As the use of single-use technologies for bioprocessing grows, sensor manufacturers have expanded their offerings to include single-use sensors for pH and dissolved oxygen (DO) measurements. These sensors are typically incorporated into another manufacturer’s disposable bioreactor system and sold to customers as a single unit. The two types of single-use sensors utilized in such systems are optical and electrochemical. One advantage of optical single-use sensors is that unlike electrochemical sensors, there is no electromagnetic interference from the material used to make the bags used in bioreactors. Companies offering single-use optical sensors for pH and DO include Finesse Solutions, Polestar Technologies, PreSens Precision Sensing and Sartorius Stedim Biotech. Such sensors are typically used for in situ monitoring of bioprocessing applications. For both upstream and downstream applications, many companies showcased in this article prioritize upstream because the current measurement range of single-use sensors is better suited for upstream than downstream, which requires a greater range.

Single-use sensors are designed to be less expensive and to make for a faster workflow than traditional sensors. They can also lower the risk of contamination, eliminate the need for user-performed calibration and prevent product loss associated with traditional sensors’ decline in performance after repeated use. To establish themselves in the market for single-use sensor technology for pH and DO measurements, manufacturers of such single-use optical sensors have utilized flexibility in regard to product offerings, as well as partnerships.

Finesse Solutions introduced its first single-use optical sensor, the TruFluor DO, in 2008. The following year, the company launched the TruFluor pH single-use sensor. Both sensors utilize fluorometric detection in real time, in which a fluorescent dye detects the presence of the intended analyte. The sensor is one part of the control system, which also encompasses a disposable sheath, an optical reader and a transmitter. The single-use sensors can be incorporated into different products it manufactures. “By 2012, single-use optical sensors were a default standard in our systems, and in some cases, such as DO, were the only sensor used,” said CEO Barbara Paldus. The sensors are available for control systems for parameters other than pH and DO. In April, Finesse launched SmartParts line of transmitters and actuators, which work with the company’s bioreactor controller systems and incorporate TruFluor pH and DO transmitters, as well as electrochemical pH, DO and temperature sensors and single-use pressure sensors for plug-and-play control of any size of upstream container. The company has also incorporated its sensor technology into products other than control systems, such as the SmartBags it introduced in June. SmartBags employ SmartPuck sensors, which utilize the TruFluor technology and are welded into the bags, which can be installed in rockers. SmartPuck sensors simultaneously measure pH, DO and temperature for upstream cell culture.

Finesse Solutions has partnerships with three large-scale disposable bioreactor manufacturers: Thermo Fisher Scientific, Millipore and ATMI. The company has worked with Thermo for five years as part of a bilateral supply agreement. Its sensors and automation are incorporated in Millipore’s Mobius CellReady single-use bioreactor, and ATMI uses its control systems. “Our partnerships leverage the materials expertise and single-use container manufacturing capabilities of our partners,” said Dr. Paldus. “In exchange, our partners benefit from Finesse’s expertise in optical sensor development and automation technology, so that together we provide state-of-the-art solutions to the market.”

Polestar launched its digital signal processing–based (DSP) sensor technology soon after the company’s inception in 2005. In 2008, the company introduced its Peel and Stick disposable sensors. “Peel and Stick offers an end-user the option of placing a sensor inside a disposable plastic container, flask or cell stack and use our technology to get a reading,” said CEO Steve Grant. “Typically, a customer had to have a port to insert a bioprobe with a sensor on the end. This wasn’t feasible in many applications, so we developed the Peel and Stick.” In 2009, Polestar released the iDOT pH and DO sensors for single-use bioprocessing. The iDOT sensor configuration is the company’s most commonly used for disposable bioreactors and can also measure carbon dioxide. The disk form allows the sensor to be welded into a disposable bioreactor bag. IDOTs use ratiometric fluorescence analysis and fluorescence lifetime to measure pH and DO, respectively. Polestar’s optical single-use sensors can be used in a variety of vessels. Peel and Stick sensors are generally used inside a glass beaker or glass tube, and iDOTs are generally used in both disposable and fixed bioreactors. In addition to offering its technology in different formats, Polestar also provides customized solutions. “We also, in some cases, build to manufacturer specifications depending on volume and material costs,” he said. “The optical technology hasn’t changed, but rather the ability to adapt to what the customer may require in terms of weldable materials.”

Polestar has partnered with bioreactor manufacturers to enable its sensors to be sold as integrated units with bioreactors. The company’s partners include Applikon and ATMI. These companies also purchase Polestar’s controllers, since the controllers are calibrated to the iDOTs. Polestar stops short, however, of signing formal agreements with bioreactor manufacturers. “We want to be supportive of [the manufacturer’s] effort, but we don’t want to lose control of our business,” explained Mr. Grant. The company focuses on manufacturing instead of on sales. “We don’t typically ‘try’ to sell single-use sensors,” said Mr. Grant. “The business usually just comes to us via the large-scale bioreactor manufacturers.”

PreSens is another company that has made its mark on the single-use optical sensor market for pH and DO. The company formed as a spinoff from the University of Regensburg in Regensburg, Germany, and introduced its optical sensor technology for pH and DO in 1997. The company’s technology consists of an optical waveguide that has a light-transmitting substrate with an analyte sensitive dye. The sensor emits fluorescence, which increases or decreases when it touches the analyte. The sensor spots are attached to the inner surface of the bioreactor, and pH and DO are measured through the vessel’s wall. The company now provides single-use optical pH and DO sensors for a variety of disposable systems, including microplates, tubes and bioreactors. “For more than ten years, PreSens is now supplying single use optical sensors for DO and pH,” said Communications representative Christina Schlauderer. In its early stages, the company initially offered only microsensors and now has expanded to offer flexible solutions. “We offer a wide range of configurations like optics with and without fibers, microsensors, etc.,” she said. The company’s probe-based microsensor can be used in disposable bioreactors, although the sensor spots are predominantly used for this. “PreSens—one of the first suppliers for chemical optical sensors—has grown together with this market and in its other branches, e.g., food and beverage, and is therefore in the position to meet customers’ expectations and needs, quite often even with customized solutions.”

Working with partners has been a key component of PreSens’s market strategy. “Right from the beginning, PreSens developed its products in close cooperation with academia and industry,” said Ms. Schlauderer. “The company is a sought [after] partner for publicly sponsored products in Germany and the EU.” One such collaboration is PreSens’s participation in the EU’s Seventh Framework Program initiative BIO-COMET, which is a four-year project to develop a sensor-based bioreactor system for regenerative medicine research. Sartorius told IBO that it also works with the company in the field of chemical optical DO and pH measurement.