The success story behind the use of ion-selective field-effect transistors (ISFET) as biochemical or biological sensors started 50 years ago. It led to the development of unbreakable pH sensors, a significant breakthrough for hygienic applications.
The first significant publication around the use of ISFET was written in 1970, and in the years that followed, developments took off in different directions, one of which was pH measurement. This development was driven by the prospect of being able to build an unbreakable, glass-free pH sensor for the food and life sciences sectors. This had been needed for some time because glass breakage in standard pH glass sensors often led to entire production batches being discarded.
Research & development
It wasn’t until the mid-1990s that the first commercially available ISFET suitable for process conditions was launched by an American manufacturer. In 1996, Endress+Hauser began a research project to develop an ISFET pH sensor in collaboration with the Fraunhofer Institute in Germany. As part of the research work, a new material emerged that greatly improved long-term stability and operating life. In 2002, the first pH ISFET sensors from Endress+Hauser were launched on the market and quickly established themselves in the key industrial sectors of food & beverage, chemical and life sciences.
However, this first ISFET generation still had one weak spot, making them difficult to use, at least in the food & beverage sector. The usual alkaline cleaning process used in this industry (cleaning in place or CIP) affected the sensor material, making them unusable after a few cleaning cycles. The common solution to the problem was to use a retractable assembly, which removes the sensor from the process during cleaning, subjects it to an acidic cleaning process in the assembly and then inserts the sensor back into the process. The cumbersome nature of this procedure was outweighed by the benefit of break resistance. Nonetheless, this provided the incentive for the development of an improved, more alkali-stable material.
New generation
The outcome of this development is the new ISFET generation, which Endress+Hauser launched on the market in 2019 exclusively with Memosens technology. Three new ISFET sensors, the CPS47D, 77D and 97D, completely replaced the previous generation.
Thanks to the new material used, these sensors are six times more stable during CIP. In addition, the risk of the sensors being contaminated has been reduced and the cleanability greatly improved. Customers who switch from the earlier sensors with Memosens technology to the new Memosens ISFETs do not need to make any adjustments to the transmitter because both the hardware and software work straightaway with the new product.
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