check with your silicone oil supplier for cleaning agents compatible with glass surfaces.


Working with Paints or Glues

When working with paints or glues it is critical to not let the sensor dry out. Often, depositions of paints and glues cannot be removed anymore after they have dried. Flush the sensor with cleaning agents recommended by your paint or glue manufacturer that are compatible with glass. Ensure that you have found a good cleaning procedure before performing the first tests, and always clean shortly after emptying the sensor.


Working with Alcohols or Solvents

Unlike most other fluids, alcohols and solvents are not critical and a short flush of acetone followed by IPA (or only IPA) is sufficient to clean the capillary walls.


Other Liquids or Applications

If uncertain about your application and how to clean the flow sensor, please contact Cellix for additional support.


Cleaning methods that are not recommended

  • In general, any cleaning by mechanical means should be avoided. Never enter the sensor’s flow path with sharp objects that could scratch the glass surface.

  • Furthermore, no abrasives or liquids containing solids that can grind the surface clean should be used. Anything that affects the glass wall will cause deviations in the measurement performance or permanently damage the sensor.

  • Strong acids and bases should also not be used to clean the sensor. Acids can sometimes be used in low concentration and at low temperatures. Before using the acid check how compatible it is with borosilicate 3.3 glass (Pyrex® or Duran®).

Click here to learn more about Cellix’s Microfluidic Flow Sensor.

If you have any more questions or if you’d like a quote, contact us now.

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