Biosensors for Environmental Monitoring

Fluorescence Illuminates Chemical Warfare Agents

What is a Biosensor?

• A device that uses specific biochemical reactions mediated by isolated enzymes, immunosystems, tissues, organelles or whole cells to detect chemical compounds usually by electrical, thermal or optical signals.

• It is the common name of sensors even though enzymes may not be used at all.

• Uses for biosensors continues to grow.

Types of Biosensors• Calorimetric – changes in heat used to determine concentrations • Potentiometric - pH-meter used for measuring reactions generating or

absorbing hydrogen ions

• Amperometric - function by the production of a current when a potential is applied between two electrodes

• Piezo-electric – measures quartz vibrations under the influence of an electric field

• Immunosensors - to detect and amplify an antigen-antibody reaction

• Optical - involve determining changes in light absorption between the reactants and products of a reaction, or measuring the light output by a luminescent process

Functional Component

• The transducer makes use of the specific changes that accompany reactions in order to produce an electrical signal.

Transducers can produce signals from

• the heat of the reaction (calorimetric biosensors) • changes in the distribution of charges causing

an electrical potential to be produced (potentiometric biosensors),

• movement of electrons produced in a redox reaction (amperometric biosensors),

• light output during the reaction or a light absorbance difference between the reactants and products (optical biosensors)

• effects due to the mass of the reactants or products (piezo-electric biosensors)

Makings of an ideal biosensor.

• must be highly specific for the purpose of the analyses, be stable under normal storage conditions and show good stability over a large number of assays

• The reaction should be as independent of such physical parameters as stirring, pH and temperature as is manageable. This would allow the analysis of samples with minimal pre-treatment.

• The response should be accurate, precise and reproducible • If the biosensor is to be used for invasive monitoring in clinical

situations, the probe must be biocompatible• The complete biosensor should be dummy proof• There should be a market for the biosensor.

Plans for a new optical sensor

• Again, optical biosensors read light output from luminescence or absorption differences. This sensor will utilize luminescence.

• This new idea stems from the urgency to detect chemical warfare agents very quickly.

The Coumarine Oximate detector is

• replacing calorimetric devices for detection.

• replacing alcohols in previous mechanisms.

• currently is stand alone

• not yet integrated into a working sensor

• still in the process of becoming a practical application

Coumarin: benzene + pyran + ketone =

benzopyrone

Oximes

Synthesis of Coumarin Oximate

• A coumarin aldehyde is converted to a coumarin oxime.

• The oxime loses a hydrogen when base is added to become an oximate.

• Special base is used to avoid interference with the nerve gas.

Mechanism

Phosphoryl Fluorides

What makes it glow?

Chemically Initiated ElectronExchange Luminescence

• Hydrogen peroxide reacts with the oxalate to give peroxalate.

• Dioxitane dione considerd to be the key intermediate step in producing chemiluminescence

• The electron transfer drives the chemliminescence

Reaction of Coumarin Oximate with no DFP Present

• In this case, no CW agent or model yields no light.

• What ends up happening is the oximate binds to the oxalate.

• No reaction with hydrogen peroxide can take place.

• No chemiluminescence

• Here we see that DFP rather than the base attaches to the oximate.

• The oxalate is free to react with hydrogen peroxide.

• Chemiluminescence is observed.

• What is not apparent is how exactly the reactants can get back to their starting point.

• There needs to be a way to hold back the oxalate from reacting with hydrogen peroxide.

Recap

• Biosensors are sophisticated tools for detection and monitoring.

• New technology is allowing more specificity and quicker, more accurate readings.

• New methods and uses for biosensors continues to grow with increasing demand.

References• Martin Chaplin and Christopher Bucke, Enzyme Technology, (Cambridge

University Press, 1990). • Himali S. Hewage,a Karl J. Wallaceb and Eric V. Anslyn, Novel

chemiluminescent detection of chemical warfare simulant, Received (in Cambridge, UK) 2nd May 2007, Accepted 26th July 2007First published as an Advance Article on the web 8th August 2007 DOI:10.1039/b706624d.

• Karl J. Wallace,a Ruth I. Fagbemi,a Frantz J. Folmer-Andersen,a Jeroni Morey,b Vincent M. Lyntha and Eric V. Anslyn, Detection of chemical warfare simulants by phosphorylation of a coumarin oximate ,Received (in Cambridge, UK) 11th July 2006, Accepted 11th August 2006 First published as an Advance Article on the web 1st September 2006 DOI: 10.1039/b609861d.

• IUPAC Compendium of Chemical Terminology 1992, 64, 14 2nd Edition (1997).