BIOSENSORS FOR ENVIRONMENTAL MONITORING

Sampling and laboratory analysis of contaminated environmental samples can be slow and expensive; thus limiting the number of samples that can be analysed with in the time and money constraints.
Biosensors provide cheap, reliable, and accurate monitoring of the environment which will also give real time analysis.

BIOSENSOR:
A biosensor can be defined as an analytical device with a biological sensing element in close proximity or integrated with a signal transducer inorder to quantify a compound or conditions.

Various Biosensors can be developed and used for monitoring the quality of air, water and soil. Some of them include:

• B.O.D Biosensors
• Pesticide Biosensors
• Phenol Biosensors
• Biosensors for detecting Heavy metal

BOD Biosensors

BOD is used as a measure of water quality. The greater the BOD of a water sample the more polluted it is. BOD is a measure of the amount of metabolizable material in a sample. Conventionally BOD-5 technique is used to measure BOD and it takes 5 days to estimate BOD using this technique.

Two types of BOD Biosensors are in use:

• Film type BOD Biosensor
• Respirometer type BOD Biosensor

In a film type BOD Biosensor a microbial film is sandwiched between a porus membrane and oxygen permeable membrane of the Clarke oxygen electrode. The microbial cells utilize the oxygen while metabolizing any material in the sample. The amount of oygen utilized is proportional to the amount of metabolizble material in the sample. The Clarke oxygen electrode measures the amount of oxygen consumed and thus BOD can be estimated. ()

Pesticide Biosensors:

Two immobilized enzyme systems are currently in use to constuct biosensors for measuring Pesticide concentrations. They are:

• Organoposphate hydrolases and
• Acetylcholinesterase + Choline Oxidase

Organoposphate hydrolases System
Organoposphate hydrolase catalyse the hydrolysis of a wide spectrum of organophosphate pesticides. Substrate dependent changes in pH at the local vicinity of the ezyme is used in the assay of the organoposphates using this enzyme. The pH change is monitered using FITC( Flourescene Iso Thio Cyanate) which is labelled to the enzyme covalently. The FITC-labelled enzyme is immobilized on PlyMethylMethacrylate Beads. A Flourescence analyzer is used to measure the analytes. Examples: ethly parathion, methyl parathion etc., are estimated using this technique.
One of the potential application of the above system is that it can be used in the continuous monitoring of Bioremediation Process. It has been shown that this assay has an effectiveness relatively close to that of HPLC in case of Coumaphos measurement in Bioremediation samples of Cattle dip wastes.

Acetylcholinesterases and Choline Oxidase system
Acetylcholinesterase converts acetylcholine to choline. Choline is converted to Betaine and H2O2 by CholineOxidase.

Acetylcholine --------(a)-----------> Choline ---------(b)----------> Betane + H2O2

where (a) is : Acetylcholinesterase and
(b) is : Choline Oxidase

H2O2 can be measured by O2 electrode. Pesticides inhibit the activity of acetylcholinesterase and therefore results in a reduction in peroxide formation which can be corelated to pesticide concentration.

Phenol Biosensors:

Tyrosinase enzyme is used in the construction of Biosensors for measuring Phenol Concentration. This enzyme degrades phenols to catechols and quinones. This process requires Oxygen. If enzyme Tyrosine is linked to an Oxygen electrode Phenol concentration can be estimated.

Biosensors for Heavymetal Detection:

Metals such as lead and cadmium have the property to inactivate their oxidases and dehydrogenases.
when these immobilized enzymes are kept in close proximity to O2 electrode they can give an estimate of the Heavymetals concentration.