Optical liquid sensor for microfludics

MLS - Microfluidic Liquid Sensor

Elveflow provides a unique microfluidic liquid sensor. It can be plugged directly onto our OB1 flow controller, or it can be used as a standalone unit with the Sensor Reader and another instrument.

The sensor is able to register the presence of fluids, trigger a signal to another instrument and act accordingly – like stop, wait a certain amount of time, allow enough flow to clear the tubing, or reset the sensor.

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The optical detection is based on the measurement of the optical path and the variation of this path when the medium flowing is changing.

Advantages :

  • Reliable non invasive technique
  • Cost effective compared to camera check
  • Based on true/false logic
  • Large compatibility: wide range of tubing size
  • Software average functions
  • Use anywhere in your setup
  • Prevents damage in cells with bubble bursts
  • Setup automation (possibility to use if conditions)


  • Bubble detection
  • Liquid level sensing
  • Blood processing equipment
  • Patent connected medical devices
  • Perform bilateral recirculation based on air detection

One particular application worth to mention is using the sensor as a bubble detector. Bubbles are a big challenge to address in microfluidics, as they can induce flow modifications or interact with the experiment and cause damage. One can monitor the apparition of bubbles (change in the working fluid) at any given point of his setup and automate the experiment accordingly like switching valves to direct the bubble in another fluidic path for instance.


Set-up diagram

Example of an application: Bilateral Medium Recirculation

Based on the liquid detection principle, you can perform Medium recirculation without any recirculating valve, using the optical sensor, the OB1 Mk3 flow controller and our powerful scheduler. See more 



Optical sensor


Organ on a chip (Aline Inc.)


Elveflow® pressure & flow control instrument (OB1 MK3)
Sample reservoirs (a Small Reservoir, Medium Reservoir or a Large Microfluidic Reservoir), one for each medium sample
Microfluidic device (here an Organ on a chip microfluidic chip from Aline Inc…)
  • Apply pressure on line 1.
  • When tube 1 is empty bubbles will appear.
  • The liquid sensor 1 detects the bubbles and then pressure in line 1 is turned off. Simultaneously a pressure is applied in line 2.
  • Then, when the tube 2 is empty, bubbles will appear.
  • The liquid sensor 2 detects the bubbles and the pressure in line 2 is turned off. Simultaneously, a pressure is applied in line 1.
  • It can be continued as many times as you want.


The liquid sensor has many applications. This is one smart way to perform bidirectional recirculation without using valves.

A light beam is emitted by a LED at known power. This light beam goes through the capillary and the fluid passing through. It is then collected by an NPN silicon phototransistor. This phototransistor converts the light power into an electrical power.

When a fluid changes, the optical index and the light absorption coefficient change accordingly. It induces a change in the electrical power and allows to detect changes in the fluid.

microfluidic liquid sensor principle

USB flow sensor software module

Microfluidc flow control software HeartBeat-ESI-2015Thanks to an intuitive interface, the Elveflow® Smart Interface allows the use of Elveflow® instruments from the simplest commands for beginners to the most complex manipulations for experts… read more


Control your experiments through C, Python,  Matlab®, Labview® or the Elveflow® Smart Interface. The Elveflow® Smart Interface is a software application offering all the functionalities that microfluidicists need.

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