Biosensors are suitable systems for on-line measurements and continuous operations. They are small in size, easy to work, quick in action, very sensitive to measure tiny amount of test molecules and relatively very cheap. So they are put into many practical uses in medicines, industries and environmental control.

A glucose biosensor coupled with a mini pump containing insulin, is used to detect blood glucose level directly and to deliver the accurate amount of insulin required by the diabetic. Usually enzyme electrode is used for this purpose.

Biosensors are used to detect mutagenic substance (eg. Mitomycin) in the body fluid.
A few biosensors are employed to detect toxic substances and heavy metals in blood samples.
Biosensors are suitable for on-line measurements of certain compounds in continuous industrial process. As they are very sensitive and quick in action, they have been put into many practical uses in industries:

A microbial sensor made up of immobilized cells of Pseudomonas fluorescens and an oxygen electrode, is used to detect glucose level in molasses.

The total amount of assimilable sugars in fermentation media and broths can be measured with a microbial sensor. This biosensor is made up of an immobilized layer of Brevibacterium lactofermenium AJ 1511 and an oxygen electrode.

An acetic acid sensor is made by combining an immobilized layer Trichosporon brassicae and an oxygen electrode. It detects acetic acid level in fermentation broths for glutamic acid within 6-10 minutes. Acetic acid level less than 22.5 mg dm-3 can also be detected sensitively.

The cell number in fermentation broth and various food items can be measured using fuel cell type biosensors. The biosensor consists of two electrodes, each of which is made of a platinum anode and silver peroxide cathode. The electrochemical changes caused by the microbes in the analyte are used to measure the cell number of Saccharomyces cerevisiae and Lactobacillus fermentum.

The cell number of Bacillus subtilis in fermentation broth can be measured with a potentiometric biosensors.

A lactate sensor is used to count lactic acid producing bacteria in fermentation media. The lactate sensor is made up of immobilized layer of lactate oxidase and a platinum electrode coupled with a volumetric device. Leuconostoc, Streptococcus and Lactobacillus are counted in this way.

An alcohol sensor is made up of an immobilized layer of Trichosporon brassicae CBS 6382 and an oxygen electrode. It is used to measure methyl alcohol and ethyl alcohol in fermentation broth and beverages.

A formic acid sensor is made with immobilized layer of Closridium butyricum and a fuel cell type electrode. It is used to measure formic acid level in fermentation broths.

Freeze dried cells of E.coli are immobilized on a silicon chip using a cellphone membrane. This sensor analyses glutamic acid in fermentation media.

A cephalosporin sensor is made by entrapping the bacterium Citrobacter freundii on a glass electrode using a collagen membrane. It is used to measure cephalosporin.

A nystatin sensor is made by entrapping the yeast Saccharomyces cerevisiae on an oxygen electrode using a collagen membrane. This is used to detect the concenteration of nystatin, in fermentation media.

A vitamin B1 sensor is made by immobilizing Lactobacillus fermenti (ATCC 9338) on a platinum electrode. It measures vitamin B1 level in fermentation broths.

A nicotinic acid sensor is assembled by immobilizing Lactobacillus arabinose (ATCC 8014) on an oxygen electrode by using agar gel. It measures nicotinic acid level in fermentation media.

Isaokarube and his colleagues have made an ISFET based biosensor using the enzyme ATPase, aminoxidase or putrescine oxidase. It detects the freshness of fishes and animal fleshes for cooking.

The UK based Cransfield Institute of Technology has developed a cholesterol sensor to detect cholesterol level in food items. This biosensor is made up of an immobilized layer of the enzyme cholesterol oxidase and an electrode.

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