report
2.2.3.1.2 Bio-arrays

Bio-arrays link several different biomolecules to a substrate in such a way that each is individually addressable.  Arrays have been made using a number of different biomolecules, but have tended to concentrate on proteins (or parts of proteins) such as antibodies and enzymes, or DNA and RNA.  These are quite mature technologies, having been developed and marketed by a number of companies for use in basic research, and diagnostic sciences (including forensics and medicine).  To date they have largely been based on microsystem technologies and been used in laboratory settings, for measuring analyte concentrations in semi-purified (e.g. filtered and buffered) samples.  Bio-arrays have the capability to simultaneously measure and quantify many different analytes (in some cases thousands).  Such arrays are a mature technology manufactured by a number of different companies and used in fields as diverse as clinical diagnostics, environmental monitoring and bioscience research.

Nanotechnology is beginning to have an impact on bio-arrays.  The advantages that it brings to such systems are: further miniaturisation, allowing more variables to be measured; greater sensitivity, thus requiring less sample material; faster detection rates, allowing read-out in real time; and novel detection methodologies (e.g. electronic, colourimetric, fluorometric, and mass changes).

There are a number of different formats for bio-arrays include planar forms, with biomolecules directly attached to the flat array surface; cantilevers, with biomolecules attached to a number of individual micro-sized levers (which resemble diving boards); and biomolecules attached to nanowires or nanotubes which in turn are attached to a planar surface, with each attachment point being a unique electronic address. 

Array technologies can be used at different stages of the food chain such as: detecting the presence of pathogens in livestock or crops; measuring the levels of toxins or nutrients in soils; and monitoring the quality of processed food.

Cantilever arrays are perhaps one of the most interesting as they detect the presence of specific target molecules in a mixed environment based on mass displacement of the cantilever when the target binds a reporter molecule attached to the cantilever[i].  In addition, they can operate in gas or liquid phases, giving rise to the electronic ‘nose’ and ‘tongue’.  These topics will be discussed in greater detail in the report on food processing.

One interesting example comes from the FP6 funded Automated Water Analyser Computer Supported System (AWACCS) project which produced and field tested an optical bio-chip, that was capable of providing information on up to 32 different analytes by means of an integrated optical chip from water from a variety of different sources with only a pre-filtration step required.  The attainable detection limits were at levels below the EU recommended safe limits, and the chip could be reused up to 500 times[ii]^,[iii].

Further information on sensor arrays can be found in the report on diagnostics, within the medicine, health and nanobio technology sector.