What is Fluorescein

Fluorescein is a synthetic organic compound that was the first fluorescent dye to be used for water tracing work. Fluorescein emits a bright green fluorescence and is used for hydraulic model studies and underground water studies. Fluorescein has been almost entirely replaced by rhodamine in recent years, however, there are still applications where the use of fluorescein is appropriate or preferred.

Aquaread Fluorescein Sensor

The sensor is fixed response fluorometer, meaning it excites the dye in the water at a fixed wavelength (470nm). It then measures the subsequent emitted fluorescence (>550nm).


Key Features

  • Dense sapphire lenses are used on our fluorescein sensor for their high clarity and scratch resistance.
  • Measurement range 0 – 500µg/l.
  • Resolution: 0.01µg/l.
  • Repeatability: +/- 5% of reading.
  • Simple to install on a wide range of Aquaprobes.
  • Easy 2-point calibration using fluorescein dye.
  • Site specific calibration with grab sample calibration option.

Our Fluorescein sensors can be installed into many of our probes, below are some examples. To see all of the probes can house the Fluorescein sensor please visit the Products section.



Single parameter Aquaprobe, for use with any of our sensors.



The Aquasonde-5000 has 4 spare ports. They can house any combination of ISE and Optical sensors.



Advanced portable multi-parameter Aquaprobe.

Simple installation

Installing the fluorescein sensor into an Aquaprobe is a very simple process. Simply unscrew the blanking plug from an appropriate aux socket, apply some silicon grease to the thread of the sensor (grease provided) and screw in the sensor. After installation full calibration is required.

Simple calibration

Part of our ethos at Aquaread is “ease of use”, so we have simplified and automated the calibration process as much as possible. The fluorescein sensor is calibrated at 2 points. A zero point and a 100µg/l fluorescein dye point. A stock solution of fluorescein dye is provided, and a small dilution of the stock is required to make the required concentration.

Once your solution is made the calibration involves placing the probe into the solution and selecting the correct calibration option from the menu. A calibration report is saved when complete.