Chemical sensing

Citation

Newman, J. (2007), "Chemical sensing", Sensor Review, Vol. 27 No. 2. https://doi.org/10.1108/sr.2007.08727baa.002

Chemical sensing

Healthcare and defence have become two of the biggest political “hot potatoes” of today. In the face of massively escalating costs and subsequent pressures on worldwide healthcare systems, public awareness and expectation of health have never been higher. Many parts of the world have also placed enormous emphasis on defence, or homeland security, as it has become known, following the increase in terrorism and the threat of further attacks. These issues have had a huge impact on chemical sensing R&D over the last few years and are set to continue to dominate the field for the foreseeable future.

Blood glucose monitoring continues to dominate the biosensor field, accounting for $5.9 billion of the current world market of around $7.0 billion. The latest developments in this industry involve the emergence of reliable continuous glucose management systems. Two types of device exist, delivering continuous glucose readings to either a pager-like device, or an insulin pump. The latter system is particularly exciting, as it offers the possibility of real-time, closed loop, insulin delivery. At present, Medtronic offer a sensor- augmented insulin pump, but this requires the back-up of a conventional “fingerstick test” before insulin delivery. Several other companies, including Abbott and Dexcom also have continuous systems under FDA review and there are many other companies with systems under development.

Non-invasive technologies were dealt two more blows following the failure of both the Cygnus Glucowatch and Pendragon's Pendra device. This now makes four major failures in this sector, which sends out alarming messages to potential investors in this type of technology. Nevertheless, many companies continue to push towards this “holy grail”.

Elsewhere, gene chips have received a lot of attention. At the time of writing, chips with 6.5 million sites on 1.28cm² chip (5mm/site) were available, with a target of 2mm/site. The technology has become highly entrained in the huge drug discovery industry, where it is now used for: target identification and validation, compound screening, lead optimisation and preclinical and clinical trials. The success of these arrays, in producing “omics” data, has generated very high expectations. With so much highly varied data, attempting to draw valid conclusions poses a major challenge. Arguably the greatest hurdle now is to develop the information technology that can transform the data into knowledge that will drive new advancements in the industry.

Recent estimates indicate that the socioeconomic cost of class A drugs, in the UK alone, amounts to £17.4 billion. The survey also suggests that 35 per cent of young men and 24 per cent of young women had tried illicit drugs in previous year. Whereas there are several FDA approved tests on market, none of these are currently accepted for Department of Transport testing programmes, yet alone for roadside testing. This is a major opportunity for a sensor or rapid diagnostic product

Between 2006 and 2010, the USA has made available $12 billion for homeland security technologies. The 2006 budget for chemical sensing and associated technologies amounts to nearly $1.8 billion and is divided as shown in the Figure 1.

Figure 1

There are many potential targets for such technology, including food adulterants, toxic chemicals, volatiles, illicit drugs, explosives, chemical and biological warfare agents and body fluid components. Many of these circumstances require hand held or portable devices, which are able to monitor a range of samples, such as food, water, soil and air. It is also important to consider specificity requirements (single chemical, or broad toxicity, for example), speed of response, cost, ease-of-use and, not least, robustness. The latter point is significant. It is often simple to demonstrate a sensor or assay in the laboratory, but in a battlefield situation, the operator may not be highly skilled and will be very likely to be wearing full protective clothing. Automated sampling, miniaturisation of the sensor and advanced on-chip sample handling, using microfluidics, all coupled to advanced signal processing makes many of the above requirements feasible. Nevertheless, developing such a system remains a significant challenge.

Biosensors have been used in Bahrain to test water supplies delivered to Navy ships. Such devices, originally designed for the defence sector, are being spun out into other areas. One instrument is being evaluated for detection of threats to the grain crop and meat supply, for example.

The above examples highlight the advantages of using biological systems for low detection limits in complex samples, since they often possess many useful properties for detection, especially where high selectivity is a requirement. However, they are often relatively unstable. This has led to considerable research in the area of biomimics – using synthetic materials that mimic the action of antibodies and other biological components. The idea is intriguing, but practical success, especially in aqueous samples, has proven more of a challenge than was originally envisaged. Nevertheless, the area remains a hot topic for research.

Jeff NewmanConsultant at Cranfield Health, Cranfield University, Silsoe, Bedfordshire, UK