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Interview: Stratophase talks optical microchips

16 Aug 2010

On-chip refractive-index monitors suit industrial process control and biodetection, as the UK company seeks commercialization partners.

Optical microchip

Winning venture capital (VC) funding is a major milestone for any start-up company. But instilling enough confidence in investors to fund multiple rounds requires a technology with undoubted potential and a visible route to commercialization. Founded in 2003, Stratophase ticks both of these boxes.

The UK-based company is pioneering the development of an optical microchip platform for real-time chemical and biochemical measurements. The company has raised a total of £3.6 million in VC funding, with the most recent instalment a £2 million round at the start of this year. Having also doubled its manufacturing capability just last month, 2010 looks set to be the year that Stratophase turns prototype into product.

Jacqueline Hewett asked Sam Watts, a co-founder of Stratophase and now its business development and commercial officer, about the technology and the applications it is finding in industrial process control and biodetection.

Jacqueline Hewett: What is Stratophase’s core technology and how have you kept investors interested?
Sam Watts: Stratophase span out of Southampton University’s Optoelectronics Research Centre in the latter half of 2003. We broadly describe our technology as an optical microchip. Our core IP is the ability to use a direct UV writing process to define waveguiding structures, such as couplers and splitters, and Bragg gratings within glass layers.

Our technology was originally designed for the telecoms industry - the idea being to produce cost-effective, large-volume add-drop multiplexers. Luckily for us, the telecoms bubble burst while we were still in the university and we had enough time to look for alternative uses.

We decided to expose our Bragg gratings to the outside world, essentially using the telecoms technology for sensing. The wavelength that a Bragg grating reflects at depends on the media on top of the chip. In essence, we have developed an optically integrated sensor chip with all of the advantages of telecom technology.

Grating writing

We have been VC-backed since day one and still are today. We have generated significant revenues for a company at our stage of technical development, with contracts worth approximately £2 million active at the moment, although we are not yet profit-making.

Our main VC is a US company called East Hill. While most VCs would look for a return on a short timescale of two to three years, East Hill has a longer-term vision. Our pitch was that we had this optical microchip technology with a raft of potential applications. We couldn’t identify the killer application but we could prove and show the potential of our technology.

JH: How does your technology work?
SW: Our chip uses a standard silicon wafer which has three different silicate glass layers (an underclad, a core and an overclad) on its surface. The central core layer is doped with germanium and the germanium defects within the glass are sensitive to UV light. As soon as you focus a UV laser into the core layer and translate the focus in the plane of the silicon chip, you define a waveguide. This also allows you to produce gratings which are controllable with respect to modulation period and place them anywhere you want on the chip.

In the final step, we remove the overclad to expose the Bragg grating to the outside world. Any liquid present on the Bragg grating changes the effective refractive index and hence the reflection peak for that grating, creating a refractive index sensor.

We measure refractive index down to better than 10-6. We also measure temperature for referencing purposes - since refractive index is a temperature-dependent quantity. Without this it would not be possible to decouple temperature effects from compositional effects.

The silicon on the underside of our chips is around 700 microns thick, making our chip a very robust device. The three glass layers have similar dimensions to a standard optical fiber. Our standard chips are 10 x 20 mm and because you can include splitters you could have between 20 and 30 sensor pads per chip.

Because our design makes use of telecom technology, we can use off-the-shelf interrogators and take two readings every second. We tend to find that this is more than fast enough for most applications, but it does allow you to do some statistical analysis to give customers more confidence in the information you give them.

Sensor in a briefcase

JH: What applications are you targeting?
SW: We have a range of applications because we view our technology as a sensor platform. We decided from an early stage that the best way for us to gain value for our technology was to tackle multiple markets. This makes it challenging as you don’t want to stay too broad but equally we don’t want to artificially narrow ourselves. The two areas that we are focusing on are industrial process control (IPC) and biodetection.

JH: How is your sensor used within industrial process control applications?
SW: IPC is effectively using our sensors to measure the refractive index of liquids in industrially relevant processes – anything from oil refining to the pharmaceutical industry. We use the temperature-compensated refractive index to give a real time indication of the chemical composition of the liquid within the process.

Delays arise when a process is checked to determine what is happening chemically, as this requires a sample to be sent to an analytical lab. Our sensor can take a reading which is dependent on the chemical composition in real time. It is not as specific as the lab test, so it can’t tell you the different chemical species, but you can use our technology to profile a process to see if it is going according to plan chemically.

We have been looking at (i) batch reactions, where there are very large volumes of liquid experiencing chemical composition changes over time and (ii) continuous flow chemistry.

A classic batch reaction is fermentation. What we do here is put a probe in the fermenter and monitor how that process evolves with time. Multiple probes reporting to a single unit allows you to monitor say six or eight fermenters simultaneously. The cost associated with scaling from a single probe to eight probes is relatively small and minimizing cost is high on the agenda. We also feel that our technology is simple, small and applicable for a process development environment before scaling up to production volumes.

In continuous flow chemistry, two reactants mix continuously within a pipe. The key is to know that your process is not drifting over time. There is no time to send samples to a lab. Our chip can alert the user to changes in chemical composition in real time. The pharmaceutical industry in particular is showing a lot of interest in continuous flow chemistry, and Stratophase’s technology may be one of the tools which proves to be enabling for these processes.

Biodetection

JH: What about biodetection applications?
SW: In biodetection, we functionalize the surface of the chip by depositing an immunoassay. This is a biochemical layer that is specifically designed to bond on to the target you are looking for, such as a virus. Essentially you are looking for specific biological agents in the liquid flowing across the chip, which will show up thanks to a change in the refractive index when a binding event occurs.

We are currently working as part of a consortium under contract to the UK Ministry of Defence (MOD) to develop a suitcase-sized system that continuously monitors the air for biological agents. Their current system is a lab in a truck. We are not looking to improve the detection capabilities, we are simply looking to create something smaller, more robust and easier to use. The prototype system being developed continuously samples the air, puts it into a liquid stream and then flows it over the surface of the detector. The chips are in cartridges that plug into the detection unit and are changed when a detection event occurs or the immunoassay is no longer effective.

Our second biodetection area is disease diagnosis, be it human or animal. We are currently involved in a UK Technology Strategy Board (TSB) co-funded project for detecting foot-and-mouth disease. The current method sends a sample to a lab but the time associated with this can have a massive impact. We hope to produce a system the size of a briefcase that can detect whether there is foot-and-mouth present in real time.

JH: What stage is Stratophase at in terms of deploying its technology commercially?
In terms of IPC, we have prototype technology demonstrators but not off-the-shelf products. We are using the prototypes to work with key customers. One of the real issues is supplying the customer with too much data. Customers need process relevant information, not the refractive index of a liquid. We are working closely with customers to develop process models and the software interfaces required to interpret the data in real-time and hope to be selling products within a year.

Our biodetection work is at an earlier stage because of the complexity associated with using immunoassays. We either use standard immunoassays or partner with people who have developed a specific immunoassay for the desired target. The problem is working out how to deposit the immunoassay on to the sensor in order to achieve the required sensitivity and specificity.

In biodetection, we want to validate the technology in the lab and don’t envisage taking it to product, especially in medical applications with the associated legislation and certification. We would be looking to partner with a company with a presence in that area to help with the heavy lifting to get the product to the consumer.

In all cases we anticipate that the long term route for the technology to widespread application by end users will be via the formation of strategic partnerships and joint ventures in the multiple market verticals which can be accessed by a platform technology such as Stratophase’s.

About the Author

Jacqueline Hewett is a freelance journalist based in Bristol, UK.

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