Print Your Own Sensor: The Top–Trends for Single

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Spotlight on sensors

MEASUREMENT Up Close - A BRIEF SYNOPSIS

A number of techniques for detecting parameters such as pH, temperature and dissolved oxygen in single-use reactors have now become mainstream. Here is a list of the key methods and technologies:

pH: detection using a pH-sensitive coating in combination with optical sensing. Printed electrochemical sensors could well become available in the future.

Temperature: temperature probe in a thermowell

Oxygen: optical detection of dissolved oxygen similar to pH detection

Conductivity: usually a measurement parameter of an invasive multi-sensor. The sensor elements and tubing are placed into the reactor prior to filling and are normally radiation sterilized together with the rest of the items.

Glucose, glutamate and lactate: silkscreened electrode with immobilized enzyme; supplied sterilized.

Pressure: disposable sensors connected by tubing to the bag or reactor container; radiation sterilized.

Getting Sensors Fresh From the Printer

Non-invasive data acquisition, especially optical detection, is ideal for single-use process analytical technology but not all parameters can be captured using optical techniques. Researchers are now turning their attention to electrochemical methods. In the future, ion-sensitive sensors for pH detection (or for measuring analytes such as NH₄⁺, NO₃^- and other ions) could simply be silk screen printed onto a plastic substrate.

The Swiss research center CSEM (Centre Suisse d’Electronique et de Microtechnique) is working on the technology with some degree of success as the team is proud to report. The researchers in Zürich presented a new disposable sensor with sensitivity and selectivity comparable to that of commercial, ion-selective electrodes. They also identified further technologies which are waiting in the wings: According to CSEM, process analysis in the future could be based on enzymatic reactions in disposable reactor bags. Printed enzymes would react with substrates in the reaction medium and the resulting electron flow in the nanoampere range would be detected. This approach would be useful for applications such as detection of glucose, glutamate or lactate concentrations.

Therefore, electrochemical and enzymatic measurement methods utilizing printing on plastic flexible substrates were presented in Zürich, giving a hint of things to come. Such technologies, that would combine reactive measurement, low-cost materials and a simple manufacturing processes suitable for mass production are considered to be something like the holy grail of single-use reactor development. Furthermore, CSEM specialist Daniel Caminada sees the possibility that the complete sensor could be printed directly onto the film during bag production, eliminating the need for component insertion altogether. If that were to happen, the entire process would be "in the bag".

* * The author is an editor of PROCESS

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