Glucose is a key nutrient for living organisms, so tracking its concentration in culture is vital for the manufacture of biopharmaceuticals. Most commercially available monitoring systems are enzymatic—they measure the change in electrochemical activity when the nutrient interacts with an enzyme. In glucose monitoring, an enzyme called glucose oxidase (GOx) is used.

While such systems are well established, they are not without shortcomings, according to Govind Rao, a professor and director at the Center for Advanced Sensor Technology at the University of Maryland, Baltimore County.

“Enzymatic sensors suffer from dependence on oxygen levels in the sensing environment, poor selectivity, and low sensitivity. Nevertheless, extensive research and development have practically eliminated most issues thanks to the increasingly high demand for clinical diagnostic requirements, making them commercially successful,” he says.

Enzymatic glucose sensors are also expansive and can only be used for a limited number of manufacturing runs before they need to be replaced.

Potential alternative technology

With these concerns in mind, Rao and colleagues have developed a potential alternative technology based on periplasmic binding proteins—receptors that change shape when they bind a ligand, glucose in this case.

“The binding protein is labeled with a fluorophore. When it binds glucose, the protein conformation changes and the resultant fluorescence change is measured using simple optical instrumentation,” says Rao. “Imagine picking up a peanut with your finger and thumb. The change in movement can easily be discerned. A similar principle is used here.”

The binding protein is immobilized on a column, which allows the sensor to be used many times. And there are other potential advantages, according to Rao, who cites enhanced sensitivity as an example.

“In contrast to an enzymatic glucose sensor such as glucose oxidase, the binding proteins have an approximately 1000-fold greater binding affinity,” continues Rao. “So you can detect micromolar levels as opposed to mill molar, allowing for facile dialysis-based sterile sampling which makes sampling any bioreactor easy.

“Finally, the binding proteins do not consume the substrate, unlike enzymatic sensors.”

The system has already attracted the biopharmaceutical industry and technology sector.

“We are working with a large pharma that wants to test it to monitor and control their bioreactors. Another large company is showing interest in commercializing the technology due to its high readiness level,” Rao says, adding “We have patents and knowhow available for licensing.”

Another potential advantage of periplasmic protein-based monitoring technology is that it can be used to track other nutrients, points out Rao, adding that “These glucose binding proteins are part of a large family, so many other analytes such as glutamine, phosphate, magnesium, and branched-chain amino acids can be measured using the same principle described in the paper.”

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