Thomas Just Soerensen and Bo Wegge Laursen with their environmentally sensitive fluorescent dye, which emits light when influenced by the surrounding environment, and a solid gel matrix which allows fluids to flow freely around the dye. (Image courtesy of Jes Andersen/University of Copenhagen.)

Researchers at the University of Copenhagen have developed a sol-gel matrix that provides accurate, rapid measurements in liquid environments. The invention will advance research and development in the food, pharmaceutical and biotechnology sectors.

This innovative sol-gel matrix overcomes the challenges inherent in conducting real-time, non-invasive measurements in liquids which need to remain sterile. The sol-gel’s components are an environmentally sensitive fluorescent dye which emits light depending on its environment and a solid gel matrix allowing free fluid flow around the dye.

Measuring Liquids in Sterile Environments

In a sol-gel matrix, monomers are converted to a colloidal solution and polymerized to form gel. The process starts from small particles, eventually yielding a solid material.

With the sol-gel matrix, targeted measurements of a liquid’s characteristics, such as pH and oxygen content, can be made by shining light onto dyes in the matrix. The reflective light is also measured.

There are many options in choosing sensitive fluorescent dyes, but while luminescent dyes are effective for non-invasive measurements, there is little way to control contamination effects.

The sol-gel process. (Image courtesy of The Royal Society.)

"Having a dye that is circulating freely in a liquid is not of great help. In and of itself, it would be a contaminant, but it would also result in unreliable measurements, when the dye might be anywhere within the fluid. With the sol-gel, we have affixed the dye, while liquid is free to circulate around it," explained Thomas Just Sørensen, associate professor at the University of Copenhagen’s Nano Science Center.

The sensitive gel is produced as fingernail-sized flat dots, and the porous sol-gel allows the liquid and dye to be in constant contact. Within seconds of being immersed in a liquid, the sensors are ready for use and reliable measurements can be taken. Accurate measurements remain possible for weeks at a time.

Researchers developing new drinking yoghurt, improving upon a vaccine or devising a more effective washing detergent enzyme all share a similar dilemma: how to monitor oxygen content and pH in liquids while avoiding direct contact with them, since current monitoring technologies break the sterile barrier.

Bioengineering Applications for Fast Liquid Measurement

Sørensen and his colleagues have plans to found a company to supply pH and oxygen sensors. They expect the sol-gel based matrix monitors will benefit researchers working in the biotech, pharmaceutical, and food industries where sterile liquid integrity is most essential. Additional applications are possible in engineering for bioreactor pH measurements, or for use during fermentation processes where sterility is important.

"It is straightforward to change dyes in the sol-gel with our method. This means we can easily investigate properties of other new dyes that we invent. In time, that will allow us to develop new sol-gel based sensor dots for measuring just about anything," said Sorensen.

For more information, visit the University of Copenhagen’s website.