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“Development of diamond-based biosensors.”  

The need to detect and measure (biological) substances has increased dramatically; not only by the growing attention for good practices and quality assurance in health and environmental management, but also as support for high-tech police tasks, like crime scene investigation, narcotics and terrorism control. Apart from medical diagnostics, food safety (Salmonella, BSE, …) and animal health become more important. Also the free choice of consumers in our free market economy must be guaranteed: it must be possible to choose for biological or genetically-modified-organism-free food.

Biosensors are the answer to these new emerging questions. With respect to chemical and physical sensors, they have the advantage that they, because they are made of biological materials, react very fast, specific and sensitive. They operate at the interface between the living (biology) and the dead world (electronics). Around the sensitive biological core, there are physical or chemical components that transform and amplify the biological signal to a signal that can be observed by the user.

Canary birds used to function as mine gas indicator. Nowadays, activemolecules, like enzymes do this detection at a much smaller level. The first real biosensor was the Clark electrode, combining an oxygen sensor with an enzyme membrane for the detection and measurement of glucose (1962). Today applications range from cheap portable do-it-yourself glucose meters for diabetics (e.g., Accu-Chek® from Roche), to expensive, fully automated laboratory equipment (e.g., GeneChip® microarray of Affymetrix). Measurement and identification of proteins by immunosensors and DNA by DNA sensors in combination with knowledge gathered by the human genome project, enable us now to detect diseases and hereditary disorders in an early stage, thus preventing worse.

Diamond is an obvious choice as building material for implantable sensors because of its biocompatibility, chemical inertness, and the ability to make it electrical semiconducting, allowing connection with integrated circuits. Such implantable sensors would stay active in the body for a long time, thus replacing repeated sampling and enabling continuous monitoring of e.g., the pH of the blood. Diamond can be artificially deposited as a thin layer on different substrates, ranging from glass to semi-conducting silicon. This way, an inert physical separator layer between body and the electronic part of the sensor is created. Part of the sensor surface however can be functionalized with biological
components to become a sensitive layer. However, the chemical inertness of diamond makes this a difficult task.

In this doctoral study, the boundaries of a new multidisciplinary research domain were explored. Knowledge about physics and biology was merged to build prototype sensors showing how diamond can be used as base material for biosensors. The first research steps towards a diamond-based biosensor were made: DNA was successfully bound to a diamond surface, and diamond was used as sensing material for pH and polyelectrolytes, the latter as a model for DNA.