Feeling out of this world

A UK team is developing lighter and more sensitive biosensors to allow future space probes to detect and identify evidence of life on other planets more precisely.

Researchers at Cranfield and Leicester universities are developing an instrument to detect the widest ever range of molecular ‘biomarkers’, molecules such as amino acids or proteins that indicate the existence of current or ancient life.

The Specific Molecular Identification of Life Experiment (SMILE) instrument, being designed by the universities in collaboration with ESA, is proposed for use on the agency’s ExoMars rover mission, due to launch in 2009.

Transducers in the SMILE instrument will be coated with biological receptors such as antibodies or enzymes which will change their properties when in contact with an extraterrestrial molecule such as an amino acid or a protein. The transducer detects this reaction and turns it into an output signal either by recording a change in the refractive index of the biosensor layer or by complex conductivity techniques that measure the electrical resistance of the molecule.

Planetary probes such as ExoMars and the doomed Beagle 2 need instruments with low mass, low volume and low power consumption and so can carry only a limited number of bulky traditional sensors. SMILE could allow a much wider range to be fitted on to the rovers. One of the likely reasons for the failure of Beagle 2 was mass-saving shortcuts made to accommodate more sensors, ESA claimed last month.

Dr. David Cullen of Cranfield University’s Institute of BioScience and Technology, who led the EPRSC-funded research, said that rovers are more likely to find evidence of life on Mars with biosensors because traditional sensor techniques can detect only a narrow band of biomarkers.

The sensors that are currently used to detect life on other planets are based on non-biological techniques such as mass spectrometry or chromatography – like the gas analysis package for detecting isotope signals on Beagle 2, he said.

‘Traditional sensors can only detect the general properties of molecules – and when you are dealing with complex macromolecules, it becomes even more difficult to identify precisely what they are,’ Cullen said.

‘This next generation of sensors will be able to answer scientists’ questions about the presence of specific biochemicals.’

The team is applying biosensor technology used in medical applications but the difficulty with terrestrial biosensors is that they use biologically derived molecule receptors, DNA and protein-based, which are unsuitable for space travel and the extreme conditions on planets such as Mars.

The team has created a class of stronger artificial receptors called Molecular Imprinted Polymers (MIPs) that mimic the way biological receptors work.

‘They have similar molecular-sized cavities to act as binding sites. These have sizes and geometries that match the molecules you want to detect,’ Cullen said.

‘MIPs are also much more robust against extreme temperatures, non-aqueous samples and radiation. And they have stronger links at the molecular level than do DNA and protein-based receptors.’

Dr. Mark Sims, from the University of Leicester (and Beagle 2’s mission manager), is involved in the project. He said MIP biosensors could also be applied to homeland security technology or environmental monitoring as the molecules can be regenerated and used many times.

‘MIPs have all sorts of applications beyond looking for life on Mars,’ he said. ‘They could potentially detect explosives residue or chemical toxins in the air.’